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The development of new technologies in diamond-bearing ore beneficiation is required to increase the stone recovery level and prevent their damage in crushing as well as to reduce the capital and operational expenses of diamond miners.
In recent years, the technology of diamond-bearing ore beneficiation by the Norwegian TOMRA company is increasingly popular and it is based on the use of the X-ray absorption method to detect diamonds. The company produces X-ray (transmission) separators - COM Tertiary XRT - that gradually replace dense medium separation (DMS) plants and X-ray luminescent separators. The COM Tertiary XRT separators use electric X-ray tubes and DUOLINE highly-sensitive innovation touch-sensitive X-ray chambers enabling the use of two independent sensor lines of varying spectral sensitivity. The data transmitted by this chamber is processed by a patented TOMRA Sorting high-speed processor that is able to identify the material atom density irrespective of its thickness. Thus, this technology allows the detection of all diamond types, including the stones with a shell, low luminescent ones and Type II diamonds (having practically no impurities). Besides, the particle size range of the diamonds extracted increases from 25-30 mm to 60 mm and higher. All this results in a high-quality concentrate requiring no additional processing before manual sorting, which reduces the operational expenses markedly. Moreover, the TOMRA separators feature low power and water consumption.
Canadian Lucara Diamond Corp. was one of the first companies to introduce the TOMRA equipment into its technological cycle. In early 2015, Lucara installed six new separators, 150 tph, at the Karowe diamond mine in Botswana, and the success was not long in coming in November, the company recovered its 1,109 carat rough diamond, the second largest rough diamond ever recovered (after Cullinan). After Lucara Diamond, other diamond miners like the Australia-based Lucapa Diamond Company Ltd and Merlin Diamonds Limited started using the TOMRA separators. The Russian diamond miners followed suit in late 2017, the TOMRA separator was installed by AK ALROSA (PAO) at its factory No.14 of the Aikhal Mining and Processing Plant in the Republic of Sakha (Yakutia) to carry out technological testing, and in October 2018, AGD Diamonds (AO) that operates the Grib diamond pipe in the Arkhangelsk Region purchased this equipment and started its commercial use.
The X-ray absorption method was incorporated by other technological enterprises. For example, DebTech (De Beers subsidiary) developed a sorting XRT Coarse Concentrator Plus (CC+) facility, and in late 2018, it introduced it at one of the worlds largest diamond mines Jwaneng in Botswana.
Simultaneously with TOMRA, the Bourevestnik innovation centre (ALROSAs subsidiary) worked on the development of X-ray separators. By 2014, the entre developed RGS-1M and RGS-2 X-ray separators that were also introduced at the ALROSAs enterprises.
To solve the problem of low luminescent diamond extraction, the Russian Irgiredmet research institute developed the method of triboelectric separation based on the electric charges generated during friction. The laboratory and industrial tests of the triboelectric separator showed that its use in the dry conditioning of a diamond concentrate was promising. The Ukrainian Prodekologiya research and production firm manufactures the triboelectric separators (Type EBS-T), however, they found wider use in another sphere - in recycling of polymers, e-wastes and cables.
Severalmaz (PAO) (ALROSA Groups subsidiary) carried out tests of the pilot plant at the Lomonosov Mining & Processing Division (MPD) in the Arkhangelsk Region; the pilot plant is based on the fast-neutron method and was developed by Diamant (OOO) against the order of ALROSA. The plant enables the detection of a diamond in the kimberlite ore without damaging it. The tests allowed determine the optimal plant capacity, 102 kg per hour, and the diamond recovery was 97%. The future Diamant plans included the development of the commercial separator based on the fast-neutron method with the capacity of 30 tons per hour.
The UK-based diamond miner, Gem Diamonds, also concerned about damaging the diamonds during their recovery from the ore has developed and tested their technique of non-mechanical crushing based on the electric power. In 2019, the company scheduled to test this technique using the tailings from the beneficiation plants at the Letseng mine in Botswana.
Among the new developments in the primary beneficiation of the diamond-bearing ores, special mention should go to the Sepair dry (pneumatic) beneficiation plant developed by the Novosibirsk-based Gormashexport company. ALROSA tested the plant in 2011 using poor cut-off grade ores at the Sytykanskaya pipe in the Republic of Sakha (Yakutia). One of the main advantages of this technology is the possibility to work at extremely low temperatures (down to minus 50oC), which is especially important in the severe climate of Yakutia.
Module beneficiation plants are used to process primary deposit ores as well as placer ones, including the ores in detailed exploration. In Russia, these plants are manufactured by Technologies, Equipment and Integration, a research and development company based in St. Petersburg.
The module equipment consists of primary jaw crushers, scrubbers, dense medium separation plants and X-ray units. The units can be used separately or as part of the beneficiation plants. For example, a beneficiation plant OK-Komplekt-4 consisting of three module units: a unit for beneficiation of bulk kimberlite samples, for beneficiation of kern kimberlite, bulk and smallsize alluvial samples, and units for conditioning of concentrates, has a capacity of 4 tons per hour. The main advantages of the module beneficiation plants include: the possibility of transportation the equipment by usual freight vehicles; the possibility of installing them on the unequipped sites near mine workings, and low power consumption.
On the whole, the technology development level for the beneficiation of diamond-bearing ores in Russia and abroad is approximately the same. That said, the main driver of the technological progress in the ore processing and diamond extraction in the country is, undoubtedly, ALROSA, the leader of the national diamond mining industry.
World demand and production of diamond both for gem and industrial purposes has increased nearly five-fold during the past 25 years. Improved mining and recovery methods together with the discovery and development of new fields has enabled mining operations to fill the growing demands. Producing areas in Canada, South Africa, South West Africa, The Congo Republic, Angola, Ghana, Tanganyika and Sierra Leone account for over the bulk of world production.
In mining, diamonds are recovered mainly from alluvial deposits which vary widely in character, often cemented; and usually contain large quantities of clay or a sticky slime fraction from near zero to about 50%. Substantial production also comes from Kimberlite pipes and dikes (Blue Ground), a basic igneous breccia, considered generally to be the originating source for nearly all diamonds. Diamonds have a specific gravity up to 3.52and are associated with minerals such as magnetite, ilmenite, garnet, tourmaline, spinel, rutile, pyrite, quartz and other minerals which due to their specific gravity makes separation from the diamonds difficult and affects the ratio of concentration obtainable through gravity methods. Since the value per ton of diamondiferous gravel seldom exceeds one metric carat per ton with an average of less than 0.3 carat, a high ratio of concentration, in the order of 1: 5,000,000 or higher, is necessary.
Many recovery methods are used and methods vary depending on the location, size and nature of the deposit. The methods include production by natives using simple hand pans to more complex mechanical means employing washing, screening, stage crushing, clear water and puddle panning, heavy media separation, jigging, attrition and differential grinding, magnetic and/or electro-static separation, flotation, grease tabling and hand sorting. Certain operations use one or more field plants to supply a central plant for reconcentration and final sorting.
This flowsheet is typical for small to medium tonnages of alluvial feed (5 to 30 tons per hour). Such material is often cemented and requires crushing by either jaw or gyratory crushers. In this flowsheet a trommel screen, with a scrubbing section, is used to break down clay and cemented fractions, before screening and rejection of the oversize to waste. The trommel undersize, 1, is fed to centrifugal diamond pans in series.
Diamond pans were developed in South Africa and have been highly successful and widely used in the recovery of diamonds. Their use for the separation of other minerals has been limited and inefficient.
