International Journal of Mineral Processing

Published by Elsevier
Online ISSN: 0301-7516
Publications
shows the reduced Kynch batch flux density functions f and logarithmic plots bk Ž. of the effective solid stress functions s f corresponding to the four experimental e studies considered in this paper. Ž. Ž. An immediate consequence of Eq. 6 is that Eq. 1 is a first-order hyperbolic partial Ž . differential equation PDE for f F f and f s f and a second-order parabolic PDE
Article
In one space dimension, the phenomenological theory of sedimentation–consolidation processes predicts the settling behaviour of a flocculated suspension in dependence of two constitutive material-specific functions, the Kynch batch flux density function and the effective solid stress. These functions depend only on the local solids concentration. In this paper, we determine these functions from published data of several experimental studies. The mathematical model is then solved numerically making use of these functions. The numerical results are compared to the respective measurements. General good agreement between numerical and experimental data confirms the validity of the phenomenological theory.
 
Article
Based on a numerical method introduced by Bürger and Karlsen [J. Eng. Math. 41 (2001) 145], a software was developed for the simulation of batch and continuous thickening. The paper recalls the application of the phenomenological theory of sedimentation–consolidation processes to batch settling and continuous thickening of flocculated suspensions. The software presents two alternatives, one for each of these possibilities. For batch thickening, the initial and critical concentration and the height of the initial suspension must be entered together with the parameters of the flux density function and the effective solid stress. The output is a settling plot showing as many lines of constant concentration as requested and a plot of the concentration profile for selected times. For continuous thickening, only the steady state is simulated. The input is the solid feed flux and the required underflow concentration or volume underflow rate. If the thickener area is known, the capacity and the concentration profile in the equipment can be predicted. On the other hand, if the capacity is known, the required settling area and the resulting concentration profiles are predicted. Several examples show the application.
 
Article
A new method based on cone-beam X-ray microtomography is described for direct determination of the three-dimensional liberation spectrum of multiphase particles 100 microns in size or less. Such a technique may provide the basis for more detailed and accurate liberation analysis in the 21st century. Previous research had demonstrated the ability to use traditional medical X-ray CT scanners to determine the liberation spectrum of coarse coal particles of 1 cm in size (washability analysis). Rather than stacking a series of two-dimensional slices for volumetric imaging as is commonly done in traditional medical computed tomography, a three-dimensional reconstruction image array is prepared directly from the two-dimensional projections for cone beam geometry. The advantage of high spatial resolution (approximately 15 μm) with a microfocus X-ray generator combined with the benefit of direct processing of three-dimensional data, provide an excellent opportunity to overcome many of the limitations of current polished section techniques being used for the liberation analysis of multiphase particles.
 
Article
The interaction mechanism of sodium-diisobutyl dithiophosphinate (DTPINa) with galena and pyrite was investigated using zeta potential, microflotation and FTIR measurements. To evaluate metal ion effects on both minerals, sulfides were conditioned in both water solutions and solutions containing Pb2+, Fe2+ or Fe3+. Results show that sodium-diisobutyl dithiophosphinate adsorbs onto galena and pyrite by a chemisorption mechanism. Collector shows a pronounced affinity toward lead species, either in the mineral lattice or adsorbed on the mineral surface as metal-hydrolyzed species. Pb-ions adsorb onto pyrite, thus promoting collector adsorption and a decrease in selectivity. DTPINa shows less affinity toward iron species.
 
Article
The influence of silver and iron concentration and the presence or absence of oxygen was investigated in the silver-catalyzed chalcopyrite leaching. The leaching tests were performed at two different temperatures (35 and 68 °C) in stirred flasks (180 rpm) containing 0.5 g of mineral and 100 mL of Fe3+/Fe2+ sulphate solutions at pH 1.8 and at an initial redox potential of 500 mV vs. Ag/AgCl. The addition of a great excess of silver favoured the transformation of chalcopyrite into copper-rich sulphides, such as: covellite, CuS, and geerite, Cu8S5. These sulphides prevented the formation of CuFeS2/Ag2S galvanic couple and, thus, the regeneration of silver. In addition, oxygen in solution plays a key role in the regeneration of silver ions acting as the main oxidizing agent for Ag2S.
 
Article
Variability in the chemical composition, textures and electrical properties of the major sulphide mineral pyrite may be one cause of variation in the flotation and leaching properties of different sulphide ores. This report summarises the results of a review that has been conducted to establish the range in variability of natural pyrite with regard to chemical composition, texture and electrical properties.The S/Fe ratio in pyrite is generally very close to 2, suggesting that stoichiometric variability is small in this mineral. However, minor deviations from the ideal are reported. Pyrite typically contains a host of minor and trace elements, including: Ag, As, Au, Bi, Cd, Co, Cu, Hg, Mo, Ni, Pb, Pd, Ru, Sb, Se, Sb, Sn, Te, Tl and Zn. Minor elements are often present within the mineral lattice at levels up to several percent, these include; As, Co, Ni, Sb and possibly Cu, Ag, Au and Sn. Arsenian pyrites may contain up to 10% As, and such specimens are typically rich in other minor and trace elements, particularly Au. As-rich pyrites typically appear to have formed at relatively low temperatures and often exhibit habits that suggest rapid precipitation; these As-rich pyrites may be metastable and, therefore, relatively reactive.Considerable variation has been reported in the semiconducting properties of pyrite. Natural pyrites are either n- or p-type semiconductors and reported conductivities vary by four orders of magnitude. The rates of galvanic processes in mineral pulps are likely to vary with the mineral conductivities. Typically p-type pyrites exhibit low conductivities and are As-rich and are suggested to have formed at relatively low temperature, whereas relatively highly conducting n-type pyrites are typically As-poor and suggested to have formed at high temperature.Based on comparative measurements of rest potential, iron pyrite is the most electrochemically inert of the common sulphide minerals, with a rest potential of the order of 0.6 (cf. sphalerite and galena with rest potentials of 0.46 and 0.40 V. vs. SHE, respectively). Variability in the rest potential of different samples of this mineral are generally small. However, based on the extent of pyrite reaction during a peroxide dissolution procedure, the chemical reactivity of pyrite samples may differ significantly.
 
