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By K. V. Fedotov, E. V. Zelinskaya, O. V. Ulanova

"Mining enterprises, in particular, those on the territory of the Siberian platform, produce large amounts of pumped water, which cannot be recycled because of its high mineralization and, thus, is discharged as liquid waste either back into the ground or onto the surface. However, groundwater is often a valuable raw material and a source of useful chemical substances. Brines are unique groundwaters. In the current environmental and economic situation, the huge loss of natural raw materials and their deliberate conversion into wastes is unaffordable. The exploration of non-traditional sources of minerals such as the hydromineral resources (including pit water) is a matter of rational nature management. The industrial value of brines of the Siberian platform is due to the high contents of rare alkali and earth alkaline elements (lithium, rubidium, cesium, strontium, bromine, etc.). The absolute concentrations of these elements in brines are tens of times higher than the lower limits of the mining cut-off. The long-term data analysis was performed to estimate the environmental impact of liquid waste from two mining enterprises, namely, Korshunovskii (Irkutsk region) and Udachnaya (Southern Yakutia). The study was focused on the prospects of hydromineral resources as non-traditional sources of valuable elements and the exploration of technological processes for the selective extraction of rare alkali and earth alkaline metals from natural multi-component brines aimed at decreasing their negative environmental impact. The environmental and economic efficiency was proved for the processing of complex brines and the integrated selective extraction of rare earth metals from sodium chloride brines of the Korshunovskii plant and calcium chloride brines of the Udachnaya plant based on the ion exchange sorption, eluent chromatography, flotation, crystallization, and freezing techniques. The basic technological schemes were developed for the metal extraction from pit water and brines.INTRODUCTION In the Irkutsk region (the Angara–Lena artesian basin) and in Yakutia (the Olenek and Tunguska artesian basins), several mineral deposits are developed and, incidentally, aquifers bearing brines of different types are opened, which are eventually converted into liquid production waste (Rusetskaya et al., 1994) This raises the issue of the burial or utilization of brines since their use within the water circulation is impracticable under the existing technological conditions while their discharge into the surface watercourse is unacceptable because of the harmful environmental impact."

Jan 1, 2018

By Wieslaw Wszolek, Kazimierz Trybalski, Ryszard Tadeusiewicz

"The present work is an attempt of neural networks application to the description of complex technological processes of useful minerals enrichment. Neural networks are among the most convenient tools that have been added recently to the professional toolbox of modelling specialists, and they are particularly useful in realisation of multiple practical tasks, characterised by great complexity and relatively low amount of available a priori knowledge about the nature of the modelled processes. They are successfully applied in a wide variety of problems related to data processing and analysis, their prediction, classification or process control. The object of the study was the technological site for copper ore enrichment by floatation, being a part of technological line in the Ore Enrichment Plant ZG „Polkowice”, KGHM „Polska Miedz” S.A.The main floatation is described by parameters measured by the supervision and control system, which can be grouped with respect to the functions performed for the object:a) input function: aFG - copper contents in the feed material for the main floatation [% Cu]b) control: LFG I - level in the first section of the floatation unit [%], LFG II - level in the second section of the flotation unit [%], LFG III - level in the third section of the floatation unit [%], LFG IV - level in the fourth section of the floatation machine [%]. These quantities compose the five elements long input vector.c) output function: ? - copper contents in the waste from main flotation (final waste) [% Cu]The measurement data, containing the above-mentioned parameters, have been collected during the normal operation of the plant. The data contain momentary values of the parameters, registered every 10 minutes, covering the period of 196 hours of the plant’s operation (1176 measurements for each quantity).For construction of the model used in the study classical multi-layer perceptron-type neural network has been used, with one hidden neuron layer, trained by the error back propagation method."

