tailings in mining

paterson & cooke on tailings - mining journal

"Dewatering of tailings is very much in focus now. Getting the water out of the tailings is one of the key avenues to ensuring a reliable TSF design post-discharge, and certainly there has been a lot of focus on that with the TSF failures in recent years," according to Matt Treinen, Director at Paterson & Cooke. Matt sat down for an interview for Mining Journal and Mining Magazine's 2021 Tailings Program.

Paterson & Cooke is a global leader in high-level consulting and engineering of tailings solutions, including slurry systems. Treinen said the firm provides services for greenfield projects, where it helps clients understand what technology makes sense for the project, as well as at existing operations, where it helps troubleshoot how to improve their tailings systems.

It is important to look at new greenfield projects with a holistic "10,000 ft view" where you can assess the site location, dewatering requirements and overall tailings objective to select the best available tailings technology. Filtered tailings are in vogue right now but their potentially high cost means they are not always the best fit at every site.

"Most of our offices have labs adjacent to the office so the engineers can get out to the lab, see how the material behaves, understand the dewatering behavior, and look at alternate technologies to optimize the overall system."

"As the project advances into the next stages we certainly can get involved in the full engineering and design of a particular dewatering system, whether that's a thickener operation or a filtered tailings operation," he said. That is more of a 1,000 ft view.

Lastly we get involved at a "100 foot view" (about the size of many thickeners) where the firm assesses how to make improvements at existing sites. "Maybe there (have been) ore changes, or variations in properties and they're not getting the dewatering that they need. How can we optimise that? Maybe it's retrofitting, thickener technology, maybe that's looking at the slurry pump selection, maybe the (tailings) pipeline size is no longer appropriate and they're getting excessive wear." he said.

Paterson & Cooke has implemented a number of systems globally, ranging from tailings slurry pipeline systems for conventional tailings facilities, and all the way through to implementation of various dewatering technologies.

"We've been involved in quite a lot of cyclone sand systems design and implementation in the southwest United States and South America where they use that cyclone material for dam construction. We've completed countless numbers of thickener audits to help improve thickener operations, anywhere from conventional thickeners to high-rate and paste thickeners, to troubleshoot and get them back to operating where they should be operating."

They have also seen a huge interest in filtered tailings over the last few years. We're in the process of implementing a filtered tailings system in Mexico, a fairly small scale operation where they're filtering the tailings and then depositing it into a mined-out pit," he said.

"We assisted with a filtered tailings design in Canada a couple years ago where the plan was to take incremental steps: they've gone from conventional tailings, moving to thickened tailings and then working to close out those tailings storage facilities. They could get comfortable with the thickening operation before implementing filtered tailings in the next year or two."

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alien metals provides elizabeth hill tailings update | global mining review

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Save to read list Published by Jessica Casey, Editorial Assistant Global Mining Review, Thursday, 24 June 2021 12:15

As announced on 10 March 2021, Alien entered into an exclusivity agreement over the Elizabeth Hill Silver Tailings Project in Western Australia, with a further 45-day exclusivity period agreed as announced on the 26 May 2021.

As part of its ongoing due diligence, the company commissioned a series of metallurgical and recovery tests on a 200 kg bulk sample taken from across the tailings. Due to the continued high demand for testing done at the Perth laboratories, the company has been granted a further 30-day extension to the exclusivity period to enable this detailed study to be completed and full results interpreted (the extension).

This extension will allow Alien to undertake further assessment over the potential retreatment and recovery of the silver tailings as discussions continue regarding the potential acquisition of the project.

A summary of the test work being carried out by ALS Perth includes homogenising the 200 kg bulk sample to ensure its as representative of the entire tailings as possible, further analysis of the grades of the samples being used, testing the optimum particle size for extraction purposes and several recovery methods to find optimum method of extraction in terms of chemical and economic factors.

Bill Brodie Good, CEO and Technical Director of Alien Metals, commented: "We are thankful to the Wombat Resources team for this additional extension to the exclusivity agreement on this project without further cost, and are pleased that they understand the current delays being encountered at the labs due to the overwhelming demand stemming from significant mining activity in Western Australia.

"The ALS laboratory in Perth has commenced a detailed suite of metallurgical and recovery tests on the larger bulk sample we took earlier in the year. This analysis will give us the best understanding of the economics of this project and its potential to generate income for Alien to put back into the ground in exploration dollars."

In this webinar, Chris Pearson, Group Business Development Director at MMD Group, will discuss in detail their Fully Mobile Surge Loader (FMSL), its key requirements, and implementation considerations.

Australian mining news Silver mining news

In this webinar, Chris Pearson, Group Business Development Director at MMD Group, will discuss in detail their Fully Mobile Surge Loader (FMSL), its key requirements, and implementation considerations.

treatment of tailings in mining operations | condorchem envitech

Condorchem Envitech offers efficient solutions for the mining sector through advanced treatment processes that allow companies to produce clean water for reuse or discharge into the environment without any danger.

Wastewater can be produced in various ways in a mining operation, depending on whether the mine is underground or open pit, whether it has a positive or negative water balance and depending on the refining process.

Tailings represent an important environmental responsibility for a mining operation, since they occupy large areas of land and contain water contaminated with metals, which will eventually need to be treated during operation or after the mine closes down.

Given the high cost of treating and pumping wastewater produced from a mine, it is important to have processes and technologies that are cost-effective that help prevent uncontrolled discharge of wastewater, resulting in salinization and contamination of surface or groundwater.

Some of these technologies can be combined to achieve the most efficient result, both in environmental and financial terms. The available technologies for the treatment of mining effluents are detailed below:

The zero discharge process is carried out by a state-of-the-art membrane treatment that can reach the discharge limits and subsequent treatment by evaporation and crystallization to concentrate the brine from the membrane reject.

Wastewater enters aeration tanks that promote the precipitation of dissolved metals, such as manganese and iron. Subsequently, it is transferred to a crystallization tank where chemical softening to reduce alkalinity and hardness occurs. Once rinsed in a sedimentation tank, the mineral sludge is pumped into a drainage system, which may be a press filter or a centrifuge.

A 1- or 2-stage reverse osmosis (RO) system together with an electrodialysis reversal (EDR) system perform desalination. The RO system consists of parallel skids, each containing multiple reverse osmosis stages. The EDR treats the concentrate from the RO modules and farther concentrates it up to 15% TDS.

The reject from stage 2 is a concentrated brine that contains dissolved solids and other components removed from the feed wastewater. The brine is sent to a secondary softening system to remove calcium and magnesium ions before being sent to a heat treatment process consisting of an Envidest evaporator and a Desalt crystallizer, both designed by Condorchem Envitech.

The evaporator concentrates the RO+EDR reject and separates most of the water efficiently and cost-effectively. The evaporator and crystallizer are from the MFE (Multiple-Effect Evaporator) series and are heated by waste heat: either hot water or steam from the first effect and cooling water for the final effect.

Another option is the MVR (Mechanical Vapor Recompression) series evaporators and crystallizers that compress the steam created by concentrating the brine and then recycle the steam for use in the heater housing to provide a heat source for the evaporation process.

1. Zero liquid discharge (ZLD) technologies use evaporation and crystallization as reference processes. These produce salt and water concentrates. This water can be reused in the industrial process or in the aquifer regeneration process itself. The salt concentrate can be crystallized and treated as waste or as a valuable resource.

3. A zero liquid discharge system is a good option where water is scarce, or when environmental regulations require high water quality after the process. These systems can treat large volumes of wastewater.

5. A zero liquid discharge system can recycle the wastewater in situ, which has two advantages: (1) the treated water can be reused and (2) liquid waste is not transported in tanks, with the corresponding extra cost this logistical solution implies.

6. Zero liquid discharge (ZLD) technologies require significant energy, although the use of waste heat reduces the cost associated with this. In each case, a detailed analysis of the energy costs and availability has to be done.

7. Zero liquid discharge (ZLD) processes normally have two phases: A pre-concentration stage and an evaporation / crystallization stage. Preconcentration can be done by RO, ED/EDR (electrodialysis), FO (forced osmosis) or MD (membrane distillation).

8. MD (membrane distillation) uses the different vapor pressure between both ends of the membrane allowing heat and mass transfer of the volatile solution components, such as water. It is a relatively simple method that can use waste heat.

9. Pre-concentration is required for good performance in zero liquid discharge processes. Pre-concentration is carried out using the other aforementioned technologies (ED/FO/MD). The pre-concentration phase reduces energy consumption in a zero discharge process.

