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By G. P. Karmakar, K. K. Chandan

"The drilling mud is an essential part of the drilling process, which plays a major role in keeping safe and efficient oil and gas well drilling. In the oil industry, bentonite clay dissolved in water produces the simplest type of drilling muds. Bentonite clay contains montmorillonite particles. These particles are dispersed uniformly in water and such dispersions are used in various industrial products like paints, ceramics, pesticides and drilling muds. The bentonite clay easily dissolves in water and increases the viscosity of the water, which is one of the most important properties of a drilling mud. Bentonite has the highest swelling capacity, which is responsible for building up of the viscosity of the clay-water system. The flocculation behavior of bentonite is one of the major concerns for the performance of the water-based drilling mud in the oil and gas well drilling process. The behavior of drilling mud greatly depends upon the quality and quantity of bentonite clay, as well as the additives that are used in their formulations. In this work, a comprehensive study has been carried out to find out the effect of added polyacrylamide (PAM) polymer, surfactant, pH and salt concentrations on the dispersion/ flocculation characteristics of bentonite clay-water system. It has been observed that the increase in PAM dosage reduces the residual turbidity and improves the settling rate of the bentonite particles. The flocculation rate has also been found to be better under higher pH conditions. The combined effect of salt concentration and PAM dosage improved the overall flocculation efficiency of the system.INTRODUCTIONIn the oil industry, bentonite clay dissolved in water produces simplest type of drilling muds. Bentonite clay containes montmorillonite particles. These particles are dispersed uniformly in water. Such dispersions are used in various industrial products like paints, ceramics, pesticides and drilling muds (Akther et al., 2007). The bentonite clay easily hydrates in water and increases the viscosity of the mud system (Razi et al., 2013; Meng et al., 2012). Bentonite clay in the drilling mud increases the viscosity which is one of the most important prop erties of a drilling mud. Bentonite has the highest swelling capacity, which is responsible for the building up viscosity of the clay-water system (Sonmez et al., 2013). The drilling mud is an essential part of the drilling process, which plays a major role in keeping a safe and efficient oil or gas well drilling (ASME, S. S. C., 2005). The flocculation behavior of bentonite is one of the major concerns for the performance of the water-based drilling mud in the oil or gas well drilling process. This behavior of drilling muds greatly depend upon the quality and quantity of bentonite clay, as well as the additives that are used in their formulations (Yu and Amanullah, 2005; Akther et al., 2007). Bentonite particles form aggregate under certain conditions including high temperature, and high concentration (Luckham and Rossi, 1999). If the quality of bentonite is not sufficient to accomplish intended viscosity of the muds, it is essential to add certain additives to increase the viscosity and prevent aggregation of the system (Razi et al., 2013). The anionic polymer bearing sample can build up inter-particle bonds between the polymer and clay particles. The addition of various additives like, polymers control the dispersion and enhance the viscosity of the mud by controlling the flocculation of montmorillonite particles in bentonite dispersion (Heller and Keren, 2002; Mahto and Sharma, 2004)."

Jan 1, 2018

The Sydvaranger magnetite mine was shut down in 1996 due to low iron ore prices. It was reopened in 2009. The flowsheet has remained more or less as in the old plant, based upon two grinding steps followed by magnetic separation. The Sydvaranger magnetite is free of harmful elements and should therefore be sold on the high quality market. This requires a concentrate containing less than 2 % SiO2. In the old plant, this grade was achieved by amine flotation. Amine was preferred as collector because it could be used in process water from the sea. The use of amine has been restricted by the Norwegian pollution authorities during the time the mine was shut down. Test work to replace cationic with anionic flotation is therefore done. Research on activation of quartz with Ca or Mg ions prior to anionic flotation was shown by basic research in the period from 1960 to 1980 to be effective under simplified laboratory conditions. This old research has now been followed up from a practical/empirical point of view. The basic work was mainly done on quartz and iron minerals only. In this case, an actual feed containing a number of minerals common in iron ores is used, in order to demonstrate that a commercial process is possible. Calcium activation is shown to work excellently but requires too high pH to be environmentally and economically attractive. Magnesium activation is a more difficult process, because the maximum concentration of MgOH+, which was shown to be the activator, is about 100 times lower than the alternative CaOH+. Flotation success depends partly upon the ore, some amphibole minerals are more difficult to float than pure quartz. Ordinary batch flotation test work is time consuming. A South African microflotation test cell has shown promise, because work can be focused upon flotation of the more critical coarser fractions of the Sydvaranger ore. Keywords: iron ore concentration, anionic flotation, mineral activation, microflotation, Sydvaranger

