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By N. Syna

The selection and preparation of activated carbon suitable for specific application can often involve exhaustive adsorbent preparation and testing. This work examined an emerging technique based on modelling the correlation of observed adsorption capacity to the carbon characteristics as a means of decoupling the roles of carbon textural and surface chemical properties. The insights to these specific roles are then used in tailor-making adsorbents and in establishing the optimal carbon properties for specific application. In this study, a series of activated carbons prepared from bagasse by physical and chemical techniques and commercially available carbons were used in developing the models. These carbons were tested for the adsorption of thiourea-gold (I) chloride complexes. Thiourea is an important alternative gold lixiviant with the potential to address current ecological and safety concerns in the extraction of gold. A four-component model, which correlated the adsorption gold capacity to carbon textural and surface chemical properties, was proposed. The model fit was assessed using multi-linear regression and a partial F-test. This was followed by goodness of fit test achieved through r2, adjusted?r2 and mean square error (MSE) values. The results suggest the adsorption of the gold-thiourea complex is strongly influenced by the internal surface area and pH of the carbon. Tailor-made activated carbon from bagasse showed adsorption gold capacities of up to 198 mgAu/g adsorbent, demonstrating the potential of bagasse as a precursor for gold adsorbents and of this empirical modelling approach in developing adsorbents for metal recovery.

Jan 1, 2014

By G. B. Abaka-Wood

"The versatility of froth flotation has made it vital in the beneficiation of rare earth elements (REE) minerals from either high or low grade ores of complex mineralogy. There has been a significant increase in the tonnage of rich iron oxide tailings obtained from extraction of primary commodities such as copper and gold in Australia, which have been identified to have very low grade rare earth oxides (REO) (= 1%). There is a vast knowledge gap in the upgrade of REO from such tailings. The aim of this research is to investigate the feasibility of the use of fatty acids for the upgrading of REO from selected iron-oxide rich tailings. Two forms of fatty acid collectors (oleic acid and sodium oleate) were employed in this investigation. Bench scale flotation tests were carried out using a Denver D-12 cell.The effects of pulp pH, fatty acid dosage, particle size distribution (-150 +75 µm, -75 +38 µm and -38 µm) and conventional depressants (sodium silicate and starch) dosage on flotation recovery of REO were investigated. A comparison of the flotation results indicated that sodium oleate was the more efficient fatty acid for REO flotation at all the pulp pH investigated. The flotation performance is demonstrated to be particle size-dependent. The results on the effect of depressants dosage indicated that both sodium silicate and starch were unselective in reducing the recovery of hematite (Fe2O3) and quartz (SiO2) with corresponding decrease in REO recovery. Generally, Fe2O3 and SiO2 formed substantial contents of the flotation concentrates obtained, both in the absence and presence of depressants, which indicates liberation is a major challenge in achieving selective REO upgrade and recovery.The flotation tests carried out on the iron-oxide rich tailings suggest the possibility of REO upgrade using fatty acids, although particle size distribution and minerals liberation are key limiting factors in achieving selective REO upgrade and recovery."

Jan 1, 2018

By L. X. Zeng

The low-grade nickel resource is very abundant in the western China. To make the best of the low grade nickel ore, we studied the process mineralogy and beneficiation process of nickel ore in the Yangliuping of Sichuan province. The grade of nickel is 0.45% in the nickel ore and the nickel exists in the sulfide including pyrrhotite, nickel pyrite, chalcopyrite primarily. The nickel distributes in pentlandite and magnetite over 90% and the copper does in the chalcopyrite over 95%. The carri-er minerals of useful elements tend to concentrate in space for concentration. As is shown in grain-size analysis of three major minerals, there are some more fine-grained grains with the percent of from 10% to 15% (<40 µm) and from 3.5% to 5.5% (<20 µm). So there will be some smaller size disseminated sulfide minerals difficulty to liberate in the process of concentration. The liberation degree of sulfide is not high and there are much associativity in the sulfides. Therefore, we should reclaim the sulfide aggregation dominating as pentlandite when concentrating. In addition, the sulphide minerals is so brittle that we should take care of preventing from crashing when grinding. The gangue mineral is mostly metamorphic mineral including serpentine, chlorite and amphibole which is easy to be argillization and difficult to concentrate.