A diamond pan is a shallow, flat bottomed circular pan with an inner well about 0.3 of the pan diameter and several inches lower in height than the outer pan wall. A vertical shaft is mounted to rotate in the center to which radial horizontal arms are attached above the pulp level in the pan. Tines extend downward from the radial arms and are adjustable to clear the pan bottom. These tines are triangular and so spaced and mounted on the radial arms to plow material on the pan bottom outward. The feed entry is tangential to the outer wall while the tailings discharge is through a weir in the center well. In operation the tangential entry of the feed combined with the stirring action of the tines causes a vertical swirl to the mass. The condition created in the pan simulates the heavy media process in that the lighter materials remain in suspension and are carried down the vortex to the center discharge weir while the heavier particles settle through the swirling mass to be plowed outward on the bottom to a concentrate discharge outlet in the outer wall. Feeds containing a high amount of clay and fine sands give the most effective results, however, many pans operate on feeds containing little or no clay or fines with reduced but still satisfactory recoveries. Capacity of diamond pans is normally 5 to 6 tons per square foot of effective area per 24 hours and require 1 to 1 horsepower per ton of feed. Ratios of concentration vary, usually from 10:1 to 50:1 depending on the amounts of heavy minerals associated with the diamonds. Recoveries up to 97% are sometimes possible.
The diamond pan concentrates in Flowsheet No. 1 are elevated to a trommel screen for sizing to eliminate 16 mesh undersize and to produce four size ranges each going to a Duplex Mineral Jig for further concentration.Mineral Jigs have proven to be very efficient in diamond treatment with recoveries near 100% being reported. The jigs are equipped with 2 mm bedding screens. No artificial bedding is added in most operations since the pan concentrates contain sufficient heavy minerals to form adequate bedding. A 2-mm hutch concentrate is produced from the jigs which are discharged to locked containers before being removed to the final recovery section. The 2-mm concentrate retained on the jig screens is removed by hand at intervals as necessary and are hand sorted for recovery of the diamonds. All phases of concentrate handling are done under conditions to insure security. All launders, jig compartments and concentrate collection points are covered, locked or protected to prevent theft.
This flowsheet was developed for diamond recovery from Kimberlite ore as mined and with properly sized equipment is suitable for tonnages up to 50 tons per hour. The mined ore is crushed to 3 followed by screening and secondary crushing to 1. A picking belt is sometimes employed between crushing stages for removal of waste rock and possible recovery of large diamonds, but this step is generally considered uneconomical. Few, if any diamonds are broken in the crushing operations, as they are usually smaller than the crusher openings, and break free from the matrix without damage. The crushed ore goes to a bin for storage and for controlled feeding to the recovery circuit. A trommel screen with scrubbing sections is used to break down any soft portion of the ore before screening. Oversize material is reduced to 1 with a spring roll crusher and then joins the trommel undersize to feed a centrifugal diamond pan. The flowsheet shows one pan, however, several pans in series are sometimes found to be more effective when the ore contains high percentages of heavy minerals. The pan tailings are elevated or dewatered and conveyed to another screening and crushing step to provide a3/8 feed to asecondary diamond pan. The tailings from the secondarypan are elevated and screened to produce a + 1/8 fraction as a final tailing, and a 1/8 product which passes to a Duplex Mineral Jig for recovery of any small diamonds remaining. The concentrates from the primary and secondary pans are each separately fed to two Duplex Mineral Jigs in series for reconcentration. The use of Mineral Jigs in series on the unclassified feed eliminates the necessity of classification or screening to produce sized feedfractions often necessary when plunger type jigs are used. The ratio of concentration on jigs in this service ranges from 10:1 upward depending on the amounts of heavy minerals in the pan concentrates. Feed rates vary from 200 to 1000 pounds per square foot of compartment area per hour.
The final recovery of the diamonds from gravity concentrates is accomplished by several steps of reconcentration which differ in many cases due to the amount and nature of the associated gangue minerals. When appreciable amounts of heavy minerals are present the concentrates are sized to give a 1/8 fraction which is dried and passed through magnetic and/or electrostatic separators to eliminate affected materials, before being further reconcentrated on grease tables. The recovery method shown in Flowsheets No. 1 and No. 2 is frequently used when the gravity concentrates are wet screened to three or more size ranges as the feed to separate grease tables and to reject 16 or 28 mesh materials.
The grease tables are of several types being usually either mechanically or electrically vibrated with the movement normal to direction of flow. The decks are made both flat and stepped, being adjustable in slope to give proper flow velocity for the different size ranges of feed. The stepped decks have from 4 to 8 removable compartments or pans each being 8 or more in width by 3 to 4 feet in length, each pan being mounted in steps down the table. Each step is coated with + thickness of a special petroleum grease which is given a surface covering of about 1/16 of another type grease. In operation the sized feed is uniformly fed across the table into a flow of water to carry the material across and down the table steps. The diamonds being non-wettable adhere to the grease while most of the other minerals are carried off the table by the water and are rejected as waste. After 45 to 60 minutes of operation the 1/16 surface layer of grease, together with the diamonds and some other trapped minerals, are scraped from the tables. This grease layer is placed in grease pots having perforated sides. The pots are
covered and placed in boiling water for removal and recovery of the grease. The diamond concentrates after degreasing are hand picked and sorted under diffused light. This final operation is very exacting work and is carried on under close observation and security conditions.
This flowsheet illustrates a more complex diamond recovery method developed in recent years. With variations it can be used to process 100 to 500 tons per hour of Kimberlite ore and is also arranged to handle weathered or soft ores. For the hard ore as mined the flowsheet follows conventional methods of stage crushing and screening to reduce the ore to . The weatheredore is intensely scrubbed to break down the soft fractions and then screened as shown. All the 1 ore is wet screened to produce +10 mesh and 10 mesh sizes. The 1, +10 mesh fraction goes to a heavy media separator from which the sink product, after media screening and washing, goes to concentrate storage. The float product is washed and screened to reject all 3/8 to waste. The +3/8 size is crushed and screened to 3/8 +10 mesh for retreatment to the heavy media circuit.
All 10 mesh material from the screens ahead of the heavy media process and from the screen following the scrubber is dewatered and wet screened to give a 10 mesh, +16 mesh size range for treatment either by heavy media separation through cyclone separators or by Duplex Mineral Jigs as illustrated.
In the recovery section a number of reconcentration methods are used. Attrition grinding using a light grinding charge at near 40% of critical speed reduces part of the heavy minerals without damage to the diamonds. The mill discharge is screened to eliminate 16 mesh or in some cases 28 mesh and to split the remaining concentrates at about 7 mesh. These two size ranges being treated separately with the 7 mesh going to a mill to effect a differential grind to further reduce the waste materials. This product is wet screened and the oversize is dried, screened to remove dust before passing through an electrostatic separator. The diamond concentrates are then hand sorted. The +7 mesh concentrates are sized, usually to four size ranges, each separately conditioned to remove any coating from the diamonds which interfere with collection on grease tables or grease belts. Grease belts are a recent development and require less attention and labor than grease tables. They are similar to short conveyors and are mounted in a framework so that the slope can be adjusted for correct flow velocity. The concentrates are fed to spread a thin layer over the belt surface down which a stream of water flows. Grease is continually applied to the belt at the upper end and is scraped off at the lower end with the diamonds. The diamonds are degreased and processed by hand sorting.