Article
Previous studies have suggested that the extraction of copper by hydroxyoxime extractants involves mass transfer with chemical reaction. This paper reports the results of experiments where an aqueous copper solution (4.94 g dm−3 copper, 5.26 g dm−3 H2SO4) is contacted with a 5% v/v LIX 64N solution in Escaid 100, in a diffusion cell with a stagnant interface. The concentration-distance distribution of the diffusional band of copper complex which appeared in the organic phase was measured at various times, and the results can be modelled by equations based on diffusion about an interface with and without interfacial resistance.If the previously measured diffusion constants for copper in the aqueous and organic phases were used in the model, then an unrealistically high resistance (200,000–300,000 s cm−1) would have to be chosen to obtain a correlation. If a low resistance (1,000 s cm−1) is assumed and the previously measured diffusion constants for copper in the aqueous phase (5.2·10−6 cm2 s−1) and copper in the organic phase (5.0·10−6 cm2 s−1) are taken, then it is necessary to reduce the organic phase diffusion constant to 2·10−6 cm2 s−1 to obtain correlation of the model with the data. It is proposed that as the organic product film develops, the diffusivity of the copper complex is reduced.
 
Article
The mechanism of copper-activation of sphalerite was studied at pH 9.2. The study was conducted using a carbon matrix composite (CMC) electrode containing sphalerite particles. Rest potential measurement and voltammetry experiments conducted on the CMC electrodes showed that a CuS-like activation product was formed when the electrode was activated in 10−4 M CuSO4 solutions at open circuit. When the electrode was activated at lower potentials, a Cu2S-like activation product was formed. Sphalerite activated under slightly oxidizing conditions produced hydrophobic species on the surface, possibly copper polysulfides.
 
Article
A review is given on general characteristics of corrosion and wear processes in both wet and dry environments. Laboratory methods for corrosion and wear studies are also reviewed including a detailed account of a jet slurry impingement apparatus used by Pitt and Chang at the University of Utah to study grinding ball metal corrosion-wear processes. Workers in the field have found that corrosion-wear processes are highly complex and subject to a great number of experimental variables such as load, pH, oxygen partial pressure, relative hardness of two interacting surfaces, impact and nature of the protective film formed on the metal surface. Effects of interactions of particles and surfaces under varying conditions are discussed. Synergistic effects between corrosion and wear are also discussed. Larger particles, higher impingement velocities and more corrosive conditions tend to increase the synergism between corrosion and wear. Methods of decreasing the corrosion rate in grinding mills are discussed along with the role that laboratory tests can play in preventing corrosion and wear of the ginding media.
 
Article
Flotation behavior of apatite and dolomite, both of crystalline and sedimentary varieties, was studied using an octadecylamine-kerosene mixture. In a single mineral flotation, dolomite floated better than apatite. When dolomite was mixed with apatite and conditioned at high-percent solids, apatite floated preferentially to dolomite. Pulp density in conditioning played a role in inducing the selectivity of separation. Crystalline and sedimentary minerals behaved alike, but the crystalline minerals had much lower surface areas and consumed less collector than the sedimentary minerals. Both minerals approached respective equilibrium pH values upon addition of acid or alkali. Their flotation behaviors were relatively insensitive to the pulp pH. Electrophoretic mobility measurements suggest that the electrostatic model of adsorption of aminium ion in these minerals may not fully account for the foregoing flotation behavior.
 
Article
Laboratory results of marked-ball wear tests are used to discuss the relative significance of corrosive and abrasive wear in wet grinding. The electrochemical mechanism was investigated by correlating the corrosive wear with the corrosion current obtained from polarization curves under abrasion. Slurry rheology governs the manner in which ground slurries coat grinding balls, thereby influencing not only the grinding efficiency but also abrasive wear. The effects of percent solids and a grinding aid are illustrated.
 
Article
The adsorption characteristics of polyacrylamide flocculants on kaolin surface have been studied at 25 °C as a function of concentration in the presence and absence of surfactants. The adsorption density of flocculants corresponding to maximum settling rate (Γoptfloc) and minimum value of specific resistance of the cake to filtration (ΓminSRF) have been computed and compared with the adsorption density for monolayer coverage (Γ∞).It has been established in this study that the optimum flocculant concentration for the highest settling rate corresponds to about 50% coverage of the solid surface (i.e. Γoptfloc≈Γ∞/2) for untreated as well as surfactant-pretreated kaolin. Flocs suitable for filtration and dewatering are obtained by flocculation of either untreated or surfactant-pretreated kaolin. But in each case, the requirement of polymer concentration for achieving the minimum specific resistance to filtration (SRF) is sufficiently lower than that required for optimum flocculation. The adsorption density of polymer corresponding to minimum SRF is less than about 25% of the plateau adsorption (i.e. ΓminSRF≈0.25 Γ∞). This has been found to be valid for flocculation with any of the anionic, cationic or nonionic polyacrylamide flocculants used in this investigation.
 