Sep 1, 2012

By W. Pawlos

"The paper will present the methods of visual observation and recording of movement paths of coal grains of different physical properties in the paramagnetic liquid. The paths were recorded with a video camera in the working chamber by means of a specially constructed device, acting as a periscope, which were then transformed into digital images.Experimental movement paths were confronted to the paths obtained in a theoretical way by means of solving differential equations of movement. The outlet level of a grain of the same physical properties from the separator is a random variable with normal distribution which modal value is equal to the outlet level of a spherical grain, calculated from the solution of grain movement equations. At these assumptions it is possible to calculate the height of the passage from the separator working chamber to separate a given product with a given separation accuracy, measured by a probable error and to determine separation conditions."

Jan 1, 2003

By Brian Hart, Rong Fan, Roger Smart, Andrea Gerson, Ning Xu

A complete strategy has been developed for identification of the reasons for losses in recovery and/or grade, due to changes or complications in mineralogy and in mineral surface conditioning, and their subsequent correction. The sequence of methods starts with comparison of mineral phases between QEMSCAN/MLA (compositional) and Rietveld XRD (crystalline diffraction) with bulk assay reconciliation. This methodology has recently led to identification of unrecognised amorphous content (12-40 wt.%), previously attributed to crystalline phases, in the fine fraction (<35 µm) of some problematic flotation feeds. Attached amorphous silica, talc- and chlorite-like fines have direct influence on the hydrophobic/ hydrophilic ratio on value mineral surfaces adversely affecting flotation. SEM/EDS is used in the backscattered imaging mode to determine possible problems with liberation (e.g. remnant local locking), not detected in standard liberation analysis, resulting in gangue flotation. EDTA extraction is used to assess bulk feed pre-oxidation and sequential oxidation product loading through the circuit. Changes in circuit solutions are assayed with speciation modelling of precipitates and potentially adsorbing species. ToF-SIMS with principal component analysis is then used to correlate surface species with specific minerals and can be used to assess the effectiveness of specific reagents particularly collectors. This approach identifies unwanted activating species and interference with value surfaces by adsorbed hydrophilic ions, precipitates and fine particles. When the interference or ineffective reagents are specifically identified, remedial action can be targeted. This method has identified residual talc-like layers (<10 nm thick) inducing gangue flotation of pyroxene and chromite in PGM flotation. Recent case studies of application of the full methodology to losses of molybdenite at KUCC and to sphalerite activation in the Cu/Pb circuit at Brunswick Mines with remedial action are discussed.

Jan 1, 2014

By Kang N. Zhong, Hui H. Luo, Yi H. Wei, Yu L. Wang

"More than 85% of phosphorous reserves in China occur as middle-low grade phosphate of sedimentary origin. The main gangues are dolomite, quartz, silicates, and clays. The characteristics of minerals are finely disseminated. Flotation results have shown that the floatability of apatite of this kind of ore is much worse than that of igneous and metasedimentary origin because of its high specific surface area. Although some effective depressants, such as naphthalene sulfonate and phenanthrene sulfonate, are used to decrease the MgO content in the P2O5 concentrate, its presence is still high (about 2%) in the Chinese concentrates. Meanwhile, the wastewater may cause some environmental problems. Batch flotation results and measurements of specific surface area and CO3 2- have revealed that there is a relationship between the floatability of apatite and the surface area.A two-stage flotation flowsheet, which includes a combination of direct and reverse flotation, was developed for beneficiating sedimentary phosphate ores. The direct flotation was conducted in an alkaline medium and most of the apatite and carbonate minerals floated leaving quartz and siliceous gangue in the sink. In the reverse flotation circuit, the floated product was further beneficiated in an acidic medium to eliminate the carbonate as a float product. Apart from the high quality of concentrate, the two-stage flotation also facilitated the treatment and the recycling of wastewater. A wastewater recycling procedure was developed and tested in a continuous flotation process. The key factor was the careful selection of effective and non-toxic reagents."