Rio Tinto Iron Ore's low-grade ore beneficiation plant in the Pilbara was commissioned in 1979. Initial engineering, design, and construction were undertaken by KBR (Kellogg Brown and Root) and Minenco (RTIO information provided to author, 2013). The plant separates closed-circuit crushed ROM into 31.5+6.3mm and 6.3+0.5mm streams for feeding their DMS drum and cyclone plants, respectively (Figure 10.5).
To evaluate an iron ore resource, develop processing routines for iron ore beneficiation, and understand the behavior of the ore during such processing, extensive mineralogical characterizations are required. For calculating mineral associations, mineral liberation, grain size and porosity distribution, and other textural data, reliable imaging techniques are required.
Automated optical image analysis (OIA) is a relatively cheap, robust, and objective method for mineral and textural characterization of iron ores and sinters. OIA allows reliable and consistent identification of different iron oxide and oxyhydroxide minerals, e.g., hematite, kenomagnetite, hydrohematite, and vitreous and ochreous goethite, and many gangue minerals in iron ore and different ferrites and silicates in iron ore sinter. OIA also enables a distinction to be made between forms of the same mineral with differing degrees of oxidation or hydration.
To reliably identify particles and minerals during OIA, a set of comprehensive procedures should be automatically applied to each processed image. Generally, this includes next stages: image improvement, particle and mineral identification, particle separation, porosity identification, identification of unidentified areas, and correction of mineral maps. This is followed by automated measurements of final mineral maps and statistical processing of results.
High resolution, imaging speed, and comprehensive image analysis techniques of modern OIA systems have made it possible to significantly reduce the cost and subjectivity of iron ore and sinter characterization with a simultaneous increase in the accuracy of mineral and textural identification.
World demand for iron ores to meet the ever-increasing requirements of iron and steel industries has made it imperative to utilize all available resources including lean grade ores, mined wastes, processed tailings, and blue dust fines accumulated at mine sites. Most of such resources exist as finer particles, while lean-grade ores require fine grinding for liberation of associated gangue minerals. Hematite is the most abundant iron ore mineral present in available resources while the major impurities include silica, alumina, calcite, clay matter, and phosphorus. Conventional beneficiation processes such as flotation, electrostatic and magnetic separation, gravity methods and flocculationdispersion using chemical reagents to treat the finer iron ore resources often prove to be inefficient, energy-intensive, costly, and environmentally-toxic.
Why microbially mediated iron ore beneficiation? Any microbially induced beneficiation process will prove to be cost-effective, energy-efficient, and environment-friendly compared to chemical alternatives which use toxic chemicals. Microorganisms which find use in beneficiation are indigenously present in iron ore deposits, tailing dams, and processed wastes. Mining organisms inhabiting iron ore deposits are implicated in biomineralization processes such as hematite, magnetite, and goethite formation as well as their oxidationreduction, dissolution, and precipitation in mining environments. Similarly, gangue minerals such as silica, silicates, clays, calcite, alumina, and phosphates are often biogenically entrapped and encrusted in the hematitemagnetite matrix.
Autotrophic, heterotrophic, aerobic, and anaerobic microorganisms such as Acidithiobacillus spp., Bacillus spp., Pseudomonas, Paenibacillus spp., anaerobes such as SRB, yeasts such as Saccharomyces sp., and fungal species inhabit iron ore mineralization sites. Many such organisms find use in beneficiation processes because they are capable of bringing about surface chemical changes on minerals. Microbial cells and metabolic products such as polysaccharides, proteins, organic and inorganic acids can be used as reagents in mineral flotation and flocculation.
Isolation, characterization, and testing the usefulness of mining microorganisms inhabiting iron ore deposits hold the key towards development of suitable biotechnological processes for iron ore beneficiation. Because many microorganisms inhabit iron ore deposits contributing to biogenesis and biomineralization, there is no reason why one cannot isolate and use them to bring about useful mineral processing functions. Though innumerable microorganisms are known to inhabit iron ore deposits, only a few of them have been identified as of now and among them, still only a few have been tested for possible iron ore beneficiation application.
Costly and toxic chemicals used in conventional beneficiation processes can be replaced by biodegradable, mineral-specific, biologically derived reagents such as exopolysaccharides, bioproteins, organic acids, biodepressants, and bioflocculants.
Iron ore beneficiation can be brought about through three approaches, namely, selective dissolution, microbially induced flotation, and selective flocculationdispersion. The bioprocesses are specially suited to treat fines, slimes, and waste tailings.
Potential applications includei.Dephosphorizationii.Desulfurizationiii.Desiliconizationiv.Alumina and clay removalv.Biodegradation of toxic mill effluentsvi.Clarification, water harvesting from tailing poundsvii.Recovery of iron and associated valuable minerals from accumulated ore fines and processed tailings.
For D. desulfuricans, an anaerobe, as the cell count increases, sulfate concentration decreases, because the organism reduces sulfate to sulfide to derive energy. During the log phase, the decrease in sulfate concentration corresponding to exponential bacterial growth was significant.
The growth of bacterial cells was monitored in the presence and absence of minerals such as hematite and quartz. When similar cell growth was attained in the presence of minerals as in control, growth adaptation to the minerals was considered achieved. Adsorption density of SRB cells grown under different conditions on hematite and quartz surfaces was found to be different. Cells grown in the presence of hematite exhibited higher adsorption density on hematite, whereas those grown in the presence of quartz attached profusely to quartz surfaces. Cells grown in the absence of minerals exhibited higher surface affinity towards hematite and rendered it more hydrophilic . Extracellular proteins and ECP secreted by D. desulfuricans in the presence and absence of minerals are shown in Table 10.19.
Extracellular proteins secreted by quartz-grown D. desulfuricans were the highest, while the secretion of ECP was found to be higher in case of hematite-grown cells. Bacterial growth in the presence of quartz promoted secretion of higher amounts of proteins, while the presence of hematite resulted in the generation of significant amounts of exopolysaccharides. Negatively charged quartz surfaces exhibit strong surface affinity towards positively charged amino group containing proteinaceous compounds, while hematite exhibited strong affinity towards exopolysaccharides at neutral to mildly alkaline pH conditions.
Protein profiles of bacterial cells and metabolites exposed to minerals were compared with conventionally grown cells and their metabolites. Mineral-specific protein bands of molecular weights 105, 36.5, and 25kDa were observed only in case of quartz-grown bacterial cells because they were absent in conventionally grown and hematite-adapted cells and metabolites. Secretion of higher amounts of mineral-specific stress proteins by bacterial cells was promoted if grown and adapted in the presence of quartz mineral .
Amount of polysaccharides present on hematite-adapted SRB cell walls as well as metabolites were significantly higher compared to bacterial growth in the presence of quartz. SRB cells adapted to hematite become more hydrophilic than those adapted to quartz, which were rendered more hydrophobic due to enhanced secretion and adsorption of proteins. Similarly, hematite surfaces were rendered hydrophilic due to enhanced polysaccharide adsorption, while quartz became hydrophobic due to higher protein adsorption.
Significant surface chemical changes brought about on quartz and hematite due to bacterial interaction can be made use of in their selective separation through bioflotation as illustrated in Table 10.20.
In the absence of bacterial interaction, no significant flotation of quartz and hematite would be possible. Percent weight flotation of quartz was about 45% and 35% after interaction with unadapted bacterial cells and metabolite, respectively, while it increased to about 75% and 84% on interaction with quartz-adapted cells and metabolite, respectively. Percent weight flotation of hematite was about 8% and 11% on interaction with unadapted bacterial cells and metabolite, respectively. After interaction with hematite and quartz-adapted bacterial metabolite, about 15% of hematite could be floated. Flotation recovery of hematite decreased to 2% with hematite-grown cells. Such a hydrophilic surface character of hematite (unlike quartz) is due to its high affinity towards polysaccharides.