Article
Mass balance equations for the species present in the galena-ethyl xanthate system have been derived in terms of the appropriate equilibrium constants and solved to determine not only the concentrations of the dissolved species, but also the weight(s) of the solid(s) present at a given Eh and pH. The computations have been carried out for potassium ethyl xanthate (KEX) additions of 0, 10−7, 10−6, 10−5, and 10−4 moles/l, and the results have been used to generate: (1) plots of the equilibrium concentrations of the various dissolved species as a function of pH at a given Eh; (2) Eh-pH stability diagrams for each xanthate addition; and (3) plots of the amounts of lead xanthate and/or dixanthogen formed as functions of Eh and pH. In addition, the results have been used to quantitatively explain the anodic dissolution of galena in acidic conditions.
 
Article
Electrochemical behaviour of chalcopyrite was investigated in collectorless condition and in the presence of dithiophosphate (DTP), which is a selective collector for chalcopyrite, by cyclic voltammetry (CV) study. Diffuse Reflectance Infrared Fourier Transformation (DRIFT) spectroscopy was employed to identify surface species of DTP at chalcopyrite surface. CV tests established the certain degree of irreversibility in the absence of DTP possibly due to preferential dissolution of iron ions in slightly acid solution, and irreversible surface coverage by iron hydroxides in neutral and alkaline solutions. Cu(DTP)+(DTP)2 formation as major DTP-compounds on chalcopyrite in slightly acid and neutral conditions was estimated from DRIFT spectroscopy study. However, heavy surface oxidation inhibited the identification of collector species in alkaline condition.
 
Article
The chemical composition of galena, sphalerite and pyrite surfaces has been analysed after dry and wet grinding, and after treatment with water and aqueous solutions of potassium alkylxanthate by means of Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. The total metal concentration in the aqueous phase has been determined by means of atomic absorption spectrophotometry. The reaction between aqueous galena slurries and ethylxanthate ions has also been studied calorimetrically. In the reaction between oxidized galena and alkylxanthate ions in aqueous solution solid lead(II) alkylxanthate is formed on the surfaces. The formation takes place via dissolution of soluble oxidation products of galena on the surface followed by the precipitation of solid lead(II) alkylxanthate. It has been shown that lead(II) alkylxanthate is formed as the only detectable alkylxanthate species on the surface. Chemisorbed complexes of ethylxanthate ions are formed on sphalerite surfaces in aqueous and acetone slurries. The ethylxanthate ions are coordinated to zinc(II) ions in the outermost surface layer of sphalerite. Dialkyl dixanthogen is formed as the only surface species in the reaction between oxidized pyrite and aqueous solution of potassium alkylxanthate. Adsorbed oxygen and iron(III) have been excluded as possible oxidation agents. The oxidation products of the disulfide ion in pyrite, e.g. S2O72− and S2O82−, are instead proposed to be responsible for the oxidation of alkylxanthate ions to dialkyl dixanthogen. The formed diethyl dixanthogen is physisorbed on the surfaces of pyrite.
 
Article
The technique of fluorescence REFLEXAFS was used to examine the activation by copper of sphalerite, ZnS, and the subsequent interaction with a xanthate collector at pH 10 and 12. ZnSe was used as an isostructural analogue of ZnS to avoid the contribution from the xanthate S on the mineral surface being swamped by that from the substrate S. On activation, the copper interaction with the Se or S atoms is clearly seen and Cu–O bonds are formed. On the addition of xanthate, the oxygen is displaced by sulfur and a covellite-like species develops at the surface. The iron at the surface in natural sphalerites is bonded to oxygen, inhibiting initial copper activation but appears to catalyse covellite formation on xanthate addition. The technique succeeds in producing direct structural information, providing information complementary to other investigative techniques.
 
Article
Wet grinding is a nonlinear process and hence, estimation of breakage rates based on the linear model cannot be strictly used. Also the use of a functional form for breakage rates in an estimation scheme can produce artificially unrealistic values. In this study a technique for estimation of breakage rates for all size classes is investigated without imposing any functional form. A method known as the G-H scheme is used for estimation. A natural spline-interpolation technique is used to generate short time grinding data based on real experimental data obtained for relatively long grinding time intervals. Using natural spline techniques combined with the G-H scheme, acceleration or deceleration of breakage rates of all individual size classes in wet grinding is determined when the grinding environment is varied.
 
Article
This article examines the business practicality of integrating an environmental management system (EMS) into mining and related operations, describes how it can contribute to cleaner production (CP) in the industry, and provides guidelines to facilitate implementation. An EMS, which is the component of the overall management system that includes organizational procedures, environmental responsibilities, and processes, can help a mining company comply with environmental regulations, identify technical and economic benefits, and ensure that corporate environmental policies are adopted and followed. To date, a number of multinational (mining) corporations—namely, the companies with economical and technological flexibility—have implemented comprehensive EMSs at sites, the key in such cases being the formation of working partnerships with administrative bodies and international organizations. A number of other mine sites worldwide, however, despite having important environmental management practices such as audits and policies in place, have received insufficient assistance and/or simply lack the requisite resources to integrate an effective EMS into operations. The article sketches a series of guidelines for mining companies keen on adopting comprehensive EMSs at sites, and argues that to facilitate widespread EMS implementation throughout the industry, expanded inputs are needed from governments, international environmental organizations, educational facilities, and the companies themselves. More specifically, regional governments must provide assistance to the more resource-deficient operations, local universities must provide the necessary EMS educational assistance to local miners and finance environmental technology demonstration projects, and international organizations must help disseminate valuable EMS information to mine managers and technical staff.
 
Article
This paper summarizes the theoretical and experimental contribution of the authors towards the complicated problem of separating carbonates from phosphate ores by flotation. A concise review of the previous work is presented. A detailed thermodynamic analysis of the phosphate-carbonate-water system is carried out. This analysis shows that it is possible to float carbonates from phosphates in acidic media using an oleate collector in the presence of phosphate and calcium precipitating and complexing ions. The theoretical concepts are confirmed experimentally using pure samples. Three calcitic-dolomitic phosphate ores are successfully upgraded by flotation in acid medium as an application to this systematic thermodynamic analysis.
 