Jan 1, 2003

By Arkady Senchenko, Sergey Rybkin, Svetlana Lagutina, Alexander Aksenov

"The application of autoclave leaching technology for sulfide concentrates containing base and precious metals is spreading nowadays. In the process of concentrate leaching silver accumulates in the forms of jarosite compounds, transforms into passive chemical state and is mostly found in solid phase. Effective technology development for silver recovery from solid phase of concentrate autoclave leaching raises the necessity for comprehensive research of silver forms of occurrence and their properties in this product. The possible form of silver presence in solid phase of concentrate from autoclave leaching is argentojarosite. This article is about the study of physical and chemical properties and structure of synthetic argentojarosite - AgFe3(SO4)2(OH)6. A method of argentojarosite synthesis has been developed under conditions simulating the process of autoclave leaching of sulfide concentrate, and includes silver dissolution in the form of Ag2SO4, Fe3+ sulfate hydrolysis, AgFe3(SO4)2(OH)6 build-up. X-ray data of synthesized argentojarosite completely correspond to those of natural mineral. The structural formula of this complex compound has been studied and confirmed. The chemical properties of synthetic argentojarosite, its solubility in acids and alkalis have been investigated. Phase changes when heating argentojarosite with the build-up of iron oxide and silver sulfate stop at the temperature equal to 650 ºC. Based on the results received the technological solutions for solid phase of autoclave leaching of concentrate have been developed with silver recovery of 95-98%."

Jan 1, 2014

By S. Banisi, A. R. Ghasemi, M. Maleki-Moghaddam

Direct observation of the charge shape and its motion in industrial mills are not possible, it is then customary to use transparent end, small-scale mills (i.e., model mills) to determine the charge trajectory directly by visualization methods. Because of a short length of the model mills, the end-wall effects could introduce a significant bias on the observed charge trajectories and shape. The shorter the mill, the stronger the bias. This could be due to some material bridging between the end walls. In this research, the end-wall effects were investigated by gradually increasing the model mill length and analysing the charge trajectory and shape variation at a given operating conditions (i.e., ball filling, mill speed, liner type). The unbiased mill length was assumed to be beyond the mill length where no significant change observed in the charge trajectory and shape. For all tests, the torque of the charge was also measured by a torque sensor. The special design of the model mill with the diameter of 100 cm made possible to increase the mill length in steps of 3.6 cm up to 21.6 cm. Four types of liners, five steel ball fillings (10, 15, 20, 25, 30% v/v) and three mill speeds (55, 70, 85% of critical speed) were tested. The ball sizes ranged from 4 to 12 mm. The results indicated that when the mill length was below 10.8 cm the end walls prevented the charge from free falling. This resulted in lower impact point angles and lower power draws compared with the case of no end-wall effects. When the same experiments were performed using an iron ore instead of balls with the same size range, the impact of end-wall effects was more pronounced. For an increase of 30% in the speed (from 55 to 85%), the torque due the change in the charge shape decreased by 41% (from 3.7 to 2.2 kgf.m) when mill filling was 30%. At the same operating conditions when steel balls used the torque decreased only by 19% (from 9 to 7.2 kgf.m). This was expected due to irregular shapes of the ore particles which facilitated bridging. Three-dimensional DEM simulations also resulted in the similar conclusions.

Jan 1, 2014

By Andrzej Luszczkiewicz, Magdalena Duchnowska, Jan Drzymala

A selected flotation system of beneficiation of the copper ore at KGHM Polska Miedz S.A. has been analyzed in the article. It was found that a proper assessment of upgrading must be based on two elements, that is the upgrading process selectivity and working point of the considered flotation unit, both determined, preferentially by means of the Fuerstenau recovery-recovery upgrading curve. The Cu recovery - non-Cu components recovery upgrading curve was selected for calculations because its background lines (no separation and ideal separation) are insensitive to changes in the grade of feed of the processed material. This approach allows a comparison of upgrading results for feeds having different grade, being upgraded in various flotation machines and under different physicochemical conditions. It was shown in the paper that the main criterion for comparison of two working in parallel systems is selectivity of upgrading. However, when two flotation machines, despite of the same selectivity, produce concentrate and tailing of different grades, it is necessary to analyze their working points using upgrading curves. The proper position of the working point depends on the criterion imposed on the process and is a result of not only basic parameters of the upgrading process such as feed, concentrate and tailing grades but also on economic parameters such as costs associated with the production of concentrates and the time needed for their production.

