about beneficiation plants

beneficiation plants: latest news & videos, photos about beneficiation plants | the economic times - page 1

Domestic prices of Diammonium phosphate (DAP) and nitrogen, phosphorous and potash (NPK) have seen a drop as raw material prices in the global market fell, said Rakesh Kapur, joint MD at Indian Farmers Fertiliser Cooperative Ltd (Iffco).

On Thursday, the ministry issued a notification that overturned its January 2014 regulation that made it mandatory for all coal-based power plants located 500 kilometres or more from the pit-head or coal mine to use raw or blended or beneficiated coal with no more than 34 per cent ash content.

"This is not true that the price (of LPG) is constantly increasing. This month it was hiked due to the international market. However, there are indications that the prices may come down next month. During the winters, LPG consumption increases, which creates a pressure on the sector. This month, the price increased while next month it will reduce," he said.

Britain's biggest carmaker Jaguar Land Rover said it will go down to a three-day week at its Central English Castle Bromwich plant just days after its boss warned about the impact of Brexit and diesel policy.

10 best ore beneficiation plants for sale (with costs) | fote machinery

Before purchasing an ore beneficiation plant, people have lots of concerns: Which equipment I should choose to process my iron ore? Is this ore processing flowsheet best? Can these machines help me remove sulfur in iron ore beneficiation? Would they increase the recovery rate of tailings?

Then how to choose the right ore beneficiation plant depends on a lot of factors including physical properties of raw ore, capacity demands, final ore product requirements, geological situations of ore mines, and so on.

Here Fote Group would love to share valuable information about mining market trends, ways to build a high-quality ore beneficiation plant, and ten different ore processing plants which have been proved successful by our customers. If you have any most pressing questions and concerns, please contact our professional engineers who can make customized solutions according to your actual situation.

Our ore beneficiation plants sale to many countries, such as India, Australia, the USA, the UK, Canada, Switzerland, Philippines, Malaysia, Thailand, South Africa, Sudan, Egypt, Kenya, Indonesia, Nigeria, etc.

Nowadays, with ways of ore processing are getting more and more diversified and intelligent, the investment is not only limited to gold ore beneficiation but enlarged to many other items. From precious metals to coal, and to non-ferrous metals, investors can profit and bring more economic benefits to society.

Over 80 kinds of ores are widely used minerals in the world. Due to large output and high international trade volume, there are the several most common and important ores such as iron ore, copper ore, gold ore, bauxite, coal, lead&zinc ore, nickel ore, tin ore, and manganese ore, etc.

Nothing can replace iron ore in developing infrastructures as well as coal ore in the electricity industry, those ores making a great contribution to countries' economic growth. Gold ore mining ranks in a top position, attracting lots of investment for closed relations between the gold price and currency market.

The screening and crushing process is used to release useful minerals from the gangue. Different types of crushers reduce large sizes of raw ore into smaller ones, then vibrating screen with different mesh would help to get the desired size of ores. During the process, how many crushers need to be installed according to your real situation.

Usually, there are crushers with three crushing stages: primary crushers like jaw crushers, secondary crushers like cone crushers, roll crushers and impact crushers, tertiary crushers like compound crushers and fine crushers. Vibrating screens also have different types: Circular motion vibrating screens, horizontal Screens, high-frequency Screens, and trommel/ drum screens.

Only by crushers cannot get ore products with fine granularity, that's why mill grinding machines necessary in the beneficiation process. The mill grinding process is almost carried out in two consecutive stages: one is dry grinding (coarse grinding) and the other is wet grinding (fine grinding). The key grinding equipment are ball mills and rod mills, and the latter is now mostly used for wet grinding to finally produce fine and uniform ore products.

The beneficiation process is most crucial during the whole plant, helping people extract high value and pure ore concentrate products from ores no matter its grade high or low. The beneficiation process can be carried out in a variety of ways as needed but you ought to select a piece of optimal equipment to avoid inefficiency and waste in the entire process. The most common beneficiation equipment includes flotation machines, electrostatic and magnetic separators, and gravity beneficiation equipment.

Ore drying equipment may appear in any stage of a mineral processing plant (from raw ore-concentrate-finished product). The purpose of drying is to remove the moisture contained in the ore, ensuring the integrity of the product, and maximizing the value. In addition, drying process can also reduce product transportation costs and improve the economic efficiency of storage and processing.

