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By L. E. Veki, S. M. Luukkanen, J. P. Karvonen, J. O. Leppinen

Today there is a consensus that xanthate adsorption on sulfide minerals is primarily controlled by redox reactions occurring at specific potentials on these semi-conductive minerals. Consequently, it is possible to control xanthate adsorption by controlling electrochemical conditions in the system by using oxidizing and reducing agents. The scope of this study was to investigate the possibilities to increase the selectivity of Cu-Fe-Zn ore flotation by applying electrochemical control in the conditioning of the flotation feed. In this work, mild steel grinding in a nitrogen atmosphere was used as the basis to provide a negative starting potential and minimize the amount of oxidation products on sulfide mineral surfaces. To study how different potential levels affect flotation results, a controlled conditioning procedure was utilized maintaining potential at a desired level by titrating the pulp with air. Xanthate adsorption kinetics during conditioning was examined by taking pulp samples for spectrophotometric analysis and laboratory flotation tests were conducted for samples that underwent the controlled conditioning procedure in the potential range of -200mV to +200mV vs. SHE. A clear correlation was detected between chalcopyrite recovery and the potential during controlled conditioning indicating that there was a constant increase in chalcopyrite recovery when the potential was shifted to more anodic values. It is possible that utilizing potential control in the conditioning stage, a smelter grade copper concentrate can be achieved directly in rougher flotation without cleaning stages. Conditioning in favorable conditions had significant positive effects on flotation selectivity of chalcopyrite. The improvement in copper concentrate grade being predominantly caused by the depression of pyrite. By applying the controlled conditioning procedure pyrite recovery in rougher flotation was reduced even low as under 1%, while in the tests without controlled conditioning, pyrite recovery varied between 7.5 – 65.7%. The result of this work indicate that affecting collector adsorption by electrochemical control in the conditioning stage can provide significant improvement in sulfide mineral flotation and industrial applications could lead to decreased chemical consumption, reduced equipment and maintenance costs.

Jan 1, 2018

By E. V. Koporulina, I. Zh. Bunin, M. V. Ryazantseva

"We studied the mechanism of structural and chemical transformations of columbite, tantalite, zircon and feldspar surface during the treatment by high – power electromagnetic pulses (HPEMP) using the methods of X - ray photoelectron spectroscopy (XPS), analytical electron microscopy (SEM - EDX), Kelvin probe force microscopy and flotation experiments. According to XPS and SEM - EDX data, major changes in the atoms chemical state of investigated minerals surface are related with formation and modification of functional cover and changing in concentration (% at.) of hydroxyl groups on the mineral surface, leading to increase in the contrast of technological properties of the rare metals minerals. Research has identified the optimal parameters of HPEMP - treatment of rare - earth minerals Npuls ? 104, Ttreatment ? 100 sec. improving the selectivity of the flotation separation of columbite and zircon. The difference in mineral recovery into the froth (? e) before and after HPEMP - treatment was about 11 % and 24.5 %, respectively. No significant increase was observed in the flotation activity of feldspar. This study's findings demonstrate the effectiveness of HPEMP - treatment in inducing a controlled change in the structural and chemical properties of rare - earth minerals and improving the process efficiency for the processing of rougher tantalum - niobium gravity concentrates.INTRODUCTIONThe importance of improving the processing methods of tantalum-niobium ores and concentrates is explained by the mineralogical properties of rare - earth ores. These are properties such as the variable mineral, chemical, and grain size composition, complex morphometric properties, and the dissemination of ore mineral grains of micro - and nanometric size. Iron oxide and hydroxide films on the mineral surfaces neutralize the surface physicochemical and absorption properties of the minerals. Both in Russia and globally, nonconventional (non - mechanical) methods are being developed based on physicochemical, electrochemical, and pulsed energy impacts to improve the efficiency of disintegration and liberation processes of disseminated mineral complexes and to enhance the contrast of the structural, chemical, and technological (floatability) properties of refractory ores. This study is devoted to the investigation of the applicability of high – power electromagnetic pulses (HPEMP – treatment) for the change in the structural and chemical properties of rare - earth minerals and improving of the flotation properties contrast."