Jan 1, 2014

By Hakan Gürsoy, Kemal Bilir, Bahri Öteyaka, Ali Uçar, Oktay Sahbaz

"Jet diffuser flotation column (JDFC) is a flotation device resembles Jameson flotation cell (JFC) in terms of operational principles, but it has significant difference structural points of view. This difference is an essential change in the downcomer to provide an increase of performance of the cell for the coarse particles. By using the hydrodynamic and fluid mechanics principles (Sahbaz et al., 2013) downcomer was changed as a diffuser, therefore turbulence at the end of the downcomer was reduced to provide better aggregate stability and homogeneous dissipation of the bubbles in the separation tank. According to experimental results carried out in pilot scale JDFC, not only higher flotation performance comparing with Jameson cell was obtained specifically for coarse talc particles in a certain condition, but also quiescent froth layer was acquired. In these tests, vertical pipe of JDFC having inlet diameter of 6 cm and outlet diameter of 11.5 cm was used with separation tank having the diameter of 39 cm. By using the data, pilot scale JDFC having 410 cm vertical pipe integrated with separation tank was produced and flotation tests were carried out by using the naturally hydrophobic mineral (talc). Finally, the talc recovery obtained as 94% by the use of JDFC, while Jameson cell has the recovery of 77% for the particle size of 250 µm."

Jan 1, 2014

By Cristian Melipichun, Leopoldo Gutierrez

The effect of the presence of fine particles of kaolinite and montmorillonite on the induction time for attachment of bubbles to particles of a copper concentrate rich in chalcopyrite was evaluated in this study. The results obtained from induction time measurements were correlated with data of concentrate recovery achieved from micro-flotation experiments. The effect of the presence of fine clays on the stability of air-water foams was also studied through measurements of the foam volume generated in a glass column under different conditions of air flowrate and MIBC concentrations. The experimental results showed that induction time values increased under the presence of fine clays. These data agreed with results obtained from micro-flotation experiments that showed that copper concentrate recovery decreased when clay particles were added. Although a complete explanation for these results is not available, the fact that experimental observations indicated that fine clay particles tend to adsorb on gas bubbles, suggests that the interactions between fine phyllosilicate particles and air bubbles have to be taken into account when studying the effect of clays on froth flotation. Foamability tests showed that the presence of fine clay particles increased the foam volumes only at high additions of clays and low dosages of MIBC. The results obtained at higher dosages of MIBC showed that the foam volumes decreased with the addition of clays under all the experimental conditions tested.

Jan 1, 2014

By Sung. Hyejin, Kyoungkeun Yoo, Oh-hyeok Kown

The sediments near coasts and ports in Korea have been found to be contaminated with heavy metals and organic matters. So far the sediments have been dumped to landfill sites or ocean. However, the number of available landfill sites is decreasing and ocean disposal of wastes was strictly prohibited. Although physical separation processes have been found to be useful for the remediation of contaminated soil with heavy metals, because the sediments consist of fine particles, it is difficult to remove heavy metal component by physical separation processes. Furthermore, the sediments contain organic matter, so there is a concern about strong stink during the sediment treatment. The present study is aimed to develop the treatment process for removing heavy metals and organic matter from the contaminated sediments. The heavy metals and organic matter were oxidized and dissolved by electro-generated chlorine, and the chlorine used is regenerated and circulated in the leaching process. This system has economic and environmental advantages to reduce the wastewater and the oxidant consumption. The leaching results show that the metal removal efficiency increased to more than 99%, and more than 50% of organic matter was decomposed.

