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By S. J. Neethling

"This paper examines the impact of several key variables on the performance of flotation cells. The study makes use of a simulator for the froth phase of the flotation vessel, as the main purpose of this study is to separate the impact of different variables from one another. In experiments it is very difficult to separate the effect of variables from one another as a change in a singe input parameter, such as air rate, invariably also affects many of the other key variables, such as bubble size and bubble bursting rates.In order to achieve this a base case simulation that is typical of many of the rougher cells found in sulphide flotation circuits was carried out. Four key variables, air rate, incoming bubble size, surface bubble size and the fraction of the bubbles flowing out of the cell unburst, were varied in order to obtain the system.s response.The most significant results were obtained when the bubble size was varied. An increase in the incoming bubble size has the effect of reducing the pulp zone recovery, but increases the froth zone recovery. If it were possible to vary the incoming bubble size without influencing the overflowing bubble size, the impact of the change would be unclear because of these two competing effects. The effect of a change in the overflowing bubble size has an opposite effect on the froth recovery, with larger bubbles resulting in lower froth recoveries.A final interesting result is that all the effects examined affect the process to a similar degree, which implies that none of these variables can be disregarded, either in industry or in further research."

Jan 1, 2003

By S. H. Morar

Froth flotation is a physico-chemical separation process that takes place in two phases; pulp and froth phase. It is widely recognised as a complex process, due to the range of interactions present within the system. Of critical importance is the role of the froth phase within the system. The pulp kinetics governs the maximum potential recovery within a flotation cell, while the froth phase governs the selectivity via the froth?s stability. Higher froth stability improves recovery at the expense of grade, and lower froth stability improves selectivity. It is well known that the two major factors affecting froth stability are attached particles and solution chemistry. This paper looks at a flotation bank at different froth depth and frother concentrations. The air recovery to the concentrate is determined at each condition and relates the effect of the operating conditions on froth stability and transport to the amount of solids that are recovered to the froth and concentrate by true flotation. The results presented show that, for a given process objective, which in this case was a consistent mass pull profile, depending on the operating conditions, solids recovery in the pulp is affected by the air rate required to maintain the target mass pull. To a smaller extent, the changes in the pulp composition affect down-stream pulp recovery. The variation in solids recovered into the froth drives the froth stability at the start of the flotation bank, while the frother drives the froth stability at the end of the bank. The performance in between these two extreme conditions arises from an interaction of these two effects. The consequences of these interactions can give rise to counter-intuitive responses that can confound efforts to optimise the performance of the bank.

Jan 1, 2014

By Reza M. Rahman

The froth phase plays an important role in the flotation and upgrading of the final concentrate. At present, the techniques that have been used in the mineral industry to measure the froth recovery have limitations. The aim of this paper is to investigate the performance of the froth in an industrial flotation cell. A unique device has been developed which is capable of decoupling the froth zone from the pulp zone. It consists of two concentric tubes. The inner tube acts as a dropback collection chamber or catcher. The particles that detach from the froth phase fall directly into the catcher and are collected as froth dropback. The froth recovery measurements were carried out in a rougher bank of a copper concentrator treating sulphide minerals. The dropback device is designed so that it can be immersed into a plant size flotation cell and plant froth recovery measurements can be taken at any given time. During the experiments, the bubbles laden with valuable mineral particles entered the device from the plant flotation cell, subsequently rising to form a froth layer at the top of the device. The particles that detached from the froth zone were collected in the dropback collection chamber whereas the concentrate sample was collected by a launder. By drying, sizing and chemical analysis of the concentrate and dropback samples, the froth recovery, was estimated on the basis of the valuable component. The effect of air rate on froth recovery was also investigated. Keywords: flotation, froth, dropback, froth recovery