Jan 1, 2018

The multiphase reactive flow in process equipments, e.g., fluidized beds, involves complex coupling among flow, heat/mass transfer and reaction kinetics over scales ranging from molecules, sub-particle eddies up to equipments. Conventional two-fluid model (TFM) ignores the effects of meso-scale structures, and hence is not suitable for describing the intrinsically multi-scale heterogeneity within multiphase systems. To be consistent with the meso-scale structures, we proposed a structure-dependent multi-fluid model (SFM), and closed its drag force by invoking the stability condition defined in the energy-minimization multi-scale (EMMS) model. The SFM reduces to the conventional TFM if homogeneous distribution is assumed within each grid, and reverts to the original EMMS model if it is used to describe steady state, global behavior of a fluidized bed. The multi-scale computational fluid dynamics (CFD), which is characterized by coupling of TFM and EMMS drag coefficient, can then be viewed as a simplified solution of the SFM. We demonstrate that the SFM significantly improves the accuracy and at the same time enables higher efficiency by allowing for much coarser grid used than in TFM. Recent application of it in 3D, full-loop, transient simulation of industrial processes, e.g., fluid catalytic cracking, coal combustion, gasification, kaolinite clay calcinations, shows its advantages in helping design and troubleshoot multiphase process equipments. Keywords: meso-scale, SFM, multiscale, CFD, simulation, structure, EMMS, multiphase

Sep 1, 2012

By M. F. He

There are three polymorphic modifications in pyrrhotite (monoclinic, hexagonal and orthorhombic), with monoclinic and hexagonal polymorph being more abundant. The floatability of different crystalline structures of pyrrhotite (monoclinic and hexagonal) is studied in this paper. It is shown that the floatability difference of monoclinic and hexagonal is obvious and that the flotation recovery of monoclinic pyrrhotite is greater than that of hexagonal pyrrhotite using different collectors . Using butyl dithiophosphate as collector, the flotation recovery of pyrrhotite is higher than when sodium diethyl dithiocarbamate and sodium butyl xanthate are used as the collectors. Monoclinic and hexagonal pyrrhotites are more easily activated by Cu2+ in acidic conditions than in alkaline conditions, while Cu2+ can not activate hexagonal pyrrhotite when sodium diethyldithiocarbamate was used as the collector. By the measurement of contact angle, it is indicated that monoclinic and hex-agonal pyrrhotite float well and are easily activated by Cu2+when dithiophosphate was used as the collector. Using sodium diethyl dithiocarbamate as a collector, the flotation behavior of pyrrhotite was investigated. The relationship between potential and pH range for pyrrhotite flotation was established. The results show that the flotation of pyrrhotite is dependent on pulp potential at certain pH values.

Jan 1, 2014

By Shuji Owada, Yang Geng, Natsuko Kuroki

Micro-bubble flotation is considered to be an ideal method for the separation of fine or ultra-fine particles, which are difficult to be separated with conventional flotation and other solid separation technologies. Micro-bubble flotation can increase the probability of bubble-particle collision more than conventional milli-bubble flotation. However, there are also some problems. For example, it is known that the rising velocity of micro-bubble is quite low; therefore, the flotation rate reduces. And also, the bubble-particle adhesion probability becomes lower than that of milli-bubble flotation, which is proved in our prior research. In this paper, we applied ultrasonic irradiation to the micro-bubble flotation system in order to solve the above problems and focused on the bubble-bubble and bubble-particle interactions. For clarifying the behavior of bubble-bubble interaction, bubbles behavior was recorded by high-speed camera under irradiation of various ultrasonic frequencies. As a result, in the case of bubble-bubble interaction, it is proved that bubbles are highly coalesced by ultrasonic irradiation especially in the lower frequency and it can enhance more precise separation. In the case of bubble-particle behavior, it is found that the floatability become higher with the ultrasonic irradiation of higher frequency, and it is indicated that ultrasonic irradiation might improve the bubble-particle adhesion probability. Additionally, it is also found that the apparent CMC of the micro-bubble flotation under the ultrasonic field become much lower with higher frequency than with lower frequency, and it is suggested that the dramatic improvement of hydrophobization is achieved.

