Minerals Engineering

Published by Elsevier
Print ISSN: 0892-6875
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The Ok Tedi copper concentrate was bioleached under optimal oxygen- and carbon dioxide enriched air conditions. Three cultures, T. ferrooxidans, Sulfobacillus accidophilus and Sulfolobus were employed for bioleaching process. The increase in copper leaching rates demonstrated the positive effect of using enriched air in the experiments. Galvanic interaction during the leaching of copper was suggested by the low redox potentials. The x-ray diffraction (XRD) analysis of leach residues confirmed the toxicity of metal ions and formation of precipitates.
 
Wollastonite finds an important place among industrial minerals due to its high chemical and thermal resistance and also as a substitute for asbestos. With the depletion of high-grade ores and increased demand, it becomes inevitable to process low-grade ores. Flotation can be employed effectively for processing these ores. Flotation behavior of wollastonite was studied using tallow-1,3-diaminopropane as collector in the Hallimond micro-flotation cell. The flotation recoveries obtained were correlated with contact angle measurements. Dissolution studies clearly bring out the incongruent dissolution of wollastonite, resulting in a silica rich layer on the surface of the mineral. The release rates of calcium and silicon decrease with the particle size. Maximum flotation obtained at 1 × 10−5 M diamine concentration. DRIFT studies indicate that the intensity of alkyl chain bands increases with increasing diamine concentration, thus corroborating increased presence of diamine on wollastonite resulting in maximum contact angle and flotation recovery. Surface free energy values of wollastonite were determined by different approaches using contact angle data of well-defined components of polar and apolar liquids. An attempt has been made to correlate between the flotation response and the surface free energy values of wollastonite in the presence diamine.
 
This paper describes experiments to investigate the adsorbent properties of an iron sulphide material produced by sulphate reducing microorganisms when they are grown with a substrate containing appreciable quantities of iron. It is found that the material when compared with other adsorbents has excellent adsorptive properties with respect to specific uptake of a range of metals and the level to which the concentrations of the metal ions can be reduced when in contact with the adsorbent. The structure of the adsorbent revealed by EXAFS corresponds with no known iron sulphide and an examination of the adsorbed ions shows that many are chemisorbed. When the adsorbent is stored in the presence of air for periods of a few months a mixed oxide of iron is formed.
 
Pilot plant testwork has been conducted in an attempt to reduce the iron losses from the -106 μm size fraction in the spiral plant of Quebec Cartier Mining Company. The spiral feed was sized at -212 μm, providing a coarse and fine fraction which could be treated using operating conditions suitable for the two separate size fractions. In comparison to the existing plant average for the -212 μm material, the pilot plant testwork resulted in an increase in concentrate grade and recovery of 3.2% and 6.5% respectively. The most significant of these two results is the improvement in concentrate grade since there are certain advantages to marketing separate fine and coarse concentrates. This has not been possible in the past due to a grade of only 63.5% Fe in the -212 μm fraction. When these results are projected to the overall plant, the increase in concentrate grade and recovery is 1.0% and 3.7% respectively.
 
As the minerals industry nears the 21st century, the good news is that global population is expending with concomitant demands for raw materials. Tat will be accompanied, however, by social, economic and legislative pressures for drastic conservation of energy and materials.Forces for change will include broadscale substitution at every level of the materials cycle; environmental pressures to reduce, if not totally ban, mining in the advanced nations; the 3 Rs, recycling, reclamation and remanufacturing of finished goods; and all aspects of the minerals industry influenced by information technology.Three opportunities for the industry are: to be more proactive and positively engage the forces for change; to apply many of the techniques developed by the industry for the remediation of disturbed lands to use outside the industry; and to advocate enforcement mechanisms and global standards for mining. Now is the time to be proactive, statesman-like and global in perspective.
 
Solvent extraction following pressure acid leaching (PAL) is becoming the technology of choice for treating nickel laterite ores as it allows high recoveries of both the nickel and cobalt from these ores. Early plant experience, however, indicate that impurity control particularly in the solvent extraction stage still hinders full optimisation of this technology.Dissolved chromium, both as chromium(III) and chromium(VI), is one of the major impurities of PAL-generated pregnant leach stream (PLS) and little is known about its solvent extraction behaviour with Cyanex® 272, the predominant extractant for the separation of nickel and cobalt. Only a few studies have been reported and with apparently conflicting results.This study investigated the solvent extraction behaviour of chromium with Cyanex® 272. The effects of various experimental variables such as the metal oxidation state; pH; presence of anions such as nitrate, chloride, sulphate and acetate including the conditions of extraction relevant to the separation of nickel and cobalt directly from the partially neutralised PLS as well as the effect of the extracted species on stripping are discussed. The nature and forms of the extracted species are inferred from slope analysis and UV–VIS spectroscopy data.
 