Sep 1, 2012

By Marco Le Roux, Quentin Campbell

"Most coal supply contracts include strict limitations on the moisture content of the products. This limitation exists because of calorific, transport cost, and handling reasons. Managing the retention time on product stockpiles to facilitate drainage commonly controls the moisture content in coarser coal products. A large-scale pilot rig has been commissioned to facilitate research in this regard. A stockpile of about 15 tonnes of a typical washed power station feed coal from the South African Witbank coalfield was loaded onto a 6 x 6 m platform on load cells. The platform was shielded from the elements, like rain and wind, and an artificial rain sprinkler system was installed. A variety of rainfall intensities and durations were simulated and the water accumulation and run-off was measured. The material was also sampled for moisture and particle size before and after the series of tests. At the same time, the drainage characteristics of the same coal were determined in smaller scale drainage columns for comparison. Data is presented in this paper on the drainage rates, maximum accumulated moisture, final moisture, and the effect of evaporation. The results showed that for all rainfall patterns tested, drainage ceased after 2 - 3 days, but evaporation continued for at least the time period under investigation, albeit at a low rate. Evaporation contributed to dewatering at rates that depended on wind, temperature and humidity conditions. This caused a slow reduction in moisture content even after the run-off had ceased. The value of the final moisture depended on the coal PSD. It was also found that the intensity and duration of the more intense rainfall events did not significantly affect the maximum water accumulation, with drainage rates equaling the corresponding water addition rates which suggested that water ran off over the surface of the stockpile with limited penetration. During more intense rainfall scenarios, some penetration was apparent."

Jan 1, 2014

By Ljudmil S. Grigorov, Eric Forssberg, Hanumantha Rao Kota, Robert J. Pugh, Lidia B. Alexandrova

"The effects of mixed collectors on some physicochemical parameters (thin film lifetime, kinetics of expansion of the three-phase contact, equilibrium three-phase contact angle and surface tension) involved in the elementary act of flotation were investigated experimentally.We have used the microscopic thin balance developed by Scheludko et al (1970) to study the stability and interactions within the thin film between the silica surface and air bubble with (i) a long chain C10 amine and (ii) a cationic/anionic surfactant systems consisting of mixtures of a long straight C10 chain amine with long straight chain C8, C10 and C12 sulfonates at 1:1 molar ratio. The experiments were performed at a range of concentrations at pH 6.5. The equilibrium contact angle was measured with a microscope technique using the modified Mingins-Sheludko method (Mingins and Scheludko, 1979). The surface tension was measured by the method of Wilhelmy (Adamson, 1960). It was found that the mixed surfactants caused lower contact angles, lower rates of the thin film rupture and longer film lifetime, compared to the pure amine system."

Jan 1, 2003

By A. Javadi

"Our recent studies revealed that the sulfide minerals in contact with water during grinding produced hydrogen peroxide (H2O2) where the amount of H2O2 production by the minerals found to be in the order of pyrite > chalcopyrite > sphalerite > galena. The H2O2 effect on the oxidation of pulp components and its influence on the concentrate grade and recovery in flotation have been studied and the results have been presented and discussed in this paper. Studies have also been carried out to build correlation between percentage of pyrite in the concentrate, grinding conditions and concentration of OH•/H2O2 in the pulp and as well of controlling the formation of these species through known chemical means for depressing the generation of the oxidant. Flotation tests using a complex sulfide ore with the same reagent scheme that is being used at Bama concentrator in Iran but with the addition i) Na2S reductant and ii) inorganic (EDTA) and organic (TETA) surface modifiers, during grinding stage have been performed to judge the beneficial or detrimental role of H2O2 on the selective flotation of sulfides. The results demonstrate that the selectivity of metal sulfides against pyrite increases with increasing generation of H2O2 in the pulp liquid.INTRODUCTIONOur recent studies have illustrated the formation of hydrogen peroxide (H2O2) by metal-sulphides during grinding in the presence and absence of oxygen (Javadi Nooshabadi & Hanumantha Rao, 2013a; Javadi Nooshabadi & Hanumantha Rao, 2013b; Javadi Nooshabadi & Hanumantha Rao, 2013c; Javadi Nooshabadi & Hanumantha Rao, 2014). In the absence of oxygen, it was found that pyrite surface is catalytically active and able to breakdown water molecules to form OH• free radical and thereby deriving oxygen in the formation of H2O2 from water molecules. The in-situ formation of H2O2 and its influence on sulphide flotation has not been addressed yet. The presence of strong H2O2 oxidant in the pulp liquid and its selective oxidation of pyrite would be beneficial in depressing pyrite flotation. Therefore, it is important to build correlation between percentage of pyrite in the concentrate, grinding conditions and concentration of OH•/H2O2 in the pulp as well as to study possible ways of flexibly controlling the formation of these species through known chemical means for depressing the generation of the oxidant."