Selective separation of quartz from a binary mixture of quartz and hematite was also studied after interaction with bacterial cells and metabolite. Interaction with unadapted bacterial cells and metabolite resulted in only 10% and 9% flotation recovery for hematite. After interaction with quartz-adapted bacterial cells and metabolite, the percent flotation of quartz from the mixture was about 76% and 81%, respectively. The above results clearly establish that efficient separation of silica from hematite could be achieved through selective flotation after interaction with cells and metabolites of an SRB (D. desulfuricans). However, prior bacterial adaptation to the respective minerals (especially quartz) is essential to bring about efficient separation. Addition of starving quantities of silica collector would be beneficial in enhancing quartz floatability and depression of hematite.
Uncertain parameters are assumed to behave like fuzzy numbers and FEVM approach has been applied to an industrial case study of ore beneficiation process. A modified form of NSGA II, FENSGA-II has been utilized to solve the deterministic equivalent of the multi-objective optimization problem under uncertainty. Results of credibility, possibility and necessity based FEVM are presented and thoroughly analyzed. PO solutions obtained from possibility based FEVM have the optimistic attitude. Similarly, PO solutions obtained from necessity based FEVM have the pessimistic attitude. This gives a key to decision maker to select any point based on existing risk appetite.
Screening is an important step for dry beneficiation of iron ore. Crushing and screening is typically the first step of iron ore beneficiation processes. In most ores, including iron ore, valuable minerals are usually intergrown with gangue minerals, so the minerals need to be separated in order to be liberated. This screening is an essential step prior to their separation into ore product and waste rock. Secondary crushing and screening can result in further classification and grading of iron ore. The fines fraction is usually of lower grade compared with lump ore.
Hematite and magnetite are the most prominent iron ores. Most of the high-grade hematite iron ores (direct shipping ore (DSO)) are subjected to simple dry processes of beneficiation to meet size requirements. This involves multistage crushing and screening to obtain lump (31.5+6.3mm) and fines (approximately 6.3mm) products. Low-grade hematite ores need to be upgraded to achieve the required iron content, which involves more complicated ore beneficiation processes. The level of comminution required for the low-grade hematite ore is similar to high-grade ores to deliver the same products, lumps and fines. In most cases, the fines product requires additional separation/desliming stages to remove fines containing a high level of clay and other waste minerals.
Although most of the current world iron ore production is represented by hematite ores, the magnetite reserves are significant and the growing demand for steel has opened the way for many new magnetite deposits to be developed. Compared to direct shipping hematite ores mined from the upper regolith, magnetite deposits require significant and different beneficiation, which typically involves grinding of the run-of-mine ore to a particle size where magnetite is liberated from its silicate matrix. The amount of energy required to produce a magnetite product suitable for sale as pellet plant feed is an order of magnitude higher than an equivalent direct shipping lump and fines hematite project.
Due to the depleting reserves of DSO ores and increasing development of low-grade hematite and magnetite deposits, the need for iron ore beneficiation is increasing. Even the DSO ores are requiring a higher level of processing as the depth of existing mines is increasing (below water table) where ores are wet and more sticky, which creates challenges for conventional crushing and screening.
This chapter reviews the current state of iron ore comminution and classification technologies. Firstly, it discusses the most commonly used crushing and screening technologies, including most common flowsheets and a short review of new trends. This is followed by review of comminution circuits and equipment for magnetite ores including most typical flowsheets and advances in comminution technology.
Variations in iron ores can be traced and mapped using cluster analysis and XRD quantification. Paine et al. (2012) evaluated a large number of iron ore samples from an iron ore deposit. Using cluster analysis and mineral quantification, the ores could be classified into defined theoretical grade blocks, which included high grade, high grade with minor gibbsite, high-grade beneficiation, low-grade beneficiation, low-grade other, and waste. As a result, material with a propensity for higher degrees of beneficiation was identified and delimited.
For iron ore beneficiation, the mineral quantities in the ores is essential to establish the degree of upgrading that can be achieved. In a study of the removal of aluminum in goethitic iron ores, mass balance calculations assisted greatly to assess the maximum amount of Al that can be removed without appreciable iron loss, mainly from the goethite. This is shown graphically in Figure 3.6, which shows that 68% of the Al in the sample is distributed in goethite. The goethite also contains 60% of the iron in the sample and cannot be removed. Therefore, if Al is to be removed, only kaolinite and gibbsite can be eliminated without major iron loss, and only as little as 22% of the Al can be removed by flotation or other methods.
Lattice constant refinement can be used to assess the substitution of impurity elements, especially in fine-grained goethite and hematite, as determined by Schulze (1984) and Stanjek and Schwertmann (1992), respectively.
The use of XRD can therefore give a quick assessment of the extent of Al and OH substitution in hematite and the amount of Al substitution in goethite. This was done for five goethite-rich iron ores and is shown in Table 3.4.
Biogenic iron oxides display intimate association with microorganisms inhabiting the ore deposits. In natural sediments, iron oxide particulates are found to occur in close proximity to bacterial cell walls containing extracellular biogenic iron oxides and various biopolymers. Iron-oxidizing and iron-reducing bacteria colonize the biofilms formed on many iron oxide minerals .
Several types of microorganisms growing under extreme environments altering between acidic to neutral pH, aerobic and anaerobic, as well as mesophilic and thermophilic conditions are capable of microbial oxidation of ferrous iron and reduction of ferric iron.
Some examples are Acidithiobacillus sp., Gallionella sp., Leptothrix sp., Leptospirillum sp., and Thermoplasmales (archea). Leptothrix spp. can form FeOOH sheaths around iron oxide minerals through production of exopolysaccharides as a protection mechanism.
Ancient biogenic iron minerals contain biosignatures as in banded iron formations (BIF). Nanocrystals of lepidocrocite on and away from the cell wall of Bacillus subtilis have been observed due to ferrous iron oxidation. Diverse group of Gram-negative prokaryotes such as Vibrio, Cocci, and Spirillum constitute magnetotactic bacteria which synthesize intra- and intercellular magnetic minerals (such as magnetite) and magnetosomes. Several magnetotactic bacteria (living under aerobic and anaerobic conditions) and their magnetosomes have been isolated and characterized from the Tieshan iron ore deposits in China . Microbially induced iron ore formation has been confirmed at Gunma iron ore mine, Japan .
Ubiquitous microorganisms inhabiting iron ore deposits are useful in iron ore beneficiation (e.g., removal of alkalis, silica, clays, phosphorous, and alumina). Because the presence of phosphorous in the iron ore promotes bacterial growth (as an energy source), iron oxide particles having higher phosphorous contents were seen to be colonized by different bacterial cells. Microbial phosphorous mobilization in iron ores has been reported. A polymer-producing bacterium (B. caribensis) has been isolated from a high phosphorous Brazilian iron ore . Microorganisms such as Acidithiobacillus, Clavibacter, and Aspergillus isolated from iron ores are good phosphate solubilizers, because they generate inorganic and organic acids.