Jan 1, 2014

By Maurício Torem, Gabriela Huaman, Antonio Merma

The purpose of this review paper is to succinctly present the most significant works related to Mineral Processing and Environmental Bioremediation and developed by the Mineral and Environmental Technology Group (METG) of the Materials Engineering Department of the Pontifical Catholic University of Rio de Janeiro (PUC-Rio). In mineral processing it was emphasized the use of the Rhodococcus opacus bacteria as a bioreagent in the bioflotation of some mineral samples (magnesite, calcite, hematite, quartz and apatite). The adsorption of the bacterial cells on the mineral surface can be due to specific and/or non-specific interactions, which will depend on several factors, as their surface charge and hydrophobic character. The zeta potential evaluation of the mineral particles before and after interaction with the R. opacus cells showed that the biomass modified the zeta potential profiles of the minerals, which confirm the adsorption of bacterial cells on the mineral surface. Moreover, the bacterial cells adsorbed caused a change in the mineral flotability which is related to a change in their hydrophobic character, thus, the mineral bioflotability was found to be dependent on the pH and the bacterial concentration. On the other hand, the environmental bioremetiation assessed the biosorption potential of three metal ions (lead, copper, and cobalt) by four different biomass Streptomyces lunalinharesii, Rhodococcus opacus, Rhodococcus ruber and coconut shell powder. For this purpose, biosorption process was characterized under different operating conditions such as initial pH and biosorbent dosage. The Freundlich and Langmuir isotherm models were applied to the equilibrium data obtained at different concentration.

Jan 1, 2014

By Thi Hien Tran, Ngoc Anh Tran, Thi Thu Hien-Dinh, Duy Anh Dao

"Natural graphite exists mainly in three types of amorphous graphite, flakes graphite and lump graphite. Graphite from Bao Ha mine, Lao Cai province is with 11.8 carbon-graphite %, forms in flakes and dense crystals. The paper presents the comparison among enrichment of Bao Ha’s graphite by two types of froth flotation with 90 g/t kerosene oil as collector, 50 g/t montanol 800 as frother, in natural pH, and at 20 wt.% of solid. The differences among three flow charts indicated that using middling flotation and re-middling flotation for the cleaning tails and the scavenger concentrates, the final concentrate was improved and containing up to 94 carbon-graphite % of flakes graphite, up to 82 carbon-graphite % of fine graphite with 93.48 % total recovery, moreover, carbon-graphite in the final tail is 0.86 % with 6.52 % recovery. However, a refining mill and a classification stage were applied before doing the middling flotation stages.1. INTRODUCTIONGraphite (black lead or plumbago) is used in many industrial applications due to its high electrical and thermal conductivity, lubricity, and chemical inertness. High quality graphite can be used in metallurgy, molding, brake linings, batteries, and fuel cells. Graphite, composed exclusively of the element Carbon, is rather common mineral, but fine crystals are rare. Graphite is soft (hardness: 0.5-1 Mohs scale); has a layered, planar structure; occurs in platy or acicular (occasionally) morphology (Minerals.net; Pierson, 1993).USGS (2017) reported, global consumption of natural graphite continuing increase in the period of 2012-2016. In 2016, China used up 35% while produced 66% of the world’s graphite. Graphite mining are being developed in Madagascar, Mozambique, Namibia and Tanzania, but production reduced in Canada from 2015. Based on the statistic of Statista.com shows from 2011 to 2014 and a forecast to 2020, the global graphite demand is mostly in refractories, batteries, others, lubricant/crucible, foundry and pencil, and that is increase every year.Graphite Vietnam lies on the fault of the Red river from Yen Bai to Lao Cai, the reserves is estimated around 29.3 million ton and mostly in Lao Cai province where has Nam Thi graphite mine and Bao Ha graphite mine (MOIT, 2008). Vietnamese graphite products could reached to ~92% graphite carbon (Cg) (Tran Thi Hien et al., 2008). Studied samples was collected in Bao Ha graphite mine, is located in Lao Cai province. Graphite Bao Ha exists in two types as graphite flakes and amorphous (Hoang Thi Minh Thao et al., 2017)."