Cobalt (II) and nickel (II) were simultaneously extracted from magnesium and calcium synthetic sulphate solutions using the carboxylic extractant Versatic 10. The two metals were then separated by extracting cobalt using the phosphinic acid Cyanex 272. Statistical design and analysis of experiments were used throughout in order to determine the main effects and interactions of the solvent extraction factors, which were the extraction pH at equilibrium, temperature, extractant concentration and organic to aqueous phase ratio. A statistically designed experiment was also carried out in order to study stripping of the loaded, with cobalt and nickel, Versatic 10 organic phase by using synthetic nickel spent electrolyte. Cobalt was recovered from the loaded Cyanex 272 by synthetic cobalt spent electrolyte, in order to produce a solution suitable for cobalt electrowinning. The slope analysis method was used to determine the nature of the cobalt and nickel complexes extracted with each of the extractants. The number of stages required for extraction and stripping processes of cobalt and nickel was also evaluated. The results of the continuous, counter current, mini plant tests clearly demonstrated the feasibility of the simultaneous recovery of cobalt and nickel from magnesium and calcium sulphate solutions by Versatic 10, as well as their separation by Cyanex 272.
 
In this study, a second order rate equation was used successfully model the rate of nucleation and crystal growth during the precipitation of alumina trihydrate. In unseeded liquors, 3,4 DHBA reduces the rate of nucleation and crystal growth significantly. It hinders the agglomeration of nuclei and crystals, producing less dense products compared to those precipitated from pure liquors. It was also found that alumina hydroxide nuclei need to crystallise before crystal growth occurs, and 3,4 DHBA delays the crystallisation process. In seeded liquors, 3,4 DHBA causes an exponential increase in the number of secondary, nuclei and a decrease in the rate of crystal growth. It also causes an increase in induction time. Provided this induction time is known the whole system can be characterised by the second order equation. Accumulated kinetic and induction time data can be used for the simulation of the precipitation process.
 
The kinetics of the alkaline stripping of vanadium(V) previously extracted by Aliquat® 336 is investigated. The influence of parameters such as the stripping temperature, NaOH concentration and pH at the extraction stage (pHext.) is reported. The limiting step of the stripping process consists in the slow transformation of the extracted polyoxometallate species (e.g., H2V10O284−) into HVO42− or/and VO43− ions. The stripping rate law and the values of the corresponding kinetic constants are similar to those observed for the alkaline decomposition of decavanate in homogeneous phase, although the stripping reaction is biphasic.
 
A comparative study of the solvent extraction of vanadium in sulphate media using primary amine PRIMENE 81R and tertiary amine ALAMINE 336 dissolved in kerosene has been carried out. pH conditions for both amines, mechanism proposal and extraction isotherms have been determined, yielding best results for primary amine. Equilibrium studies were used to assess the conditions of vanadium recovery in a continuous counter-current process using leaching solutions.
 
Tests were performed to evaluate the galvanic interaction of synthetic mixtures of galena (valuable mineral) and pyrite (gangue mineral) on their flotation response, both in air and nitrogen atmospheres, when the anionic collector sodium-di-isobutyl dithiophosphinate is added. The effect of lead activation of pyrite is also examined. Floatability of galena from mixtures is similar to that of galena alone indicating that the galena–collector interaction is not affected by the galvanic contact. In the presence of oxygen the floatability of pyrite from mixtures increases slightly compared to pyrite alone, due to the migration of Pb species, arising from galena dissolution, which adsorb onto pyrite as hydrolysed lead species. Galena–pyrite galvanic contact lowers the adsorption of lead species (from a Pb-bearing solution) onto pyrite, compared to that observed with pyrite alone. When the galvanic interaction is weakened due to the absence of oxygen (e.g., by using a nitrogen atmosphere), the concentration of lead onto pyrite surface increases to levels similar to those of pyrite alone. The collector chemisorbs onto galena forming a layer of low electroactivity that slows down the dissolution of the mineral; nevertheless, this layer does not completely prevent the galvanic interaction with pyrite.
 
An automated 3D tracking technique, Govender (2000), is employed to study the motion of particles deep within the tumbling ball charge of an experimental grinding mill. A Biplanar Angioscope, coupled with a fully automated imaging technique, accurately locates the 3D coordinates of the particles anywhere in the mill. Particle trajectories for five speeds, ranging from 55 to 85 percent critical, two lifter profiles, 90 degree and curved, and a range of tracked-particle sizes and densities were used in the experimental work. The final 3D coordinates of the tracked particle trajectories are accurate to within 0.2mm. With an average of 32 circulations per run, the data can be used for rigorous and accurate verification in the numerical modelling of the tumbling ball motion in mills.
 
The selective extraction and concentration of nickel from ammoniacal solutions containing nickel and cobalt by an emulsion liquid membrane (ELM) technique using 5,7-dibromo-8-hydroxyquinoline (DBHQ) as extractant has been presented. ELM consists of a diluent (kerosene), a surfactant (Span 80), an extractant (DBHQ), a modifier (tributyl phosphate), and a stripping solution (very dilute sulfuric acid solution containing EDTA as complexing agent, buffered at pH 4.25). Cobalt (II) in feed solution with 6 mol/L ammonia was oxidised to Cobalt (III) by H2O2 and pH of this ammoniacal solution was adjusted to 10.0 with the addition of hydrochloric acid (HCl). The important variables governing the permeation of nickel and their effect on the separation process have been studied. These variables were membrane composition, ammonia concentration in the feed solution, mixing speed, surfactant concentration, extractant concentration, pH of the feed and the stripping solutions, complexing agent concentration in the stripping solution, and phase ratio. After the optimum conditions had been determined, it was possible to selectively extract 99% of nickel from the ammoniacal solutions containing Ni and Co. The separation factors of nickel with respect to cobalt, based on initial feed concentration, have experimentally found to be of as high as 88.1 for about equimolar Co–Ni feed solutions.
 