Article
Xanthates are used in the flotation of sulfide ores although their aqueous solutions are not stable under certain conditions. Their stability in acidic and weakly acidic aqueous solutions was therefore investigated, as these media are required for some processes.The peak absorbances of ethylxanthate ion and carbon disulfide were first determined in aqueous solution. The decomposition of ethylxanthate ion was analyzed by measuring variations in absorbance (at 301 nm) and pH with respect to time. A pH regulation system was then used while measuring variations in absorbance and productions of protons caused by xanthate decomposition.The results concerning xanthate half-lives show good agreement with the literature, but the kinetic results deviate substantially. The following relation was obtained for half-life: We established that ethylxanthate decomposition at pH 4 is a first order reaction with respect to ethylxanthate concentration, and postulating this order to the other pH values, the following kinetic relation was found: where v is the rate of decomposition (mol l−1 min−1), and [EtX−]∞ is the ethylxanthate concentration when the decomposition equilibria are reached (mol l−1). The better concentration was found to obey the law:
 
Article
The present understanding of the surface chemistry of acidic ferric sulphate dissolution of chalcopyrite is critically reviewed with regard to hindered dissolution and how the hydrometallurgical limitations, especially for microbial heap leaching operations, might be overcome. In particular the surface science investigations of what surface phases might be responsible for hindered dissolution are reviewed. Some other mechanistic issues are also considered which require further investigation. The possible phase candidates for hindered dissolution are examined, with most discussion focussed on elemental sulphur and jarosites. Phases such as polysulphides are rejected as candidates. The physical reality of metal-deficient sulphides is also questioned.A conceptual 4-stage model is proposed which explains all the general dissolution behaviour that is widely observed, i.e. of an induction period and a parabolic rate curve that may or may not be followed by linear rate behaviour. The general conclusion is that thick over-layers of sulphur cause the initial parabolic behaviour, and a thin systemic sulphur layer is responsible for the rate-limiting step, even in the linear region. Depending upon solution conditions, either unhindered near linear dissolution may occur, or jarosite precipitation that will cause a second parabolic region. Sulphur formation remains a systemic phase in the context of heap bioleaching but is not a problem of any consequence for mixed culture systems unlike jarosites. Suggestions are made as to a low-cost jarosite precipitation pond for iron removal and advantages that could result.
 
Article
During the activation of zinc sulphide with the heavy metal ions CuII, CdII and PbII, metal-ion uptake follows a logarithmic dependence on time. A reaction mechanism is proposed which is consistent with experimental observations. Incident radiation has a strong influence on the activation reaction, an effect which is interpreted in terms of semiconductor theory.
 
Article
Presence of sulfide minerals in flotation tailings poses an environmental threat due to enhanced acid formation and heavy metal ion dissolution. ‘Acidithiobacillus’, group of microorganisms, play a significant role in acid generation from sulfide-bearing tailings through microbial oxidation of associated pyrite and other sulfide minerals. Removal of sulfide minerals from abandoned tailing dams holds the key for environmental protection. In this paper, the role of some Acidithiobacillus group of bacteria such as Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans in the removal of pyrite, chalcopyrite and sulfur from tailing substrates such as quartz is discussed. Surface chemistry of the above microorganisms is illustrated with respect to interaction with pyrite, chalcopyrite, sulfur and quartz. Dispersion and flocculation behavior of the above minerals before and after interaction with the above microorganisms was studied. Surface hydrophobicity and hydrophilicity of the above minerals were also assessed with respect to selective flocculation. Separation of sulfides from quartz through selective flocculation/dispersion was achieved through prior biotreatment.
 
Article
This paper discusses the selective depression of pyrite from chalcopyrite and arsenopyrite by biomodulation using Acidithiobacillus ferrooxidans under natural conditions of pH. The effect of bacteria–mineral interaction on the surface charge of mineral and bacterial cell was studied by microelectrophoresis. Adhesion experiments were conducted to establish the relationship between cell adhesion to specific minerals and the electrokinetic behaviour of the minerals subsequent to interaction with cells. Effect of bacterial interaction on the xanthate-induced flotation of all the minerals was assessed. Adhesion of A. ferrooxidans on pyrite was rapid and tenacious and subsequent to interaction with cells, pyrite remained hydrophilic even in presence of xanthate collector. The collector, on the other hand, was able to render good flotability to chalcopyrite even after interaction with bacterial cells. Copper activated arsenopyrite was able to retain its hydrophobicity in presence of cells due to poor attachment kinetics of cells to the mineral surface. Thus, by suitably conditioning with the cells and collector, it was possible to effectively depress pyrite from chalcopyrite and arsenopyrite.
 
Article
An economical process for recovering nickel from large quantities of low grade laterite is needed. With this in mind heterotrophic microbial leaching was investigated as an alternative to the energy expensive existing extraction process. Organic acids were screened for the ability to solubilize nickel, iron and cobalt from laterite ores and the results compared with sulphuric acid treatment of limonite type laterite at pH 2.3 and 28°C which solubilized nickel, cobalt and iron. Citric, tartaric and pyruvic acids significantly increased the yield of soluble nickel extracted at pH 2.3 with sulphuric acid. Despite their reported efficacy for other mineral systems, lactic, glycollic and oxalic acids were not effective solubilizers of nickel from Indonesian laterite and 2-ketogluconic, lactic and glycollic acids did not effectively solubilize nickel from West Australian laterite.Metabolites generated from glucose by the natural flora of limonite type laterite ore were associated with significant solubilization of metals from the ore at acid pH due to their chelating activities. The leaching solutions generated from glucose retained activity when recycled, an important consideration if the solution is to have industrial application.The leach liquors from these studies were analyzed for the extent of metal extraction and the presence of microbially produced metal chelators. Cellulose acetate electrophoresis provided proof that chelated nickel complexes were present amongst nickel ions solubilized at acid pH by metabolites of glucose generated by the natural flora of the ore. This technique also provided proof that citric acid functions as a chelator of divalent metal cations at strongly acid pH, a point hitherto the subject of conflicting reports in the literature. Atomic absorption spectrometry and X-ray diffraction studies confirmed the findings from cellulose acetate electrophoresis.
 