Jan 1, 2018

By Q. Huo

The alumina production might not continue when the sulfur content of bauxite was too high. In order to bring down the sulfur content in bauxite, we studied on the bauxite desulfurization by bacteria screened from the acid mine drainage at mines of high sulfur content. The screened bacteria were domesticated by the high sulfur content bauxite. The experiments of bauxite desulfurization were carried out under the conditions of 5% pulp density, temperature of 30?, rotate speed of 120rpm. Bacterial desulfurization for 30 days, the sulfur content of the bauxite was reduced from 5.73% to 1.55% and the desulfurization percent was 72.9%. The recovery percent of alumina was 94.3%. The study showed that it was feasible to bring down the sulfur content of bauxite by bioleaching and this technique might make full use of the low grade bauxite.

Jan 1, 2014

By Z. Cheng, Y. Han

"For non-sulphide minerals such as oxidized minerals, fluoride minerals, and oxysalt minerals, there are generality in the molecular structure of their floating collectors, and similarity in crystal structure of the minerals. In the paper, adsorbing mechanism of these collectors on the surface of these mineral particles in different pH pulp was investigated by means of Pauling's rules & valence bond theory, Valence-shell electron pair repulsion theory (VSEPR) theory, Crystal and ligand field theory, and quantum chemistry simulation by DMol3 and CASTEP modules of Material Studio software. Besides, the role and status of hydrogen bond in the floating adsorption mechanism were studied emphatically, and the confirmation and characterization of hydrogen bond were explored also based on the test results. What is more, the conclusion “the effect of hydrogen bond can not be overlooked in adsorbing mechanism of flotation collectors on the minerals” and a new viewpoint of multi-polarity collaboration and hydrogen bond coupling were summarized eventually based on analysis of the measurements. Finally, a novel collector 2-Amino-3-Methyl Heptyloxy-Propylamine (AMHP) was developed based on the new viewpoint of molecular structure design, and its collecting performance was exhibited.INTRODUCTIONWhen it comes to the recovery of flotation, it is necessary for researchers to investigate the flotation mechanism of collectors. In traditional theory, when collectors were used to collect minerals, the attractions between collectors and minerals were divided into chemical, electrostatic and physical attractions (Wills, B.A., 2006). Especially, because of the reaction between sulphide minerals and sulphydryl collectors is complex and various mechanism has been proposed (Yoon and Basilio, 1993), when collectors were used to collect non-sulfide minerals, it can be classified into oxyhydryl anionic collectors and cationic collectors. In traditional theory, the adsorption of oxyhydryl anionic collectors were due to water-repulsion, and the adsorption of cationic collectors were due to electrostatic attraction between the polar head of the collector and the charged electrical double layer on the mineral surface (Wills, B.A., 2006)."