This paper reports a 57Fe Mössbauer spectroscopic study of the kinetics of roasting process of chalcopyrite at two different temperatures and for different time intervals. Iron compounds formed at different stages of roasting have been identified and a possible scheme of transformations has been suggested to explain the observed kinetics.
 
The passivation of chalcopyrite in the presence of ferric sulphate solutions was investigated at 68 °C. The effect of different variables (pulp density, pH and the presence of oxygen) on both the copper dissolution rate and the formation of solid compounds was studied. The leaching tests were carried out in stirred flasks at 180 rpm with 100 mL of a Fe3+/Fe2+ sulphate solution, varying the pulp density between 0.1 and 5% and the pH between 0.5 and 2.0 and both in aerobic and anaerobic conditions. Ferric ion seems to be responsible for the oxidation of chalcopyrite but also promotes its passivation. Ferrous ion plays a key role in the process by controlling the nucleation and precipitation of jarosites, which finally cause the passivation of chalcopyrite.
 
Experiments were carried out an a 76mm Vorsyl Separator Treating Coal in the Size Range -2.0 + 0.5 mm in Magnetite Medium. The results obtained indicate that there exists a minimum limit to the length of the vortex finder below which the performance of the separator becomes poor. This has been analysed in terms of classification of magnetite and separation of coal. In the range of experimentation, the specific gravity of separation has been found to increase linearly with the specific gravity of the feed medium. The separation specific gravity has been found to be less than the feed medium specific gravity when shorter vortex finders with narrow openings were used.
 
A membrane transport process is described. The process was developed for use in the recovery of copper from nitric acid leach residual solutions. The flux and the extraction extent of copper with 5-dodecylsalicylaldoxime dissolved in Kermac 500-T (an industrial diluent) were measured at 30°C by using a membrane extractor made of a holow fibre. The content of carrier extractant in the wall of the porous fibre presented the biggest influence on metal extraction rate and its extractability. The results were explained by a diffusion model which considers that the extraction chemical reaction would occur at the inner interface of the liquid membrane, taking account that diffusion of copper-oxime complex through the membrane would be the rate-controlling step.
 
The influence of temperature on the equilibrium adsorption of gold and hydroxide ion at elution conditions was examined. Experiments were conducted for both single and multiple solute adsorption of gold and OH− ion at the temperaturesbetween 80 and 120°C. Two models were employed to model the equilibrium adsorption of each solute at the single solute level. These consist of Freundlich isotherm (FI) and the Modified Freundlich isotherm (MFI). In the case of the multiple solute adsorption, the Freundlich-type isotherm and a General multi-component isotherm were used for the modelling.Elution kinetic data was also generated. Models depending upon surface diffusion and film transfer were also developed. A plug flow model was developed and simplified using the method of characteristics. These models were solved simultaneously with the Modified Freundlich isotherm to simulate the experimental data obtained. It was observed that the model was less sensitive to the diffusion coefficient. The model was modified to be film transfer dependent and this modification was found to represent the experimental data very well.
 
The present paper attempts to identify the spatial patterns of soil nutrients in the abandoned Haizhou opencast coal mine and waste disposal site, in China. A geostatistical approach was used to overcome problems due to the heterogeneity of the site (some parts have been abandoned for more than 30 years, lack of clean soil, presence of overburden and low-grade ore, co-disposal of wastes from adjacent sites) and the limited number of available samples. One hundred and eight soil samples were collected from an area of 332 ha and analyzed for pH, organic matter (OM), NH4–N, available phosphorus (AP) and available potassium (AK). The results indicate that nutrients exhibit different spatial distribution and only NH4–N showed strong spatial dependence and a relatively large nugget effect. Relatively high content of OM, NH4–N, AP and AK was seen in the northeastern part, whereas pH was higher in central north and southern parts of the site. The determination of the spatial variability and heterogeneity of nutrients in mining and waste disposal sites assesses the need for amendments and assists in the selection of the most feasible revegetation scheme.
 
Waste rock from a South African gold mine was tumbled in a 600mm diameter mill. Factors influencing the rate of abrasion of the rock and the product size were examined, including rock mass, pulp hold-up, distribution of rock sizes, mill speed and lifter configuration. Tests were conducted on pebbles which had been rounded in the mill.It was demonstrated that abrasion rate per unit mass increases significantly with rock mass. A simple laboratory test for rock ‘hardness’ was shown to be correlated to the rate of abrasion. The rate of production of finished product from the coarse rock compares well with conventional grinding under certain conditions. The implications of the findings for circuit design and control are discussed.
 