Jan 1, 2014

By Peter Ay, Elena Geldt, Satyanarayana Narra, Claudia Glaser

"As part of an extensive research and development project, the technical and technological implementation of the patents DE 10 358 245 B4 and WO/2006/056172 was developed with the goal to present a system for the innovative roll- agglomeration method exhibiting a) a modular setup, b) high productivity and c) suitability for the use of fibres of different applications and product qualities (high technical availability). The processability of the rarely adapted raw fibre materials into high-value intermediates brings forward their application in various processing industries dealing with the production of fibre reinforced plastic composites, heat and sound insulation materials as well as with the gas and liquid cleaning systems. The innovative fibre agglomeration presented in this work is performed by a combination of rolling and pressing the fibres inside a geometrically pre-defined roller table, in which the fibres are forced to bound through entanglement / interlocking and develop into agglomerate. The agglomeration process is carried out in a circular roller path with a rectangular cross-section. For improving the adhesive properties, and thus the quality of the agglomerates, the boundary surfaces can be covered / patterned / lined / coated with various materials. The resulting roll-agglomerates are characterized by different quality parameters such as mass, shape, porosity and stability. The properties of the agglomerates can be modified based on the end-product requirements by slightly modifying the process parameters such as filling ratio, residence time, roll-geometry, procurement of the boundary surfaces, etc. as well as the input material properties such as fibre type, fibre fineness, fibre length, etc. This work carries extensive work on the roll-agglomeration system to assess the effectiveness and the variability based on the product specifications. Agglomerates were produced with wide variations of system parameters with varying roller table liners and based on evaluation of the produced agglomerates with respect to their mass, the geometrical dimensions, their porosity and stability."

Jan 1, 2014

By Ramon V. V de Araújo, Roberto B. E Trindade, Pablo R. Fica-Piras

"Lead has been reported to affect blood vessels and kidneys. It also produces adverse effects in the mental and physical development of children and nervous system of adults. It is also considered as a possible cause of cancer. Because of all these threats to the human life, the reduction of its environmental occurrence, by means of recycling, is an important additional advantage to the usual ones derived of the procedures of the secondary metallurgy: lead can be recycled several times maintaining its characteristics equivalent to the primary one.Furthermore, this way of producing the metal avoids the environmental impacts of primary lead melting. Also, as an additional advantage, it triggers the metallurgical process with a raw material in what we observe higher lead content than in the natural ores. Some of the potential sources for these purposes are: ashes, slags, electrode residues, anodic muds, spent electrolytes, solid and liquid wastes, industrial or automotive catalysts, worn-out or obsolete equipment components and/or final consumption products.About 40% of world’s lead production comes from automotive batteries, mainly composed of four parts: plastic box, electrolyte (diluted sulphuric acid), contacts and connectors of Pd-Sb and plates (PbSO4, PbO2 and PbO). The plates represent 75% of the total mass. Metallic parts can be melted at moderate temperatures and then refined. The remaining fraction, constituted by the non-metallic portions, can be recovered by hydro and electro-metallurgical routes. These routes are preferred instead of pyrometallurgical ones due to the ultimate emissions of lead particulates and sulphur dioxide.The principal constituent of the residual paste of batteries is the lead sulphate. In this process, the paste is treated in two stages: in the first, lixiviating with Na2CO3 (desulphurization of the paste), obtaining PbCO3 and Na2SO4; in the second, the lead carbonate is lixiviated with HNO3, producing Pb(NO3)2, soluble, that can be converted to metallic lead by electrolysis. The reaction of PbSO4 with Na2CO3 in aqueous solutions is fast: the global rate is limited by the diffusion of the carbonate ions inside the reaction medium."

Jan 1, 2003

By M. H. Moys, M. M. Bwalya

The use of the Discrete Element Method (DEM) to simulate the interaction of particles in dynamic environments is growing rapidly. This technique is also being applied in the study of milling extensively. However, to date more focus has been on the validation of the model. In spite of the advantages of the detailed information that is available from the simulator, appropriate application of this information remains a daunting task. In this paper a technique that combines particle breakage probability data with the energy spectra generated from the DEM is discussed.