Jan 1, 2018

By Junwei Han, Wenhua Li, Wenqing Qin, Fen Jiao, Wei Liu, Jiaqi Xu

"A novel technology was developed to study the process of recycling copper from waste printed circuit boards (WPCBs), which are the main source of metal production in the next decades. The chemical compositions of the WPCBs were investigated. The results indicated that the PCB powder was mainly composed of copper (38.5 wt.%), iron, aluminum, and non-metallic materials. Copper is mainly in the form of Cu and is the most valuable metal for the recycle of WPCBs. The concentrated WPCBs powder, obtained by the mechanical process, were pressed as the anode, which was directly electrolyzed to produce copper. The effects of H2SO4 concentration, Cu2+ concentration, current density, pole pitch, and liquid-to-solid ratio on the voltage, current efficiency, and copper extraction were investigated. The results indicated that the optimum conditions were liquid-to-solid ratio of 30 mL/g, current density of 571 A/m2, sulfuric acid concentration of 180 g/L, 50 g/L of copper ion, polar distance of 3 cm. Under the conditions, a desired current efficiency could be achieved. Meanwhile, about 95.62% Cu was recovered from the WPCBs. The experimental studies also revealed that the purity of copper obtained at the highest current efficiency was higher to 99.98%. Produced copper sheet were characterized by X-ray diffraction (XRD). XRD analysis indicated that the copper was the main phase. INTRODUCTION With the rapid development of electronic industry, more and more waste electronic and electrical equipments (WEEE) are generated every year (Fogarasi et al., 2012; Liang et al., 2013). The production of printed circuit boards (PCBs) is the base of electronic industry, because it is the essential part of all electrical and electronic equipments (Schlummer et al., 2007). As a result, a considerable amount of waste PCBs containing plenty of heavy metals have to be treated. In general, PCBs contain about 28% metals that are abundant non-ferrous metals such as Cu, Pb, and Sn. Printed circuit boards can be considered as a secondary resource for recycling rather than wasting. The contents of gold and silver respectively reach 80 g/t and 3300 g/t, which are much higher than that of primary ores. Copper is the main metal of PCB and its content is as high as 26.8% ( Zhang et al., 2009)."

Jan 1, 2018

By I. Ngoma, Marijke Fagan, Susan Harrison, Rebecca Chiume

"Heap bioleaching is an unsaturated hydrometallurgical extraction process which is commonly applied to the recovery of copper from low grade sulfide ores as well as for preparatory treatment of gold ores. The leaching reactions occur in the liquid phase, catalysed by iron and/or sulfur oxidising micro-organisms. Contact of the mineral grains with the leaching solution is consequently essential for metal recovery. Additionally, the liquid is responsible for the transport of the liberated metal out of the heap under gravitation-driven flow. However, the highly inhomogeneous structure of the heaps coupled with low irrigation rates cause the flow to vary between being gravitationally and capillary dominated, resulting in non-uniform wetting of the ore. In this study a 132 kg agglomerated ore ‘slice’ is used to examine the effect of liquid distribution on microbial colonisation and mineral recovery in a long term bioleach (> 500 days) when irrigation from a single drip emitter source is employed. The novel setup enabled sample collection from ports positioned along the length and height of the ore bed, so that 2D maps of the degree of wetting and microbial colonisation could be generated at different times in the leach. Lateral movement of the liquid increased with bed depth; the majority of flow was below the irrigation point while the top corner of the bed that was not irrigated remained the driest region of the heap throughout the experiment duration. The lowest cell numbers were also recorded in the driest regions. Specifically, cell numbers in the top corner of the bed, 400mm from the irrigation point, remained at undetectable levels until the 283rd day measurement, in line with typical heap operation durations. This indicates that slow colonisation of the heap in the regions between irrigation points may be a significant issue in heap optimisation."