Jan 1, 2014

By Fangming Liu

The key problems of current flowsheets and equipments are analyzed. A new steel slag&apos;s crushing flowsheet whose key equipments are the improved inertia cone crusher and inertia vibrating jaw crusher is proposed. An advanced two stage open-circuit crushing method is adopted in the flowsheet, with 90% of particle size crushing under 6mm. Using inertia vibrating technology and selective crushing principle the crushers can realize steel slag separating fully into steel and slag and with flexible transmission mechanism the crusher can be protected when iron lump is passing. The flowsheets can enhance the recovery of metal greatly, and expand the application range of tail slag and added value.

Sep 1, 2012

By S. Banisi, E. Arghavani, Gh. Parsapour, S. Mousavi

Maximization of water recovery in thickeners is an essential step in the mineral processing industries. The Gol-E-Gohar iorn ore processing plant uses a center pier thickener with a diameter of 38 m and depth of 4 m. The feed rate is 50 t/h solids with a concentration of 5% (w/w), and it has been designed to provide an underflow containing 50% solids. The performance of the thickener was not as expected judged by the overflow stream containing 0.6% solids and water loss of 52 m3/h in the underflow. A criterion called the index of flocculation incorporating the perimeter-based fractal dimension of flocs, floc size, and settling velocities was proposed and used to determine the optimum flocculant dosage which was found to be 20 g/t. The fractal dimension of flocs in a pulp containing 5% solids was found to be between 1.16 (no flocculant) and 1.56 (40 g/t flocculant) which indicated highly branched and loosely bound structures for the flocs as flocculant dosage increased. At these conditions, the size of the flocs which was recorded by a digital microscope increased from 93 µm to 403 µm. A new feedwell with a special design with the aim of preventing flocs breakage and maximizing energy dissipation of pulp was constructed and installed. These modifications led to an increase in the thickener drivehead torque from 5% to 18% of the rated torque, indicating a higher bed depth. Finally, installation of a PID controller reduced the drivehead torque relative oscillation from 52.0% to 12.7%. These changes increased the solids concentration of the underflow from 49.0% to 56.9%, decreased the overflow solids concentration from 0.6 % to values smaller than 0.01% and resulted in a reduction of 27% in water loss in the thickener underflow.

Jan 1, 2014

By A. Vilinska

Microorganisms have a tremendous influence on their environment through the transfer of energy, charge, and materials across a complex biotic mineral-solution interface. Recent developments in biotechnology have not only aided hydrometallurgical leaching operations but also shown great promise in mineral beneficiation processes. The adhesion of bacteria on minerals alters the surface properties relevant to flotation and flocculation of minerals. The biomodification of mineral surfaces occurs through the attachment of microbial cells, oxidation reactions and adsorption or chemical reaction with the metabolite products. Several types of heterotrophic and chemolithotrophic bacteria have been successfully applied in flotation and flocculation processes for the last two decades. Al-though the potential of microorganisms in minerals beneficiation has been realised by several re-searchers from their laboratory investigations, the studies were mostly confined to pure mineral systems and there is hardly any sincere effort to apply the methodologies on ores. This paper presents a brief summary of the literature in bioflotation and bioflocculation, and attempts to outline new dimensions of research for a practicable application of this technology in mineral industry.

Jan 1, 2014

By Abhilash

Different methods of utilizing refractory bauxite and disposing red mud are practiced throughout the world, but none of them are known to be environmentally innocuous due to the complexity and /or high cost, and none has been found to be feasible on an industrial scale. Under these conditions, the use of bioleaching process seems promising. The present study emphasizes on the isolation of native extremophiles from the source Indian bauxite and red mud, with their detailed cellular and physio-chemical, and biochemical characterization. These organisms were tested for their ability to thrive in physically or geochemically extreme conditions. The gram positive capsule rich mesophiles and thermophiles were tested for removal of gangue minerals from the bauxite and red mud samples. Keywords: refractory bauxite, red mud, extremophiles, bio-beneficiation, gangue