With almost 50 years' extensive experience, Fote engineers are professional in integrating, designing, fabricating, commissioning, maintaining, and troubleshooting various beneficiation plants. The company aims to provide customers with the best mining equipment and the most reasonable beneficiation plants. Its final goal is to increase the potential profit that customers can obtain from the ore and enable mining companies to improve the overall profitability.

5TPH low-grade gold ore beneficiation plant in India 10 TPH gold ore beneficiation plant in South Africa 20-35TPH gold ore beneficiation plant in Egypt 10 TPH iron ore beneficiation plant in the USA 10-50TPH copper ore beneficiation plant in Pakistan 50-100TPH manganese ore beneficiation plant in Kenya 150TPH Bauxite ore beneficiation plant in Indonesia 50TPH lateritic nickel ore beneficiation plant in Philippines 200TPH zinc & lead ore beneficiation plant in Nigeria 250TPH chrome ore beneficiation plant in Russia

As a leading mining machinery manufacturer and exporter in China, we are always here to provide you with high quality products and better services. Welcome to contact us through one of the following ways or visit our company and factories.

Based on the high quality and complete after-sales service, our products have been exported to more than 120 countries and regions. Fote Machinery has been the choice of more than 200,000 customers.

beneficiation plant: latest news & videos, photos about beneficiation plant | the economic times - page 1

Domestic prices of Diammonium phosphate (DAP) and nitrogen, phosphorous and potash (NPK) have seen a drop as raw material prices in the global market fell, said Rakesh Kapur, joint MD at Indian Farmers Fertiliser Cooperative Ltd (Iffco).

On Thursday, the ministry issued a notification that overturned its January 2014 regulation that made it mandatory for all coal-based power plants located 500 kilometres or more from the pit-head or coal mine to use raw or blended or beneficiated coal with no more than 34 per cent ash content.

"This is not true that the price (of LPG) is constantly increasing. This month it was hiked due to the international market. However, there are indications that the prices may come down next month. During the winters, LPG consumption increases, which creates a pressure on the sector. This month, the price increased while next month it will reduce," he said.

Britain's biggest carmaker Jaguar Land Rover said it will go down to a three-day week at its Central English Castle Bromwich plant just days after its boss warned about the impact of Brexit and diesel policy.

:: promacindia.com | engineering excellence ::

Promac can offer complete turnkey solution for Mineral processing industries especially Gold, Iron Ore, Copper, bauxite etc. The complete solution ranging from Raw material handling, Communition (crushing & Grinding), Classification, Physical and Chemical process solutions for processing minerals can be engineered and offered suiting client needs.

Promac was awarded order for Complete Design, Engineering, Manufacture, Assembly, Testing, Supply, Packing, Forwarding, Transportation of Equipment, unloading, Storage, Erection and Commissioning of Equipment/Materials with all accessories including Civil works for 1000 TPD Gold Ore Processing Plant at Gadag, Karnataka, India.

a review of cassiterite beneficiation fundamentals and plant practices - sciencedirect

Role of particulate properties in gravity concentration and flotation is reviewed.Chronology of surfactant inventions in cassiterite flotation is presented.Adsorption characteristics of different surfactants onto cassiterite are summarized.Cassiterite beneficiation plant practices and their developments are reviewed.Advanced gravity concentrators are assessed for the recovery of ultrafine particles.

Tin has many important properties and thus it finds wide applications in metal coating, tin plating, alloying, soldering, and plumbing, as well as in the electronic, electrical, and organotin compounds industries, etc. The metal is chiefly produced from the mineral cassiterite, which is generally beneficiated following gravity concentration and flotation techniques. Cassiterite beneficiation has contributed significantly to the understanding of fundamentals in mineral processing. In particular, the influence of particle size in gravity concentration and flotation techniques has been revealed. Basic research on flotation, such as the development of specific surfactants and the adsorption behaviour of these onto mineral surfaces has been performed. In the present review paper, an attempt has been made to summarize the role of particulate properties in gravity concentration and adsorption behaviour of flotation surfactants with regard to cassiterite. Past tin beneficiation plant practices are reviewed in detail including process flowsheet developments which have taken place over time.