Article
The mechanism of the action of sodium silicate in the flotation of phosphate was investigated by studying the nature of the silicate species both in solution and on the mineral surfaces and the influence of the silicate species on the flotation performances of the valuable mineral (apatite) and the gangue mineral (hematite). Two models of equilibria were used to calculate the distribution of silicate species in solution. The first was based on monomers and tetramers and the second, more sophisticated model, was based on 29Si NMR studies and potentiometric titrations (Sjoberg et al., 1985) which includes a variety of polymeric silicate species in solution. The latter is supported by our attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopic studies of the silicate solutions. X-ray photoelectron spectroscopic (XPS) analyses have also provided strong evidence for the adsorption of polymeric silicate species on hematite from silicate solutions with concentrations typical of those used in flotation, viz. 10−3 to 10−2 mol L−1. Polymeric silicate species have a stronger depressing effect than monomeric silicate species and colloidal amorphous silica particles. Selective depression of flotation of hematite from apatite can be achieved under conditions of moderate depression (Gong et al., 1992b) and this is shown to correspond to silicate solutions containing moderately polymerized silicates and/or very small colloidal silica particles. It is proposed that under such conditions of moderate polymerization the adsorbed silicate on hematite reduces oleate adsorption whereas on apatite, oleate can displace adsorbed silicate, and render the surface hydrophobic.
 
Article
Phenomena occurring in the froth zones of mechanical cells and columns during flotation have a significant effect on flotation results. For example, they affect recovery because a substantial proportion of the particles detach themselves from the bubble surface after coalescence and return to the pulp. In the framework of the Union European Impexflotcol project, coalescence and the role of one of the most common frothers, the MIBC, were studied in the laboratory, in order to understand the phenomena controlling the selectivity of column flotation. A new equipment was set up in order to observe the consequences of one coalescence between two bubbles mineralized in the conditions of an industrial operation (almost fully loaded by particles). A selectivity in the detachment of particles during coalescence was observed in relation to their hydrophobicity. The frother is one of the factors that can favour coalescence and thus selectivity. The importance of its action in flotation froths (Klimpel and Isherwood, 1991: Int. J. Miner. Process, vol. 33, pp. 369–381) led us to study its properties. A method was developed enabling the quantification of (1) the ability of MIBC to reduce the coalescence of bubbles, and (2) the foaminess of the reagent in the presence or absence of solid particles. Foaminess measurements show that MIBC frothing properties are closely linked to mineral hydrophobicity. The presence of more hydrophobic particles (chalcopyrite) leads to greater maximum foam heights compared to those obtained with less hydrophobic particles (sphalerite) and without particles. The influence of particle size and concentration has also been shown.
 
Article
The interaction forces which control the stability of the thin film between the approaching air-bubble and depressant coated mineral particle are described in terms of the electrostatic and dispersion contribution and the structural hydration forces. Although all three types of interactions are important, it appears unlikely that the electrostatic and dispersion terms can solely account for the depressant action.It is suggested that strong repulsive hydration forces may arise from adsorbed organic macromolecule depressants such as starch, dyes, tannins etc. (which contain a multitude of hydrophilic groups). These may impose a structure on the localised aqueous environment through strong iondipole effects which may be of sufficient magnitude to repel the approaching air-bubble and particle.
 
Article
Floatability and surface characteristics of sphalerite in the presence of different concentrations of copper sulphate and K-ethylxanthate, for various times of activation and collection, were studied. The resulting changes on the sphalerite surface were determined by infrated attenuated total reflection spectroscopy and correlated with electrokinetic measurement and floatability test results.The collectorless flotation of the examined sphalerite was very weak in alkaline media, independent of whether the mineral was activated with copper or without copper treatment. However, copper showed an activating effect on KEX sphalerite flotation in the alkaline region. Copper ions of high concentration provoked an “apparently depressing effect” on KEX sphalerite flotation, reacting with EX− to form copper-ethylxanthate-like species in the bulk of the solution. After decantation of the solution, before KEX was added, the depressing effect disappeared and sphalerite flotation was virtually complete.Cu(I)-ethylxanthate was the main surface product under the different experimental conditions. The kinetics of the copper-ion adsorption and KEX adsorption was relatively fast.
 
Article
The effect of the addition of activated carbon on the bioleaching of chalcopyrite concentrate, which contained pyrite, sphalerite and galena as sulfide gangue minerals, has been investigated using Thiobacillus ferrooxidans. The addition of activated carbon accelerated the dissolution of copper from the chalcopyrite concentrate. The recovery of copper increased with increase in the amount of activated carbon and with decrease in particle size of activated carbon. In the chemical control, activated carbon also enhanced the dissolution rate of copper and zinc from the chalcopyrite concentrate. These results indicated that the enhanced rate of leaching could be attributed to the galvanic interactions between activated carbon and chalcopyrite or sphalerite. The presence of Thiobacillus ferrooxidans could accelerate the galvanic interactions.
 