Jan 1, 2003

By Aubrey Mainza, Malcolm S. Powell

"A hydrocyclone with two vortex finders, named the three-product cyclone, has been successfully tested in the Platinum industry for dealing with the dense chromite found in UG2 ores. This dense component preferentially reports to the cyclone underflow, resulting in an over-ground fine chromite component in the final product. The dense media effect caused by a high chromite concentration in the cyclone feed produces a coarsening of the cyclone overflow, which results in loss of recovery through over-size material in the float feed. The fine barren particles of chromite that report to the overflow are recovered through entrainment in the flotation process, resulting in detrimental contamination of the slag produced from the concentrate.With the three-product cyclone a middlings product has been extracted that has a higher concentration of fine chromite. This volumetric stream flow represents a small percentage of the total cyclone feed and it is thus possible to treat it separately via fine screening to remove the fine chromite from the system and recover coarse silica."

Jan 1, 2003

By Grigory Voyloshnikov, Sergey Petrov, Vladimir Petrov

"The treatment of high-grade copper gold-bearing ores is practiced extensively. However, due to low concentration of copper the application of a separate process for copper recovery can make this process uneconomical. The copper, in particular: in oxide minerals, intensively bounds with cyanide during conventional cyanidation. In this case, cyanide is not able to react with precious metals and the consumption of cyanide increases. The resulting copper cyanide complexes have a negative effect on the recovery of gold. Due to decreasing of the process parameters, a repeated use of the recycled solutions can be hindered, especially in the case of heap leaching. The technology of copper removal from the process solutions with simultaneous regeneration of free cyanide from copper-cyanide complex and producing of a saleable high-grade copper concentrate was developed. An important feature of this technology is simplicity, the absence of complex or dangerous operations and the use of common reagents. The choice of equipment depends on the ore treatment option: heap or vat leaching. Also, simpler equipment schemes are available. The studies, tests and industrial practice show that if the concentration of copper can be decreased down to the first numbers of mg per ppm or lower, it is reasonable to maintain the process copper grade in the recycled solutions at 30-50 mg/L. In this case, recycling of cyanide-bearing solutions is unlimited. The regeneration of free cyanide from that of bound with copper and other cyanide complexes is 95-98%. The grade of copper in the concentrate is 55-60%. This technology is an economically competitive option, in particular: with the account of the sales of copper concentrate. The removal of copper has a positive effect on gold recovery, especially during heap leaching. In addition to, this offers significant benefits in reduced costs."

Jan 1, 2014

By Janusz S. Laskowski

"Frothers offered by different manufacturers are marketed with some information on their chemical and physical properties (e.g. density, viscosity, color, water-solubility, safety/toxicity, etc.). But frothers are used in flotation to generate fine bubbles and to stabilize the forth, and this information is only provided in a very qualitative description of the visual appearance of bubbles and froths. The terms “powerful” and “selective”, which have been commonly used to characterize frothers, have intuitive rather than scientific meaning.This paper introduces the DFI (Dynamic Foamability Index) plotted vs. CCC (Critical Coalescence Concentration) diagrams to classify flotation frothers (Fig. 1). The frothers characterized by low CCC and high DFI values have properties of strong flotation frothers, while those with high CCC and low DFI values are more selective. The proposed frother classification system, based on simple CCC and DFI measurements, provides, for the first time, a solid ground-work for characterization of the flotation frothers."

Jan 1, 2003

By Francisco Vicuña, Miguel Becerra, Nelson Iglesias

"The following article presents the development of a dynamic tool for the estimation of Jb/Jc rate (ball filling level / total load filling level) of a SAG mil operating in a single stage mode. Using the methodology detailed in this article, it is now possible to have a dynamic estimation tool in the operation, which enables strategic decision making and achieving a continuous development in process optimization. The estimating of the load filling level (Jc) was conducted using a power model, which in this case corresponds to the C-Model developed by (Morrell, 1993) that was calibrated by measuring the load filling levels (Jc) and balls (Jb) using the FARO laser scanning technology by means of Grind-Out and Crash-Stop procedures during the year 2013 and 2014. Finally, to estimate the dynamic filling level of full charge, Jc, three independent models were developed that allowed to feed the adjusted power model: •,SAG mill discharge grate slot wear model •,SAG mill internal volume wear model •,Ball filling level estimation model."