the beneficiation of tailing of coal preparation plant by heavy-medium cyclone | springerlink

Dense-medium cyclones have been used for beneficiation of fine particles of coal. In this study, the usability of cyclones in the beneficiation of tailings of a coal preparation plant was investigated. For this purpose, separation tests were conducted using spiral concentrator and heavy medium cyclones with the specific weight of medium 1.31.8 (g/cm3) on different grading fractions of tailing in an industrial scale (the weight of tail sample was five tons). Spiral concentrator was utilized to beneficiate particles smaller than 1mm. In order to evaluate the efficiency of cyclones, sink and float experiments using a specific weight of 1.3, 1.5, 1.7 and 1.9g/cm3, were conducted on a pilot scale. Based on the obtained results, the recovery of floated materials in cyclones with the specific weight of 1.40, 1.47 and 1.55g/cm3 are 17.75%, 33.80%, and 50%, respectively. Also, the cut point (50), which is the relative density at which particles report equally to the both products are 1.40, 1.67 and 1.86g/cm3. The probable errors of separation for defined specific weights for cyclones are 0.080, 0.085 and 0.030, respectively. Also, the coefficients of variation was calculated to be 0.20, 0.12 and 0.03. Finally, it could be said that the performance of a cyclone with a heavy medium of 1.40g/cm3 specific weight is desirable compared with other specific weights.

Coal is specified as one of the most important energy resources in the world. Approximately 28% of the energy of the world is provided by coal (BP Statistical Review of World Energy; 2017). Considerable amounts of coal particles are accumulated in the tailing dams of washing plants which can lead to serious environmental problems. Recovery of these particles from tailings has several economic and environmental advantages. Maintaining natural resources and reducing the amount of material discharged to the dams are the most important ones (Ashghari et al. 2018). Various investigations have been explored environmental impacts of coal tailing piles on air, soil and groundwater (Meck et al. 2006; Battioui 2013; Kotsiopoulos and Harrison 2017). It is reported in some cases acid mine drainage (AMD) of coal tailing dams contained an amount of sulfates, nitrates, chlorides and heavy metals higher than the average value defined by the World Organization of Health (WHO) (Battioui 2013). These AMDs can cause harmful effects on groundwater quality, river flows and ecology their deposits proximity (Sengupta 1993; Simate and Ndlovu 2014; Kefeni et al. 2017; Peiravi et al. 2017). Moreover, cone shaped damps of coal tailing can potentially be a source of self-ignition and possible explosion (Siboni et al. 2004; Adiansyah et al. 2017). Offering a solution to recover them, can reduce the volume of tailing and increase the number of productions and efficiency. In fact, producing coal from tailing is cost-effective, economical and environment friendly. Reprocessing tailings of coal preparation plants is a new approach to coal washing industry.

Gravity separation and flotation are the most common techniques in coal processing and recovery of coal from tailings in large scale (Wills 2011; John et al. 2002). Heavy media separation method is one of the gravity separation methods, which was patented in 1858 by Henry Bessemer (Napier et al. 2006). This method is so advantageous due to the high capacity and efficiency of separation. One of heavy media separators is hydrocyclone which was developed in the 1950s and in the chemical industries due to the simple design, suitable performance and high capacity (Delgadillo and Rajamani 2005). The heavy media cyclone is used extensively in coal processing and in the primary treatment of metal ores such as Pb and Zn. The modern cyclone for coal preparation is the most effective option for size fraction of 0.550mm (Chu et al. 2012). In this separator, the centrifugal force causes the heavy particles such as dust or ashes to move to the wall of the cyclone where the particles get down because of the axial velocity and discharge through the underflow of the cyclone (Chu et al. 2009). The heavy media cyclones are installed inclined or upside down (Rayner and Napier-Munn 2002).

In order to determine the specific weight of the heavy media liquid of the cyclones, the results of heavy liquid tests are used in different specific weights. Also, evaluation of the separation method or the operation of a gravity separator is usually based on the decomposition of the sinkfloat, and the washing ability curves(Gupta and Yan 2006). In an ideal separation process, all the particles with a specific weight less than separation density are recovered to concentrate or the light product (coal), and all the particles with a specific weight more than separation density are introduced to tailings or the heavy product(Majumder and Barnwall 2011). It can be stated that there is no ideal separation in any of the separators, and some of the materials are mistakenly divided.