Jan 1, 2018

By F. K. Ikumapayi

An approach to environmental sustainability and improved process economy, in sulphide minerals production is recycling of process water in flotation of complex sulphide ores, although the chemistry of process water may be a critical issue to flotation efficiency. The influence of major components of calcium and sulphate ions in process water on xanthate collector adsorption and flotation response using pure chalcopyrite, galena and sphalerite minerals were investigated by Hallimond flotation, zeta-potential measurement, FTIR and XPS spectroscopy studies, while bench scale flotation tests were also carried out using complex sulphide ores. The impact of the species in flotation was comprehended using deionised water, tap water, process water and simulated water containing equivalent amount of calcium and sulphate species in process water. Hallimond flotation results showed a decrease of chalcopyrite and galena recovery in process water and also in the presence of calcium and sulphate ions in both deionised and process waters, whereas sphalerite does not respond to flotation. The adsorption of calcium and metal ions but not sulphate ions on the minerals is evidenced by zeta-potential data. FTIR and XPS studies revealed the presence of surface oxidized sulfoxy species and surface calcium carbonates on chalcopyrite in the presence of process water and water containing calcium ions, surface oxidized sulfoxy and carbonate species on galena in the presence of deionised water, process water and water containing calcium and sulphate ions, all at flotation pH 10.5, and these surface species influenced xanthate adsorption. The presence of surface oxidized sulfoxy and carbonate species at the sphalerite flotation pH 11.5 were seen in the presence of deionised water, process water and water containing calcium and sulphate ions, but the surface species does not influence xanthate adsorption. Bench scale flotation using two different complex sulphide ores showed that chalcopyrite, galena and sphalerite recoveries are better in process water than tap water. The studies showed that the process water can be recycled in flotation with no detrimental effect on grade and recovery of sulphide minerals. Keywords: sulphide minerals, flotation, zeta-potential, FTIR, XPS

Sep 1, 2012

By Kym Runge, Wei Huang, Fengnian Shi, Christian Antonio

"This paper presents an emerging High Voltage Pulse (HVP) technology for ore pre-treatment. Unlike previous studies where HVP was utilized as a crusher to pulverize ore particles to micron size ranges for downstream processing, the researchers at the Julius Kruttschnitt Mineral Research Centre (JKMRC) use HVP to enhance ore processability. Application of relatively low levels of HVP energy to selectively break mineralized particles from barren rocks, followed by size-based screening separation enables the feed ore to be split into high grade and low grade products. During HVP treatment, cracks/micro-cracks are generated which results in pre-weakening of the treated ore particles, which ultimately results in energy savings in the downstream comminution processes. HVP treatment followed by conventional grinding also results in improved liberation of the valuable minerals in comparison to that achieved with traditional conventional comminution, subsequently improving downstream separation efficiencies. The three major improvements in ore processability through HVP pre-treatment have the potential to facilitate rejection of low grade ore prior to processing, increase production rates, reduce the energy required for comminution and improve flotation separation recoveries. This paper summarizes the major research outcomes of HVP pre-treatment demonstrated using ores from various mining operations conducted by the JKMRC. It also discusses the barriers that must be overcome before it can be adopted by industry with confidence in a continuous high tonnage rate application.INTRODUCTIONThe challenges of declining ore grades and increased plant throughput rates, resulting in higher energy consumption and operational costs, require the mining industry to adopt new technologies to make future ore treatment economically viable. Over the past 50 years, many researchers have engaged in investigating novel comminution techniques. Since Yutkin (1955) first demonstrated the potential to generate shock waves with pressures exceeding 103 MPa via electrical breakdown of water, several applications of electrohydraulic crushing by shock waves have been reported (Curley-Macauly, 1968). Interest in this technique was bolstered when Andres (1977) demonstrated that electrodynamic fragmentation results in superior liberation of mineral grains as compared with conventional grinding techniques. Despite mounting laboratory-scale evidence of the efficacy of electrodynamic fragmentation for mineral liberation, development of the technology for full-scale operation has stalled, primarily because the energy required to achieve desirable mineral liberation is approximately two to three times that of mechanical comminution, amounting to approximately 100 kWh/t for typical mineral ores (Andres et al., 2002)."