Article
The adsorption of ethyl xanthate on pyrite, pyrrhotite, chalcopyrite and sphalerite has been studied using FTIR-ATR techniques and microflotation. Non-activated minerals and minerals activated with copper sulfate have been investigated at different pH values and xanthate concentrations. Diethyl dixanthogen is formed on non-activated pyrite, pyrrhotite and chalcopyrite. Iron xanthate co-exists with diethyl dixanthogen as a monolayer form on pyrite and a copper xanthate surface compound co-exists with diethyl dixanthogen on chalcopyrite. After copper sulfate activation a copper (I) type xanthate compound exists on all of the minerals studied. Acidic pH favours the adsorption of ethyl xanthate on non-activated minerals, whereas the neutral pH range is most favourable for xanthate adsorption on activated minerals.
 
Article
The effect of dry milling in a vibratory mill on the structural changes and microstructural characteristics of hematite using different methods was investigated. We have described the line profile analysis (LPA) to extract the size of coherently diffracting domains and the lattice strain of activated hematite in a vibratory mill. The Warren–Averbach and Williamson–Hall methods were used as the main tools for characterization. The changes in the particle size, surface area and new phase formation of hematite concentrate were also investigated. It was concluded that the breakage and agglomeration of particles take place mainly at lower and higher levels of specific energy input, respectively. The pores in agglomerates remain accessible for the nitrogen gas. Milling of hematite increased specific surface area up to 18.4 m2/g. The hematite milled under various levels of specific energy input did not undergo a significant reaction or phase transformation during milling. The Williamson–Hall method confirms its merit for a rapid overview of the line broadening effects and possible understanding of the main causes. The anisotropic character of line broadening for deformed hematite as a function of specific energy input was revealed. Higher level of specific energy input favors the generation of small crystallite size, higher microstrain, BET surface area, amorphization and line breadth. The Warren–Averbach method suggested that the nanocrystalline hematite with grain sizes of 73.5–12.2 nm was formed by mechanical treatment using different milling intensities in the vibratory mill. The root mean square strain (RMSS) at L = 10 nm varies between 1.7 × 10− 3 and 4.0 × 10− 3 depending on the level of energy input. Limits in the applicability of Williamson–Hall method and reliability of the results are discussed in detail.
 
Article
The effect of sodium bisulphite on the collectorless flotation of copper-activated sphalerite has been studied at pH 9 with nitrogen purging. X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF-SIMS) and ion chromatography (IC) have been used to identify a mechanism of interaction of sulphite ions with sphalerite particles. The results indicate that sodium bisulphite acts as an effective depressant for the collectorless flotation of copper-activated sphalerite and has a specific effect on the surface chemistry of sphalerite particles under the experimental conditions studied. It is suggested that sulphite ions react with the surface of copper-activated sphalerite and subsequently decompose the hydrophobic sulphur-like species responsible for flotation. Most likely, sulphite ions specifically interact with the reduced coordination sulphur atoms associated with copper activation and report into solution as a thiosulphate, which is then oxidised to sulphate. At the same time, zinc hydroxide is formed at the sphalerite surface. The consequent reduction in surface hydrophobicity explains the depression of copper-activated sphalerite in the presence of sulphite.
 
Article
In this study, the changes in surface area, morphology and leachability of antimony and arsenic from tetrahedrite, jamesonite and enargite mechanically activated by a high-energy planetary mill were investigated. It appears that the leaching of antimony from tetrahedrite and jamesonite and arsenic from enargite in alkaline solution of sodium sulphide is temperature-sensitive reaction. The temperature dependencies of all reactions were investigated in the interval 313–363 K. Resulting experimental activation energies were Ea = 111–182 kJ mol− 1 for mechanically activated minerals. The values of Ea are characteristic for processes controlled by surface chemical reactions.
 
Article
A statistical analysis was done to investigate the relationship between grinding variables and structural changes during mechanical activation of hematite concentrate. Experiments were carried out according to a statistical design by varying the grinding time, media surface and mill type. Several multivariate techniques are applied to interpret the grinding processes.The variance analysis revealed that the media surface and grinding time significantly influence the five main response variables at 95% confidence level. The use of multivariate analysis allows the projection of high-dimensional data to a low subdimensional subspace. An overview of principal component analysis (PCA) on 27 variables yielded a three component model explaining 89% and predicting 76% of the total variance. It was found that the observations belonging to low and high levels of media surfaces fall into two groups. Most of the microstructural characteristics such as microstrain, dislocation and amorphization and granulometric surface area, BET specific surface area, specific energy input, stored energy, portion of smaller particles and stress energy coincide with high level of media surface group. The variables crystallite size, peak intensity and mean particle size appear with lower media surface. The PLS-DA (partial least squares discrimination analysis) made it possible to discriminate the three types of mills. From the projection of dummy variables, it was concluded that the vibratory mill caused comparatively less structural changes in hematite than the other mills in spite of releasing higher stress energy. The planetary mill introduced relatively higher dislocation defects and generated higher lattice strain. The hematite ground in the tumbling and planetary mills had comparatively higher X-ray amorphization degree and subsequently higher excess energy than the hematite ground in the vibratory mill. The tumbling mill produced relatively lower specific surface than the others. It was concluded that the products of the tumbling mill represented higher defect concentration (amorphization) per unit surface area despite releasing lower stress energy level. From the PLS modeling of the five main response variables, it was found that the X-variables specific energy input and stress energy are the most influencing factors.
 