Parameters that influence the mistake of particle splitting are the geometry of separators, machine mechanisms and settings, the composition and feed rate, and product crop, media rheological properties, and relative separation density. In addition, the time required to separate a particle and the settling rate of the particles are effective in the recovery. The performance of a gravity separator in coal treating is commonly determined by plotting a Tromp (distribution) curve which is basically a plot of partition coefficients in term of average specific gravity (Mohanta and Mishra 2009). The separation efficiency can be obtained from the slope of the distribution curve (or the curvilinear curvature). This curve depends on the size of the particles and the type of separator and it is also independent of the operation of sinking and floating (Burt 1984). In Fig.1, the distribution curve is shown in two ideal and realistic modes. According to the shape, when the curve slope is increasing in the 50% distribution coefficient, the curve is changed from the realistic mode to the ideal one (vertical slope). This shows that increase in the efficiency of a separator. The greater the slope of the distribution curve is plotted, the better performance of the device is observed(Farzanegan et al. 2013).

In this study, reprocessing of tailings from the Anjir Tange processing plant using a heavy media cyclone was investigated. Gravity separation tests by the heavy media cyclone and sinkfloat were performed in both industrial and laboratory scale for different size fractions. Finally, the efficiency of heavy media cyclone devices has been evaluated using by Tromp curves. The Tromp curve is an indicative of actual performance of the separation unit since it is independent of feed quality. In case of coal washing, the degree of misplacement is directly depended to the amount particles with a specific weight close to gravity of separation (near-gravity material). However, the coal containing high near-gravity material can be effectively processed by choosing the right process and correct operating parameters.

Coal tailings samples were collected from the coal preparation plant of Anjir Tange which actively produces washed coke in central AlborzIran. Three methods of hand sorting, gravity, and flotation are applied in thia plant to supply coke. The tailings aforementioned processes are accumulated in two depots of flotation tailings and the other processing methods. The mass of the piled tailings is 2 million tons with the average ashes between 40% and 45%. According to studies, 70% of tailings are produced from jig process with the 44% valuable coal and 56% ashes.

In order to investigate the possibility of reprocessing of tailings from Anjir Tange coal preparation plant by using heavy media cyclones, approximately five tons of tailings sample from tailing dumps were tested with heavy liquids. The spiral tests were also performed in an industrial scale. After the classification of the sample in various grain fractions, heavy media tests were conducted in specific weights of 1.4, 1.5, 1.6, 1.7 and 1.8g/cm3.

Based on the results of these experiments, the specific weight of the media were selected, and the heavy medium cyclone tests were carried out on an industrial scale with specific weights of media 1.40, 1.47 and 1.55g/cm3. Then, to investigate the efficiency of heavy media cyclones, on both products of tailings, sinkfloat experiments were carried out in specific weights of 1.3, 1.5, 1.7, 1.9g/cm3. Finally, the efficiency of cyclones has been investigated by plotting the corresponding distribution curves.

The particle size distribution (PSD) and the amount of ash in each size fractions of the sample are presented in the Figs.2 and 3. Giving the results of the sieve analysis and the amount of the ash of the coarse-grained tailing, about 50% of the total samples were in the range of 112mm. The maximum amount of ash is belongs to the fraction of 1225mm with the ash content of 69.70%, which is 21.90% of the total weight of sample. In Fig.3b, the results of the sieve analysis and ash content of the flotation tailings are shown. According to this analysis, about 80% of particles are larger than 40 micrometers with a cumulative ash value of 23.80%.

In order to investigate the reprocessing capability of the tailings by gravity separation method, heavy liquid tests were carried out in the specific gravity of 1.4, 1.5, 1.6, 1.7 and 1.8g/cm3. The results of the heavy media tests in each size fraction are presented and discussed in the following bullet points:

Particle size greater than 25mm Fig.4a shows the heavy media test result for this size fraction. Based on the results, using a solution with a specific weight of 1.5g/cm3, a concentrate with 10% recovery and 16.40% ash content and a final tailing with 70.20% recovery and 73% ash content was obtained.