The goal of this paper is to propose, build and test an abrasion apparatus that will allow the investigation of tumbling mill steel media abrasive friction and wear as a function of the energies/forces acting in abrasion in a given mill. The following development is based on the possibility of estimating energy/force spectra in abrasion by using a discrete element charge motion model for mill simulation. The objective of the abrasion test is to develop forces in abrasion similar to those estimated in an industrial mill and determined from DEM charge motion simulations. The paper describes the test developed based on the ASTM G65 abrasive wheel test and standard where applied forces are increased and the abrasion wheel torque is measured. Initial tests explore abrasion behaviour using Ottawa foundry sand as the abrasive medium and two steels (1018, 1045). Test results look at abrasive wear over a range of applied forces, wheel rotation speeds, energies as well as wheel torque. Wheel torque is used to determine the friction coefficient over these test conditions. Future tests will look at the effect of various ore types on abrasive friction and wear of mill steel media.
 
The recycling of fridges results in the production of a mixed plastic product containing high impact polystyrene (HIPS) and acrylonitrile butadiene styrene (ABS). These plastics are difficult to separate because they have similar physical properties, such as density. Froth flotation using selective wetting agents is one possible separation technique.The use of acetic acid, methanol and quebracho as selective wetting agents have been investigated. All are shown to be potentially selective given idealised flotation conditions, with similarly sized particles. The use of quebracho at pH 11 gave the most promising results producing selectivity over a wide particle size range.
 
This paper contains the results of Hallimond tube flotation tests conducted with pyrite arsenopyrite and quartz using a cationic type collector called hexyl thioethylamine, as well as the results of electrophoretic mobility (E.M.) tests for the same minerals measured under various conditions. The purpose of this study is to investigate the effect of surface charge of sulphide minerals on the attachment mechanism of a cationic collector. In this regard, the influence of pH and collector concentration on the electrophoretic mobilities of pyrite, arsenopyrite and quartz were monitored. The mobility measurements at various pH values were made in the absence and presence of collector, and the effect of collector concentration on the electrophoretic mobility was determined at constant pH. The results were evaluated in terms of flotation, electrophoretic mobility, adsorption and IR data. The experimental results indicate that flotation of pyrite induced by hexyl thioethylamine is not dependent on the surface charge of the particle.
 
To quantitatively measure and compare the ability of different materials in absorbing microwave energy, a new practical method, only using a home microwave oven with microwave radiation out of the bottom of the cavity as the major apparatus, was developed. During the measuring process, each target material and water, separately contained with two microwave transparent containers, respectively, were simultaneously placed in the oven cavity for microwave irradiation. The water container was above the tested materials container, and the water acted as the medium to absorb the microwave energy surplus to that absorbed by tested materials. By determining the water temperature and then calculating its absorbed microwave energy, the microwave energy absorbed by the target materials could be obtained. According to this method, seven bulk solid materials of reagent grade were tested and the results agree well with previous research reports. In addition, the principle and control of the measuring conditions of the novel method were discussed in this paper.
 
This research was designed to accelerate the biological oxidation rate of low-grade suphidic gold ores. The biological oxidation by tamed Thiobacillus ferrooxidans bacteria with a mixed low-grade refractory gold ore was investigated. These bacteria could well tolerate up to 18.0 g/L of arsenic (III). The effect on the oxidation rate due to the presence of a magnetic field on the culture medium was examined as well as the influence of surfactants (tween-80, tween-20 and emulsifier-OP) and selected ionic metals such as Ag+, Bi3+, Co2+ and Hg2+. The results showed that, based on a 60% oxidation rate for arsenic, the oxidation time was shortened by 83 hours, 90 hours, 98 hours and 100 hours under the optimal conditions of tamed bacteria, magnetized water, concentrations of tween-80 and Ag+ respectively. Under the combination of the above parameters, the biooxidation rate was shortened by 120 hours to achieve a 60% oxidation rate for arsenic. However it did not produce a simple additive effect on the biooxidation.
 
A method of computation of an accelerating blade profile of a centrifugal rotor-impact mill, providing maximal absolute particle velocity, was developed. The effect of friction coefficient on the optimal blade profile was studied. A comparison of calculated optimal blade profiles with both straight-linear and log-spiral ones was carried out. The calculated optimal profiles enabled significant increase in particle velocities.
 
In this paper the control performance of the flotation process is evaluated as a function of the measurement accuracy and sampling frequency of an on-stream analyzer. First, the performance of rule-based control and model predictive control (MPC) strategies is studied using discrete flotation models and the respective performance indices. Next, the net smelter return (NSR) is calculated for varying sampling rate and accuracy combinations using the PI controllers-based control strategy, mechanistic flotation models and the industrial process data as input. The control and economical performance of the process declines strongly when the sampling cycle is increased. The results also indicate that the speed of on-line analysis has a significant effect on the production economics, calculated as the average net smelter return.
 
A novel heap bioleaching technology called GEOCOAT®, developed by GeoBiotics, LLC, for the processing of sulfide base metal and gold concentrates is discussed. In this process, thickened flotation is contacted during heap stacking with gravel-sized support rock, forming a thin adherent concentrate coating on the support rock particles. The temperature measurements support the theory that the incoming air tends to produce the coolest zone at the bottom of the heap. Initial levels of low free acid appear to have impacted the zinc extraction kinetics.
 