Jan 1, 2014

By B. McFadzean, K. Moller

"The mechanism whereby thiol collectors adsorb onto a mineral surface has been widely studied. Most of these studies examine the mineral surface at equilibrium state and, often, well above monolayer coverage. However, the formation of species at the mineral surface is a complex process that is both kinetically and thermodynamically controlled. In a typical industrial application, the dosage of collector will be around monolayer level. This study uses isothermal titration microcalorimetry to measure the heat evolved during the reaction of sodium ethyl xanthate (SEX) and sodium isobutyl dithiocarbamate (SIBDTC) and their mixtures with galena and chalcopyrite. The sensitivity of the instrument allows heats of reaction of sub-monolayer quantities of thiol collector to be measured.The study found that both the magnitude and kinetics of the reaction between a collector and a mineral surface was dependent on the type of mineral and the type of collector. Proposals are made for the reactions based on literature and the evidence from this investigation. It was found that when collectors were reacted with mixtures of galena and chalcopyrite, that the magnitude of the reaction was lower compared to that measured for the pure minerals alone. This may be due to galvanic interactions between the minerals, resulting in a passivating effect on one or both of the minerals."

Jan 1, 2014

By Wayne van Drunnick, Mervyn Ruthnasamy, Olvier Guyot, Christophe Bouché

"Anglogold’s Mponeng Mine is situated in South Africa’s North West Province approximately 80km from Johannesburg. The reefs being mined in this area are among the deepest deep level mining operations in the world. These shafts often exceed several thousand meters making these operations complex and expensive.The gold plant is fed with run-of-mine ore which is stored in mill silos. Feedrate to the mills is controlled by a variable speed belt. Three parallel SAG mills (4.85 x 9m) treat 80-100tph, operating in closed circuit. Hydrocyclones classify the mill discharge, returning the oversize to the mill feed. Cyclone feed density and pressure are measured and are used with typical control loops to determine water addition rates to the mill. Control loops at PLC/SCADA level were historically used with limited success in the control of the milling circuits. Mill control for an installation of this type used mill mass (measured by load cells) and feedrate to control throughput. An online particle size analyser (PSI) was installed to assist grind control in tandem with pressure/density control on the cyclones. Although the accuracy of the measured grind was reliable, long term consistency of the PSI could not be guaranteed. Economic pressure from the business sector requires consistent mill throughput at optimum grind conditions. Fluctuations in production targets can manifest due to inconsistent control and the lack of real-time information from the process.This sensitivity to process movements may vary between shifts and also with changes in ore competency.Whilst tools are available to improve control, few have the sensitivity to process movements to provide real-time information for optimal grind control. For this reason an Advanced Control solution was sought. Advanced Control is often described as the supervision of basic PLC/SCADA control. Advanced control systems have to seamlessly compliment the existing control strategy and bridge the gap that exists between basic control and optimised control. A solution was found in the Metso Minerals CISA’s OCS (Optimising Control System). This French designed system makes changes to process setpoints to achieve peak performance and is distinguished from others by its soft sensor capabilities. The soft sensor is an embedded module in the OCS package that can be configured to estimate values normally obtained from field instruments. Advanced control using a Fuzzy Expert System assisted by Statistical tools (such as moving averages and a Soft Sensor using Phenomenological Models) would serve to bridge that gap. Metso Minerals CISA’s OCS is a modular system with various capabilities.It was successfully used to provide on-time process information via Soft Sensors. Circuit stability was achieved using Rule Based Expert Control in complete synergy with Fuzzy Logic. Two rule-based strategies were developed for this circuit. The first uses the online product size analyser as a primary control variable. The second uses a calculated kWh/t value and a modelled mill discharge density as primary control variables. The latter had more availability than the particle analyser and is currently in use."