Sep 1, 2012

By Guanghua Ai, Xiong Huang, Huashan Yan, Ting Li, Tingsheng Qiu

"Cyanide tailings of gold and silver concentrates contain considerable quantities of copper-lead-zinc sulfide minerals that can be recovered. However, the strong inhibition effect of cyanide often makes it difficult to recover these sulfide minerals effectively. In this research, a sample of cyanide tailings was investigated based on the principles of process mineralogy; activating flotation tests were carried out for the target minerals in the tailings, and the activation mechanism of the activator and its influence on the target minerals were investigated by Fourier transform infrared spectroscopy (FTIR). Mixed flotation of copper and zinc was carried out using QJ-01, a combined agent containing sulfite, as the activator of copper and zinc minerals, and ammonium dibutyl dithiophosphate (ADD) and butyl xanthate (BX) as the combined collector. Copper concentrate was obtained from the mixed concentrate by using a combined inhibitor of sodium sulfide and zinc sulfate to inhibit the zinc mineral. Zinc concentrate was extracted from the copper tailings by using copper sulfate as the activator and BX as the collector. The flotation test yielded copper concentrate with a grade of 22.56% and recovery of 76.96%, and zinc concentrate with a grade of 42.56% and recovery of 82.29%, which shows that comprehensive recovery of the sulfide minerals – copper and zinc –from the cyanide tailings was realized. The FTIR analysis showed that CN- was chemisorbed on the surface of chalcopyrite and sphalerite following cyanide treatment, while the combined activator QJ-01 containing sulfite reduced CN- into SCN- and weakened the complexing ability of CN- with metal ions on the mineral surface, thus achieving a good activation effect on chalcopyrite and sphalerite. The results of this study can provide practical guidance in increasing the resource utilization ratio of cyanide tailings in gold mines, and thus contribute to alleviating environmental problems caused by stockpiling cyanide tailings. INTRODUCTION Cyanidation, the most widely used technology for extraction of gold, has several advantages such as high recovery, process maturity, low cost, etc. According to available data, the annual discharge of cyanide tailings from China's gold mines exceeds 20 million tons (Li et al., 2011). Lower grades of exploitable gold ore entail increased discharge of cyanide tailings. Huge quantities of cyanide tailings are regarded as waste and stored, resulting in significant wastage of land resources. Moreover, residual beneficiation reagents, cyanide ions, and heavy metal ions in cyanide tailings cause severe pollution of water and land (Laitos et al., 2013; Donato et al., 2007; Mudder and Botz, 2004). In addition, cyanide tailings often contain valuable elements such as gold, silver, copper, lead, zinc, sulfur, and iron, which, if not recycled, would result in considerable wastage of resources. Hence, it is imperative to study the reduction and safety of cyanide tailings, and the mineral resources present in them."

Jan 1, 2018

By V. Panayotov, M. Panayotova

"The combined use of semiconductor properties and specific flotation characteristics of minerals under different conditions with external influences ensures a possibility for process control and management. This work presents the relations between the volumetric and surface characteristics of minerals and the minerals' flotation ability (flotability), as well as the possibility for the flotability purposeful change. Results from proprietary laboratory and industrial research are presented showing how controlled impacts on minerals and flotation pulp improve flotation technology. Such an approach reveals prospects for the creation of new technologies for the minerals' beneficiation.INTRODUCTIONThe decrease of the useful components content in the ores, the increasingly complex nature of the raw materials, the increasing energy consumption per the unit of production, and the need to solve the problems related to the environment pollution require solutions different than the existing classical ones. One of the ways to find such solutions is the detailed consideration of the fundamental properties of minerals and, in particular, of minerals having semiconductor properties. The studies of Plaksin et al. (1968), Chanturia and Shafeev (1977), Chanturia and Vigdergauz (2008), Carta et al. (1973), Hoberg and Shneider (1975), Rao et al. (1992) have given an idea of the energy state of the minerals, their flotation ability, and the ways in which this ability can be changed in one or the other direction. The main line in these works is the study and use of the relationship between bulk and flotation properties of minerals. To improve the efficiency of the process, it is also necessary to consider the relationship between the surface properties of the minerals, especially minerals-semiconductors, and their flotation ability.THEORETICAL BACKGROUND IN BRIEFA quantitative estimation of energy changes in a solid phase in the process of flotation may be made by taking in account the changes in the Fermi level. Its position in the forbidden band is an indicator about the direction and the intensity of electron exchange between solid and liquid phases. The Fermi level energy EF enables the estimation of flotability, intensity of needed external impact before flotation, as well as efficiency of the process going on. Quantitative estimation of these processes can be made by means of the flotability coefficient Kf."