Jan 1, 2003

By Sergey Ulianov, Arkady Senchenko, Alexey Shvets, Arkady Bakotin

"This paper is devoted to ultrafine grinding of processing products. This process allows one to include into operation complex ores which earlier were considered as inefficient and economically inadvisable to treat. Fine dissemination of valuable component often does not allow its liberation via standard grinding in ball mills, and therefore requires modern methods of ultrafine grinding (UFG). An example of successful ultrafine grinding usage is its application for crude flotation concentrates regrinding before cleaner flotation stages. A problem often arises with a commercial copper concentrate production in the course of copper ore flotation. Crude flotation concentrate regrinding in a ball mill does not provide for good liberation of the material before cleaner stages. UFG application allows one to get commercial copper concentrate with copper grade of 20% and higher. Another example of ultrafine grinding application is its usage for highly refractory pyrite product received after gold-lead scavenger flotation of polymetallic ore. Earlier this product treatment was economically inefficient. At current application of ultrafine grinding down to 85% minus 20 µm and subsequent gravity processing it is possible to pass major part of gold (73.4%) into concentrate. The constraining factor for UFG application in processing may be the chemical activation of minerals. In the result of this, flotation selectivity may decrease. Therefore ultrafine grinding application extends the areas of efficient usage of metallurgical processes. New technologies allow increasing the level of valuable metals recovery."

Jan 1, 2014

By S. Gaydardzhiev

Initial experiments towards preparation of hollow ceramic microtubes by dip-coating of fibrous plants with water based alumina gel-casting slurries using hemp and coconut fibres as templates have been done. It has been found that the wettability of fibres and accordingly the stability of the developed ceramic layer on their surface during slurry gelation varied significantly within the different fibre types. Good correlation between the diameters of the template fibres and the resulting channels has been found at the level of solids loadings used, 31 %. Hemp fibres used as bundles have led to formation of multi channel patterns while the coconut fibres-templated process resulted in uniform monochannel materials. The micro tubes have show good mechanical handling.

Jan 1, 2014

By Fuqiang Zheng, Shuai Wang, Feng Chen, Yufeng Guo, Guanzhou Qiu, Tao Jiang

"The direct reduced iron powder and Ti-V-rich material was prepared from vanadium titanomagnetite concentrate by solid-state reduction-magnetic separation. The result indicated that under the studied conditions, adding KS can effectively improve the metallization rate of pellets. 2% KS was well mixed with vanadium titanomagnetite concentrate to make the pellets. The green pellet was preheated at 900 ? for 6 min. The preheated pellet was reduced at 1050 ? for 100 min, then crushed and ground to more than 80% was below 0.045 mm. The direct reduced iron powder and Ti-V-rich material were separated from the slurry by wet magnetic separation at 800Gs. The TFe content of magnetic material was 90.63%, and the Fe recovery rate reached 96.53%. The TiO2 and V2O5 contents of Ti-V-rich material were 28.40 % and 1.64 %, respectively. The TiO2 and V2O5 recovery rates were 69.05% and 96.82%, respectively. 1. Introduction The ilmenite and rutile are the main titanium resources which can be used in the present technical level and economic conditions[1,2]. However, with the rapid development of China’s economy, the market demand of titanium products is increasing sharply. The current supply of ilmenite and rutile cannot meet the needs of chemical industry[3]. China is rich in vanadium titanomagnetite concentrate which contains abundant titanium and vanadium resources. The TiO2 and V2O5 content of vanadium titanomagnetite concentrate are usually about 7% and 0.3%, respectively[4]. Because the TiO2 and V2O5 grades are low, it generally requires pre-concentrated to Ti-V-rich material before extracting the titanium and vanadium. Therefore, it is vital to find effective processes for pre-concentrating the titanium and vanadium in vanadium titanomagnetite concentrate. There are many methods[5-13] developed or under development to pre-concentrate Ti-V-rich material from vanadium titanomagnetite concentrate, including the blast furnace process, pre-reduction electric furnace process, to utilized vanadium titanomagnetite concentrate are direct reduction-electric furnace smelting, sodium salt roasting-direct reduction-electric furnace smelting and direct reduction-magnetic separation and so on. The blast furnace process and other methods cannot effectively utilize the titanium and vanadium resource due to the technical or environmental problems[9]. In this study, the vanadium titanomagnetite concentrate was obtained from Panxi region of China, the reserves of which account for 11.6% of vanadium and 35.17% of titanium all over the world[3]. The preparation of direct reduced iron powder and Ti-V-rich material based on reduction-magnetic separation is proposed. The process utilizes a new catalyst for titanium ore reduction in rotary kiln followed by magnetic separation. Using this novel technology, the titanium-vanadium and iron are successfully separated. Compared to the traditional reduction of Ti-bearing ore, the reduction temperature reduced to 1050 ?, leading to higher efficiency, lower energy consumption and investment, and broader applications."