10. ED (Electrodialysis) techniques are optimal for working at high salinities above 70,000 ppm, since they have a high useful life and their cost is less than that of evaporation / crystallization. Ion blocking is compensated for by changes in polarity. This does not allow for the treatment of microorganisms or organic pollutants. These procedures are limited by a specific charge density, which causes dissociation of the water and is a limitation for the procedure.

11. Forced osmosis (FO) allows the treatment of high salinities with an optimal use of energy, since it can combine thermal energy from waste heat and electrical energy. The disadvantage is that it requires high control of pollutant concentrations and can result in concentration polarization problems.

12. Membrane distillation (MD) processes can separate at lower pressures and temperatures than other techniques, and can use waste heat. This technique has fewer flow limitations caused by concentration polarization. As disadvantages, forced osmosis has high modular costs; surfactants can cause wetting problems in the membrane and lead to a low permeate flow compared to other processes that require pressure.

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mine tailings - an overview | sciencedirect topics

Mine tailings are the finely ground residue from ore extraction. The grain size of the tailings depends on the nature of the ore and the milling process. Size measurements (Robertson, 1994) of tailings from four mines in Ontario, Canada, indicated the tailings materials to be predominantly silt and fine to medium sand with <10% clay content. Tailings are transported from the mill and are discharged into an impoundment as a slurry containing 30 wt.% solids. The method of deposition affects the distribution of tailings particles within the impoundment. Discharge commonly takes place at elevated perimeter dams; hence there is potential for extensive hydraulic sorting, with coarser fractions settling near the discharge point and finer fractions settling in distal portions of the impoundment (Robertson, 1994). At some sites, tailings are thickened to >60 wt.% solids prior to deposition. Thickening the tailings allows a more rapid settling of the solids, which therefore reduces the potential for hydraulic sorting, resulting in a more uniform grain-size distribution than is observed in conventional tailings areas (Robinsky, 1978; Al, 1996).

During tailings disposal, water is continuously added to the impoundment and the water table remains near the impoundment surface. After tailings deposition ceases, precipitation becomes the dominant source of recharge to the impoundment. The water table falls to an equilibrium position controlled by the rate of precipitation, the rate of evapotranspiration, and the hydraulic properties of the tailings and the underlying materials (Dubrovsky et al., 1984; Blowes and Jambor, 1990).

The fine grain size of mine tailings results in a high moisture-retaining potential for these materials, which is a situation distinctly different from that in waste-rock piles. Whereas waste-rock piles commonly have a large open and free-draining porosity, mine tailings drain slowly, maintaining a large residual moisture content under gravity drainage. Measured moisture contents of conventional tailings impoundments vary from 10% to 100% saturation (Smyth, 1981; Blowes, 1990). The residual moisture content of thickened tailings is greater than that observed for conventional tailings (Robinsky et al., 1991; Al and Blowes, 1996). The high residual moisture content of mine tailings results in a low gas-filled porosity, and in rapid changes in hydraulic gradient in response to precipitation (Blowes and Gillham, 1988; Al and Blowes, 1996).

Precipitation that falls on the impoundment surface migrates downward and laterally through the tailings impoundment into underlying geological materials (Figure 9). Groundwater velocities in tailings impoundments are relatively low. Coggans et al. (1999) estimated that the groundwater vertical velocity ranged from 0.2ma1 to 1.0ma1 at the Inco Ltd. Copper Cliff Central Tailings area in Sudbury, Ontario, whereas horizontal velocities were on the order of 1015ma1. At the Nickel Rim tailings impoundment, also near Sudbury, Johnson et al. (2000) estimated groundwater vertical and horizontal velocities were in the range 0.10.5ma1 and 116ma1.

The surface areas of tailings impoundments vary from less than 10 ha to several square kilometers, and the thicknesses of the tailings deposits vary from a few meters to more than 50 m. The relatively low groundwater velocities and the large areal extent of tailings impoundments result in long time intervals between the time of groundwater infiltration and the time of groundwater discharge to an underlying aquifer or to the surface-water environment (Figure 10). These long travel times result in the delay of measurable environmental degradation at the groundwater discharge point until long into the life of the impoundment. The severity of the negative environmental effects associated with tailings impoundments may not be evident until long after mine closure and decommissioning of the impoundments. The subsequent prevention and remediation of low-quality drainage waters are more difficult than during the active mining. The long travel distances and low groundwater velocities result not only in the potential for prolonged release of contaminants from the tailings impoundment, but also in large long-term treatment costs. For example, Coggans (1992) combined estimates of the rate of sulfide oxidation with estimates of groundwater velocity at the Inco Copper Cliff Central Tailings area in Sudbury, Ontario, and predicted (i) that the peak release of sulfide oxidation products will occur 50 yr after the impoundment is decommissioned, and (ii) that high concentrations of oxidation products will persist for 400 yr thereafter.

In most tailings impoundments, gaseous diffusion is the most significant mechanism for oxygen transport. The rate of diffusion of oxygen gas is dependent on the concentration gradient and the diffusion coefficient of the tailings material. The diffusion coefficient of tailings is dependent on the air-filled porosity of the tailings; the coefficient increases as the air-filled porosity increases, and the coefficient decreases as the moisture content increases. Several empirical relationships have been developed to describe the dependence of the gas diffusion coefficient on the tailings moisture content (e.g., Reardon and Moddle, 1985). These relationships indicate a maximum diffusion coefficient at low moisture contents, with a gradual decline in diffusion coefficient as moisture content increases to 70% saturation, followed by a more rapid decline as the moisture content increases further. The relationship between moisture content and diffusion coefficient results in rapid oxygen diffusion in the shallow portion of the vadose zone of a tailings impoundment, where the moisture content is low. The rapid diffusion of oxygen in this zone replenishes oxygen consumed by the oxidation of sulfide minerals. As the sulfide minerals in the shallow portion of the tailings are depleted, the rate of sulfide oxidation decreases due to the longer diffusion distance and the higher moisture content of the deeper tailings.

In many tailings impoundments a variety of sulfide minerals is present. Jambor (1994) reported a general sequence of sulfide-mineral reactivity observed in several tailings impoundments, from the most readily attacked to the most resistant, to be pyrrhotitegalena-sphaleritepyrite-arsenopyritechalcopyritemagnetite. Blowes and Jambor (1990) observed systematic variations in sulfide-mineral alteration versus depth at the Waite Amulet tailings impoundment, Rouyn-Noranda, Qubec. On the basis of the observations, the degree of alteration was classified into a numerical scale as shown in Table 12. The sulfide alteration index indicates the relative degree of alteration of sulfides. Because pyrrhotite is the sulfide mineral most susceptible to alteration, the extent of its replacement forms the basis for the alteration index. When plotted versus depth on a vertical axis, the alteration index estimates made at the Sherridon Mine, Manitoba, correlated well with geochemical parameters measured in adjacent drill-holes, and with gas-phase O2 concentrations (Figure 11).

The microbially mediated oxidation of sulfide minerals within mine-tailings impoundments generates acidic conditions and releases high concentrations of dissolved metals. Mill tailings at the Heath Steele mine in New Brunswick contain up to 85 wt.% sulfide minerals (Blowes et al., 1991; Boorman and Watson, 1976). Pore-water pH values as low as 1.0, and concentrations of dissolved SO4 up to 8.5104mgL1 were observed in the shallow pore water of the tailings impoundment (Figure 12;Blowes et al., 1991). This water also contained up to 4.8104mgL1 Fe, 3,690mgL1 Zn, 70mgL1 Cu, and 10 mg L1 Pb. The shallow pore waters at the Waite Amulet tailings impoundment in northwestern Qubec contain 2.1104mgL1 SO4, 9.5103mgL1 Fe, 490 mgL1 Zn, 140 mgL1 Cu, and 80 mgL1 Pb. The pH of this water varies from 2.5 to 3.5 (Blowes and Jambor, 1990). High concentrations of dissolved zinc (48mgL1), copper (30mgL1), nickel (2.8mgL1), and cobalt (1.5mgL1) were observed in the shallow groundwater at the inactive Laver copper mine in northern Sweden (Holmstrm et al., 1999). These low-pH conditions and high concentrations of dissolved metals occur within the shallowest portions of the tailings impoundment. As this water is displaced downward through the tailings, or through adjacent aquifer materials, the pH gradually rises, and many metals are removed from solution by precipitation, co-precipitation or adsorption reactions. High concentrations of Fe(II) and SO4, however, move down through the tailings and aquifer sediments relatively unattenuated (Dubrovsky et al., 1984; Johnson et al., 2000). As this groundwater discharges from the tailings impoundment, Fe(II) oxidizes and precipitates as ferric (oxy)hydroxide and ferric hydroxysulfate minerals. These reactions release H+, generating acidic conditions within surface waters. The transport of Fe(II) along the groundwater flow path, therefore, provides the vehicle for transporting acidity long distances from the oxidation zone to the surface-water flow system.