Jan 1, 2018

By X. Q. Chen

According to the different characters of the middle-low grade bauxite, based on the normal flotation & reverse flotation technology, the author innovates the new technology which is named bi-flotation, it integrates the advantages of normal flotation & reverse flotation, while avoids their disadvantages. Take Henan middle-low grade bauxite as research object, according to the pilot experiment of bi-flotation technology, the concentrate A/S is 9.37 and the recovery of alumina is 80.18% by flotation separate the raw ore which A/S is only 4.19.

Jan 1, 2014

By M. Schneider, J. Regler, Th. Neesse, AKW A. + V GmbH & Co., J. Dueck, F. Donhauser

"In practice the advantages of high-quality hydrocyclone separation are often reduced due to varying feed suspension properties, solids concentrations and particle size distributions. Therefore, a new control system for a battery of hydrocyclones with a nominal diameter of 150 mm was developed for bentonite slurry regeneration associated with tunnel excavation using bentonite slurry as a transport aid and lubricant.As can be seen from Fig. 1, the hydrocyclone battery has been modified for regulation purpose. The battery was manufactured with an overflow collector as a closed pressure chamber (1) with a discharge pipe (2) where the throttling valve (3) was installed.With increased stepwise throttling of the overflow, the volume split is changed with the effect that the solids discharge in the underflow is increased. To stabilize the total throughput, the feed pump speed is simultaneously increased so that the pressure drop ?p across the hydrocyclones (9) remains approximately constant. However, this causes the increasing pressure inside the hydrocyclones, which results in a further intensification of the underflow discharge. After the detection of the break through of the air core (transition state) by the capacitive sensor (4), the throttle valve is shortly opened, and a new regulation interval can start again. The control concept is focused on maintaining the optimum operating state, characterized by the underflow discharge shape at the transition state between rope and umbrella discharge."

Jan 1, 2003

By M. Prasad

Growing concern over increased levels of atmospheric carbon dioxide has prompted new interests in development of materials and techniques for its sequestration. Various research and developmental work on different aspects of carbon capture technology are being extensively carried out worldwide. The main objective of the present work is to synthesize a HAS material having high capacity and robust ability for recycling to capture greenhouse gases with special reference to carbon dioxide (CO2) from the sources from where it is released to the atmosphere. Existing CO2 capture techniques involves the use of solid materials that lack sufficient stability for repeated use or liquid adsorbents that are expensive and require significant amounts of energy. Keywords: greenhouse gases, carbon capture, solid adsorbent, HAS material

Sep 1, 2012

By I. Nishkov, I. Grigorova, N. Valkanov, M. Ranchev

The processing of sulphide ores with variable and complex mineral composition and physical properties, such as those processed by two-stage selective flotation scheme in “Erma reka” concentrator, Minstroy Holding JSC, requires excellent selectivity in order to achieve acceptable concentrate grades. The lead-zinc ores from the hydrothermal lead-zinc deposits mainly contain galena (PbS), sphalerite (ZnS), pyrite (FeS) and chalcopyrite (CuFeS2), as well as non-metal minerals such as quartz, carbonates and clinopyroxenes skarns. One of the main impurities present in sphalerite is iron, which is known to be detrimental to the rate of sphalerite flotation and its recovery. The results from the conducted laboratory and industrial tests, presented in the previous study, showed that it is possible to depress the iron rich sphalerite by adding MINFIT® (modified sulfur-oxy depressant) at the pH of approximately 9.5 in rougher lead flotation circuit, leading to reduction of zinc sulphate consumption and complete elimination of cyanides from the flotation process. Furthermore, the consumption of copper sulphate, which reactivates the surface of the zinc minerals, was significantly reduced. Consequently, the optimisation of the reagent regime in the Erma reka concentrator, led to notably improved qualitative (grade, recovery) properties of the final lead and zinc concentrates. Moreover, when comparing the reagents consumption for 2014 and 2016 – when the processing plant have been applying the new optimized reagents regime, comprises the use of MINFIT as the primary depressant, the following results have been achieved: ZnSO4 decreased by 30%; CuSO4 consumption decreased four times and full rejection of cyanides from the process. Finally, this paper provides a state-of-the-art review of the obtained results during the period of application of the new flotation reagents regime in the Erma reka concentrator, Minstroy Holding JSC.