Shewanella oneidensis, an iron-reducing bacterium which produces mineral-specific proteins exhibit surface affinity towards goethite under anaerobic conditions. S. oneidenisis are capable of recognizing (sensing) goethite under anaerobic conditions. Shewanella sp. prefers FeOOH and not AlOOH. Such a preferential microbialmineral affinity could be beneficially used to separate alumina, gibbsite, and aluminum silicates (clays) from iron oxides. Microbially secreted proteins are involved in metal reduction. Protein secretion and transport as well as biosynthesis of exopolysaccharides are very important and useful in iron ore transformation. Shewanella putrefaciens, a facultative anaerobic, Gram-negative bacterium can reduce ferric iron oxides and attach preferentially to magnetite and ferrihydrite. Enhanced adhesion of phosphate-utilizing organisms on iron oxides promotes formation of iron phosphate complexes [17, 18].
Magnetite particles formed by dissimilatory, extracellular iron reduction are generally poorly crystallized. Ferrous ions can react with excess ferric oxyhydroxides to form mixed Fe (II) and Fe (III) oxides as magnetite.
BIM of magnetite has been possible in the presence of cultures of Shewanella and Geobacter. Possibility of intracellular deposition of minerals also exists. For example, intracellular iron sulfide formation within cells of SRB such as Desulfovibrio and Desulfotomaculum species has been reported .
Biomineralization brought out by prokaryotes has practical significance in environmental ore deposit formation, mineral exploration through biomarkers, and also in bioremediation of metal-contaminated waters and soils. For example, formation of extensive Precambrian BIF has been attributed to iron-oxidizing bacteria. Biologically formed minerals may be useful as bioindicators on earth and ocean floors.
An example of BCM is the generation of magnetic minerals by Magnetotactic bacteria. Two types of such bacteria are often mentioned, namely, iron oxidetypes which mineralize magnetite (Fe3O4) and the iron sulfidetypes which mineralize greigite (Fe3S4) .
BIF are the largest iron sources distributed globally dating back to about 4 billion years. They contain up to 50% silica and between 20% and 40 % iron and are sedimentary in origin. Main iron minerals such as hematite and magnetite found in BIF are considered to be of secondary origin. Earlier categorization showed domination of carbonates such as siderite and ankerite. It is likely that different mechanisms might have prevailed in BIF .
One traditional model assumed the oxidation of hydrothermal Fe (II) through biotic and abiotic oxidation. Microfossils found in Australia suggested the existence of Cyanobacteria which display various potential biomarker molecules. The presence of oxygen also has been found from the composition of rocks. Formation of ferric iron oxides without oxygen, involving photo-oxidation of ferrous iron by UV radiation has also been suggested. Another recent hypothesis offers direct biological Fe (II) oxidation by anoxygenic phototrophic bacteria.
The presence and nature of minerals of primary and secondary origin in BIF have been widely analyzed. The presence of iron phases such as magnetite, ferrosilicates, siderite, ankerite, and pyrite needs to be considered. Secondary origins of magnetite have been described. Magnetite could have been formed when microbially reduced ferrous iron reacted with initial ferric oxyhydroxides. Oxidation of siderite could also have occurred.
The majority of iron ores that are currently being mined are known variously as banded iron formation (BIF), taconite deposits, or itabirite deposits and were deposited about 2 billion years ago (Takenouchi, 1980). These ores constitute about 60% of the world's reserves. The BIF is a sedimentary rock with layers of iron oxides, either hematite or magnetite, banded alternately with quartz and silicates. The sediments were deposited in ancient marine environments and all were subjected to weathering and metamorphism to a greater or lesser extent.
Prior to enrichment, these sediments normally contained 2030% Fe. Over time, the action of water leached the siliceous content and led to oxidation of the magnetite and enrichment of iron, forming hematite and goethite ore deposits. The grades of the ore and the impurity content varied with the extent of weathering and metamorphism. For example, in tropical and subtropical areas with high precipitation, high-grade deposits that require little or no beneficiation were formed. In temperate climates with less precipitation, the deposits remained as intermediate-grade deposits that require some form of beneficiation. Grade in all deposits tends to decrease with depth due to reduced enrichment by the action of water, and so upgrading is going to become increasingly important as (deeper) mining continues into the future.
The magnetic taconite deposits of the Mesabi Iron Range of Minnesota are typical BIF-type deposits. They contain quartz, silicates, magnetite, hematite, siderite, and other carbonates (Gruner, 1946). They assay about 30% Fe with about 75% of the iron in the form of magnetite and the remainder is largely iron carbonate and iron silicate minerals.
The principal separation in iron ore beneficiation, therefore, is between the iron minerals, hematite and/or magnetite, and silica, principally in the form of quartz. The use of flotation, either alone or in combination with magnetic separation, has been well established as an efficient method for rejecting silica from these iron ores. There are, however, other impurities in some deposits that also require rejection.
Aluminum-containing minerals in iron ore are detrimental to blast furnace and sinter plant operations. The two major aluminum-containing minerals in iron ore are kaolinite (Al2(Si2O5)(OH)4) and gibbsite (Al(OH)3). Some progress has been made in using flotation to separate kaolinite from hematite.
High levels of phosphorus in iron ore attract a penalty because this makes steel brittle. In magnetite, phosphorus is often found in the form of discrete phosphate minerals, such as apatite, which can be removed by flotation. In hematite and goethite ores, however, the phosphorus tends to be incorporated into the lattice of the iron minerals, often goethite. In this case, separation by flotation is not an option. This type of phosphorus contamination needs to be rejected by chemical means.
Besides the BIF deposits, there are also smaller magmatic and contact metasomatic deposits distributed throughout the world that have been mined for magnetite. These deposits often carry impurities of magmatic origin such as sulfur, phosphorus, copper, titanium, and vanadium. While magnetic separation can reject most of these impurities, it cannot eliminate sulfur if it is present in the form of monoclinic pyrrhotite or an oxide such as barite. Flotation may provide an option for reducing the sulfur content of magnetic concentrates when it is present in the form of metal sulfides. It is not an option for oxides such as barite.
Comminution is needed for the liberation of low-grade ores so that the iron content can be upgraded by gangue removal. This necessitates grinding to such a size that the iron minerals and gangue are present as separate grains. But comminution is an expensive process and economics dictates that a compromise must be made between the cost of grinding and the ideal particle size.
Traditionally, grinding has been carried out using rod, ball, autogenous, or semiautogenous mills usually in closed circuit, that is, after grinding, the material is classified according to size with the undersized portion proceeding to the flotation circuit and the oversized portion being returned to the mill. The major benefit of fully autogenous grinding (AG) is the cost saving associated with the elimination of steel grinding media. In the last 20 years, more efficient grinding technologies, including high-pressure grinding rolls (HPGRs) for fine crushing and stirred milling for fine grinding, have provided opportunities to reduce operating costs associated with particle size reduction. A HPGR has been installed at the Empire Mine in the United States for processing crushed pebbles and its introduction has resulted in a 20% increase in primary AG mill throughput (Dowling et al., 2001). Northland Resources operates the Kaunisvaara plant in Sweden, treating magnetite ore with sulfur impurities in the form of sulfide minerals. The required P80 of the ore, in order to achieve adequate liberation, is 40m. This plant uses a vertical stirred mill after AG rather than a ball mill to achieve this fine grind size with an energy cost saving of 35% or better (Arvidson, 2013).
An important part of the comminution circuit is size classification. This can be accomplished with screens or cyclones or a combination of the two. Since cyclones classify on the basis of both particle size and specific gravity, cyclone classification in the grinding circuit directs coarse siliceous particles to the cyclone overflow. In a reverse flotation circuit, these coarser siliceous middlings can be recovered through increased collector addition but at the expense of increased losses of fine iron minerals carried over in the froth. However, if the required grind size is not so fine, then screening can be used instead of cycloning to remove the coarser particles for regrinding and, thus, produce a more closely sized flotation feed (Nummela and Iwasaki, 1986).