Jan 1, 2018

By Ronald Díaz

"Cerro Corona is a porphyry ore with different geometallurgical units and alterations produced by an extensive family of geological failures that have determined a special type of mineralization. With the increasing depth of the mine, it is estimated that the host rock will be less altered. Consequently, the ore will have a higher resistance to breakage accompanied by associated problems such as lower throughput. In light of this reality, various projects have been carried out with the objective to optimize mineral processing of ore with low clay content and high hardness, including reducing the blasting grid, increasing the load factor, using adequate mixtures of hard ore, reducing crusher settings, installing air guns in the transfer chutes, increasing ball charge, and changes in the lifter design, wear control in the hydrocyclones, syntonization of control logics, supervisor control of the SAG mil, characterization of feed ore, etc. However the most important factor was the teamwork between mine and plant personnel, aiming at common objectives for the company. These projects started in 2011, including characterization of mineralogical domains, breakage and blasting characteristics, and also a revision of the actual operating conditions in the crushing and grinding circuit. The development of different designs of the SAG mill lifters and the unloading grates, a 16% ball charge increase, improvements in the blasting process, reduction of the primary crusher setting, weight reduction on the feed lid, and variation of operational parameters, all allowed the company to achieve its objectives of maintaining impact control and steel recharge within the expected operational parameters. The achieved throughput is above design capacity, sustainable, and not without new challenges for maintaining and optimizing this production level."

Jan 1, 2014

By Felipe Henríquez, Daniel Silva

"Traditionally, the implementation of an automated advanced process controller in any mineral processing complex is a challenge, mainly due to the quality of resources and technologies required, the uniqueness of each control solution and the uncertainty of the engineering hours needed to complete the task. Thus, the use of advanced and proven control technology becomes a key factor when deploying the control strategy. However, success would still not be possible without the presence of common sense, process knowledge and fundamental process data. Minera Los Pelambres, taking advantage of such factors and its accumulated process experience, implemented a novel and successful combination of MPC (Multivariable Predictive Control) and advanced control for secondary grinding and regrinding stages at its copper concentrator plant. In both cases, the control objectives are: being capable of processing a variable feed from the upstream process while at the same time avoiding to become a process bottle neck and yet, maintaining an adequate product quality (in terms of size distribution) to the process downstream. Additionally, for the case of the vertical regrinding mill (vertimill), the control system should also be capable of keeping an adequate circulation load and making an efficient use of the available grinding power. In either case, extending hidrocyclones availability while maintaining their performance is a must, since both factors are required for process and maintenance purposes. Thus, the process control problem becomes one with a multi-variable type of process with multiple control objectives to satisfy simultaneously. In trying to solve it, many mineral processing operations have implemented basic or conventional control or even better yet, expert systems. Minera Los Pelambres believes that better and faster results can be achieved using a combination of MPC and advanced control. Such strategy was successfully implemented, reducing considerably process variability while maintaining high throughput and keeping the process well within constraints limits. Their control philosophy, implementation process, main results and their key performance indicators are discussed here."

Jan 1, 2014

By Alejandro Rubio-Lopetegui, Gonzalo Montes-Atenas

The occurrence of Enargite (Cu3AsS4) in hydrometallurgical plants bears a number of challenges. One question lies on how Copper and Arsenic can be selectively extracted from the solid surface structure when immersed in aqueous solution. The leaching of Enargite in ambient conditions has been extensively studied; nevertheless, challenges regarding the process kinetics and surface structures enabling the extraction process remain ill-understood. Prior knowledge indicates that different conditions of pH, Eh, temperature, speciation of the aqueous phase or variations of these parameters defines the overall rate at which metals and other elements will be transferred to the solution. One aspect that the research studies have seldom addressed involves studying the main features of the surface structures formed during the leaching process at the outmost surface atomic layer. Such structures will mediate between the solid bulk and the solution to undertake subsequent stages of leaching process. The aim of this research work is to critically analyze the state of the art of Enargite electrochemistry from the mediator formation-dissolution mechanisms standpoint occurring at the mineral-solution interface. The most probable mediator species reported in the literature were found to be: Arsenolite and Sulfur (acidic media), Covellite (acidic and alkaline media) and Tenorite (alkaline media). As a result of this analysis, it was observed that the surface speciation was not in full agreement with the previous knowledge suggested to explain Enargite leaching reactions and, therefore, modified Eh-pH diagrams are presented. The acquired insights on the surface structures rising from the Enargite-aqueous solution interactions is further revised to provide new experimental protocols towards selectively separating Copper and Arsenic through hydrometallurgical paths.