Article
Effects of dry milling on the carbothermic reduction of celestite were examined. Celestite and coke mixture was milled up to 120 h in a planetary ball mill. Unmilled and milled mixtures and their black ashes from carbothermic reduction were characterized by a combination of X-ray diffraction (XRD) analysis, scanning electron microscope analysis, thermogravimetric analysis, particle size analysis and leaching tests. XRD diffraction peaks for celestite in the milled mixtures are lower and broader than those for the unmilled mixture, mainly due to a disordering of celestite crystal structure. Size of the particles significantly decreased by 1 h of milling, so that d50 decreased from 79.4 to 6.1 µm. But, milling for longer periods shifted the particle size distribution to coarse size region, mainly due to the agglomeration of fine particles. By milling the celestite–coke mixture for 1 h, formation temperature of SrS decreased from 957° to 900 °C, whereas 24, 72 and 120 h of milling decreased nearly to 700 °C. At low roasting temperatures, the mass loss by reduction increased with extending of the milling and the milled mixtures gave a high degree of soluble strontium in the black ash. However, sintering process prevailing at higher temperatures during the roasting of the milled mixtures became active, and the effects of disordering of the celestite structure vanished and subsequently the reduction reaction was retarded. It was concluded that although milling in a planetary ball mill produces more X-ray amorphous SrS, together with SrC2, carbothermic reduction reactions occur at lower temperatures as the milling time increases.
 
Article
A new mass-spectrometric technique, capable of the quantitative detection of very low levels of elemental sulphur on sulphide mineral surfaces has been developed. It is shown that elemental sulphur is formed, under certain conditions, on zinc sulphide surfaces activated by CuII, CdII and PbII. The findings are interpreted in terms of semiconductor theory.
 
Article
The chemical and morphological changes induced on the surface of millerite by mechanical activation have been studied by means of X-ray diffraction, electron microprobe, scanning electron microscopy and infrared spectra. Leaching tests in water, dilute nitric and hydrochloric acids have been carried out. The mechanical activation of millerite grains due to their disintegration is accompanied by an increase in the number of particles and generation of fresh previously unexposed surface. The agglomeration of grains and a partial oxidation of sulphide to sulphate ions were observed. The increase in leachability of the activated millerite may well be due to the combination of mechanically induced structural defects and chemical modification of millerite surface.
 
Article
Chlorite and lizardite are often the major MgO silicate gangue minerals in nickel ores. Although hydrophilic, they nevertheless report to the concentrate as fine particles by entrainment or as locked in composite particles with sulphide minerals. In this study, we have found that chlorite and lizardite, but also quartz, can be activated with Cu(II) and Ni(II) and floated with xanthate in the pH region 7 to 10. In this pH region, copper and nickel hydroxides are stable species and by adsorbing/precipitating on the mineral surface they promote xanthate adsorption (formation of the hydrophobic xanthate species, copper–xanthate and dixanthogen) and therefore the flotation of these minerals. Copper is a much stronger activator of these minerals than nickel between pH 7 and 10. Therefore, chlorite and lizardite may also report to the concentrate by true flotation in the pH range 7 to 10, especially when copper sulphate is added to activate the slow flotation of pentlandite.
 
Article
Activation of sphalerite by lead in the presence of ethyl xanthate was investigated by microflotation, EDTA extraction, and X-ray photoelectron spectroscopy (XPS). Activation was significant below pH 7 and declined to zero at pH 11. Interactions in the sphalerite/lead/xanthate system to account for the response are proposed. Flotation as a function of surface concentration of Pb, [Pb]surf (mg/cm2), showed a unique response regardless of source of lead (from solution or contact with galena).The [Pb]surf is linked to a Pb ion production model to try to estimate the grade of galena with the potential to cause accidental activation.
 
Article
The activation of sphalerite by some metal salts has been briefly reviewed and the influence of lead nitrate on sphalerite in the presence of potassium ethyl xanthate has been investigated by a combination of batch flotation tests and solution analyses on pulps containing a mixture of sphalerite and quartz. The effect of lead addition, of pH and of complexant on the flotation behaviour has led to the conclusion that in mildly acidic conditions the activating entity is lead ion whereas in mildly alkaline conditions the activating entity is lead hydroxide. Some comparisons between lead activated sphalerite and galena have been made. The consequences of these findings in the separation of galena from sphalerite in practical flotation have been briefly discussed.
 
Article
The chemistry of the activation of sulphide minerals by Cull) and other cations is reviewed, with special emphasis on work published in the past two decades. An attempt is made to resolve anomalies in the published results and theories, and to suggest directions which further work should take so as to advance understanding of the processes and to improve performance in the selective flotation of sulphide ores.
 
Article
Processes induced by mechanical activation of the natural titanite CaTiSiO5 using a laboratory agate mechanical mortar and a planetary mill AGO-3 have been studied. Titanite consumes substantial amounts of atmospheric carbon dioxide during prolonged dry grinding in air. Carbonisation of titanite occurs alongside with its amorphyzation. According to FT-IR spectroscopic data CO2 is present in the ground sample in the form of distorted CO32− groups resulting in the characteristic double band in the 1500–1430 cm−1 region. Previously similar processes were revealed for Ca and Mg containing silicate gangue minerals such as enstatite MgSiO3, diopside CaMgSi2O6, åkermanite Ca2MgSi2O7, and wollastonite CaSiO3. The CO2 content in the ground titanite reached 4.0 and 7.0 wt.% after grinding in the laboratory agate mechanical mortar for 36 and 108 h, respectively. The amount of carbon dioxide consumed due to grinding increases with increasing CaO content in the chemical formula of minerals and correlates with Gibbs free energies of reactions of the crystalline minerals with CO2. The following sequence concerning carbon dioxide sorption ability was revealed: enstatite<diopside<titanite<åkermanite<wollastonite. Preliminary mechanical activation results in considerable rise of titanite reactivity with respect to 5–20% nitric acid. According to the results obtained the release of Ti and Ca increases with increasing extent of mechanically induced crystal structure disordering and amorphyzation. In contrast to other titanium containing minerals such as leucoxene, ilmenite, rutile, anatase preliminary mechanical activation of titanite in planetary mill for 30 min allows to reach practically complete leaching of Ti with diluted nitric acid at room temperature.
 