Figure 12. Pore-water chemistry and saturation indices versus depth at the tailings site of the Heath Steele mine. IA represents saturation indices calculated using an ion-association model, and SII represents saturation indices calculated using a specific ion-interaction model (after Ptacek and Blowes, 2000).

Waters draining abandoned mines, mine spoils, and tailings deposits are often characterized by low pH and elevated concentrations of soluble metals (particularly iron) and sulfate (Table 3). These are generically referred to as AMD waters (or acid rock drainage in North America). Acidity in such waters derives from the presence of soluble aluminum, manganese, and iron (mineral acidity) as well as hydronium ions. Extremely acidic lakes may develop naturally in volcanic area, for example, Lake Kawah Idjen in Indonesia, which has a pH of 0.7. Acidic mining lakes, in contrast, are relics of opencast mining, where worked-out voids have not been backfilled, and become progressively filled with rising groundwater or river water. Where the surrounding bedrocks are rich in sulfide minerals (normally chiefly pyrite and marcasite) and contain small amounts of carbonates, the oxidative dissolution of the former can lead to the formation of extremely acidic mine lakes. Acid mine lakes are particularly abundant in central Europe, in parts of Germany, Poland, and the Czech Republic. In past times (up to the end of the twentieth century) the extensive reserves of lignite in these areas were extracted by opencast mining on enormous scales, leaving a legacy of a very large number of man-made lakes of varying sizes and chemistries. In the Lusatia district of eastern Germany alone there are an estimated 200 mining lakes of >1ha that have pH values of <3.

Source: Data are from Johnson DB (2006) Biohydrometallurgy and the environment: Intimate and important interplay. Hydrometallurgy 83:153166, and Nordstrom DK, Alpers CN, Ptacek CJ, and Blowes DW (2000) Negative pH and extremely acidic minewaters from Iron Mountain, California. Environmental Science and Technology 34: 254258.

Source: Data are from Johnson DB (2006) Biohydrometallurgy and the environment: Intimate and important interplay. Hydrometallurgy 83:153166, and Nordstrom DK, Alpers CN, Ptacek CJ, and Blowes DW (2000) Negative pH and extremely acidic minewaters from Iron Mountain, California. Environmental Science and Technology 34: 254258.

The microbiology of AMD streams has been the subject of a number of reviews in books and journals. Knowledge of how biodiverse these flowing waters can be has expanded considerably since At. ferrooxidans was first isolated from an AMD stream draining a bituminous coal mine in the United States in 1947. The most important factors in determining which microbial species are present in AMD appear to be pH, temperature, and concentrations of dissolved metals and other solutes. At the most extreme end of the AMD spectrum, the microbiology of mine waters within the Richmond mine at Iron Mountain, California (which can have negative pH values), has been studied extensively. Within this abandoned mine, pyrite is undergoing oxidative dissolution at a rate that is sufficient to maintain air temperatures of between 30 and 46C, and produce mine waters containing 200gl1 of dissolved metals. A novel iron-oxidizing archaeon, Ferroplasma acidarmanus, was found to be dominant in waters within the mine that had the lowest pH and highest ionic strengths, while L. ferriphilum and L. ferrodiazotrophum were also associated with exposed pyrite faces. Sulfobacillus spp. were more important in some of the warmer (43C) waters. At. ferrooxidans was rarely found in sites that were in contact with the ore body, though it was found in greater abundance in the cooler, higher pH waters that were peripheral to the ore body. In contrast, a microbiological survey of much cooler and higher pH mine waters at an abandoned subarctic copper mine in Norway showed that an At. ferrooxidans-like isolate (closely related to a psychrotolerant strain found subsequently in a mine in Siberia) was the dominant iron oxidizer present. L. ferrooxidans was only detected in enrichment cultures using mine water inocula. The Norwegian AMD waters also contained significant numbers of acidophilic heterotrophs related to some species (Acidiphilium, Acidocella, and Acidisphaera) that had previously been observed in acidic environments, and one (a Frateuria-like bacterium) that had not.

The importance of At. ferrooxidans-like bacteria in cooler (<20C) mine waters of pH 23 has also been supported at sites in other parts of the world. For example, biomolecular analysis (from clone libraries) of four AMD sites at the Dexing copper mine in the Jiangxi province of China found differences in the distribution of acidophiles with water pH. In the most acidic site (pH 1.5), Leptospirillum spp. (L. ferrooxidans, L. ferriphilum, and L. ferrodiazotrophum) were the dominant species in the clone library, while in pH 2.0 AMD L. ferrodiazotrophum was the single dominant species detected. In slightly higher pH (2.2) AMD, most clones recovered were related to At. ferrooxidans, while in the highest pH waters (3.0) most were related to the heterotrophic moderate acidophile Acidobacterium. Where mine waters have pH values of above 3, however, there is increasing evidence that moderately acidophilic iron oxidizers assume a more important role than At. ferrooxidans. The dominant iron oxidizer in AMD flowing from an underground coal mine in south Wales was found to be a Thiomonas-like bacterium, and similar strains (given the novel species designation Thiomonas arsenivorans) were isolated from an abandoned tin mine in Cornwall, England, and a disused gold mine (Cheni) in France. Other acidophilic Bacteria isolated from the Cornish site included Acidobacterium-like and Frateuria-like isolates, and an iron oxidizer related to Halothiobacillus neopolitanus. Further evidence of the importance of previously uncultured acidophiles in AMD has come from a study of acidic (pH 2.73.4) iron- and arsenic-rich water draining mine tailings at Carnouls in France. The dominant bacteria found in clone libraries were betaproteobacteria, many of which were related to a Gallionella-like sequence previously reported in a chalybeate spa in north Wales. The sole Gallionella sp. that has been characterized (Gallionella ferruginea) is a neutrophilic iron oxidizer that grows best under microaerophilic conditions, and the circumstantial evidence for the existence of an acidophilic (or acid-tolerant) species of Gallionella is intriguing. Researchers also found evidence of SRB distantly related to Desulfobacterium in AMD at Carnouls. SRB may also be found in sediments (and microbial mats) underlying AMD, though the pH in such sediments is frequently much higher than the AMD itself.

Microbiological studies of acid mine lakes in Germany have focused on phototrophic eukaryotes as well as acidophilic bacteria and have also examined how dissimilatory microbial reductive processes may be stimulated in order to ameliorate water acidity and immobilize metals. A survey of 14 acidic lakes in Lusatia (ranging in pH from 2.14 to 3.35, and conductivities from 690 to 4460Scm1) found a positive correlation between the relative numbers of the iron-oxidizing heterotroph Fm. acidiphilum and concentrations of aluminum. However, it was concluded that indicator groups of bacteria, rather than single species, were better correlated with different lake chemistries. Addition of organic carbon, nitrogen, and phosphorus to enclosed water columns in a pH 2.6 mine lake was shown to induce changes in both water chemistry and microbiology. Treatment of water resulted in increased microbial diversity, and SRB (Desulfobacter spp.) were among the microorganisms detected in the amended water columns.

One other important extremely acidic ecosystem that has been studied extensively is the Rio Tinto, a major river, some 92km in length, located in southwest Spain (Figure 3). The source of the river is the Pea de Hierro (Iron Mountain) in the Iberian Pyrite Belt, and from there it flows though a large and historic area of copper mining (the Riotinto mines), eventually reaching the Atlantic Ocean at Huelva. Interestingly, even above the Riotinto mines, the river is acidic and enriched with metals, but this is very much accentuated as it flows through the (now abandoned) mining district. The river has a mean pH of about 2.2 and its distinctive red coloration derives from its soluble ferric iron content (2gl1). Primary production in the river is carried out by both photosynthetic and chemoautotrophic acidophiles. A study of the indigenous prokaryotes showed that >80% were Bacteria, and that Archaea accounted for only a relatively small proportion of cells. A variety of different iron oxidizers (At. ferrooxidans, Leptospirillum spp., Fm. acidiphilum, and Fp. acidiphilum) as well as the iron-reducing heterotroph Acidiphilium were identified. A geomicrobiological model involving cyclical oxidation of ferrous iron and reduction of ferric iron has been proposed to account for the remarkable chemical stability of the river ecosystem.