Size fractions of 1225mm according to the results of the analysis, the ash content of the feed is 69.70% and 21.90%. Based on the results of sink and float experiments (Fig.4b), in a solution with a specific weight of 1.5g/cm3, a concentrate with 16% ash and 8.80% recovery was achieved. In specific weight of 1.6g/cm3, a product with 14.40% weight percentage of feed and 21.40% ash with 75.60% recovery to the tail and 60.60% ash was obtained.

Particle size fraction of 112mm This fraction makes up 48.90% of the feed weight with 60.60% ash. Based on Fig.4c, in the specific weight of media 1.6g/cm3, the weight percent of the concentrate is 24.30% and the ash content is 15.10%. In a solution with a specific weight of 1.7g/cm3, a product with 28.50% recovery, and 19.20% ash was obtained; in this case, the final tailings was 69.90% of the feed weight with 78.20% ash.

Particle size greater than 1mm the particles which are larger than 1mm contain 87% of the total feed weight. The results of the heavy liquid test on this size fraction are shown in Fig.4d. According to the figure, in a specific weight of 1.5g/cm3, the weight percent of the concentrate is 15.20% with 12.20% ash. Concentrates with 21.40% and 29.50% recovery and 18.50% and 22.60% ash content, respectively were achieved in special weights of 1.6 and 1.7g/cm3. The final tail in the specific weight of 1.7g/cm3 is 71.70% recovery to the tail and 78% ash.

The fraction with the particle size less than 1mm This fraction consists 12.80% of the feed weight with 54.80% ash. 12.40% of this fraction is between 1.00 and 0.15mm, and 0.40% is less than 150m. In this part, the primary operation was successful and the particles with a size less than 150m were removed by using the industrial spiral. The results of this experiment are presented in Fig.5. According to the results, a product with 32% recovery and 15.30% ash was obtained, which is considered as a desirable result.

After preparing thin blade from sample size fraction larger than 12mm, microscopic studies was conducted and degrees of liberation was obtained. It was observed that coal has a good purity in this fraction, but on the other hand, it has a high degree of contamination with the tail. Despite the unusually crumbling of the coal, to increase the recovery and reduce the amount of ash, this section was dimensioned from the grinding sample, and then a heavy liquid test was performed on fraction of particles which is larger than 1mm. The results of crushing and heavy liquid tests are presented in Figs.6 and 7. According to the results, grinding has not had a desirable effect on reducing the amount of ash in this fraction.

According to the results, by carrying out heavy media test on the tailings of Anjir Tange coal preparation plant, the products of different qualities are produced. The particles which are in the size fraction larger than 1mm generated three products with 7% ash and 19% recovery, 12% ash and 30% recovery, and 45% ash with the recovery of 22.50%. In the case of combining the spiral product and the fraction larger than 1mm, concentrate with 18% ash and 48.50% recovery is obtained which constitutes about 22.50% of the feed weight.

To conduct a large-scale heavy media test on an industrial scale, the feedstock was analyzed by using a 20mm sieve mesh size. Based on the results, 50% of the feed was smaller than 20mm and about 20% of it was removed from the circuit during the irrigation stage. Eventually, about 18 tons of feed was introduced into the heavy duty cyclone by the DMS (Dense Medium Separation) process (GSZs feed method). Based on the results (Table1), after the separation of materials in the cyclone, a concentrate with a weight of approximately 6 tons was obtained which consists 10% of the total feed and 20% of the feed to the cyclone.

The results of sink and float experiments are used to select the specific weight of fluid in the hydro-cyclone apparatus. In this research, based on the results of heavy media tests performed at industrial scale, the specific weight of the hydro-cyclone medium was selected and the gravity separation tests of coal tailings has been done in specific weights of 1.40, 1.47 and 1.55g/cm3 at industrial scale.

At the entrance of the heavy media cyclone devices, there is a sieve that assumes particles that are smaller than the crater as tailings. Based on the analysis of the gradient carried out on the concentrate and tailings of each of the heavy media cyclones (Fig.8), it was observed that more than 70% of the particles are larger than 2mm, so it can be said that the size of the span which is embedded at the entrance of the heavy media cyclones is 2mm. Therefore, heavy media cyclone experiments were performed on particles 215mm in size. The results of these experiments are given in Table2 for specific weights of 1.40, 1.47 and 1.55g/cm3.