Jan 1, 2018

By C. A. Perez

Estimation of rock composition in mineral plants is important to determine rock size and grindability which in turn may improve control of the grinding process. Variations in ore grindability and size distribution directly affects mills power consumption and throughput. Therefore, it is desirable to develop new tools to estimate rock lithological composition. In this paper, a new method for lithological classification based on machine vision is proposed. The method is based on a single video camera and employs information about texture using several different spatial scales. Texture information is extracted from rock images using Gabor filters that can be adjusted at different spatial scales and orientations. After feature extraction, rock images are classified using support-vector machine (SVM). The method was tested on a database containing sub-images of 64x43 pixels of five ore types as follows: massive sulphide (MS), disseminated sulphide (DS), net textured (NT), gabbro (G), and peridotite (P). These ore types were assigned to three grindability classes: soft (MS), medium (DS and NT) and hard (G and P). The database was divided in 2 subsets for training, cross validation, and for test. Classification accuracy is compared with previously published results on a dataset with three different classes of rocks according to their hardness. Results show that our proposed method reached significant improvements (between 13%-20%) in classification accuracy relative to previously published results. Keywords: rock classification, lithological classification, grindability estimation, Gabor feature extraction, texture features

Sep 1, 2012

By D. Pirouzan

It is customary to use more than one stage of flotation to obtain an acceptable level of separation of valuables. Flotation circuit design is usually accomplished by applying empirical rules which usually results in operations not working at their optimum conditions. Given the capabilities of genetic algorithms (GA) in finding an optimum solution in a very disturbed search spaces, they can be used to obtain the desired flotation circuit configuration. In flotation circuit configuration and optimization problem, a combination of metallurgical parameters such as yield and concentrate ash content could be used as the fitness function for the genetic algorithm. The multi-objective nature of the problem justified to use Pareto method to arrive at a set of solutions. The appropriate configuration based on technical or economical considerations could then be chosen. To obtain the fitness function for any given configuration, it is necessary to model every flotation stage. The proposed method was used to find the optimum circuit configuration for a coal washing plant. The objective was to arrive at the highest yield while producing a concentrate with a certain ash content (< 11%). The feed to the flotation circuit was characterized based on the size fractions and their flotation rate constants. Results showed that with a 95% confidence, the absolute difference between the modeled and measured values were 2.9-5.5% for yield and 0.4-1.1% for concentrate ash content. When the proposed GA-based circuit configuration was implemented in the plant, the yield increased from the original value of 57.6% to 65.7% while producing concentrate ash content (10.9%) within acceptable limits. By adding one stage to the current three-stage circuit, it was predicted that the yield could further increase by 3.8% while keeping the quality of the concentrate within the appropriate level. Keywords: modeling, optimizing, flotation circuit configuration, genetic algorithms

Sep 1, 2012

By A. V. Byvaltsev

Adsorption of cyanide complexes of gold, silver, copper, mercury, nickel, cobalt, iron, zinc and cadmium has been studied. Adsorption isotherms of the mentioned metals from individual solutions for different free cyanide concentrations have been obtained. Values of the constants of Freundlich isotherm equation have been calculated. Metal cyanide complexes affinity to activated carbon was determined.

Jan 1, 2014

By L. C. Zhou

The floatability of andalusite and associated minerals are studied and their action mechanisms of andalusite and associated minerals with collector alkyl benzene sulphonate are also studied. Through the mensuration of electrical potential and the infrared spectroscopy, as well as desorption tests, it is confirmed that the interaction of andalusite with sodium dodecyl benzene sulphonate (SDBS), is in addition to physical adsorption, but also is chemical adsorption. The study results of the pure minerals are used for the flotation of actual andalusite mineral. By flotation from contain-ing 45.68% andalusite ore, the fine andalusite concentrate is gained which Andalusite grade is 85.88%, containing Al2O355.29% and Fe2O3 less than 1.5%.