The development of functional technosols from mine tailings is possible after an initial rapid weathering and addition of OM amendments (Li and Huang, 2014; Uzarowicz and Skiba, 2011). Subsequently in weathered tailings with a much reduced sulfide content (eg, <5%) and neutral pH conditions, the development of physical structure (ie, aggregates and pores) and of soil-like heterotrophic microbial communties is fundamental for the formation of technosols with soil-like biogeochemcial processes (Li and Huang, 2014).

Improving aggregation in base metal mine tailings is an important step in the engineered pedogenesis to rehabilitate functional root zones for direct revegetation with native plant communities. The organomineral association critical for microaggregation can be stimulated in OM amended tailings through the interaction between functional organic ligands in the OM and charged surfaces of minerals in the tailings. In a pot experiment that lasted 40 days, neutral Cu/Pb-Zn tailings were amended with sugarcane residue (SR) or its compost (SRC), which were planted with or without a pioneer plant species, red flinders (Iseilema vaginiflorum) (Yuan, 2014). It was found that the organic amendments (particularly the SRC) with functional organic ligands (eg, amine, carboxylic, hydroxylic, alcoholic, and phenolic hydroxyls) mainly stimulated microaggregation in the Cu/Pb-Zn tailings, while the role of plant roots in the tailings was mainly related to the formation of macroaggregates. Therefore, both organic amendments rich in functional groups and pioneer plant growth may be adopted to improve physical structure and stimulate the development of technosols in Cu/Pb-Zn tailings.

In weathered sulfidic tailings of base metal mines such as Pb-Zn-Ag mines, OM amendments or organic carbon sources from plant roots were useful to stimulate further weathering of unstable minerals and induce the shift of microbial communities toward heterotrophic ones in the root zones (Li etal., 2013b, 2014; Li and Huang, 2014). Community composition, which was compared in Pb-Zn-Cu tailings with and without revegetation under subtropical and semiarid climatic conditions, was characterized by using 16S rRNA gene based pyrosequencing with universal primers (Li etal., 2014). Bacterial diversity, as indicated by both the operational taxonomic units (OTU's) number and the Shannon index of the revegetated samples, was significantly higher than that of the sample from the pure tailings. At the phylum level, Proteobacteria and Bacteroidetes were remarkably higher in the revegetated samples compared to the pure tailings; this is possibly related to the change in the organic carbon pool. Phylotypes belonging to Thiobacillus were found thriving in the revegetated tailings (Li etal., 2013b).

Large quantities of radioactive waste and mine tailings are being generated annually worldwide from mining and processing uranium ores for nuclear energy. Radioactive tailings represent a large clean-up challenge to the mining and nuclear energy industries. Therefore in the first few sections of this chapter we detailed the physical, chemical, storage, transportation and disposal of radionuclides, and which ones are more dangerous to the environment and human health. The conclusions arrived at suggest that a common-sense approach to radioactive waste and its safe disposal involves the following four steps:

Assess all options for the management of radioactive waste. Most radioactive waste management assumes the need for off-site storage, but the option of storing waste where it is produced needs re-evaluation. Even if centralized facilities exist, waste is inevitably stored at the sites of production for too long, and on-site storage facilities must be adequately constructed and regulated.

Scientific and environmental strict criteria must be used in choosing operational and management options. Since technologically safe solutions are now available for radiation, we have no right to transmit unprocessed nuclear waste to future generations in an open-ended way.

Invest in phytoremediation of radionuclides, a technology already demonstrated on a pilot-scale; but it needs to be developed at an industrial and commercial level. Phytoremediation of radioactive contaminants is still in development, and more research is required to address plant species that will be most effective in different radioactive waste scenarios. Plants must be able to survive and thrive in contaminated waste, yet be able to mitigate the toxic radioactive pollutants.

To summarize, much of the technology for safe handling and storage of radionuclides is available. There is not one solution but rather several complementary solutions to the problem of managing radioactive waste. We must pursue research on radioactive safety encased in inert substances, continue to reprocess spent fuel and immediately begin work on underground storage. Public involvement in decisions and informed consent to proposals is also essential from a practical point of view, because there is a long history of communities successfully mobilizing to force the abandonment of nuclear projects.

The majority of this chapter, however, is devoted to the growing importance of phytoremediation of radioactive waste sites. A brief description of non-plant based remediation methods is outlined, followed by a detailed evaluation of plant based remediation methods, including hyperaccumulation, radioactive tolerance, uptake and distribution, aquatic phytoremediation and cost estimates. Phytoremediation has become a fast growing field of research and development for application to radionuclide waste. Phytoremediation, although still an emerging technology for radioactive contaminated sites, has become more attractive due to its low cost, high public acceptance and environmental (green) acceptability. It is not a method to be used for all radioactive waste problems, but it is well worth considering as a major supplement to existing technologies. A number of important areas of research and development in phytorermediation still need to be improved, and future research should focus on these. Topics to be better understood include the role of soil chelation and soil acidity on extraction of radionuclides. Increased growth and biomass of selected plants for remediation, and in particular trying to achieve greater rates of transpiration in plants that is the driving force for radionuclide hyperaccumulation is required. There will also need to be better identification of plant species with increased resistance to radiation, and careful selection for better adaptation of plants to radiation poisoning. Clearly, different approaches using different plants are going to be the normal way of dealing with different radionuclides.

Phytoremediation technology has been demonstrated in a number of different situations and for a number of different toxicants (including radionuclides), but has not yet been commercially exploited. More research is required for the development of plants tailored to remediation needs, and the use of transgenic fast-growing woody trees like willow and poplar, where genetic engineering is going to play an important role. The use of trees and transgenic technology is well advanced in some phytoremediation situations and superior seedlings of quick-growing trees are already available. The concept of manipulating plant genes for toxic metal (and perhaps radionuclide) uptake is today a cutting-edge research topic; however, these technologies are not likely to be a total substitute for more basic, site and field testing of various phytoremediation methods. Neverthless, transgenic plants would provide more suitable plants for increased secretion around roots to aid radionuclide uptake and binding, and better overall growth and biomass to absorb and remediate radioactive sites. The use of trees and forests leads to considerable savings in remediation of radioactive sites, as clearly demonstrated by removal of tritium in wastewater. The likelihood of public acceptance of genetically engineered plants for phytoremediation should be welcomed, since it has the potential to clean up the environment of toxicants; however, as in the whole public debate on radioactive waste, public involvement in decision making and good information is critical. Phytoremediation technology has attracted a great deal of attention in recent years and the expectation is that phytoremediation is likely to capture a significant share of the environmental remediation market. It is expected that phytoremediation of radionuclide wastes will become an integral part of the environmental management and risk reduction strategy for governments, industry and society.

Composts have also been added to soils to assist phytoremediation. In mine tailings restoration when clay loam soils were amended with composted biosolids, willows growing in such medium were very effective in phytoextraction of Mn, Cu, and Cd (Boyter etal., 2009). Compost amendments (obtained using wasted tea leaves as the main carbon source and swine manure as the nitrogen source by mixing at a mass ratio of 20 to 1) are found to be effective in assisting the growth of rape seeds, sunflowers, tomatoes, and soapworts in silt loams, and in performing the phytoextraction of Cu, Ni, and Cr from water-washed silt loams (Sung etal., 2011). Composts can not only supply nutrients to plants, but also can create loose and ventilated soils for plants growing in hostile soils. It is seen that both the CEC and the organic matter increase in the test soils after adding the compost (Sung etal., 2011).

The main sources of Cd inputs to rice soil include P fertilizers, biosolids, and mine tailings (Table 4.5). Cadmium input through P fertilizers can be reduced by either selective use of PRs with low Cd or treating the PRs to remove Cd. Superphosphate fertilizer manufacturers in many countries including New Zealand and Australia are introducing voluntary controls on the Cd content of P fertilizers. For example, the fertilizer industry in New Zealand achieved its objective of lowering the Cd content in P fertilizers from 340mgCdkg1P in the 1990s to 280mgCdkg1P by the year 2000 (Bolan etal., 2003a; Rys, 2011). The Cd content as determined by the PR source is the most difficult to control because supplies of PRs with low Cd contents are limited and sources with higher Cd contents continue to be used in many countries for practical reasons. A number of PRs (e.g. Jordan (El Hassa) PR and Morocco (Khouribga) PR) are low in Cd, and these can be used for the manufacture of superphosphates. Alternatively, since Cd has a low boiling point (BP=767C), it can be removed by calcining the PRs. Phosphoric acid used in the food industry is manufactured mostly only after the removal of Cd through calcination of the PRs. Calcination of PRs may not be a likely option in the fertilizer industry because it is expensive and calcination decreases the reactivity of PRs making them unsuitable for direct application as a source of P (Ando, 1987).