The extraction of titanium (IV) from sulfate, and nitrate solutions has been studied using tri-n-butyl phosphate (TBP) in kerosene. Extraction of titanium was affected by acid concentration over the range of 0.5–4 mol L−1. The titanium distribution coefficient reached a minimum between 1 and 2 mol L−1 acid for both sulfate and nitrate solutions. Third phase formation was observed in the extraction of titanium from acidic media at all condition tested. At the next stage, the stripping of titanium was studied using H2SO4, H2SO4 + H2O2 and Na2CO3. The kinetics of the stripping were very slow for H2SO4. The use of complex forming stripping agents (H2SO4 + H2O2) and Na2CO3 significantly improved the kinetics of stripping. About 98% recovery was achieved by extracting titanium from an aqueous nitrate solution using TBP and stripping with sodium carbonate.
 
The effect of Cr3+ on the cathodic current efficiency (CE), deposit morphology, crystallographic orientations and polarisation behaviour during nickel electrodeposition from acidic sulfate solutions containing boric acid was investigated. A progressive decrease in CE was seen with increase in Cr3+ concentration showing a maximum decrease in CE of ∼10–13% at concentration ∼100 mg dm−3. The presence of Cr3+ did not change the fcc structure of the electrodeposited nickel but affected the peak intensities of the crystal planes. Polarisation of the cathode was seen in the presence of Cr3+ in the electrolyte along with a shift in the electroreduction potential of nickel (II) ion towards more negative values. The effect of Cr3+ on the electrokinetic parameters: Tafel slope (b), transfer coefficient (α) and exchange current density (i0) has also been investigated.
 
High-purity nickel is mainly produced by electrowinning from sulphate and chloride solutions in the presence of high concentrations of boric acid as a buffer. The generally used pH is in the range 3–4 if Ni concentration in the electrolyte is higher than 10 g/l. Lower Ni concentration, as in the case of either industrial liquid effluents and in situ low grade Ni ore leaching, needs pH values ranging from 10 to 11 in order to hinder the evolution of hydrogen. Ni electrowinning from acidic and alkaline solutions is studied to determine in both cases the best operative conditions. Particularly Ni concentration, additive presence, pH values, temperatures, cathode material, current density and voltage, to be used in the case of low Ni concentration, have been considered to obtain low energy requirements together with pure nickel having a good morphology.
 
This research was designed to investigate zinc and lead extraction by combined sequential biooxidation and acidic brine leaching from a raw complex sulfide ores containing sphalerite, pyrite, and galena. For the biooxidation, the zinc dissolution from the sulfide ores by the adapted bacteria was examined. The effects on ore particle size, pH, pulp density, and temperature on bacterial leaching was studied systematically. From the experiments it was shown that about 95% of zinc was extracted after 20 days of bioleaching at 30 °C. Subsequently, 98% of the lead was extracted from the bioleached residues using an acidic sodium chloride solution as the lead lixiviant at a temperature of 60 °C for 90 min leach. Leaching kinetics indicated that diffusion through the product layer was the rate controlling process during zinc bioleaching, and that the overall rate of chemical reaction at the surface was the rate controlling process during lead brine leaching. The relative activation energies of the overall rate during the two different leaching stages were calculated to be 32.09 and 44.35 kJ/mol, respectively.
 
In the present study, flow-through column experiments using a series of continuous-flow columns were conducted to investigate the performance of Fe0 permeable reactive barriers (PRB) for the treatment of acidic leachates generated in active or abandoned mining and waste disposal sites. Simulated AMD solutions of low and high metal ion concentration were pumped at different flow rates into the laboratory system. Concentration profiles under steady-state transport conditions were developed by measuring metal ion concentration at various sampling ports. Results show that metal ion removal is mainly accomplished via redox reactions that initiate precipitation of mineral phases. Sulfate green rust was identified from the analysis of precipitates formed on the iron surface; sulfate and heavy metals uptake by green rust is a secondary clean up mechanism. Experimental results as well as geochemical modeling by PHREEQC-2 indicate that cadmium and copper are removed by redox reactions while aluminum, manganese, nickel, cobalt and zinc are mainly removed as metal hydroxides. It is therefore seen than zero-valent iron barriers can be used as an environmentally and economically viable remediation technology for the clean up of acidic leachates loaded with several inorganic contaminants and sulfates and the subsequent prevention of groundwater contamination.
 
Ash flow temperature is one property that specifically gives more information on the suitability of a coal source for combustion or gasification purposes. Therefore the chemistry and mineral interaction have to be understood in order to determine the suitability for fixed bed gasification purposes with regards to ash flow properties. Various authors ([Seggiani, M., 1999. Empirical correlations of the ash flow temperatures and temperature of critical viscosity for coal and biomass ashes. Fuel 78, 1121; Alpern, B., Nahuys, J., Martinez, L., 1984. Mineral matter in ashy and non-washable coals—its influence on chemical properties. Commun. Serv. Geol. Portugal 70 (2), 299]) have expressed the fusibility of coal ash as a function of the content of the principal oxides frequently found in coal ash, i.e. SiO2, Al2O3, TiO2, Fe2O3, CaO, MgO, Na2O and K2O. However, coal ash fusibility characteristics are difficult to determine precisely, partly because coal ash contains many components with different chemical behaviours, and may very from coal source to coal source.
 