Article
This study is aimed at explaining the effect of copper activation in flotation systems which contain free gold and gold locked in pyrrhotite and pyrite. Unlike other studies, the effect of the sequence and amount of copper added to the slurry in relation to the xanthate conditioning period is investigated and the results are discussed in terms of how the two gold bearing types respond to true particle–bubble attachment and entrainment during flotation. The results indicate that increasing the dosage of copper sulphate increases the entrainment of refractory gold when the copper is added before the potassium amyl xanthate (PAX), because there is a greater flux of water upwards to the froth, which results in a decrease in the amount of sulphide material that is attached to the air bubbles. When the true flotation of refractory gold decreases, there is also a higher degree of entrainment. True flotation of free gold increases since there is a larger proportion of non-mineralised surface sites on the bubbles where attachment can take place. When copper sulphate is added after the collector the recovery of free gold increases dramatically so that there is an overall increase in total gold recovery of up to 6% compared with the usual sequence of adding the copper first.
 
Article
It is possible to characterise in situ the conductive properties of mineral pulps from complex impedance measurements at high frequency (0.4–150 MHz). The method allows the detection of sulfide activation and deactivation of malachite. The effects of frequency, ionic strength, temperature, particule size, gangue content, sulfide and depressor concentration are described.
 
Article
During the differential flotation of polymetallic sulphide ores, some selectivity problems may appear: it is sometimes difficult to prevent the collection of the sphalerite in the lead and/or copper concentrates. Laboratory batch flotation tests performed respectively on pure minerals and on natural ores have shown that the main factors affecting sphalerite collection may be related to sulphide oxidation. This suggests that sphalerite collection is the consequence of its activation by metallic cations released by the sulphides present.These tests show that: 1.(1) activation is fast, and even almost instantaneous when the sulphides are oxidized. Otherwise, it depends on the time of aeration of the pulp.2.(2) Large amounts of cations are involved: they vary with the degree of oxidation of the sulphides, pH and the presence of pyrite.With the use of ESCA, it has been shown that the lead activating the sphalerite may occupy up to 30% of the cationic sites of the first ten atomic layers.
 
Article
An understanding of the processing of aluminosilicate mineral wastes is important for the development of large-scale waste-based geopolymerisation, especially for the encapsulation of heavy metals. This paper examines the effect of alkali metal silicate precursor solutions on geopolymerisation. Specifically, it addresses the effect of the degree of polycondensation of silicate solutions on the microstructure of waste-based geopolymers containing heavy metals (Pb and Cu). The microstructural mechanisms of heavy metal immobilisation were assessed through a variety of techniques such as X-ray diffraction (XRD), Infrared (IR) spectroscopy and Scanning Electron Microscopy (SEM) and compared to alternative polysilicate remediation methods. Nuclear Magnetic Resonance (NMR) spectroscopy was used to investigate the effects of pH and alkali metal on the speciation and equilibria of silicate solutions. The role of variable calcium sources on the physical and chemical characteristics of the final product was also investigated. Calcium silica hydrate (CSH), although present at pH 12, was largely unobserved at high pH (pH=14), which is the optimal condition for geopolymerisation.
 
Article
The elitist non-dominated sorting genetic algorithm with the modified jumping gene operator (NSGA-II-mJG) is used to optimize the performance of froth flotation circuits. Four example optimization problems (Mehrotra and Kapur, 1974; Green, 1984; Dey et al., 1989) [Mehrotra, S.P., Kapur, P.C., 1974. Optimal–sub-optimal synthesis and design of flotation circuits. Sep. Sci. 9, 167–184; Green, J.C.A., 1984. The optimization of flotation networks. Int. J. Miner. Process. 13, 83–103; Dey, A.K., Kapur, P.C., Mehrotra, S.P., 1989. A search strategy for optimization of flotation circuits. Int. J. Miner. Process. 26, 73-93.] of varying complexity are solved using single-objective functions. In one example, the overall recovery of the concentrate stream is maximized for a desired grade of the concentrate and a fixed total cell volume. The interconnecting cell linkage parameters (fraction flow rates) and the mean cell residence times are the decision variables. In all these cases, the optimal solutions obtained using NSGA-II-mJG are superior to those obtained by earlier techniques (which converged to local optimal solutions). Thereafter, a few two-objective optimization problems are solved. In these, the performance of the circuit is optimized, and simultaneously, the number of connecting streams is minimized so as to give simple circuits. Pareto optimal sets of equally good (non-dominating) solutions are obtained. This is probably the first study involving the multi-objective optimization of flotation circuits with one aim being to simplify them.
 
Article
Bioleaching of marmatite flotation concentrate by the adapted strains of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans in mixed cultures was carried out at initial pH of 2.0, temperature of 35 °C, particle size of −42 μm (over 90%), pulp density of 15% and air flow of 500 L min−1 in a 10-L air-lift reactor. Experimental results showed that the addition of Fe2+ ion was favorable to improving the growth and activity of leaching bacteria and increasing the dissolution rate of marmatite. In the leaching system with Fe2+ ions added, the weight loss of the concentrate was over 70%, the leaching ratio of zinc was over 80% and the concentration of zinc ions in the leach liquor was about 50 g L−1 after 10 days of bioleaching. The technological feasibility of a microbiological process using the adapted strains of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans in mixed cultures for extracting zinc from a marmatite flotation concentrate has been demonstrated.
 
Top-cited authors
John Ralston
  • University of South Australia
Douglas Fuerstenau
  • University of California, Berkeley
Jannie S J Van Deventer
  • University of Melbourne
Janusz S. Laskowski
  • University of British Columbia - Vancouver
Jan D Miller
  • University of Utah