As noted above, the evaluation of the separation method or the performance of a gravity separation device is usually based on the decomposition of the sinking and floating and the washing ability curves. For this purpose, for assessing the efficiency of heavy media cyclones in different specific weights, sink and float experiments were carried out on concentrates and tailings of hydro-cyclone on a laboratory scale. Heavy liquid solutions required are obtained from dissolving zinc chloride in water. Based on the similar experience obtained from the processing factories, Eps probability error rate for this plant was considered 0.05 and the weight of especially heavy liquids were calculated using Eq.(1):

Due to limitations in the preparation of heavy media solutions as well as their cost, the value of n was considered to be 2 and liquids with specific weight of 1.3, 1.5, 1.7, 1.9g/cm3. The results of sink and float experiments for the feed of heavy media cyclones in two particle fractions larger than 2mm and 12mm are shown in Fig.9. Also in Fig.10, the results of analyzing the amount of ash in the feed with the size greater than 1mm at each specific gravity are presented.

In Fig.11, the results of the heavy liquid tests are shown for concentrate and tailing of heavy media cyclone devices with the size of larger than 2mm. The amount of floated concentrate of the cyclone with a specific weight of 1.40g/cm3 in a solution of 1.4g/cm3 is about 80% of the feed weight. The proportion of floated coal in the cyclone with the specific weight of 1.47g/cm3 in a solution of 1.5g/cm3 is 68%, this amount for a cyclone with a specific weight of 1.55g/cm3 is 50%.

In order to carry out more precise studies, sink and floating experiments were also performed on size fraction of 12mm concentrates and tailings of cyclones. Figures12 and 13 show the results of these experiments. The heavy liquid test does not have a good result for particles of less than 2mm in size. Therefore, the experiment was not conducted on this fraction.

According to the results of the sink and floating experiments and analyzing the amount of ash, the amount of floated concentrate of the cyclone with a specific weight of 1.40g/cm3 in a solution of 1.4g/cm3 is over 95% of the feed weight and the ash contents less than 12%. The specific gravity of the cyclone floated coal is 1.47g/cm3 in a solution of 1.5g/cm3 is about 78% with 15%, and this value for the cyclone with a specific weight of 1.55g/cm3 is 68% with 20% of ash.

The performance of gravity separation equipments is evaluated by distribution curves. Determining the distribution curves for controlling gravity separation processes is important and can provide a proper correction for controlling a given process, and it is possible to simulate and predict the results (Ferrara and Bevilacqua 1995). The distribution curve is obtained by calculating the distribution coefficient by the average density in each fraction. In order to plot the distribution curve, weighting the concentration of concentrate and sinkfloat tests for concentrate and tailings should be performed. The weight recovery of the concentrate can be obtained through direct weighting or using mass balance equations. With regard to weight recovery, as well as sink and floating data, the feed can be restored. The data from sink and floating experiments for cyclones with specific weights of media 1.40, 1.47 and 1.55g/cm3 are presented in Tables3, 4 and 5 for plotting the distribution curve.

According to the data obtained from the sink and floating experiments on the concentrate and tailings of the heavy medium cyclone of Anjir Tange and Eqs.(2) and (3), at a specific weight of 1.40g/cm3, the efficiency of floated materials is 17.75% and efficiency of submerged material is 82.25%. Also, using the specific weight of 1.47g/cm3, these values are 33.80% and 66.20%, respectively. The efficiency of floated materials in cyclones with a specific weight of medium 1.55g/cm3 was also 50 percent, and the efficiency of submerged materials was also calculated to be 50 percent. Then, the separation curves or Tromp curves were plotted with a distribution coefficient relative to the mean density range for the three specified weights (Fig.14).

From the Tromp curve many common performance parameters can be estimated. These parameters include (1) cut point (50), which is the relative density at which particles report equally to both products; (2) probable error (Eps), which is half of the specific gravity interval between 25% and 75% partition values; and (3) imperfection, which relates to the shape of the partition curve (Mohanta and Mishra 2009).

According to the obtained Tromp curves (Fig.14), d50 at the density of 1.40g/cm3 is equal to 1.40g/cm3, and at 1.47 and 1.55g/cm3, this value is 1.67 and 1.86g/cm3, respectively. The actual separation curve shows that the efficiency of the particles with their density at the separation density is the highest, and the efficiency is reduced for particles whose density is close to the separation density (the separation limit). Therefore, given the equalization of the separation density (d50) at a specific weight of 1.40g/cm3, it can be claimed that the performance of the machine was more appropriate at this particular specific weight.