Jan 1, 2014

By M. Eraydin

Dewatering fine particles (e.g., flotation concentrates) is inefficient, energy intensive and often requires large capital and operating costs. To address these issues, a series of advanced dewatering technologies have been developed at Virginia Tech. These include novel dewatering aids and a hyperbaric centrifuge. Typically, the moistures obtained using these methods are 30% to 50% lower than those obtained using conventional methods, as demonstrated in laboratory and pilot-scale test programs. With another novel dewatering technology that has been tested in bench-scale tests, the moistures can be reduced to levels once believed to be attainable only through the use of thermal dryers. In this communication, test results obtained with these advanced dewatering technologies are presented and compared.

Jan 1, 2014

By Ingvar Ymén, Alexandra Lundmark

"The depressive effect of dichromate on galena was evaluated with chemical experiments and small-scale depression experiments at a pH of around 12. The depressive effect was measured with Dynamic Vapor Sorption (DVS), which measures the water uptake of a sample as a function of the % relative humidity. The depression is due to PbCrO4PbO, which in the presence of Ca2+ and SO4 2- forms a more or less amorphous solid solution (Pb,Ca)(CrO4,SO4)PbO, which clogs to the surfaces of the ore. Free Pb2+- ions are needed for depression to occur and at high pH Pb2+ - hydroxide complexes, supply enough Pb2+ - ions to precipitate (Pb,Ca)(CrO4,SO4)PbO. In air CO2, precipitates CaCO3 which slowly lowers pH, precipitating more (Pb,Ca)(CrO4,SO4)PbO and CaCO3 on galena. Similar experiments where performed with five alternative depressors whereof phosphate, which forms an amorphous precipitate of approximate composition Pb3Ca13(PO4)10SO4, gave the best results. Phosphate was tested in laboratory scale flotation experiments giving encouraging results.INTRODUCTIONWithin Boliden Mines, concentrating of copper and lead from complex sulfide ores is performed by bulk flotation, meaning that copper and lead are concentrated in the same product. Downstream, copper and lead are separated by flotation of chalcopyrite, and depression of galena. Boliden has for many decades used sodium dichromate to depress galena (reference 1). Dichromate is both toxic and carcinogenic and Boliden has for many years investigated several alternatives. So far, however, the best results have been obtained with dichromate. Since Boliden has tried to substitute dichromate for a long time without finding a process as effective, Boliden decided to clarify the function of dichromate in the depression of galena and on the basis of the outcome find alternative depressors with similar function. This study was given to RISE Bioscience and Materials / Surface, Process and Formulation as a consultancy assignment. This paper presents the outcome of the combined efforts of Boliden and RISE."

Jan 1, 2018

By V. A. Luganov

Methods of treatment of pyrite concentrates differ, depending on the content of pyrite and non-ferrous metals: oxidation roasting, sulphatization roasting, smelting, direct hydrometallurgical treatment and so on. Existing technologies do not provide for high recovery of metals, expenses associated with existing technologies are high, and environmental issues, associated with the existing technologies need serious attention. We have developed universal technology of the activating-dissociating autogenous roasting of pyrite concentrates using air based, or air, enriched with oxygen, blow. The basic process is taking place in accordance with the following reaction: (1-x)FeS2 + (1-2x)O2 = Fe1-xS + (1-2x)SO2 +Q The products of this reaction are pyrrhotinized cinder and roasting gases, rich in SO2 (up to 18 % in case of air blow) and poor in SO3, that contain up to 1 % of elemental sulphur. Cinder contains different forms of pyrrhotite. These forms of pyrrhotite differ by its content (from Fe0.843S to Fe0.945S), thermodynamic, magnetic (from 4.10-1 to 3.6 SI units), flotation properties (with pyrite dissociation the ?-potential of the product is moving towards more electrically positive charge, from 0.95 for pyrite to 0.2 for dissociation products) and other properties that depend on the conditions of roasting. The combination of pyrrhotizing roasting with different methods of cinder treatment allows to increase the level of sulphatization of non-ferrous metals during the roasting; reduce the amount of blow used during the processing; reduce dust losses to the gas phase; reduce the capacity of gas cleaning system and increase resistance to corrosion of the gas-treatment system, used for the production of sulfuric acid from pyrites. This combination of treatments also allows to use magnetic separation and flotation for separation of ferrous and non-ferrous metal compounds during cinder treatment; perform de-arsenation of arsenic containing concentrates and by-products. Pyrrhotinized cinder may be treated by oxidizing and non-oxidizing hydrometallurgical methods. Keywords: Pyrite, polymetallic ores, sulphidization roasting, pyrrhotite, magnetic separation, arsenic sulphide