Chien etal. (2009) mentioned in a recent review that if a water-soluble P (WSP) fertilizer contains a high Cd content, granulation of WSP fertilizer with potassium chloride (KCl) may result in a higher Cd uptake by crops compared to the same, but bulk-blended PK fertilizer. They suggested that a possible explanation would be that in granulated PK fertilizers, KCl- and Cd-containing P fertilizers are in the same granule and thus are in close contact, thereby increasing the possibility of forming readily bioavailable CdCl20 and CdCl1+ complexes. They also added that it would be less likely that the complexes would form when KCl- and Cd-containing P granules are physically separated in bulk-blended PK fertilizers.

The above hypothesis was tested and confirmed by Chien etal. (2003) in a preliminary greenhouse study using upland rice and soybean (Glycine max (L.) Merr.). In their study, all P and K sources produced by either granulation or bulk blending had the same granule size (1.683.36mm diameter). The results showed that the agronomic effectiveness in increasing crop yield was the same with Cd-containing SSP and the reagent-grade monocalcium phosphate [(MCP) (0% Cd)], whether granulated or bulk blended with KCl. However, they noticed that concentrations of Cd in plant-tissue samples of all crops were much lower for MCP than for SSP. In all the plant-tissue samples, Cd concentrations obtained with granulated (SSP+KCl) fertilizers were higher than that with bulk-blended (SSP)+(KCl) fertilizers. Their results demonstrated that bulk blending of Cd-containing P fertilizers with KCl can reduce Cd uptake by crops compared to the same, but granulated, PK fertilizers (Fig. 4.2). Although PK sources, instead of NPK sources, were used in their study, they expected that inclusion of N will not affect the results, and, if proven true, the process of bulk blending, compared to granulation in decreasing Cd uptake, would also apply to NPK compound fertilizers.

Figure 4.2. Grain yield of upland rice and Cd concentrations in rice grain and straw. GL, granulated; SSP, single super phosphate; BB, bulk-blended; MCP, mono calcium phosphate (Chien etal., 2003). Means followed by the same letter within the treatments are not significantly different at p<0.05.

Another possible mechanism for producing a healthier plant is reduction of metal toxicity in contaminated soils and mine tailings that, under normal conditions, almost completely inhibits plant growth. Although the bacterium tolerate only moderate levels of metals and other toxic compounds (see previous reviews Bashan and Holguin, 1997; Bashan and Levanony, 1990; Bashan et al., 2004; also Kamnev et al., 2005, 2007), it apparently contributed mechanisms allowing plants to grow in mine tailings or contaminated soils. Cadmium causes severe inhibition of growth and nutrient uptake in barley. In the presence of CdCl2, inoculation with A. lipoferum partly decreased Cd toxicity, possibly through the improvement of mineral uptake. Additionally, inoculation slightly enhanced root length and biomass of barley seedling treated with Cd and the amount of nutrients absorbed by the inoculated plants increased significantly. There was only some protection against Cd toxicity, but no uptake of Cd, since Cd content in the inoculated plants was unchanged (Belimov and Dietz, 2000; Belimov et al., 2004). A. brasilense Sp245 associated with wheat changes the speciation, bioavailability, and plant uptake of arsenic. Plants inoculated with Azospirillum accumulated less arsenic than did uninoculated plants (Lyubun et al., 2006). Inoculation of the wild desert shrub quailbush (Atriplex lentiformis) growing in extremely stressed environment with A. brasilense strains Sp6 and Cd, such as acidic mine tailings having high metal content, resulted in a significant increase in production of plant biomass (L.E. de-Bashan et al., unpublished data). Similar results were obtained when wild yellow palo verde desert trees (Parkinsonia microphylla) were inoculated with A. brasilense Cd in rock phosphate tailings (Bashan et al., unpublished data).

Plants have been used to correct human error over the ages. A few species are capable of revegetating Roman lead and zinc mine tailing in Wales (Smith and Bradshaw, 1979). Of these, plants that can withstand toxic wastes after they have been taken up are of interest for phytoremediation. Two types of multi-cut species are usually considered for phytoremediation, with the cut material burnt to extract the heavy metals or to oxidize the organic wastes: herbaceous species such as B. juncea and Spartina spp. (cord grasses), which are most efficient at dealing with surface wastes and trees such as Populus spp., for dealing with deeper wastes (Pilon-Smits and Pilon, 2002)

Heavy metal tolerance has been brought into B. juncea (Indian mustard) from slow-growing Thlaspi by protoplast fusion (along with many other genes; Dushenkov et al., 2002). It was better yet to transgenically transfer genes leading to enhanced glutathione content (Bennett et al., 2003) to make the necessary phytochelatins that complex the heavy metals. A single cropping of B. juncea does not clean up a toxic site. Many growth cycles are required, with multiple harvests and natural reseeding. B. juncea, even more than its close relative B. napus (oilseed rape), is not fully domesticated, and the multiple cycles of cropping would allow the possibility of selecting for ferality. Thus, mitigation seems necessary to prevent volunteers from becoming feral. One gene that might specifically fulfill the need for a mitigator gene is over-expression of a cytokinin oxidase (Bilyeu et al., 2001), which reduces cytokinin levels. This in turn led to phenotypes with far reduced shoot systems (unfitness to compete) but with faster growing, more extensive root systems (Werner et al., 2003), all the better for extracting toxic wastes. Genes that delay or prevent flowering may also be useful with the Brassica species, allowing multiple cuts of larger vegetative plants and preventing gene flow.

Heavy metals and metalloids are the major contaminants that accumulate in soil through emissions from industrial areas, disposal of metal wastes, mine tailings, animal manures, pesticides, sewage sludge, coal combustion residues, atmospheric deposition, wastewater irrigation, and spillage of petrochemicals (Khan et al., 2008; Zhang et al., 2010). The heavy metals found mostly at contaminated sites include Zn, Cu, Cr, Pb, As, Cd, Ni, and Hg. Metals unlike organic contaminants do not undergo degradation by microbes and chemicals (Kirpichtchikova et al., 2006). After introduction into soil, their total concentration persists for a long time (Adriano, 2003). Contamination of soil by heavy metals poses a threat to the ecosystem and humans through the food chain, ingestion, or contact with soil, drinking of groundwater, land tenure problems, and food insecurity due to reduction in usable land for agricultural production (McLaughlin et al., 2000a,b; Ling et al., 2007).

A variety of approaches can be used for the remediation of contaminated soil. The technologies have been broadly classified by the US Environmental Protection Agency (EPA) into two categories: (1) containment remedies and (2) source control (Maslin and Maier, 2000; McLaughlin et al., 2000a,b). Containment remedies involve the construction of caps, liners, and vertically engineered barriers (VEB) for the prevention of contaminant migration. Source control includes ex situ and in situ treatment technologies. Ex situ treatment technologies involve the removal or excavation of contaminated soil from the site, whereas in in situ treatment technologies there is no need to excavate contaminated soil; it is treated at its original site.

The selection of any remediation technology depends on a number of factors, according to Wuana and Okieimen (2011), including: (1) long-term effectiveness, (2) cost, (3) general acceptance, (4) commercial availability, (5) applicability to mixed wastes/organics and heavy metals, (6) applicability to high metal concentrations, (7) volume reduction, (8) toxicity reduction, and (9) mobility reduction. Reliable methods to detect environmental pollutants, their dynamics and fate, are required to evaluate their impact on soil quality and living organisms. Techniques used to monitor volatile and semivolatile pollutants in soil include physicochemical techniques such as solid phase micro-extraction (SPME), followed by analysis by GC-MS, use of bioindicators, and use of sensing technology (e.g., electronic nose) (Cesare and Macagnano, 2013).

The increase in human population has raised the quantity of waste and introduced many different types of pollutants into water bodies; these were not considered pollutants earlier but are now seen as harmful to the environment and public health. The pollutants include pharmaceuticals, toxins, hormones, viruses, and endocrine-disrupting chemicals (Xagoraraki and Kuo, 2008). Heavy metals (e.g., Cd, Pb, Mn, Fe, Zn, Cu) are also major contaminants of water (Opaluwa et al., 2012). Human activity is the major source of most of the water pollutants, whereas some amount of them are added by natural activities such as volcanic eruptions.