Jan 1, 2014

By Girolamo Belardi, Silvia Serranti, Giuseppe Bonifazi, Roberta Palmieri

Ore textural and structural characterizations play a fundamental role in any preliminary study (i.e. comminution, classification, separation) addressed to the design and set up of beneficiation flow sheets. The possibility to utilise automatic tools able to perform a classification, and a quantitative description, of the mineralogical and petrographical characteristics of raw ore samples thus represents an important step to define, to control and to verify the entire set of parameters, ore-texture-related, that can affect the final beneficiation results. The procedure usually adopted is based on the analysis of polished sections and more in details the recognition of the different mineralogical species and associations and the measurements of some quantitative parameters estimating both the geometrical characteristics of each species and the possible spatial relationships between them. This approach, originally carried out by experts, utilising optical and/or electronic microscopy, was ‚replaced? during the years by more and more sophisticated devices integrating analytical facilities and acquired data processing. Such integrated analytical devices formed the breakthrough platforms into what is now known as modern Process Mineralogy. In this paper the possibilities offered by chemical imaging based devices and techniques, to perform ore minerals recognition/classification, and to perform their topological assessment, are presented. Tests have been carried out and are discussed in order to analyze the problems related to the development of suitable and low cost strategies addressed: i) to realize a full mapping of ore minerals/gangue inside selected samples, ii) to define the optimal data-flow handling to optimize the speed of processing versus the quality of the results and iii) to start to define logics and procedures finalized to implement innovative smart detection engines, chemical imaging based, for mineral processing addressed to perform both a preliminary characterization of the ore, at laboratory scale, and a further possible control of the different processed minerals flow streams.

Jan 1, 2014

By Paula Olea, Gonzalo Montes-Atenas

Froth flotation operation is a large tonnage process aiming at selectively separate economically valuable minerals from gangue material. The wellbeing of an industrial froth flotation operation has been historically assessed and understood in terms of many variables known to somehow affect the process performance. Among these variables, air dispersion have been pointed out as key to secure the correct transport of hydrophobic particles to the froth phase and, then, to the concentrate. One of the classic parameters assessed when evaluating the air dispersion in flotation tanks is the superficial gas velocity. Many reports have focused on studying the superficial air velocity profiles across the pulp phase and theories have been based on the fact that the measurements should be performed in the so called "quiescent zone", which is a volumetric region inside a flotation cell of difficult determination. The hypothesis behind this research work is that the reporting of particles to the concentrate would provide a better correlation with the effective air flowrate pattern created in the froth phase. The aim of this study, as a first step towards developing a flotation model fully froth phase-based, is to estimate the effective surface area used in a flotation cell derived from results obtained with a specific setup at laboratory scale. The methodology considers running a thin lateral flotation cell cut at different superficial air velocities, with and without particles. It was found a non-linear correlation between the superficial air flow rate and the characteristic distance between the vertical wall next to the cell lip and the cut point where the foam or froth flowrate almost stops contributing marginally to the overall amount of solid particles transferred to the concentrate. The presence of hydrophobic particles reduced the mobility of the froth phase reducing the characteristic distance.