Copper was removed from an acidic mine drainage (AMD) using a liquid emulsion membrane contactor. The acidic drainage was a harmful natural acidic solution generated by bioleaching and chemical leaching of copper and iron sulfides, with average pH between 2 and 4. Normally the content of copper in AMD is low, which makes its recovery by SX uneconomical. The kinetics of copper removal in a stirred transfer cell was studied, using a salicylaldoxime as mobile carrier extractant and Span-80 as surfactant. It was found that the initial extraction rate of copper was affected by the carrier concentration in the liquid membrane and by the pH and metal content in the mine water. A minimum content of surfactant in the organic phase was required to stabilize the emulsion. A transport mechanism based on a diffusion model, which includes the extraction chemical reaction between the metal and the carrier extractant is discussed.
 
In this study different strategies were employed for adapting Acidithiobacillus ferrooxidans cells to both Zn2+ ions and high grade sphalerite concentrate. The serial subculturing was found to be a very efficient strategy for adapting A. ferrooxidans cells to higher Zn2+ concentrations, as well as high grade sphalerite concentrate, provided that a suitable protocol was employed. Adaptation of A. ferrooxidans cells to 30 g/L Zn2+ significantly enhanced the rate of bioleaching of Zn2+ from high grade sphalerite concentrate. Preadaptation to Zn2+ ion also shortened the time required to adapt the cells to the concentrate. A. ferrooxidans PTCC 1642, exhibited a higher rate of Zn2+ bioleaching from high grade sphalerite concentrate compared to A. ferrooxidans DSMZ 583; however, due to the adaptation protocol employed the difference in performance of the two strains was not very great. Based on the results obtained in this study suggestions were given for the mechanisms during the adaptation of A. ferrooxidans cells to high grade sphalerite concentrate.
 
In this paper, the experiments were conducted in a concentric cylinder shear device. The effect on oxidation activity of ferrous iron by Acidithiobacillus ferrooxidans was tested under different shear conditions achieved through regulating the rotating speed of the inner cylinder. The results suggested that the fluid shear rate had little adverse effect on the oxidation activity of At. ferrooxidans. In this study, silicon dioxide powder was added to the medium to investigate the effect of particles collision on the oxidation activity of bacterial cells, and it was found that the oxidation rate of ferrous iron by At. ferrooxidans was greatly decreased with the increase of silicon dioxide concentration.
 
In this work, the monitoring of the bacterial and chemical dissolution of bornite was evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS); the mineral surface was examined using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The analysis of CV results allowed attributing the different peaks observed in both direct and reverse potential scanning to the oxidation of bornite to a secondary covellite and its reduction via different non stoichiometric copper sulphides intermediaries. EIS data for bornite were obtained in control medium up to 78 h of immersion, when a cellular suspension of A. ferrooxidans was added and the experiments continued up to a 192 h of test. The EIS response was different when bacteria were added in the beginning of the test or after some hours of immersion in acid solution. The experiments were performed in different cell configurations and a model of the electrode/electrolyte interface. The correspondent equivalent electrical circuit was used to fit impedance spectra for all studied conditions. A common equivalent circuit used for corrosion processes where anodic (degradation of the mineral) and cathodic (oxygen reduction) reactions occur in parallel, together film and biofilm formation was proposed.
 
A research-grade mineral sample that contained marcasite and pyrite (FeS2) was subjected to the oxidation by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Oxidation of FeS2 by A. ferrooxidans produced acid, and the redox potential increased with sulfide dissolution and the oxidation of Fe2+. Jarosite was detected in solids from spent cultures. Preferential oxidation of either mineral was not consistently observed across all treatments. Neither iron sulfide was oxidized by A. thiooxidans.
 
Jarosite precipitation is a very important phenomenon that is observed in many bacterial cultures. In many applications involving Acidithiobacillus ferrooxidans, like coal desulphurization and bioleaching, it is crucial to minimize jarosite formation in order to increase efficiency. The formation of jarosite during the oxidation of ferrous iron by free suspended cells of A. ferrooxidans was studied. The process was studied as a function of time, pH and temperature. The main parameter affecting the jarosite formation was pH. Several experiments yielded results showing oxidation rates as high as 0.181–0.194 g/L h, with low jarosite precipitation of 0.0125–0.0209 g at conditions of pH 1.6–1.7 with an operating temperature of 35 °C.
 