The main anthropogenic activities that cause water pollution include agricultural waste, livestock waste, industrial chemical waste, pesticides, fertilizers, mine drainage, untreated municipal sewage, spillage of petroleum products, spent solvents, and so forth. Once pollutants are discharged into any of the surface water bodies or the groundwater, they enter the water cycle. Pollutants may also undergo physical, biological, and chemical transformations (Xagoraraki and Kuo, 2008). The contaminants in water bodies, such as heavy metals, are also bioaccumulated in the flora and fauna of that region and so enter into the food chain. The contaminated water, whether used for drinking, irrigation, or other purposes, may lead to many health issues. For example, chemical pollutants can damage functional systems (e.g., immune system and nervous system) and major organs (e.g., kidney and liver), and pathogenic microorganisms in the water lead to gastrointestinal problems.

Increased cancer risk is also a major threat posed by enhanced concentrations of pollutants in drinking water (Xagoraraki and Kuo, 2008). An atomic absorption spectrophotometer (AAS) is used to assess the presence and amount of heavy metals in polluted water (Opaluwa et al., 2012). Adsorbents, such as activated carbon, can be used to remove heavy metals from contaminated water; however, it is an expensive material. So, instead of using commercial activated carbon, researchers used materials (e.g., sawdust, chitosan, mango leaves, coconut shell) that were inexpensive, had a high-adsorption capacity, and were locally available (Renge et al., 2012).

Contaminants enter plants when they are grown in soil that has various types of them, such as heavy metals, or when irrigated with polluted water containing contaminants. The plants show growth reduction, altered metabolism, metal accumulation, and lower biomass production (Nagajyoti et al., 2010). Some metals (e.g., Mn, Cu, Zn, Co, and Cr) are important for plant metabolism in trace amounts. When these metals are present in bioavailable forms and in excess, they become toxic to plants. Few heavy metals are very toxic to metal-sensitive plants, so result in growth inhibition and may also cause death of the organisms. The uptake of heavy metals does not show a linear increase with an increasing metal concentration. A number of factors affect the uptake of heavy metals by plants, which includes the growing environment. Some examples are soil aeration, soil moisture, soil pH, temperature, competition between plant species, type and size of plants, plant root systems, type of leaves, the elements available in the soil, and plant energy supply to roots and leaves (Yamamato and Kozlowski, 1987).

Metal contamination affects various biochemical and physiological processes in plants such as carbon dioxide fixation, gaseous exchange, respiration, and nutrient absorption. The toxic effects of six heavy metalsMn, Cd, Cr, Hg, Co, and Pbwere studied on Zea mays by Ghani (2010). Cd was found to be the most toxic and Cr to be the least toxic metal. The phytotoxicity of the six heavy metals was found in this order: Cd>Co>Hg>Mn>Pb>Cr. Heavy metals in plants lead to production of reactive oxygen species (ROS) such as hydrogen peroxide, superoxide radicals, and hydroxyl radicals. The ROS can oxidize biological molecules, lead to major cellular damages, and ultimately cell death. Hydroxyl radicals produced in the DNA proximity can remove or add hydrogen atoms to the DNA backbone or bases, respectively (Pryor, 1988). This resulted in 104105 DNA base modifications in a cell in one day (Ames et al., 1991). Fe2+ ions, free in solution or coordinated with ring nitrogens or complexed to a phosphate residue, were involved in these DNA alterations mediated by the hydroxyl radical (Luo et al., 1994).

Metal ions also lead to oxidative modification of proteins and free amino acids (Stadtman, 1993). The oxidation in proteins most commonly occurs at arginine, histidine, methionine, proline, cysteine, and lysine residues. Transition metals (e.g., iron) and oxygen lead to lipid peroxidation and damage to biological membranes. Plants cope in a number of ways with metal toxicity. The ROS generated in leaf cells are removed by enzymes of the antioxidant system of plants such as ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione reductase (GR), and catalase (CAT). Proline is reported to detoxify active oxygen in Cajanus cajan and Brassica juncea under heavy metal stress (Alia et al., 1995).

Burning of coal in thermal power plants and disposal of fly ash, long-term mining and smelting of the sulfide ores, runoff from mine tailings, and application of pesticides and herbicides release huge amounts of arsenic in to the biosphere. Additionally, arsenic is also used in the production of semiconductors, lead-acid batteries, and pesticides and herbicides, in the glass industry and copper refining industry, and in the hardening of metal alloys. Use of arsenic in wood preservation is very common and has increased significantly in the last few decades [14]. Wood may deteriorate by the attack of insects, fungi, bacteria, and animals, but can be protected by impregnating with CCA with the composition CuO (18.5%), Cr2O3 (47.5%), and As2O3 (18.5%). At one time, arsenic compounds such as lead arsenate, calcium arsenate, and sodium arsenate were used as pesticides for debarking trees, to control ticks, fleas, and lice, and in aquatic weed control. However, these applications have been banned due to the toxic effects of arsenic and later public awareness about food safety and environmental contamination [15].

global tailings standard highlights the importance of technology for isometrix - mining magazine

"I don't think those responsible for tailings management are embracing technology to the extent they should be." Bolton said in an interview for Mining Journal and Mining Magazine's 2021 Tailings Program.

"However," he said "things have changed since the publishing of the Global Industry Standard on Tailings Management in 2020. That's certainly shaken the industry up a bit in terms of the attention tailings dams have to be given. It does highlight where, in my view, technology can play a useful part."

IsoMetrix is a leading developer of integrated risk management software for mining companies and other risk-oriented industries such as oil and gas, renewables, transport and logistics, and waste services. Its solutions for the mining industry cover related areas such as tailings, environmental and carbon management, HSE management, ESG reporting, enterprise risk, compliance, stakeholder engagement, resettlement and socio-economic development.

"Previously - or even perhaps to this day - if someone went to a site and gathered information, it would take several days until a decision-maker might see that information, and by that time it might be too late." he said.

Another related challenge is that policies from a corporate level do not always get delivered to individual tailings facilities, with the result that recommended actions are not always implemented, in Bolton's opinion.

Having a tailings management system (TMS) - a recommendation of the Global Industry Standard, and something which IsoMetrix provides - is key to ensuring information flows between the right people in a timely manner.

"Having a TMS means that you know what's happening to the data, what's happening to the audit findings, the details and status of incidents and what's happening to the engineer's recommendations for example. It brings clarity to questions such as Where are they managed? How are they actioned? How are you closing out those actions?' Management systems can bring a lot of efficiencies when it comes to these types of details." he said.

"When data does not conform to the limit or threshold, you can set triggers and notifications so that the right person is made aware of a situation, and they can respond and react a lot quicker than previously. That response time can be cut right down using technology."

Water management was another essential challenge identified by Bolton and other participants in the 2021 Tailings Program. According to Bolton, there is a need not only to monitor the water within the dam, but also the water going into and out of the facility - such as water being discharged into the environment or water being reused for mineral processing.

"There have been advancements in using devices and technology to capture certain measurements, namely flow measurements, water quality measurements, and pressures within a tailings facility. There is a lot of technology available nowadays. However, is it being used extensively at present? I don't think so." Bolton said.

Other available technologies that Bolton said have not been "explored or utilized enough" include devices that can help with air quality, weather information, seismic activities, thermal activity, and other critical indicators around a dam.

"There's definitely technology available. It can be linked up to the Internet of Things (IoT) and provided to any third-party, or the company itself. There's a myriad of ways in which data can be managed, such as using data warehouses for example, and systems can be set up in a way so that only exceptions or certain summaries are sent to the relevant people who want to see the information."

For example, "We offer the ability to conduct your inspections and audits and capture the findings. If corrective and preventative actions are needed, we provide the capacity to notify the relevant people and track these actions until closure."

"As an example, a potential drill could be to see how quickly a community can evacuate from a potential flow path if a tailings dam collapsed. You can run that drill, make observations, capture the findings, and then implement additional controls from those observations to improve." Bolton said.

"Maybe the warning siren did not go off, or maybe people took too long to get out of the way. These are details which you can capture in a system, track and close out. We have dashboards that can show all the data, facilitating a holistic approach to tailings dam management."

IsoMetrix has recently been focusing on aligning its solutions with the Global Tailings Standard. This has seen it introduce modules around change management and training, aspects which IsoMetrix has previous experience in building for other industries.

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from tailings to treasure? miners make money reprocessing tailings

The environmental concerns associated with mining are well known. Mining operations produce waste that must be responsibly processed and disposed of to prevent environmental damage. As a previous blog, Mining and the Environment: What Happens When A Mine Closes? explains, tailingsmineral waste productsare a major pollutant. Tailings may be dumped in or near water or transported by wind or water to contaminate the surrounding area. Mine sites typically manage tailings by constructing ponds secured by dams.