Jan 1, 2003

By Victor Avdokhin, Valery Morozov, Valery Stolyarov

"The adaptation-determination method provides for keeping given relationship between concentrations of ionic and molecular components of a pulp liquid and correction of parameter of the model on the basis of analysis of ore composition, technological parameters of flotation, and cost of valuable components.• optimisation program “ADDEFLOT” and combined analyzer of pulp “RA-931”An adaptation-determination method provides for two-level control of bulk and selective flotation of polymetallic ores. The lower level provides for control of reagent dosing on the base of control of ionic composition parameters in the pulp liquid phase. The control goal is to keep the basis relationship among parameters of ionic composition (ions A, B, C) in pulp liquid phase given by equations of type:• alg[A] + blg[B] + clg[C] = K (1)Values of a,b,c coefficients are uniquely determined by a physico-chemical model used. Kind of the model depends on mineral composition of an ore and reagent regime applied. As parameter of ionic composition, also values of one or two parameters (or their combinations) can be used, for instance, pH, concentration of sulfide ions, ions of collector.The upper level of control is based on calculation and use of technological results of selective flotation. At the level, an adaptation of the model (1) is conducted. A principle of the adaptation is in determining (and including in pre-setting function of the lower level) such value of K parameter, at which maximal economic effectiveness of the process is reached. As a criterion of economic effectiveness of the process, a function of losses of several valuable components, taking into account cost of the metals lost, is used. For 2-component ore, in simplified form, the function is as follows:"

Jan 1, 2003

By Gus Van Weert, Samuel A. Bolorunduro, David B. Dreisinger

"INTRODUCTIONThe objective of this work was to deport silver into a residue suitable for subsequent extraction without compromising the high base metal extraction during the pressure oxidation.RESULTS AND DISCUSSIONThe complex sulphide from the tailing pond of Cannington mine, Australia, was re-grounded and a bulk concentrate was recovered by flotation. The major economic sulphides are galena and sphalerite. The chemical analyses revealed 17.22% Fe; 4.88% Zn; 8.22% Pb; 9.49% S2- and 422 g/t Ag. The baseline cyanidation yielded 36.60% of silver at high cyanide consumption (24.17 kg/t NaCN). Pressure oxidation at 150°C (in the absence of iodide), followed by cyanidation of the residue yielded 8% silver extraction. Pressure oxidation was carried out at 110-150°C in sulphate media with additions of potassium iodide and the resulting residue was subjected to cyanidation. High recovery of silver was achieved because its incorporation into lead-hydronium jarosite during the pressure oxidation was minimised, while its deportment into the cyanide-soluble silver iodide was favoured (Figure 1). Silver recovery decreased slightly at high temperatures (140° and 150°C) because of the enhanced stability and kinetics of leadhydronium jarosite, but this could be overcome by increasing acidity and iodide concentration of the slurry."

Jan 1, 2003

By M. Pelser, Lorenzen L.

"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.A review of literature has proven that there is no conventional method for the control of calcium and or magnesium, although a number of potential processes have been identified. The technologies investigated included precipitation, ion exchange and solvent extraction, for which at least one method was found under each. To make the reader aware of these processes a short description was provided of each within the text.Of these processes, fluoride precipitation was selected for experimental investigation based on the low solubility of calcium and magnesium compared to the base metals. This process involves the addition of a soluble fluoride to precipitate CaF2 and MgF2. The experiments were designed to investigate the equilibrium of the system at varying parameters of which the level of fluoride addition, the ratio of calcium to magnesium, and the identity of the soluble fluoride was reported. In all of the instances the process showed high selectivity towards calcium and magnesium over the base metals. The experiments proofed the process to have a higher affinity towards the removal of magnesium at compositions where the molar ratio of calcium to magnesium was higher than 1:3. It is often the case that the calcium to magnesium ratio is in the region of 1: 10. From this it follows that the fluoride addition has to be stoichiometric or greater for calcium and magnesium combined, if the calcium is to be precipitated. This was demonstrated as well. On the identity of the soluble fluoride hydrogen fluoride was compared to ammonium fluoride, of which the latter was found to be preferred."

Jan 1, 2003