Jan 1, 2014

By Silvia França, Hudson Couto

"In this paper, an alternative beneficiation process was developed to recover nickel minerals from low-grade weathered ores. The studied sample, 0.3% Ni grade, is essentially composed of nickel sulfides (pyrrhotite and pentlandite); magnetite and silicates (mostly talc and amphibolites) are the primary gangue minerals. The particle size distribution was controlled using a grinding operation to avoid producing an excess of fine particles by overgrinding. The sample underwent a grinding step for the fine degree of liberation. The slimes (-20 ?m) were removed via two desliming stages in hydrocyclones (diameters of 1.5" and 2"); the ground material, which was classified in a range of (-150+20) ?m, was processed by column flotation in three different stages: rougher flotation for magnesium silicates, rougher flotation for sulfides, and cleaner flotation for sulfides, using pilot flotation columns (2" and 6" in diameter and 20 ft high). The goal of using the preliminary magnesium silicate flotation step was to remove hydrophobic minerals (mostly talc) that would float naturally with the sulfides, which would decrease the Ni grade in the concentrate, as well as to reduce the MgO content because this compound is considered harmful in metallurgical processes when a grade greater than 9% is used. The final concentrate obtained in the cleaner flotation step reached up to 2% Ni and 7.0% MgO. The global and flotation recoveries in the process were approximately 30% and 60%, respectively, due to the losses of Ni during the desliming process. Despite this low global recovery, the adopted beneficiation process can be considered an interesting alternative to produce nickel concentrate from tailings or waste materials."

Jan 1, 2014

By R. Marandi

The effective removal of heavy metals from aqueous wastes is among the most important issues for many industrialized countries, How ever biosorption, i.e. the uptake of heavy metals by non- living biomass, has gained increased credibility during recent years. Biosorption of Cr(VI) from aqueous solution, on pretreated and immobilized Aspergillus niger was investigated in a batch and countinuous reactors. A.niger biomass pretreated by boiling in 0.5 N NaOH solution for 15 min, exhibited higher Cr(VI) removal capacity than autoclaved biomass. The optimum adsorption pH value observed for Cr(VI) ions was 2. The Cr(VI)removal rate increased with a decrease in pH. The influence of contact time, pH, Cr(VI) concentration, biomass concentration and temperature on Cr(VI) removal were also evaluated. Biosorption of Cr(VI) on pretreated biomass followed the Freundlich and Langmuir adsorption models.In this study A.niger biomass was immobilized in Na-alginate matrix. The biomass beads packed in a column were able to remove metal ions.In this study we used two different flow rate in a column, 1.5 mL/min and 3 mL/min.The breakthrough data obtained for Cr(VI) was adequately by the Thomas and Yan models and the adsorption capacity of the biomass was found to less than the adsorption capacity obtaind in the batch study. When the beads containing biomass become saturated with metal ions, the adsorbed metals were eluted using 0.5 N NaOH solution. Therefor nearly 90% of Cr(VI) was desorbed by NaOH solution.

Jan 1, 2014

By S. Serranti

The recycling of end-of-life concrete into new concrete is one of the most interesting options for reducing worldwide natural resources use and emissions associated with the building materials sector. The possibility to realize a larger re-use of silica aggregates from old concrete, strongly contributes to reduce environmental impact (reduced exploitation of natural resources, reduction of CO2 emissions, airborne dust production, etc.).To reach this goal, innovative processing techniques, as well as innovative sensing units and architectures have to be developed. In this perspective an analytical approach, based on hyperspectral sensing techniques, is proposed, discussed and critically evaluated in order to perform an automatic quality control assessment, finalized to maintain a high standard of concrete demolition waste, from the earliest stage of recycling to the further processing stages, according to the detected in-situ demolition waste characteristics. The paper deals with the analysis and the evaluation of the problems related to the integration of this approach with state-of-the-art demolition and building processes and procedures. Keywords: end-of-life concrete, recycling, hyperspectral imaging, NIR spectroscopy, quality control