Jan 1, 2018

By F. Karakas

Organo-bentonite production enjoys important applications including solvent based paints and, more importantly, the production of polymer/bentonite nanocomposites. Quarternary ammonium salts in this regard are still considered as the most versatile reagents in the process of hydrophobization. In this study, a purified form of Resadiye region bentonites, which is one of the most significant sodium bentonite deposits in the world, was used. The raw Na-Bentonite was typically characterized by chemical analysis, XRD and DTA analysis and more importantly for its cation exchange capacity (CEC). Other technological properties such as swelling index, pH, apparent viscosity, water absorption, oil absorption were also conducted on the raw bentonite. The mineralogical analysis of the raw bentonite reveals that it contains about 80 % montmorillonite together with other associated gangue minerals including feldspar, quartz, calcite, dolomite, coloured impurities and other clay minerals. The raw bentonite was subjected to two stage processing involving a series of hydrocylones. Different apex and vortex diameters and different pressures were employed in order to produce a bentonite concentrate with 95 meq/100g CEC from a CEC of 71 meq/100 g. This high quality concentrate was used in the production of organo-bentontonite. The modification was performed with two different quaternary amines, i.e. Trimethyl Phenyl Ammonium Chloride (TPAC) and Hexadecyl Trimethyl Ammonium Bromide (HDTMA-Br). In the modification procedure, three parameters, i.e., adsorption density, zeta potential, swelling index and apparent viscosity were studied simultaneous-ly from the same suspension to identify both the mechanism of the process and also the degree of hydrophobicity. Adsorption measurements were made as a function of conditioning period, pH, and reagent concentration. Simultaneous examination of the adsorption density, zeta potential and apparent viscosity enabled us to pinpoint the optimum region of hydrophobicity which was subsequently tested by settling and critical coagulation concentration in both water as polar and toluene as nonpolar solvents. The results are analyzed in the light of experimental data.

Jan 1, 2014

By Y. S. Song

Flotation separation of galena, sphalerite with pyrrhotite in ethanoic acid + sodium acetate sys-tem was studied in this paper. The flotation tests show that galena and sphalerite can float but pyr-rhotite can hardly float in the pH range of 3.6 to 5.6 in ethanoic acid + sodium acetate system. The flotation tests also show that galena can be separated efficiently from pyrrhotite and sphalerite can be separated on the whole from pyrrhotite, but the separation efficiency of the former is much better than the latter. The flotation results have been investigated by ultraviolet spectrum and XPS analysis, and explained by theory of hard and soft acid and base (HSAB), hydrogen bond and galvanic coupling.