According to the web site miningfacts.org, another strategy is to produce thickenedtailings, which are pressed or have chemicals added to remove excess water. Thickenedtailingscan be mixed with cement and used in construction or as backfill in underground mines.

Now, some mining companies are figuring out ways to turn tailings to profits with novel reprocessing technologies to extract valuable metals from the waste. One example reported in Rapaport Magazine describes the efforts of De Beers Consolidated Mines (DBCM) to extract overlooked diamonds from 360 million tons of old tailings surrounding the Kimberley mines in South Africa. According to the company, thanks to advances in separating, sorting, and crushing equipment, very small diamonds can be recovered from the residue of the original diamond-bearing ore. De Beers recovered 815,036 carats of diamonds from 6,133,799 tons of tailings in 2013 and expects to continue operations beyond 2030.

Tailing may turn out to be a viable source of another valuable and highly sought-after resourcerare earth elements. An article appearing on ABC News, Old Mine Tailings: New Mother Lode for Rare Elements, reported findings from the U.S. Geological Survey indicating that discarded mine tailings may yield significant amounts of rare earth elements; modern extraction techniques would now permit their recovery. This is good news because rare earth elements, which are extremely difficult and costly to mine, are critical components in consumer electronics such as televisions, computers, cameras, and mobile phones, as well as catalytic converters and metal alloys.

Because China monopolizes the worlds supply and charges a premium, Western countries are looking for alternative sources. An article on The Wits Business School Journal website, Abandoned Mines Spark New Gold Rush, evaluates the situation in South Africa, where tailings reprocessing is gaining traction both for economic and environmental reasons. Examples include:

Australian Broadcasting Companyreports that Western Australian company Carbine Resources is investigating the technical viability of extracting an estimated million ounces of gold and 60,000 tons of copper left in the tailings at the old Mt. Morgan Mine site in central Queensland. Numerous other tailings projects are underway in Australia.

To accurately identify minerals within tailings, geologists turn to analytical technologies including both laboratory and portable X-ray fluorescence (XRF) instruments. Portable XRF analyzers provide fast, accurate analysis of tailings to quickly and easily gauge the efficiency of extraction and enrichment processes.The real-time assay data provided by a portable XRF analyzerallows for timely process adjustments, improving productivity and reducing the need for reprocessing. Happy Mothers (Lode) Day!

I bought 50 acres. Did research and found out my 50 acres was a copper mine ,original owners were eventually wanted for treason These people ( original grant land owners)were sent to Canada by King Henri VIII. They were also the first railroads builders. What should I do with all those very very very old tailings?

visualizing the size of mine tailings

On January 25th, 2019, a10-meter tall wavetraveling 120 km/h, washed10 million m3of mining waste from the Brumadinho tailings dam over the Brazilian countryside killing somewhere between 270 and 320 people.

Mining leaves behind waste in the form of tailings stored in dams or ponds around the world. This infographic takes a look at the estimated size of one part of this waste, tailings, visualized next to the skyline of New York City as a benchmark.

In the wake of the Brumadinho tailings failure, the International Council on Mining and Metals (ICMM) began a review with institutional investors and the United Nations Environment Programme (UNEP), to survey tailings facilities around the world.

However, the review estimated the total number of active, inactive, and closed facilities is around8,500. If we use the assumptions for the 1,743 estimate to calculate for the 8,500 facilities, a total of217,330,652,000 m3of tailings are in storage globally.

Tailings are what is left over after mills separate the metal from the mined rock. The processed material tailings comes from the tail end of a mining mill and comprise fine particles mixed with water forming a slurry. Mining companies will store this waste in dams or ponds.

A renewable future will be mineral intensive and will inevitably produce more mining waste, but growing awareness around minings true cost will force companies to minimize and make the most of their waste.

While tailings are waste, they are not useless. Researchers know there remains economic value in tailings. Natural Resources Canada estimated that there is$10Bin total metal value in Canadian gold mining waste.

Rio Tinto has produced borates from a mine in the Mojave Desert which has left behind more than90 yearsworth of tailings. The company was probing the tailings for gold and discovered lithium at a concentration higher than other US projects under development.

According to UBCsBradshaw Initiative for Minerals and Miningprofessor Greg Dipple, the mining industry could help society store carbon. For over a decade, he has researched a process in which tailings naturally draw CO from the air and traps it in tailings.

Mining of metal has grown on average by 2.7% a year since the 1970s, and will continue to grow. The importance of the size of tailings is critical to address proactively, before it comes rushing through the front door, as it did in Brazil.

environmental risks from mine tailings

Tailings are a type of rock waste from the mining industry. When a mineral product is mined, the valuable portion is usually embedded in a rock matrix called ore. Once the ore has been stripped of its valuable minerals, sometimes through the addition of chemicals, it is piled up into tailings. Tailings can reach immense proportions, appearing in the form of large hills (or sometimes ponds) on the landscape.

Some mining wastes become very fine after they have been ground up during processing. The fine particles are then generally mixed with water and piped into impoundments as a slurry or sludge. This method cuts down on dust problems, and at least in theory, the impoundments are engineered to let excess water flow out without leaking tailings. Coal ash, while not a type of tailing, is a coal burning by-product stored the same way, and carrying similar environmental risks.

all of the world's mine tailings, in one visualization

On January 25th, 2019, a 10-meter tall wave traveling 120 km/h, washed 10 million m3 of mining waste from the Brumadinho tailings dam over the Brazilian countryside killing somewhere between 270 and 320 people.

Mining leaves behind waste in the form of tailings stored in dams or ponds around the world. This infographic takes a look at the estimated size of one part of this waste, tailings, visualized next to the skyline of New York City as a benchmark.

In the wake of the Brumadinho tailings failure, the International Council on Mining and Metals (ICMM) began a review with institutional investors and the United Nations Environment Programme (UNEP), to survey tailings facilities around the world.

However, the review estimated the total number of active, inactive, and closed facilities is around 8,500. If we use the assumptions for the 1,743 estimate to calculate for the 8,500 facilities, a total of 217,330,652,000 m3 of tailings are in storage globally.

Tailings are what is left over after mills separate the metal from the mined rock. The processed material tailings comes from the tail end of a mining mill and comprise fine particles mixed with water forming a slurry. Mining companies will store this waste in dams or ponds.

A renewable future will be mineral intensive and will inevitably produce more mining waste, but growing awareness around minings true cost will force companies to minimize and make the most of their waste.

While tailings are waste, they are not useless. Researchers know there remains economic value in tailings. Natural Resources Canada estimated that there is $10B in total metal value in Canadian gold mining waste.

Rio Tinto has produced borates from a mine in the Mojave Desert which has left behind more than 90 years worth of tailings. The company was probing the tailings for gold and discovered lithium at a concentration higher than other U.S. projects under development.

According to UBCs Bradshaw Initiative for Minerals and Mining professor Greg Dipple, the mining industry could help society store carbon. For over a decade, he has researched a process in which tailings naturally draws CO from the air and traps it in tailings.

Mining of metal has grown on average by 2.7% a year since the 1970s, and will continue to grow. The importance of the size of tailings is critical to address proactively, before it comes rushing through the front door, as it did in Brazil.

Todays visualization comes from the In Gold We Trust report, and it shows that over the last 40 years, the purchasing power of the worlds most popular currencies have declined significantly against the precious metal.

In the first decade after the gold standard was abandoned, the international monetary system was seriously shaken. Several U.S. recessions, coupled with international conflicts and high price inflation put the worlds reserve currency under enormous pressure.

The next decade saw the rehabilitation of the dollar through a highly restrictive monetary policy run by the Federal Reserve that led to sky-high interest rates. The trend continued with the fall of the communist Eastern Bloc in the early 1990s.

Gold is still the universal reserve asset to which central banks, investors, and private individuals return in times of crisis.Since 1971, the average annual growth rate of the metal price in U.S. dollars is just over 10%. Since the Euro was introduced in 1999, the gold price in EUR has risen by 356%, or on average 7.8% per year.

Unsurprisingly, over the last 40 years, the best performing G-10 currency was the Swiss franc, largely due to its close relationship with gold. The Swiss National Bank has one of the largest reserves worldwide.

In 2020, the price of gold reached multi-year highs, in part to the impact of COVID-19 shutdowns. This renewed interest in gold spurred the plans of many gold exploration and development projects around the world.

The United States comes in fourth place with $256 million or 9% of global gold exploration dollars. Chile on the fifth spot received $254 million (9%) with one project attracting the largest amount of any on the list.