Mineral surfaces, when brought into contact with a polar medium (such as water), acquire an electric charge as a consequence of ionization, ion adsorption, and ion dissociation. The surface charge on iron oxides and quartz is accounted for by the adsorption or dissociation of hydrogen and hydroxyl ions. Because these ions are potential determining ions for both iron oxides and quartz, control of pH is important in the flotation of these minerals since the extent of surface ionization is a function of the pH of the solution.
Table 11.1 shows the points of zero charge (pzc's) for some iron oxides and quartz (Aplan and Fuerstenau, 1962). This property is important when using flotation collectors that are physically adsorbed, for example, amines. The pzc's for the three iron oxides, hematite, magnetite, and goethite, are around neutral pH (~pH 7), whereas the pzc for quartz is in the acidic region (~pH 2). The pzc is the pH at which the charge on the mineral surface is zero and is usually determined by some form of acidbase titration. Surfaces of minerals can also be investigated using electrokinetic phenomena with results generally being expressed in terms of the zeta potential. The zeta potential is calculated from measured electrophoretic mobility of particles in an applied field of known strength, and the term isoelectric point (iep) refers to the pH at which the zeta potential is zero. Generally, the iep and pzc are the same if there is no adsorption of ions other than the potential determining ions H+ and OH, but care should be taken with these measurements as evidenced by the variability in the literature regarding the pzc's and iep's of these minerals. For example, Kulkarni and Somasundaran (1976) determined the iep of a hematite sample to be 3.0, but the pzc of the same sample, measured using titration methods, was determined to be 7.1. These results were explained by the presence of fine silica in the hematite sample that influenced the surface properties measured by electrophoresis.
An understanding of the surface properties of minerals is utilized in the selective flotation and flocculation of minerals. For example, consider a mixture of hematite and quartz. The selectivity of the separation between hematite and quartz is related to differences in the surface charge of the two minerals. Below the iep, the mineral surfaces are positively charged and an anionic (negatively charged) collector can adsorb and render the mineral floatable; above the iep, the mineral surfaces are negatively charged and a cationic (positively charged) collector can adsorb and render the mineral floatable. From electrophoretic mobility measurements, the iep's for hematite and quartz are around pH 6.5 and 2, respectively. By choosing the correct collector type and pH, it is therefore possible to selectively float quartz from hematite with dodecylammonium chloride or float hematite from quartz with sodium dodecyl sulfate. This is illustrated in Figure 11.1 (after Iwasaki (1983)). This example is an idealized system, however, and in practice, the presence of slimes and various ions in solution will lead to variations to this model flotation behavior.
Figure 11.1. (a) Electrophoretic mobility of hematite (H) and quartz (Q) as a function of pH; (b) flotation of hematite and quartz with 104M dodecylammonium chloride (DACl); (c) flotation of hematite and quartz with 104M sodium dodecyl sulfate (NaDS) (Iwasaki, 1983).
In this paper, our interests are particles dispersed in a liquid (mainly water), relevant for many industrial particle processing operations. Recently, in-situ synthesis of dispersive nanoparticles has been developed [13,14]. However, there are limitations in the potential combinations of dispersive surfactant molecules and liquids which can be used. In other words, the type of dispersive nanoparticles synthesized by these methods is limited to specific conditions. In this paper, dispersion of fine particles synthesized or generated from natural ores, mainly hydrophilic oxide particles, is discussed. Such oxide particles are processed in plants in diverse fields from pharmaceuticals to natural ore beneficiation by standard separation methods, such as froth flotation, where a surfactant (collector) selectively adsorbs onto a target mineral particle to change its hydrophobicity. Air bubbles injected into the cell attach to the hydrophobic particles due mainly to the hydrophobic interaction, and the particlebubble complexes rise to the airwater interface for collection . This method relies on good dispersion of the different mineral particles from a ground ore in order to have selective attachment of the surfactant onto the target mineral particles. In other words, selective dispersion/liberation is a key to achieving the successful enrichment of the target mineral by flotation [16,17]. Common particle dispersion methods can be divided into two categories: chemical (e.g. pH adjustment (to increase the magnitude of surface charge), dispersant addition); and physical (e.g. agitation, sonication, centrifugation, filtration (to remove fine particles), wet milling [e.g. 18,19]). However, these dispersion methods often have difficulty in achieving selective particle dispersion in concentrated suspensions. For example, wet milling uses a compressive force to break the particleparticle interactions; but it is non-selective (breaking/dispersing all particles regardless of mineral type) and is also energy inefficient [e.g. 20]. Therefore, there is an urgent need for efficient selective dispersion techniques, such as the application of electrical disintegration for fine particle dispersion.
When compared to other major industries like telecommunications, oil and gas, or consumer electronics, the diamond industry is relatively small. However, as I have noted in the past, the diamond industry employs an estimated ten million people around the world, both directly and indirectly. It also inspires dazzling artistic creations, and offers savvy investors a wealth preservation asset in times of financial turmoil. But some of the most important benefits that the diamond industry creates are often the least well known to the general public and the media.
Every diamond producing country is different in the way it chooses to capitalize on the diamond resources buried in the ground within its borders, but all attempt to leverage diamonds in some way or another to benefit society as a whole. In my next series of articles, I will look at what has become known as beneficiation, or the downstream benefits that can be achieved by mining diamonds.
The primary meaning of beneficiation in the mining industry is a process in extractive metallurgy that improves the economic value of mined ore by removing non-commercially valuable minerals. The diamond industry has used the term for many years in reference to other downstream activities, such as cutting and polishing, that create additional economic value to a producer country beyond just the value of the rough diamonds it produces. In recent years, the word has been adapted even further, and many now use the term more broadly to refer to the overall benefit achieved through diamond activities in a given nation. This broad definition of the word is what I hope to explore over the next few weeks.
Although the early goals of beneficiation in any country are usually fair and just, the long-term results do not always align with the hopes of its architects. Some countries have been utterly transformed by diamonds for the good, while the benefits to others have not been equitably distributed. Conversely, some countries that have never produced a single mined diamond have become epicenters for the industry. In some places, beneficiation has become a natural byproduct of the presence of diamonds nearby, while in others it has been forced upon the industry in ways that have proven unsustainable. As countries like Namibia and Zimbabwe continue to explore ways to gain more benefit from their diamond resources, the successes and failures of other nations are on display for those who will design future strategies.
The most common form of beneficiation is when a producer nation mandates that a certain proportion of its rough production must be sold to local manufacturers to produce polished diamonds. This ensures additional employment outside of the mining, sorting, and sale of rough stones, and also helps local businesses capture any additional profit margin from manufacturing. Local firms are able to create national marketing campaigns around both the diamonds and the finished jewelry that are mined and cut locally. A Nielson study has shown that 75% of consumers say that a brands country of origin is as important as or more important than other drivers such as price, function, and quality. It is no surprise that jewelry manufacturers in many diamond-producing countries have been somewhat successful in selling locally mined and cut diamonds.
However, the largest diamond consuming nations, such as the USA, India, China, Japan, and the Eurozone, produce virtually no diamonds of their own. In contrast, producer nations like Canada, Australia, Botswana, Russia, and South Africa are not amongst the major consumers of diamond jewelry. This means that efforts to cut and sell locally are limited by the internal demand for diamonds, and the majority of finished goods are destined for foreign markets. Perhaps more importantly, the skill of local workers and the development of new manufacturing technologies are an impediment for most producer nations, as countries like India and Israel have excelled in these areas.