Jan 1, 2014

By A. S. Chekmarev, T. Z. Lygina, K. G. Egorova, A. V. Skvorcov

"We have conducted analytical and technological evaluation of sepiolite containing clay. The possible areas of application of the sepiolite have been investigated and complex methods of enrichment of natural sepiolite have been identified. It was determined that for preserving the structure of minerals after processing the most effective method of the natural agglomerates disintegration was the soft abrasion of the clay fraction up to 0,5 mm. Disintegration of sepiolite clay along with using high energy-stressed effects on the matrix can deteriorate the rheological properties of clay suspensions and reduce the yield of drilling mud and sorption properties. To improve the quality of clay powders we used combined gravity-modifying method of wet enrichment. After the wet enrichment the yield of drilling mud increased up to 12.7 m3/t, with the addition of MgO up to 20,3 m3/t. It was noted that drilling muds contenting more than 50% of sepiolite are stable in mineralized (salt) waters. Based on the studied activated sepiolite rocks we obtained the effective heat-insulating materials with relatively low thermal conductivity – 0,165 W/m·K, average strength – 7,29 MPa and water absorption-49,0%.INTRODUCTION The modern development of the Russian economy requires the implementation of scientific and technical tasks. The solutions of it involves a radical reduction in energy, heat losses and material consumption of products, rational and efficient using of all types of resources, as well as the using of new types of mineral raw materials and materials based on it. An example of a new type of mineral raw materials for Russia is sepiolite containing rocks, due to unconventional conditions for their soils accumulation in the climate of the Far North. Sepiolite is a unique type of nonmetallic mineral. It is formed in soils, marine and saline basins, occurs in carbonate and carbonate-clay rocks in the form of lenses and lens – shaped layers, rarely nodules, loose powdery masses, shell-like concretions. Sepiolite may have a soft porous macroscopic appearance or less often the structure of the fibrous mass. Color of sepiolite is from white to cream with gray, green, pink and even crimson shade depending on the degree of pollution. Sepiolite can be in two forms - a-sepiolite (parasepiolite), which occurs in the form of large packets of crystalline fibers and ß-sepiolite, which occurs in the form of amorphous aggregates or small flat rounded particles. The sepiolite fibers have a length of from 0.2 to 2 Å, width from 100 to 300 Å, the thickness from 50 to 100 Å (Geological dictionary, 1973)."

Jan 1, 2018

By Q. Cui, Z. G. Song, S. S. Lin, S. Q. Li, S. S. Lu, G. B. Zheng, A. J. Ren

"Mine tailings is one of the most important bulk industrial solid wastes, but its rate of comprehensive utilization is relatively low. Efficient separation, recovery and utilization of the valuable components is one focus of the comprehensive utilization of tailings. Beneficiation recovery of the valuable minerals is the most direct comprehensive utilization method for tailings. There are generally different kinds of nonmetallic minerals contained in the nonferrous metal mine tailings, which are secondary mineral resources waiting for further developing and recovery. Comprehensive utilization test studies on fluorite in tungsten beneficiation tailings and feldspar in molybdenum beneficiation tailings have been carried out by author and good test results are achieved. Some of the technologies developed in the test study have been applied in industrial productions, which have been working well. The economic, social and environmental benefits are remarkable. Our test studies and some production practices will be summarized and current situation and existing problems of comprehensive utilization for nonferrous metal mine tailings will also be discussed. Assumption and prospect for the future study on comprehensive utilization of nonferrous metal mine tailings will be brought at last.INTRODUCTION Mine tailings is one of the most important bulk industrial solid wastes, but its rate of comprehensive utilization is relatively low. Efficient separation, recovery and utilization of the valuable components is one focus of the comprehensive utilization of tailings. Beneficiation recovery of the valuable minerals is the most direct comprehensive utilization method for tailings. There are generally different kinds of nonmetallic minerals contained in the nonferrous metal mine tailings, which are secondary mineral resources waiting for further developing and recovery. Comprehensive utilization of nonmetallic minerals of nonferrous metal mine tailings not only can improve the value of the ore but also reduce the stock of tailings, being the key to reduce emissions at source for exploitation of nonferrous mineral resources (Cai, Yang, 2000)."

Jan 1, 2018

In many base metal sulphide concentrators reagents such as collector and cyanide are often added to the grinding mill as well as to the flotation circuit. Whilst good reasons can be cited for splitting the reagent addition in this way, the benefits of such are rarely quantified and the complex reagent-mineral-media interactions occurring during milling are often poorly understood in terms of pulp chemistry. A new laboratory batch grinding mill designed by Magotteaux allows the user to measure, monitor, and control the pulp chemical conditions during grinding when testing different ores and media. Some of these parameters include pulp pH, pulp Eh, temperature, gaseous atmosphere, and dissolved oxygen concentration. In a recent development, the mill has been coupled with a simple on-line reagent monitoring system, designed by CSIRO, which allows the levels of species such as xanthate and cyanide in the grinding pulp to also be measured continuously during milling using a robust UV detection system. In this way the uptake of collector during grinding and the rate and ex-tent of cyanide interaction with the minerals and media can be determined as a function of grinding time. A series of grinding tests using an Australian nickel sulphide ore was conducted with the coupled system in which the cyanide dose, xanthate dose, and media type were systematically varied. The xanthate and cyanide levels were monitored as a function of grinding time and the data collected are discussed in terms of the pulp chemistry of the system and implications for plant reagent dosing strategies.