Thermophilic acidophilic Archaea were enriched from samples collected from geothermally active sites in Papua New Guinea. Pure cultures (JP2 and JP3) were obtained from mixed culture enrichments and were characterised and tested for their bioleaching ability. All cultures possessed Sulfolobus-like morphology, and the presence of distinctive cyclized tetraether lipids. The two pure cultures were identified by their 16S rRNA gene sequences as being most closely related to Sulfolobus solfataricus. Each isolate was able to oxidise both Fe2+ and sulphur, and grow on both pyrite and chalcopyrite under autotrophic conditions. Leaching experiments showed that the isolates were capable of rapidly leaching a chalcopyrite concentrate (up to 91% Cu release in 108 h). Optimal temperatures for growth and chalcopyrite leaching were determined for each strain. Chalcopyrite dissolution rates for JP2 at different temperatures were determined using a previously described kinetic model. An Arrhenius plot to investigate the relationship between dissolution rate and temperature, showed that for JP2, an increase in temperature from 70 to 83 °C resulted in a 6.6-fold rate increase. Studies with both mixed and pure cultures showed that these cultures were capable of rapidly leaching a chalcopyrite concentrate at very high temperatures (up to 90 °C), but also were capable of bioleaching at 50 °C. These thermophilic acidophiles possess the ability to bioleach over a wide range of temperatures. They are potentially well suited to industrial leaching applications where considerable temperature fluctuations limit the growth of other non-thermophilic bioleaching microorganisms.
 
The effects on base metals, nickel, cobalt and copper, were investigated during oxidation of ferrous iron solution and pyritic gold concentrate with mesophilic and thermophilic cultures. In mesophiles, the oxidation ability of the bacteria was unaffected whereas that of pyritic gold decreased. In thermophiles, the mixed culture showed incomplete oxidation characteristics. The importance of adapting the bacteria to environments containing high concentrations of metal ions was revealed by the oxidizing ability of mixed culture.
 
The increasing acceptance of biological processes for the treatment of refractory gold-bearing concentrates should be considered as a positive move both in terms of process flowsheet development and its commitment to the environment. Research and development is now focusing on the application of moderately thermophilic and extremely thermophilic acidophiles in the treatment of both refractory gold-bearing and base-metal mineral sulphide concentrates. Current literature on the application of biological processes is still dominated by studies of mesophilic bacteria such as Thiobacillus ferrooxidans and Leptospirillum ferrooxidans although literature is becoming more prevalent with respect to the higher temperature acidophiles.This current experimental study highlights the problems of arsenic toxicity to certain strains of moderately thermophilic bacteria when oxidising both refractory gold and base-metal sulphide concentrates. It also concludes that these bacterial strains were capable of readily oxidising a chalcopyrite/pyrite concentrate (typical of base-metal sulphide concentrates).A mini literature review discusses some of the current and potential applications of acidophilic bacteria both within the minerals industry and in allied disciplines including treatment of metalliferous mine wastes, acid mine waters and sulphurous flue gases. Conclusions are drawn for both the experimental work presented and the literature reviewed.
 
Acidophilic bacteria found in mining environments are capable of oxidising insoluble sulfide minerals. The use of these bacteria during the oxidation of various mineral sulfides has received significant commercial interest.The attachment of Thiobacillus ferrooxidans and moderately thermophilic bacteria to sulfide minerals was investigated to further understand the mechanism(s) involved in the leaching of sulfide minerals. T.ferrooxidans (DSM 583 and ATCC 23270) and four strains of moderate thermophilic bacteria, Sulfobacillus thermosulfidooxidans, (strain TH1) and Sb.acidophilus (strains THWX, ALV and YTFI) all grown on ferrous iron, sulfur and a chalcopyrite concentrate (termed chalconc) were investigated using 3 sulfide mineral systems; pyrite, a chalcopyrite concentrate (chalconc) and an arsenic containing concentrate (termed arsenoconc). The degree of attachment of all substrate-grown cells along with contact angle measurements of both minerals and cells were determined in order to evaluate the effect of the growth substrate and the hydrophobic interactions on the attachment process. The attachment of both the mesophiles and moderate thermophiles were found to be dependant on the type of growth substrate, the substrate concentration and also the type of mineral studied. Whilst sufur-grown T. ferrooxidans (DSM 583) cells exhibited a higher degree of hydrophobicity, both ferrous iron and chalconc-grown cells showed a greater degree of attachment. This suggests that hydrophobic interactions are not principally responsible for the attachment of T. ferrooxidans to mineral sutfides. However, each moderately thermophilic strain exhibited greater attachment to the mineral sulfides when cultured on either the chalconc sample or elemental sulfur and all showed greater adhesion to the pyrite and arsenoconc samples than to the chalconc sample. Separate shake flask leaching of the sulfide samples T. ferrooxidans and Sb. thermosulfidooxidans (TH1) respectively in conjunction with the results of the attachment studies suggested that the leaching of mineral sulfides was a combination of both the direct and indirect mechanisms.
 
The use c f kaolin for both coating and filler applications in the paper industry requires a high brightness grade, so that treatment for the removal of iron, which adds color to the mineral decreasing its commercial value, is required. Bleaching of kaolin is usually carried out by reductive leaching of iron, producing effluents of considerable environmental concern. Despite little investigation, the use of organic acids seems to be a good alternative for the iron removal with the additional advantage of producing less-aggressive effluents.This paper presents a study of bleaching treatments with different samples of Brazilian kaolins using organic acids and fermented medium from cultivation as the leaching agent. The studies showed more effectiveness when oxalic acid and fermented medium were used. The brightness of a kaolin sample reached the levels for filler clay (sample not submitted to magnetic separation) and coating clay (sample submitted to magnetic separation), when fermented medium and oxalic acid were used as a bleaching agent. These results could not be obtained by more conventional methods.
 