Using a broad definition of the word beneficiation shows much additional benefit to a producing country beyond just the downstream cutting and polishing industries. Due to the topography where diamonds are most often found, major infrastructure developments are often needed to bring roads, electricity, and supplies to a diamond mine. This type of investment can, in some cases, be worth billions of dollars to local economies, and provide ongoing benefits long after a diamond mine is shuttered. In some countries, the presence of roads that were built to support diamond mining activities can continue to open up new opportunities in resource extraction and new settlements for decades to come. Electricity infrastructure is another profound benefit of diamond mining, as most diamond producing regions lack adequate power generation prior to it being delivered to support mining work. Countries like Canada and Lesotho provide examples where previously inhospitable areas are now thriving as a result of power infrastructure being distributed for diamond mining.
Further beneficiation from diamonds comes in the form of direct royalties to governments that can be used for the greater good of the economy. Virtually all companies mining diamonds must pay some form of royalty to various levels of government within the region and nation. This is a common feature of all types of mining activities. They range from as little as four percent to more than 20 percent. These royalty payments often become part of a governments general revenue, which is used as required based on the individual countrys finances. However, different nations have been more and less productive with their diamond income. Botswana, for example, has used diamond revenue to transform itself from one of the poorest nations in the world, to one of Africas richest and most productive countries. Other places, such as the Central African Republic, which has plentiful diamond resources, remains amongst the poorest and least developed areas in the world.
Over this next series of articles, I will look at the beneficiation efforts of many different countries to see how some have succeeded, while others have failed. I will try to carve out a roadmap for governments who are currently looking to establish or amend their own diamond beneficiation guidelines for the benefit of future generations.
The views expressed here are solely those of the author in his private capacity. No one should act upon any opinion or information in this website without consulting aprofessionalqualified adviser.
Diamond industrialist Ehud Arye Laniado is a man passionate about diamonds. From his early 20s in Africa and later in Belgium honing his expertise in forecasting the value of polished diamonds by examining rough diamonds by hand, till today four decades later, as chairman of his international diamond businesses spanning mining, exploration, rough and polished diamond valuation, trading, manufacturing, retail and consultancy services, Laniado has mastered both the miniscule details of evaluating and pricing individual rough diamonds and the entire structure of the diamond industry. Today, his global operations are at the forefront of the industry, recognised in diamond capitals from Mumbai to Tel Aviv and Hong Kong to New York.
Nothing on this website can be construed or constitutes an offer or a recommendation to sell or to purchase diamonds or the solicitation of an offer to purchase any diamonds nor does it constitute an offer or a recommendation to sell or to purchase any security or financial product or the solicitation of an offer to purchase any security or financial product. >> Continue to full disclaimer
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Diamonds, originally a carbon lattice formed in high temperature and high-pressure environment in the earths mantle, came to the surface with kimberlite magma during volcanic eruptions millions of years ago. This mineral, which is of little industrial value, should have been just a kind of gemstone, becoming a decoration for a lady, expensive owing to its scarcity.
But with the discovery of large diamond mines in South Africa in 1870, diamond prices faced a collapse, in which case investors set up a monopoly group, De Beers, to control the global diamond trade by controlling production and establishing a single sales channel, thus maintain the public impression of the scarcity of diamonds. In particular, the carbon crystal has been successfully portrayed as a symbol of elegance, luxury and love through large-scale commercial marketing in the past hundred years. The De Beers is the only pricing group.
The situation is different. Since the end of the 1950s, a troublemaker has emerged, but de Beers has succeeded in integrating it into its single channel system, making it a hitchhiker. Whats more, De Beers has become a subsidiary company owned by Anglo American Resources Group, and its monopoly no longer exists, but it still maintains its position as an industry leader, accounting for 35% of the global market share. And the hitchhiker of the year became the worlds largest producer of rough diamonds, and that was the Soviet Union / Russia.
In 1940, Soviet geologists pointed out that the Yakut area was similar to the diamond-rich area in South Africa and should be rich in a diamond. After tough geological prospecting, magnesia-aluminum garnet, a symbiotic ore, was finally discovered in 1953. In 1954, the first diamond-bearing rock was discovered in the western part of the Yakut Soviet Socialist Autonomous Republic, and named Flash. Since then, a large number of diamond-rich rock have been found in this area. With huge reserves, the Soviet Union is expected to jump into a diamond power. In 1957, the Soviet Ministry of Nonferrous Metallurgy decided to invest in the development of diamond mineral industry in Yakut and set up theYakute Diamond Trust.
Before the Yakutia deposit was discovered, the Soviet Union produced very few diamonds, which it secretly exported through De Beers because of the Western blockade and De Beerss monopoly. Whether to enter the market independently and break the monopoly or to continue to accept De Beerss exploitation, is a question that must be faced in the face of huge future production capacity. De Beers was also nervous about the Yakutia discovery, fearing that his monopoly would be broken. In the end, the two sides eventually agreed to avoid a self-destructive price war, with the Soviet Union losing the right to list independently and being lumped into De Beerss single channel system, and De Beers had to buy all Soviet diamonds for export. The Soviet threat to its monopoly was removed. Since Yakut diamonds are mostly tiny, De Beers had to revise its marketing strategy to promote to the public a new idea that diamond perfection is more important than size. Through the secret contract, the Soviet Union became the beneficiary of De Beers manipulation of the world diamond market, acquiring a lot of foreign exchange. Since then, the large-scale development of diamonds in Yakut has begun.
The difficulty of early exploitation period was beyond imagination. The Yakut Republic is located in the northeast of the Eurasian continent, the diamond area is located in the frozen earth near the Arctic circle, where with the harsh climate, few people tread, and shortage of infrastructure. The Yakutia diamond Trust had to recruit large numbers of workers with high welfare benefits and build infrastructures such as towns, hydropower stations, airports, and roads. As a result of the unprecedented cost of building infrastructure and high labor costs, diamond mining in Siyakut initially suffered heavy losses, resulting in long-term negative returns for the Soviet diamond industry. The exploitation of peace and luck was first developed, which gave birth to the new cities of Mirnyy and Udachnyy. Despite the harsh conditions, due to the gifts of nature and the hard work of the Soviets, the production of the Yakut Diamond Trust was amazing, rapidly surpassing the world record, and increased 25 times in just seven years. Meanwhile, the Soviet Union was dissatisfied with providing only rough diamonds and began to set up its own gem factory in preparation for getting rid of De Beers in the future. With the discovery and production of Awhar, Interstate and other mines, the production of Yakut diamonds have increased one step further. Since 1971, the production of diamonds in the Soviet Union has reached more than 10 million carats, surpassing that of South Africa, second only to Zaire. On the whole, Yakut diamonds are small in size and contain more impurities, and the quality is not as good as that of Africa diamonds.
After the disintegration of the Soviet Union, the Yakut Autonomous Soviet Socialist Republic became the Sakha Republic, and the Yakut Diamond Trust was reorganized into the Russian-Sakha Diamond Holding Company, for short, Russian Diamond. The governments of the Russian Federation and the Sakha Republic hold 69 percent of the shares. Currently, Russian Diamond account for 95 percent of Russias diamond exports and 25 percent of the global market (in Querats calculations). Its proven reserves amount to 600 million carats, perhaps a third of the worlds total, of which 65 percent are of or close to jewelry quality and can be mined continuously for 30 years.