Jan 1, 2014

By L. Weitkämper

The big challenge at present and in the future is the economization of resources. This is applied for the whole industry but particularly in fields of mineral processing. The most important resources are energy and water. The shortage and price advance of energy is worldwide noticeable whereas the shortage of water is regionally limited at present. However due to the increasing world population, associated with a rising standard of living, water will become more and more important. Studies of the Unesco from 2001 indicate that the total water consumption raised seven times since the last 100 years at a growth of population of just three times. (UNESCO-Currier, 10/2001). This trend is going to be increased. While today more than 90 % of the humanity has access to clean water, in 2050 just about 50 % will be in the same situation. These figures indicate the importance of a gentle handling with the resource water. Further more the disposal of fine products, containing most of the water, is an environmental concern and in the future the mining and processing of raw materials will become important and necessary in desert, arid or permafrost areas. In these areas just efficient dry cleaning technologies will allow an economical beneficiation or better enable the processing at all. Most of the separation technologies with high throughput rates in mineral processing are based on wet processes. This applies especially for the separation of fines. Though there are some dry technologies available for the separation of coarse materials, like pneumatic gravity separation [air jigs and air tables], magnetic separation and not least sensor based sorters. Dry separation of fines is bounded mostly on cost intensive and low throughput technologies. The pneumatic separation undergoes at present a renaissance, mainly due to the development of the all air jig by the German supplier Allmineral. This newly developed sorting device yields good results in the separation of coarse to medium size material. All these facts and figures show the potential and motivation for developing an efficient dry separation device for fines. The following article delineates the development, performance and chance of a new dry separation technology for fines.

Jan 1, 2014

By N. Panteleeva, E. Konoplev, I. Michailova, S. Titkov, S. Aliferova, T. Gurkova, T. Chumakova

Cationic flotation using alkylamines and their derivatives as collectors, and characterized by high selectivity of mineral particle separation, is finding ever growing industrial application. In recent years the industrial application has been initiated of new cationic collectors - alkylmorpholines. Efficiency of cationic surfactants operation as collectors is dependent upon their colloid and sorption properties and the availability of silicate .carbonate rock-forming mineral impurities in the ore, which sorb the cationic collector. Investigations have been carried out on the influence of frothers and organic depressors with various compositions upon physical-chemical and flotation properties of alkylamines and alkylmorpholines. On the basis of these investigations requirements for organic depressor were developed and new flotation reagents were proposed (V-1 frother and KS-MF depressor). The use of new reagents enables one to decrease considerably the consumption of expensive cationic collectors and to enhance the floatability of coarse mineral particles. Data of new reagents industrial application is presented. The reagents developed can be used for flotation processing of other ores.

Jan 1, 2003

By Tatyana A. Ivanova, Tamara N. Matveyeva, Anatoliy A. Fedorov, Tatyana V. Nedosekina, Valentin A. Chanturiya

An ingenious methodology purposively developed by the authors for comprehensive assessment of flotation properties, electrophysical characteristics and. crystal chemistry features of natural gold-bearing sulfide minerals of different origin has been used in this study. Examination of the elemental composition of the minerals, ion-molecular components of the liquid phase in suspensions, surface properties of sulfides and different flotation reagents sorption forms was performed using the methods of X-ray phase and spectral analysis, potentiometry, UV and IR spectrometry, computer image analysis, and computer simulation techniques. The role of isomorphous impurities in the formation of hydrophobic sulfhydric collector layers on mineral surfaces in complex ore processing has been elucidated. The parameters characterizing the variability of the Fe:S ratio in pyrite of different origin have been determined based on non-stoichiometry characteristics of natural gold-bearing sulfide crystals. An ingenious method of formatting and linear approximation of experimental data was used to find out the quantitative relationships between the impurity content, electrophysical characteristics, non-stoichiometry and floatability of pyrite from a number of different deposits. The effect of the impurity species present in sulfides on the characteristic pH value marking the floatability peaks as such and their trend of shift towards higher alkalinity has been revealed. A theoretical substantiation has been given to prognostic assessment criteria for processing characteristics of gold-bearing sulfide minerals with varying composition. New flotation reagents and advanced reagent systems which help to increase the contrast of processing characteristics for different gold-bearing sulfides, resulting in improved selectivity, have been developed. The mechanism of selective flotation of precious metal-bearing Fe and As sulfides achieved by using short-chain dithiocarbamates and a mixture of cyclic trithiocarbonate with oxyalkylsulfides has been analyzed.

Jan 1, 2003

By M. Pelser, C Aldrich

"The presence of calcium and magnesium in the hydrometallurgical processing of base metals, results in a number of process difficulties. These problems range from the contamination of the final product (where the final product is a precipitate) to high energy consumptions and large bleed streams during electrowinning. Calcium poses an additional problem in sulphate solutions owing to the low solubility of its sulphate salts. This can easily lead to a process stream that is supersaturated with calcium sulphate, resulting in unwanted solids formation within the process equipment.Several processes are reviewed for the control of calcium and magnesium. Of these, fluoride precipitation was selected for experimental investigation. This method involves the addition of a soluble fluoride to precipitate CaF2 and MgF2. The experiments showed high selectivity for calcium and magnesium over the base metals. The experiments also showed magnesium precipitation to dominate for calcium to magnesium molar ratios greater than 1:3.To avoid the domination of magnesium precipitation, a flow sheet is proposed whereby only a portion of the base metal stream is subjected to fluoride precipitation. For the precipitation, a 10% excess of ammonium fluoride is used to remove the maximum amount of calcium and magnesium. After precipitation and solid-liquid separation the split-stream is returned to reduce the overall calcium and magnesium concentration of the base metal stream."