Sep 1, 2012

By Å Sandström

Loussavaara-KiirunavaaraAB?s (LKAB) iron ore mine, Kiirunavaara, is of magnetite type and associated with apatite, a calcium phosphate mineral. Rare earth elements (REE) have been found in connection with the apatite but also in other minerals. An apatite concentrate was produced by flotation, in order to investigate the possibilities to extract REE from the apatite by hydrometallurgical means. The content of rare earth elements calculated as oxides (REO) was 0.44% in the concentrate. Initially, leaching was done with large excess of sulfuric acid, hydrochloric acid, and nitric acid to study the REE solubility with different acids. In sulfuric acid, the leaching recoveries of the different REE varied between 35% and 69%. The reasons for the relative low recoveries, were that the rare earth elements precipitated together with huge amounts of gypsum, that was formed during leaching. However, both hydrochloric- and nitric acid gave almost complete extraction of the REE into solution. Analysis of the small leaching residue obtained, revealed, that mainly the light REE remained in the residue indicating that a small part of the light REE were present in the concentrate, in some acid, insoluble mineral other than apatite. With the aim to separate the REE from the phosphoric acid, the solutions from hydrochloric- and nitric acid leaching were neutralized to a pH of approximately 2 with ammonia. During neutralization, REE were precipitated as phosphates with good recoveries and a concentrate of 10.5% REO suitable for further upgrading was obtained, while the remaining solution can be used for fertilizer production. In further solvent extraction studies, it was shown, that after re-dissolution the REE could be effectively extracted by Cyanex 923, thus allowing for purification from calcium and phosphate ions. The REE were finally stripped from the organic phase and a REE nitrate solution was produced. Keywords: apatite, rare earth elements, REE, leaching, solvent extraction, cyanex 923

Sep 1, 2012

By F. J. Sotiuo

Variability of the quality of phosphate ore feed to the flotation plant has been of great concern for the industry. This variability sometimes resulted in 10% to 50% decrease of P2O5 recovery, a reduction of P2O5 concentrate grade and/or both due to depression of the system. For this investigation, samples of refractory ore and easy-to-float ore were obtained from the same mining area in Central Florida; and then submitted to bench flotation tests using fatty acids (FA). To understand the cause of difference in flotation behavior of these apparently similar ores (grade, mineralogy, and physical appearance), bulk and surface characterization studies were conducted. Based on the results of characterization studies and bench flotation tests on both refractory and easy-to-float samples, it was possible to determine FA surface coverage. It was found that the surface coverage for the refractory ore was between 6.9% and 9.8%, corresponding to 0% and 80% recovery, respectively; whereas the easy-to-float ore showed surface coverage of 17.2% (89% recovery) to 24.6% (98% recovery). Since size analysis, surface area and pore size measurements showed small differences, it was thought that the surface coverage differences could be caused by the ad-sorption of natural compounds onto the phosphate ore surfaces, depressing the system. SEM, EDS, and Leaching and Solvent Extraction (LSX) studies were performed on the phosphate ores to demonstrate the proposed mechanism. This paper summarized our characterization studies, flotation results, and findings. The study showed that the new identified compounds were responsible for the flotation behaviors of the Florida refractory phosphate ores.

Jan 1, 2014

By W. S. Eu

Reduction of weathered mineral ores can initiate phase transformation which can affect either their activation or deactivation, subsequently influencing the extent of extraction of desired metals in a leaching reagent. The reduction of ilmenite ores for one occurs as a series of parallel, solid state reactions which at present has no known mechanisms, although the evidence of their effects is abundant. Understanding these reactions may well be the key to uncovering the mechanism of ilmenite activation, hence enabling precise control of its reaction process to maximize yield of TiO2 extraction. However, documenting the solid state reactions in the reduction of ilmenite is challenging due to the ore complexity, the number of simultaneous reactions and the difficulty of capturing critical intermediate reactions and phase transformations during processing. The phase transformations of ilmenite minerals reduced at temperatures up to 850°C were investigated in this study. Mineral transformations were studied in-situ using synchrotron radiation based X-ray powder diffraction with temperature resolved tests. The effect of the extent of reduction and specific mineral transformations were verified by leaching reduced ore with sulphuric acid. The re-sults suggest that transformation of major mineral phases occurs within of specific window of operation and thermal treatment appears to influence the extent of activation and leachability of ilmenite minerals.