Jan 1, 2014

By V. Sheikhzadeh, M. Saghaeian, R. Hejazi, A. Abazarpoor

"The morphology of pellet feed is known to influence several properties of iron ore pellets, including drop number, compression strength and reduction properties. The effect of grinding method on the particle size, specific surface area and particle shape of an iron ore concentrate has been studied. Grinding methods considered were ball mill and high pressure grinding rolls (HPGR). 5 different samples (Blaine= 1800, 1900, 2000, 2100 and 2200 cm2g-1) were used to compare the size, shape and specific surface of particles for each grinding methods. Particle size was meticulously examined by sieve analysis, laser sizing and image analysis. In samples ground by ball mill, it has been observed that the fraction of particles <10µm increases from 39% to 46% as the Blaine number increases from 1800 to 2200 cm2g-1. For HPGR samples, corresponding figures are 41% and 49% respectively. It is evident that for samples ground by HPGR, the fraction of fine particles is higher than that of those ground in the ball mill. To measure the specific surface area of particles, Blaine and BET were used. A higher real surface area was observed from HPGR treatment in comparison to ball mill grinding, provided by a higher porosity, cracks, roughness and new surfaces. Shape factor of particles was determined using three descriptors: circularity, roughness, and aspect ratio. It was also observed that particles produced by HPGR were more elongated, less circular, and rougher than those processed by the ball mill. 1. INTRODUCTION Particle size and shape are important parameters that can significantly affect mineral processing plants and pelletizing plant performances (Brozek and Surowiak, 2007). It has also been proposed that green pellet quality is directly related to the amount of fine particles in a pelletizing plant (Dwarapudi et al., 2008; Umadevi et al., 2008; Gul et al, 2014; Van der Meer, 2015). Particle size distribution and specific surface area (SSA) are also key factors that can control the quality of green and fired pellets. Processing circuits generally reduce the fines fraction to lower than the required specific surface area (SSA). It is therefore necessary to regrind concentrates to produce suitable pellet feed for further treatment in the balling and firing steps [1, 2]. Two main methods are used for re-grinding of concentrate; high pressure grinding rolls (HPGR) and ball mill. Given the different forces used to reduce size in these methods, it is expected the shape of particles will be different (Pourghahramani and Forssberg, 2005)."

Jan 1, 2018

By W. M. Zeng

A mixed culture of moderately thermophilic microorganisms was enriched from Acid Mine Drainage (AMD) samples collected from several chalcopyrite mines in China,which can leach copper from chalcopyrite effectively. Its tolerance to chalcopyrite was brought up to 80 g/L after being adapted to gradually increased concentrations of chalcopyrite. The effects of several leaching variables on copper recovery in Stirred Tank Reactor had been investigated. The ore contained chalcopyrite (62.2%) and galena (25.6%) as the main sulfide minerals. The results of the tests show that it is possible, operating at 8% of pulp density to attain copper extraction of 75% in 44 days. The leaching rate of chalcopyrite tends to increase with the dissolution of total iron. Microscopic counts of microorganisms in the solution tend to be higher at low pH range. Furthermore, the analyses of leached residues indicate that the passivation of this chalcopyrite is mainly due to the formation of a mass of jarosite and anglesite (about 48.3% and 21.7% in residue respectively), other than elemental sulphur layer. The bacterial community composition was analyzed by using amplified ribosomal DNA restriction analysis (ARDRA). Two moderately thermophilic bacteria species were identified as Leptospi-rillum ferriphilum and Acidithiobacillus caldus, with different proportion in the bio-pulp, 67% and 33%, respectively.

Jan 1, 2014