After years of mining, the Mirnyy Mine, which was closed in 2001 because it was no longer worthy to continue to dig down, formed a huge pit 525m deep with a diameter of about 1.2 km, produced $17 billion worth of diamonds since 1957. The mine went underground in 2009 with an annual production capacity of 1 million tons and a life expectancy of 34 years. The mine named International, located 15 km south-west of Mirnyy, was discovered in 1969 and began open-pit mining in 1971 and underground mining in 1999 with a designed annual output of 500,000 tons and a life expectancy of 27 years.
The mine named Lucky in Udachnyy is not as well known as the peace, but it is larger, with reserves of about 120m carats and a depth of 640m, although open-pit mining is nearing an end. Development on its underground mines began in 2004, is expected run to 2019. By then, the underground mine will have a production capacity of 4 million tons and will become one of the largest underground mines in the world. It is the largest diamond concentrator in Russia with an annual processing capacity of 11 million tons and is equipped with seven 9m diameter autogenous mills.
There are three mines in the Aykhal area, the Aykhal was started for open-pit mining in 1961, turned into underground mining since 2008. The celebration mine, discovered in 1975 is still in open-pit mining, originally designed to reach a depth of 500m, but recent expansion has been approved, with open pit mining reaching a depth of 700m. The Komsomolskaya mine was discovered in the 1970s but was not developed until 2001, the open pit mining depth could reach 460m.
Nyurba was the last mine to be discovered until the 1990s, the Botubinskaya mine was the discovered firstly but exploited until 2015. The newer Nyurba mine begun open pit mining at the beginning of the 21st century and has reached a depth of 300m. According to the analysis of the geological environment, the underground mining of these two mines will not be profitable so the production will be stopped when reaching 570 meters.
#1spiral classifier #2wet type mill #3vibrating screen #4froth flotation In the early days, all the mining and ore dressing equipment was made by the Soviet Union, after the 1980s, gradually adopts the western advanced equipment, like Carter 785 dump truck, Komatsu/ Demak H285S excavator, L1100 loader, etc.. The following brief introduction of the diamond beneficiation process.
All rough diamonds are sent to a diamond sorting center in Mirnyy, where they are sorted by size and color and a preliminary valuation. Because each mines diamonds are unique, experienced experts can visually identify where they are produced. Unlike minerals like gold, silver, and copper, diamonds are not standardized products and therefore do not have exchanges like bulk commodities. The value is generally based on three characteristics: size (Querat), color, and purity.
After evaluation and registration, rough diamonds can be sent to the Russian diamonds sales network. But while appreciating the brilliance of diamonds, in the face of the huge mines, dumping grounds and tailings ponds in North Asia, should human beings also think, for such a small stone whose price is artificially high, is it worth paying such a high environment cost?
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The chrome ore beneficiation processes include gravity separation, flotation, magnetoelectric separation and chemical beneficiation, etc. Because of the chrome ore composition that composed of one or more silicate, and the density difference between the chrome and silicate, the research both in home and aboard about chrome beneficiation process mainly focuses on the gravity separation process. However, using a single gravity separation process can improve the chrome grade, but fail to recover it effectively. In this paper, try to find a better way by using a combined beneficiation process of gravity and magnetic separation.
X-ray diffraction analysis The main mineral ores in the chrome sample are chromite, enstatite, anorthite, hopfnerite, diopside, albite, biotite, etc. Physical analysis The metallic minerals in the chrome samples are mainly chromite, the gangue minerals are mostly enstatite and anorthite, followed by tremolite, diopside, quartz and albite, and a small amount of biotite, serpentine and chlorite, trace amounts of calcite, chalcopyrite, sphene, etc.
Cr2O3 is found in the form of individual minerals, mostly in chromite, few in enstatite. Therefore, chromite is the target minerals to be recovered in this experiment. The following is a systematic grain size grade of chromite and enstatite. As shown in the table above, the chromite material particle mainly of middle-fine of finesse, cover in the range of 0.02-0.104mm. In which, the particle of +0.074mm account for 31.56%, -0.043mm account for 44.9%, -0.010mm only account for 1.76%. Concentrated distribution same as the chromite, the particle of enstatite mainly in 0.020mm-0.147mm, -0.010mm only account for 0.13%.
The dissociation degree of chromite monomer in the sample is 95.11%, the magnetism can be used to separate the chromite from the nonmagnetic ores. The gangue minerals, such as enstatite, tremolite, diopside, biotite, also have weak magnetism, affect the grade of magnetic concentrate. It is better to separate it by using gravity separation. In this experimental, we adopt a strong magnetic process, roughing- concentration- scavenging, to remove the impurity preliminary, then to separate the chromite from nonmagnetic ores. at next, using gravity separation process to refine the chromite concentrate and scavenging tailings, meanwhile, improve the grade and recovery rate. Chrome process equipment is wet type strong magnetic separator, and spiral chute (chrome spiral plant) of gravity separator.
The chrome raw ore is a flotation tail ore, which is mainly formed in the chromite, and the chromite is the target recovering mineral. The dissociation degree of ferrochromium ore is low, and it has a weak magnetic property. First of all, magnetic separation processing to separate chromite. Besides, the grain size is fine, so there is no need for grinding, the grading result shown in the below. Raw ore process flow: roughing- concentration- scavenging. the Cr2O3 mainly in the fine particle ore, in order to ensure the grade and recovery rate, take the roughing experimental under the high gradient separation condition, results as follows.
The results of this study show that, after the first rough separation, the grade of chromite concentrate Cr2O3 is 32.06%(13% higher than the grade of raw ore), the productivity of that is 48.88%, and the recovery rate of that is 83.04%. In order to know the Cr2O3 distribution among the concentration and tailings, make a grade sieving in the roughing concentration and tailings respectively.
As can be seen from the above table, in the concentration, the Cr2O3 mainly in the fine particle grade; in the tailings, the Cr2O3 distribute evenly. strong magnetic separation can recover the valuable minerals, but dont increase the chromite mineral grade to the metallurgical grade, that is, the Cr2O3 higher than 38%.
After the advanced concentrate process, the grade of concentrate Cr2O3 is 38.5%, reach the smelting grade, and that of tailings is 24.28%. After the scavenging process, the grade of concentrate Cr2O3 of roughing tailings is 15.07%, that of tailings is 2.4%. It turns out that the roughing process tailings and scavenging process concentrate have recovery value.
The density of chromite ore is slightly higher than that of its other magnetic gangue ore. Therefore, the separation of ferrochromium from other minerals can be realized by gravity separation. Use spiral chute to separate the concentrate process tailings and the scavenging process concentrate respectively. As shown in the gravity beneficiation process result, both of the grade of concentrate process tailings and scavenging process concentrate higher than 40%, the productivity of that is up to 70%. In conclusion, gravity separation technology can purify the chromite significantly.
As for the chrome beneficiation processes, the single gravity separation process can obtain the qualified grade but does not ensure the productivity and recovery rate. The combination of magnetic process and gravity separation can ensure all indexes of grade, productivity and recovery rate.
JXSC as a service provider of mineral extraction since 1985 all the time focus on solving trouble during the ore mining process, and supplying mineral processing solutions and equipment for various of metals including chrome, silver, gold, titanium, zinc, tin, lead, and so on. As for chrome mining, we have built close relationships with many chrome ore mines in South Africa. Visiting our customers of Chrome wash plants South Africa is a good idea for you to know us deeply from product quality and service. Contact engineer for details of chrome ore processing plant.
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