The probability error is the characteristic of a process and separators with less Ep are evaluated as effective separators. The variation of Eps dispersion criterion to centralized variation is also a violation factor. The violation coefficient, independent of the separation density, is used as an auxiliary method for comparing separation processes and is defined as the Eq.(5):

As noted above, the slope of the curve is a parameter to measure the degree of separation and indicate the separation accuracy. The slope of the distribution curve of Fig.14 is approximately linear in the distance between the distribution coefficients of 25% and 75%, so this slope can be used to represent the efficiency. Also, the slope in the density of 1.40g/cm3 relative to other densities indicates a better performance of the device in this particular weight. The linear distribution of the distribution curve (the distance between the distribution coefficients of 25% and 75%) is closer to the straight line, the Ep value is smaller and the separation efficiency is greater. In an ideal separation, this line is straight and the Ep value is zero. In this study, the calculated value of Ep for a heavy media cyclone with a density of 1.40g/cm3 equals to 0.080 and at the specific weight of 1.47, this value is 0.085. Also, this value is 0.030 for a specific weight of 1.55g/cm3. According to the Eq.(5), the coefficient of variations are also calculated for the Tromp curve at the specific weights of 1.40, 1.47 and 1.55g/cm3as 0.20, 0.12 and 0.03, respectively.

Based on the results of industrial scale experiments, by performing heavy medium tests, products with various qualities are obtained. In the size fraction larger than 1mm, the recovery will be 19% for the product with 7% ash, the product with 12% of the feed weight will have 30% recovery, and the recovery of the product with 22.50% ash is 45%. In the case of combining products with the size of larger than 1mm and spiral products (particles smaller than 1mm), concentrate with 18% ash and 48.50% recovery is produced, which is 22.50% of the feed weight. According to these experiments, specific weights of media 1.40, 1.47 and 1.55g/cm3 was considered appropriate for cyclones. The performance of hydro cyclones was investigated by conducting sink and floating experiments. According to the obtained data, in specific weights of media 1.40, 1.47 and 1.55g/cm3, the efficiency of floated materials were 17.75, 33.80 and 50 percent, and the values of sunk materials were above 82.25, 66.20 and 50%. According to the curvatures of the tromp d50, the separation curve in the density of 1.40g/cm3 is 1.00g/cm3 and in the density of 1.47 and 1.55g/cm3, this value is 1.67 and 1.86g/cm3. According to the equalization of the separation density (d50) at a specific weight of 1.40g/cm3, it can be claimed that the function of the machine is suitable for this specific weight. The calculated probability error value for a heavy medium cyclone with a density of 1.40g/cm3 is 0.080 and at the specific weight of 1.47, this error is 0.085. Also, this value is 0.030 for a specific weight of 1.55g/cm3. The value of the imperfection coefficient for the tromp curve of Anjir Tange coal preparation plant at specific weights of 1.40, 1.47 and 1.55g/cm3 are 0.20, 0.12 and 0.03, respectively.

Ashghari M, Noaparast M, Shafaie SZ, Ghassa S, Chehreh Chelgani S (2018) Recovery of coal particles from a tailing dam for environmental protection and economical beneficiations. Int J Coal Sci Technol 5(2):111

BP Statistical Review of World Energy (2017) 66th edition.https://www.bp.com/content/dam/bp/en/corporate/pdf/energy-economics/statistical-review-2017/bp-statistical-review-of-world-energy-2017-full-report.pdf. Accessed June 2017

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Bahrami, A., Ghorbani, Y., Mirmohammadi, M. et al. The beneficiation of tailing of coal preparation plant by heavy-medium cyclone. Int J Coal Sci Technol 5, 374384 (2018). https://doi.org/10.1007/s40789-018-0221-6

ore beneficiation - an overview | sciencedirect topics

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 [51]. 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 [51].

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 [1420].

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 [17]. Microbially induced iron ore formation has been confirmed at Gunma iron ore mine, Japan [21].

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 [19]. 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 [2224].

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) [25].

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 [26].

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 [15]. 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.

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