Sep 1, 2012

By Chuanyao Sun, Longli Liu, Fayu He, Guiye Wu

Utilizing thioglycolic acid (TGA) as a template and using structure-guided design, a molecular modelling approach has been used to design and screen appropriate dispersant for chalcopyrite. A series of organic dispersants based on a TGA substitution with hydroxyl and amino and sulfonic functional groups have been examined on chalcopyrite surface. 20 organic depressors of chalcopyrite have been investigated to study the quantitative structure-activity relationship (QSAR) of chalcopyrite depressors. For the chalcopyrite surface, depressor containing carboxyl and sulfonic group is generally stronger than the depressor containing hydroxyl group. Increasing the number of hydrophilic group can effectively enhance the inhibition. Increasing the number of Solidophilic group does not necessarily lead to enhanced inhibition ability; steric factor is one of the important factors to affect the interaction. Extension alkyl carbon chain length cannot enhance the interaction of depressors. Isomers principle as well as applies to the chalcopyrite depressor molecular design. Flotation verification tests further confirmes the accuracy of the molecular simulation. Through the Computer Aided Molecular Design (CAMD) technology, we can save enormous time and resources to design novel surfactants. This research and application will play a great significance role in sulfide flotation.

Jan 1, 2014

By Andrzej Wieniewski, Cezary Regula, Bozena Skorupska, Krystian Cichy

"In this paper, experiences from Polish non-ferrous metals ores enrichment plants in the copper and blende concentrates quality improvement are discussed. The blende concentrate being produced in ZGH Boleslaw S.A., with Zn content of about 54,5% is characterized by the relatively high magnesium content reaching a level of 1% resulting from the dolomite presence, while for the zinc production by electrowinning a concentrate in which magnesium content should not exceed 0,3% is required. The implemented new technology for the quality improvement of blende concentrate is based on the leaching of zinc concentrate with sulfuric acid aimed at dissolving of the contained dolomite, and then flotation of the leached concentrate. It allows to obtain a concentrate with magnesium content below 0,1% at the simultaneously increased zinc content to about 57,5%. In the paper, laboratory tests results on the development of optimal flotation flowsheet for the gypsum removal and the industrial tests results concerning the process optimization of this flotation are discussed. In turn, the copper concentrate being produced in Polish copper ore enrichment plants KGHM PM S.A., is characterized by the increased organic carbon content - above 8%. It creates problems with the smelting of this concentrate because of difficulties with the heat removal derived from the combustion of organic carbon in the flash smelting process. The implementation of segregating flotation to the industrial practice allows the effective production of two concentrates with the differentiated chemical compositions - a concentrate with increased copper content and reduced organic carbon content for the flash smelting process, and a concentrate with lower copper content and increased organic carbon content for the shaft smelting process. In the paper, conditions of the segregating flotation and the achieved results are described."