Focusing on individual projects, Gold Fields Salares Norte project in Chile received $252 million for the largest financing of the period. The company started construction this year, after a delicateoperation to remove endangered chinchillas from the site.

Silvercrests Las Chispas project in Mexicos Sonora state received $228.9 million, giving it the second largest sum. According to the company, the property hosts 94.7 million ounces of silver equivalent (AgEq) in proven and provable reserves.

Gold is Canadas most valuable mined mineral and the next 3 projects on the list show this priority. Osisko Minings Windfall Lake project in Quebec is third ($130 million), Artemis Golds Blackwater mine ($130 million) in British Columbia is the fourth, and Argonauts Magino project in Ontario ($108 million) the fifth.

The analysis found that more than half of the money raised (57%), went to 63 gold projects to advance economic studies from scoping studies or preliminary economic assessments through to bankable feasibility studies and permitting.

With $2.9 billion in capital going into gold projects around the world, the gold industry has big plans. These financings represent opportunities for host countries economies and their workers, along with more gold for investors to buy.

how to handle mine tailings safely and sustainably?

The mining business environment is constantly changing; it would not be an overstatement to say that the paradigm is shifting, as mines face new challenges. The pressing issues are not only about low-grade ore bodies and mines going deeper, but also about long-term environmental impacts.

Mining involves the processing of mined ore to separate valuable minerals, leaving behind huge volumes of waste tailings. Driven by mining volumes, globally generated tailings are estimated to total up to 3.2 billion tons for copper and up to 1.8 billion tons for iron per year. Water conservation and the cost of tailings and reclamation are also becoming increasingly significant factors for sustainable and economically viable mining and long-term survival.

The practice of dewatering tailings, however, is still limited to few areas globally. According to Metsos analysis, only ~5% of tailings generated in 2018 were dewatered into thickened, paste, or dry tailing. We estimate that by 2025 the share of generated tailings that are dewatered will increase to ~13%.

The way tailings are handled can have a long-term impact on economic efficiency as well as on community well-being and ecosystem sustainability. The recent tailings dam failures have brought safety and environmental concerns to the forefront; there have also been stronger regulatory compliances affecting the social license to operate in many regions.

Metso views dry filtered tailings as the most viable and long-term solution for tailings handling, as it not only helps in recycling significantly more water to the concentrator, but also allows for a smaller freshwater footprint compared to traditional tailings impoundments. Contrary to the conventional belief, dry tailings are much more CAPEX and OPEX efficient compared to wet or paste/thickened tailings. Technology is evolving and shifting the gears towards the adoption of smart and hybrid solutions that maximize ore and water recovery while optimizing operational costs.

Today, about 70% of the mines operated by the major mining companies are in countries where water scarcity is considered as the major risk. Therefore, responsible water use is the primary driver of the growing interest in tailings dewatering especially in countries like Peru, Chile, the US and South Africa, where the significant mines are in dry areas.

The industry needs future-ready and smart filtration solutions to solve complex tailings handling challenges. Backed by proven technology and industrial knowledge, Metso is ahead of the curve in developing the most efficient dewatering solutions with an intense commitment to maximize water recovery and reuse.

A lot of old tailings facilities have residual mineral values, or secondary metals that were not of interest at the time. With the advent of novel technologies, mining companies are now figuring out ways to extract valuable metals from tailings. There are ongoing feasibility studies and capabilities to look into legacy dams enabling customers to plan an end of the mine strategy.

Reprocessing could provide opportunities to help in environmental reclamation, while at the same time offering an attractive investment opportunity. Treating tailings ponds as a potential source for converting waste to value would surely help in changing the way the mining industry has been perceived all these years.

Well done Niclas Hllevall! Your article is revealing. I wish I could participate in any of your field projects soon as I have been involved in teaching and research in this domain at the Department of Mining Engineering, University of Jos, Nigeria. Thumbs up!

mine tailings: how to effectively manage the risk

The mood music of this years Mining Indaba in Cape Town was clearly tailings management and environmental, social, and governance (ESG), with much activity in the institutional and consultancy space directed towards these areas.

These institutions include The International Council on Mining and Metals (ICMM) with its Global Tailings Review, and the Southern African Institute of Mining and Metallurgy (SAIMM), which has convened its own tailings oversight committee. Moreover, there are an increasing number of technical solutions being offered to address the tailings problem.

Simply put, a mine needs to be able to mitigate all of the risks to its operational and social environment to as low as reasonably practical. This is most efficiently done by applying the risk-based approach that follows the guidelines set in ISO 31000 and using other relevant ISO standards as appropriate.

It is worth noting that the guiding principle of ISO 31000 is the creation and protection of value. It should not be viewed as just an onerous process, but rather something that is worth following for its own sake.

This situational awareness is critical in risk management, but it is also very useful in routine operational management. Failure to take care of the environment and the community can affect a companys social licence to operate.

Failure to exercise good governance can affect both the legal licence to operate and relationships with shareholders and providers of capital. Governments, communities and investors want to see transparency and proof of good practice and risk reduction.

There are choices, and the development of new technologies makes them broader. One approach is to look at a narrow area of what may be considered as the pressing issue, the other is to take a holistic approach and work towards an integrated solution that is cost effective and adds value. This article argues for the latter.

Most tailings disasters are actually ESG disasters. The consequences for the operator have been shown above and to them can be added: legal action against those responsible, and also increased difficulty in raising capital through institutions that are starting to demand transparent compliance with ethical standards, and evidence that it is taking place on a continuous basis; again strengthening the requirement for ground truth.

The Risk Management approach coordinates activity to determine and implement controls to reduce or remove the full range of risks. They are often connected, so a silo type approach is usually going to be inefficient in terms of both cost and process.

It is this process that must be owned by the operation because the risks are theirs. From the evaluation of each risk in context comes the identification of those critical information requirements that will enable an informed solution to be defined, a process to be established and the whole process line to be owned by the most appropriate person in management. Regular review and oversight are the critical elements once an effective system has been instituted.

Tailings should actually be addressed as part of overall water management, as water is the major risk to mining operations beyond just tailings. It requires effective management just to make the operation work cost-effectively.

While the tailings risk is unlikely to affect the actual mining effort; a collapsed tailings dam can destroy the mines value as well as a companys reputation and licence to operate. Rather than look at tailings in isolation it actually makes more sense to include it as part of water management.

These technologies are game changers and make an integrated risk approach easier to achieve. They have the ability to both enhance resilience and manage and act upon data more efficiently than humans.

The bots can send alerts to the human operator for them to action. Artificial intelligence (AI) means many things. In the case of mines, AI (machine learning) can process data to learn things, make predictions, spot trends and tell whoever needs to know details that may not be apparent based on their experience/ intuition alone.

A single digital operations room can monitor activities for any number of mines, providing a reliable, resilient and low cost service (the bots will always turn-up, work 247, do not get tired or sloppy, are accurate and do not act malevolently) that works remotely and very cost-effectively to support any mining operation, anywhere.

The risk register process raises the requirement for information about water, and associated geology, from various sources. For the pit, the requirement is to know when failure may occur in time to take preventative action, through the measurement of pore pressure.

For the tailings dam the requirement could be warning of movement in any of the X, Y or Z axes (it could also be pore pressure if desired). All these sensors collect data, which must be processed in order to produce an effect. This effect can be a validated procedure executed by a trained human, or an automated response from a robot. The connectivity is shown below.

The process outlined above can be enhanced and adapted to include the sensing of, and action on, any risk related information requirements. Its resilience can be verified by robotic oversight that will provide confidence in its reliability.

In addition, more routine aspects of efficient management such as environmental air and water quality, personnel on site, HSE and security can be monitored using this system. In the above example, it would enable oversight of the artisanal miners and compliance with ESG concerns in a verifiable way.

An integrated risk-based approach, following well-established international guidelines, can follow the principle of the creation and protection of value through an effective process of risk management.

That process can also address ESG issues and provide credible transparency to all key stakeholders, regardless of location. Finally, the potential afforded by AI and Robotics enhances the resilience of such a system.

Simon Barry, is a lead consultant: risk and standards, at The Advisory Group. Barry holds a MSc in Risk Management from the University of Leicester, is a specialist member of the UK Institute of Risk Management and a ISO 9001 lead auditor.

He has worked in mining and associated activities across sub-Saharan Africa since 2008, as well as in a number of high-risk locations. With extensive experience in aviation, logistics and management development he is a firm proponent of the team-based integrated approach to problem solving, addressing the hard questions early.

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