Jan 1, 2003

By Junji Shibata

In a present process to treat the tungsten carbide tool waste, the wastes are roasted in air and then an alkali leaching is carried out in an autoclave. An environmentally friendly process is required to recover rare metals (Co and W) from the wastes. The effect of mechano-chemical (MC) treatment on leaching of rare metals was investigated in this study. The solvent extraction and crystallization-stripping methods were applied to separate and recover tungsten and cobalt in the leached solutions. The MC treatment for the rare metal leaching is effective to dissolve rare metals from the wastes due to the change in crystalline structure of WC and oxidation of WC with KMnO4. Cobalt ions are extracted with D2EHPA by a cation exchange reaction. Tungsten in the leachate can be extracted by TOA (tri-octyl amine) as an extractant, because tungsten species exist as a form of anionic species in acidic solution. The rare metals in organic phase are recovered as insoluble salts such as oxalates and ammonium salts in the crystallization-stripping process. Keywords:unheated oxidation, solvent extraction, crystallization-stripping, recycling

Sep 1, 2012

By L. Tavares

The significant capital and operating expenditure of size reduction operations have maintained comminution on the spotlight of mineral processing research during the last century and, more recently, the concerns about the impact of these operations on the sustainability of the minerals industry, will remain to do so in the 21st century. One of the most popular approaches that have been used to deal with these challenges is the application of simulation both to reduce the uncertainty in the design and improve the operation of size reduction operations. From the initially purely empirical approaches, including the energy size reduction ?laws? and the phenomenological approaches, of which the traditional population balance model is, arguably, the best example, comminution modeling now reached a point in which more fundamental and mechanistic models are sought. The paper analyzes some of the advances that now make multiscale modeling of comminution processes realizable. On the microscale, greater understanding of the phenomena involved in fracture and fragmentation of single particles under different stressing conditions now exists. Particle breakage testing methods are currently used in a routine basis by industry and good quantitative descriptions of different breakage mechanisms are now available, although research is still required to develop appropriate models for a couple of them. On the macroscale phenomena, the discrete element method (DEM) has been successfully used not only to provide insights but also quantitative information on the transfer of mechanical energy from the machine to the grinding media in mills and to particles in crushers, while smoothed particle hydrodynamics (SPH) and computational fluid dynamics (CFD) to describe fluid flow. The paper also analyzes the importance of modeling mesoscale phenomena in size reduction, which is the interaction of particles forming assemblies or beds of particles, demonstrating some of the areas requiring further attention. Examples of application of the multiscale modeling approach to the inadvertent comminution of ore lumps during handling, to the comminution in vertical impact crushers and tumbling mills are demonstrated. Keywords: comminution modeling, DEM, SPH, CFD, multiscale modeling approach

Sep 1, 2012

By Knut L. Sandvik, Erik Larsen

Crystalline silicon solar cells are the most important solar cells manufactured today. This will most probably remain the situation the next decade. The future silicon feedstock is most likely not reject from the production of electronic-grade silicon. There will probably be a more direct solar-grade silicon route, excluding the electronic-grade silicon "detour". Estimated global solar energy demand in 2001 required approximately 5,500 tons of silicon feedstock. This required 65,000 tons of quartz. If the trend continues, the solar energy demand in 2010 would require approximately 30,000 tons of silicon feedstock and 350,000 tons of quartz, although the need for quartz probably will be lower than this. Quartzite has been regarded as the most suitable primary raw material used in the silicon solar cell production chain. This may change as the raw material requirements for the production of metallurgical-grade silicon are most likely to change. In addition, quartz or other silica-containing minerals from other rocks may be of a higher purity or contain lesser amounts of the most harmful elements. This favours increased beneficiation of primary raw materials in the future solar silicon feedstock production chain.

Jan 1, 2003