Jan 1, 2014

By Zhiyong Gao, Ruiying Fan

"Crushing and grinding are the prerequisite processes in many industries, such as minerals processing and powder technology. During crushing and grinding, minerals will cleave or fracture along the directions by broken the interlayer bonds (e.g., ionic bonds), generating some commonly exposed surfaces. The broken (or dangling) bonds at the generated surface makes the surface more active and determine the reactivity of the surface. In this work, the population of broken (or dangling) bonds on commonly exposed surfaces of fluorite mineral (a chosen model mineral) was calculated. Based on the calculated broken bonds information, the anisotropic surface reactivity of fluorite such as surface energy, surface relaxation, dissolution, wettability, surface charge and adsorbability, were discussed. The results show that the surface broken bonds density, which is positively related to the surface energy, can be used to predict the cleavage nature, surface relaxation degree and surface stability of fluorite crystal. The distribution characteristic and the number of broken (or unsaturated) bonds of surface active atoms (like Ca for fluorite crystal) can be used to predict and explain the anisotropic wettability, surface charge and adsorption mode and strength of organic molecules on different commonly exposed surfaces. It is easy to conclude that the calculation of surface broken bonds can serve as a fast and accurate way to start the mineral chemistry studies. These findings will be helpful to the mineral/material chemistry research in related interfacial science communities.INTRODUCTIONGrinding for mineral liberation is a prerequisite for a successful flotation separation. Also grinding for size reduction is a prior process for a favorable powder technology. During the grinding process, the minerals / materials will cleave and fracture along certain crystal directions with relatively weak interlayer chemical bonds1 to form a number of common exposed surfaces. Exposed surfaces are the outer boundary of a solid substance. In the mineral / material block, the bonding orbital of the atoms is filled with electrons and the atoms are in a steady state. Atoms on these exposed surfaces appear to show dangling bonds (or broken bonds) by losing chemical bonds to adjacent atoms in the previous block. Therefore, surface broken bonds serves as an initial property of a fresh surface. The lattice arrangement and crystal orientations causes differences in the number of dangling bonds on each exposed surface, i.e., anisotropic surface broken bonds2. The anisotropic dangling bonds enable the exposed surfaces to show varying degrees of surface reactivity (including surface energy, surface charge, surface relaxation, dissolution, wettability and adsorption behavior), known as anisotropic surface reactivity."

Jan 1, 2018

By Tiago de Souza, Caroline Gonçalves, Carlos Eduardo de Castro, Everton Dias

The Miraí plant from Votorantim Metais, has two screening stages to the bauxite classification after scrubbagem. The final product has hold the larger size of 0,84 millimeters (20 mesh). There are two sieves Haver & Boecker (model R-TE 3658 x 10972), which have four modules with cut size sieves of 10 mesh (1.70 millimeters) and ¼ inch (6.35 millimeters) on the primary screen, and 20 mesh (0.84 mm) on the secondary screen, all made of polyurethane. The actual configuration was established according to the empirical tests realized that aimed the increase material load on the secondary screening. However, having in mind the screening process improvement and use the fractions smaller than 0,84 mm, which have significant levels of Alumina and low reactive silica, was proposed a new test of change the sieves opening for 6 mesh in the primary screen and 28 mesh for the secondary sieve. The objective of this work was measure the ore alterations on the particle size distribution on the screening steps, increasing the plant weight and ratio recovery before and after the test.

Jan 1, 2014

By M. Saba

In cyanide leaching procedure, achieving an acceptable efficiency for silver and gold is very time-consuming, thus, enough studies have not been performed for optimization and modeling of this process. The kinetics of cyanide leaching includes two steps: first step comprises a sharp slope while the other has a slight increasing trend. In the present study, in order to reduce the time and cost, the cyanide leaching process of a sulfide silver/gold ore was optimized in the first period. The applied parameters and their ranges are: temperature 20-40 (°C); time 1-8 (hrs); cyanide concentration 1-2 (mole cyanide / mole Cu); the percentage of solid to liquid 1-2 (%) and pH 10-12. For design of experiments fractional factorial 2(5-1) was used. Also four center points were applied to increase the accuracy of the model. In addition, by analysis of variance (ANOVA) the most effective parameters were identified and the optimized condition was determined. A regression model was proposed to describe the effects of independent variables and their interacting role on silver recovery. Results showed that the model was linear for silver and nonlinear for gold. In the gold recovery process, the two important parameters are time and pH with the former being more effective. Due to the existence of cyanide ions in the medium, temperature and cyanide concentration have less influence in the gold recovery process. Solid to liquid ratio, in addition, comprises a slight negative impact on the procedure. This emphasizes the different kinetics of silver/ gold cyanide leaching. Finally, using the optimum condition the amount of silver and gold obtained were 61% and 67% in 8 hours, respectively. While in general conditions, the results were 37% and 54% in 24 hours, respectively. Keywords: cyanide leaching, refractory gold/silver ore, modeling, optimization

Sep 1, 2012