Jan 1, 2014

By M. E. Taranenko, V. A. Krivonosov, S. A. Nemykin

"In concentrating production energy-consuming power installations are wide used, the most powerful of them are the wet autogenous grinding mill operating in closed circuit with a spiral classifier. The analysis of the current state of the automation of the grinding process shows that the reserves for maximizing productivity and minimizing electricity consumption have not yet been exhausted on the existing process equipment. Usage of the achievements of the modern management theory reveals an opportunity for further optimizing of the grinding process. The purpose of the research is to develop an automated control system of complex ""the mill-classifier"" to conduct the grinding process in the most operating efficiency, ensuring the maximization of productivity and minimization of specific electricity consumption. The main idea of this work is to study the specific features of the ore grinding process and creation on this basis of automated control system complex ""mill-classifier"" which allows to find and to maintain the optimal mode of grinding based on identification of the current object parameters, observance and regulating of the object state coordinates. Research methods. We used the methods of system analysis, mathematical statistics, modern automated control theory, theory of systems identification, optimal control, modelling of dynamic processes. Developed scientific provisions: - identification algorithm of the loading sub-system management object of complex ""mill - classifier"" allowing to obtain the unbiased estimators of its parameters according to the data of normal object exploitation; - observing device, which differs from the classic version of the observer Luenberger with possibility of estimating not only the state coordinates of the control object, but also the low-frequency perturbation component; - automated system stabilizing the active power of the grinding mode on the basis of a states controller with Luenberger observer; - structure of the software and hardware that implements the developed models, algorithms, methods of control, management and optimization in the framework of the automation of grinding."

Jan 1, 2018

By Susanna G. de Jager, Francis W. Petersen

"The aim of the project was to develop a methodology applicable to different South African coal types to be able to predict with a high degree of certainty what kind of reagent will be suitable for flotation of a certain coal type.The study included 5 coal samples from different collieries and included Highveld seam 3 and 4 coal (as one sample), Waterberg coal (zone 10 -11), Highveld seam 5 upper coal and Witbank seam 2 and seam 4 coal. Seam 3 and 4 (mixture) coal, Waterberg and the seam 5 upper coal were all found to be vitrinite rich coals. The coal characterisation study included petrographic analysis, proximate analysis, float-sink analysis, oxygen-containing functional groups, surface extraction, flotation release analysis and contact angle measurements.The flotation tests showed that the best reagents to float all of the coal samples studied are iso-decanol and dodecene. These reagents produced flotation products that are near to the release curve. Statistical relationship for predicting ash content and yield that can be expected for a certain coal type and selected collector was obtained. From the relationship, the accuracy of the yield is above 95% (p-value below 0.05) with a linear regression of 0.9289. The accuracy of the ash is slightly lower with a linear regression of 0.7841 but also above 95%."

Jan 1, 2003

By M. V. Sowmya

Batch biosorption experiments were carried out for the bio-remediation of Cr (VI) ions from aqueous solutions using Serratia marcescens, a Gram negative, heterotroph and Gram positive bacterial isolates from a chromite mine. The influence of various experimental parameters such as contact time, pH, concentration of Cr (VI) ions and amount of biomass was evaluated with respect to the uptake of Cr (VI). The bio-sorption of Cr (VI) was found to be quite rapid and the percentage biosortion was found to increase with increase in the equilibrium chromium concentration. The free energy of biosorption of Cr (VI) was estimated to be in the range of -23 to -25 kJ/mol for the chosen bacteria. The uptake of chromium by the bacteria was confirmed by EDX and FTIR spectroscopy. As a follow up of this study, bacterial strains resistant to hexavalent chromium were isolated from a chromite mine in Karnataka, India and identified as Arthrobacter sp., Micrococcus sp. and Exiguobacterium sp. using 16s rRNA sequencing. The efficacy of the bacterial isolates for Cr (VI) uptake was assessed and over 90% bioremoval could be achieved for Serratia marcescens and Micrococcus sp. isolate. Possible mechanisms of chromium uptake by the microorganism are discussed. Keywords: bioremediation, hexavalent chromium, biosorption, bioreduction

Sep 1, 2012