This paper describes a convenient PC-based acoustic signal processing system and its application for monitoring hydrocyclone performance.Acoustic emissions generated from a five inch diameter hydrocyclone under different operating conditions were collected using a single 190 KHz passive acoustic sensor mounted externally on the conical section of the hydrocyclone. Subsequent analysis shows that the spectral characteristics of the signal are sensitive to the variations of operating parameters (feed pressure, solid concentrations, mass and volume flowrate and underflow solid concentrations). Use of multivariate statistical analysis techniques allows the quantitative relationships between various operating parameters of the hydrocyclone and the statistical and spectral characteristics of the acoustic signals to be established.The application of this sensor technology to audit classifiers and its potential for real-time control is demonstrated based on a laboratory case study.
 
High resolution meshes of virtual particles in the shape library classified as sub-rounded (SR), in this case produced by numerical rounding. 
Examples of some particles that have been scanned and saved in the library. 
Quartzite beach pebbles, a selection added to the group (R) was scanned for use in the shape library.
Numerical simulation that will capture the complex behaviour of rock fragment systems, e.g., in mining and civil engineering, requires both the computational mechanics capability to model particle interactions between complex shapes and an associated means to represent the kind of arbitrary or angular geometry relevant to problems involving rock fragments. This paper is concerned less with the modelling and more with the representation. Here, we focus on representation geared to ‘soft contact’ modelling using either combined finite-discrete element (FEM/DEM) methods, or non-spherical DEM methods such as multi-sphere approximations of irregular geometry. 3D laser ranging (LADAR) is used to capture astonishingly realistic rock aggregate geometries. We report on the work flow procedures to generate computationally meshed virtual particles for modelling. The design of a shape library and a suggested procedure for selecting virtual particles for input to FEM/DEM or DEM models is discussed together with the use of inertia moments for shape descriptors. Use of the shape library for shape descriptor analysis is also illustrated. DEM simulations of packing using irregular particles from the shape library are presented.
 
Occurring as impurities in ores, easily-slimed carbonate and silicate minerals markedly reduce selectivity and effectiveness of flotation. Preliminary slime flotation decreases this adverse effect. Investigations on the influence of composition of oxyethylated surfactants and polyacrylamide flocculants on the floatability of clayey-carbonate slimes have been performed and reported in this work, particularly for the flotation of potash ores.
 
As part of the separation by froth flotation of PVC and PET from waste bottles before recycling, the mechanism of action has been studied of a lignosulphonate used to selectively render the surface of PET hydrophilic. More specifically, an attempt has been made to determine the influence of cations.The results of the experimental study, based on flotation tests, wettability and zeta potential measurements, and APS analyses, demonstrate the essential role of bivalent cations such as calcium in the hydrophilization action of lignosulphonate. Calcium may play, through electrostatic interactions, the role of a bridge between the surface of the plastics and the lignosulphonate, both negatively charged.
 
Intensive mining and ore processing activities over the last fifty years concerning phosphate and polymetallic sulphidic ores at Navodari and Baia, by the Romanian Black Sea coast, have resulted in the production of millions of tonnes of hazardous wastes which contain high residual concentrations of heavy elements and radionuclides in mobile forms. At Navodari, where a chemical plant for the production of sulphuric acid and superphosphates operates, over 3,000,000 m3 of phosphogypsum and 1,000,000 m3 of pyritic cinders have been disposed of in several stacks and dumps. At Baia, over 1,200,000 † of copper tailings from the nearby located flotation plant have been disposed of since 1965 in three decantation ponds. Under the action of several physicochemical mechanisms, toxic elements contained in the tailings are mobilised migrate to the surroundings and cause severe and widespread contamination of soils, surface and ground waters and the Black Sea.In this paper, all the above mentioned sources of pollution that are currently directly or indirectly affecting humans, soils, freshwater ecosystems and the Black Sea, are identified and characterised Furthermore, in order to assess the level of risk posed by each source of pollution, at each affected area, a complete environmental characterisation study was undertaken followed by a risk analysis carried out on a source-pathway-target basis. Based on experimental and risk analysis data, a rehabilitation scheme is proposed for all affected areas, aiming at deactivating the pollution sources and rehabilitating the contaminated areas with remedial actions. This scheme involves mainly. removal of toxic and heavy elements from sulphidic tailings and leachates with biosorption and biosolubilisation techniques and development of a vegetative cover on phosphogypsum, cinders and sulphidic tailings.
 
Top-cited authors
James A Finch
  • McGill University
Jannie S J Van Deventer
  • University of Melbourne
Jorge Rubio
  • Universidade Federal do Rio Grande do Sul
Dee Bradshaw
  • The University of Queensland
Paul W. Cleary
  • The Commonwealth Scientific and Industrial Research Organisation