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An electrochemical method (potential sweep method) was utilized to investigate the nature of the absorbed gold on magnetite and to determine the gold sorption mechanism. A magnetite electrode was prepared in the laboratory, made in contact with a gold chloride solution at different conditions, and was subjected to cyclic voltammetry. The cyclic voltammogram of the magnetite electrode pretreated in a gold chloride solution recorded an anodic current peak at around 1.0 V (vs. Ag/AgCl), which corresponds to the current generated for the anodic dissolution of metallic gold in a chloride medium. The results of the electrochemical experiments suggest that gold chloride complexes are reduced to metallic gold on the surface of magnetite. A four-stage gold uptake mechanism was proposed: (i) the transport of AuC14- from the bulk solution to the magnetite surface, (ii) adsorption of AuC14- ions on magnetite surface by electrostatic attraction, (iii) electrochemical reduction of AuC14- to metallic Au, and (iv) the transport of soluble species to the solution phase. The electrochemical investigation also revealed that Fe3+ ions released from magnetite into the solution, suppressed the gold uptake at the acidic pH region.

Batch-sorption tests were carried out on the recovery of gold and platinum from NaCl solution by commercial grade magnetite powder, looking at the effect pH, contact time, and precious metal and NaCl concentration had on recovery. Au and Pt had similar pH dependent recovery curves, with peaks at pH 6-7. At this pH range, a maximum of 4.4 micro mol Au/g Fe3O4and 3.0 micro mol Pt/g Fe3O4 were recovered after 24 h at an initial metal concentration of 0.05 mol/m3. Metal recovery increased with increasing initial precious metals concentration, and decreased with high NaCl concentration. SEM images showed that the gold had agglomerated and was deposited on the magnetite surface., Batch-sorption tests were carried out on the recovery of gold and platinum from NaCl solution by commercial grade magnetite powder, looking at the effect pH, contact time, and precious metal and NaCl concentration had on recovery. Au and Pt had similar pH dependent recovery curves, with peaks at pH 6-7. At this pH range, a maximum of 4.4 micro mol Au/g Fe3O4and 3.0 micro mol Pt/g Fe3O4 were recovered after 24 h at an initial metal concentration of 0.05 mol/m3. Metal recovery increased with increasing initial precious metals concentration, and decreased with high NaCl concentration. SEM images showed that the gold had agglomerated and was deposited on the magnetite surface.

The development of environmental-friendly lixiviants as alternatives to cyanide and the increasing recycling activities to recover precious metals from waste materials have prompted researchers to find efficient methods and alternative sorbents to recover precious metals, such as Au and Pt, from aqueous solutions. This study explored the use of magnetite (Fe3O4) as a sorbent to recover Au and Pt from chloride solutions. Magnetite is a semiconductor and has the capability of transferring electrons both within the solid state and across the solid-liquid interface and has the ability to reduce metal species on its surface. The sorption of AuCl4- and PtCl62- from NaCl solution on commercial grade magnetite powder was investigated by batch-sorption experiments. The effects of pH, contact time, NaCl concentration and precious metal concentration on the recovery were studied. Sorption experiments revealed that magnetite exhibited selectivity towards other metals with the strongest affinity for Au. Both Au and Pt recoveries showed similar pH dependence curves, with peaks at pH 6-7. At this pH range, a maximum of 4.4 µmol Au/g Fe3O4 and 3.0 µmol Pt/g Fe3O4 were recovered after 24 h at an initial metal concentration of 0.05 mol/m3. Increasing the initial precious metal concentration increased the Au and Pt uptake amount by magnetite. It was also observed that the recovery decreased with high NaCl concentrations. The SEM images of the magnetite particles after the treatment showed that gold, which was confirmed by the EDX analysis, agglomerated and were deposited on Fe3O4 surface.

Jig separation of light small particles of non-spherical shape and specific gravities close in value was conducted using a TACUB jig to investigate the relationship between separation condition and fluidisation of the particles. The frequency and amplitude of the vibrations was varied. It was found that the particle layer was fluidised without turbulence by the rising water pulse, resulting in separation, but that too strong a water pulse reduced the separation efficiency. The expansion ratios of the thickness of the particle layer were measured in a cylindrical column. Pressure losses by the particle layer were calculated from the expansion ratios and the velocity of the rising flows using Ergun's equation. The curve of pressure loss against velocity of rising flow showed a maximum corresponding to the point of fluidisation. The velocity of a rising flow near the point of fluidisation defined the optimum separation condition., Jig separation of light small particles of non-spherical shape and specific gravities close in value was conducted using a TACUB jig to investigate the relationship between separation condition and fluidisation of the particles. The frequency and amplitude of the vibrations was varied. It was found that the particle layer was fluidised without turbulence by the rising water pulse, resulting in separation, but that too strong a water pulse reduced the separation efficiency. The expansion ratios of the thickness of the particle layer were measured in a cylindrical column. Pressure losses by the particle layer were calculated from the expansion ratios and the velocity of the rising flows using Ergun's equation. The curve of pressure loss against velocity of rising flow showed a maximum corresponding to the point of fluidisation. The velocity of a rising flow near the point of fluidisation defined the optimum separation condition.

Experimental results from previous investigations on gravity separation of cobalt-containing manganese nodules and crusts are reviewed. Observations and analysis of specimens from 10 different locations show that the liberation ratio of crushed product is high even at the coarse 0.5 to 4 mm fraction. If the less dense substrate rock or nucleus on which the crust/nodules form is removed with high separation efficiency, the separation product conforms to the requirement of the subsequent smelting process. Air table separation was used as a dry method and jig separation as a wet method. High grades with high recoveries were obtained for both methods., Experimental results from previous investigations on gravity separation of cobalt-containing manganese nodules and crusts are reviewed. Observations and analysis of specimens from 10 different locations show that the liberation ratio of crushed product is high even at the coarse 0.5 to 4 mm fraction. If the less dense substrate rock or nucleus on which the crust/nodules form is removed with high separation efficiency, the separation product conforms to the requirement of the subsequent smelting process. Air table separation was used as a dry method and jig separation as a wet method. High grades with high recoveries were obtained for both methods.

A carrier-in-pulp method is proposed to extract and recover heavy metals from melted fly ash. A carrier material, which recovers extracted metals from the aqueous phase, is added simultaneously with fly ash to leaching solutions and is harvested from the pulp by physical separation methods such as magnetic separation or sieving. Shaking flask experiments were conducted under various conditions using NaCl solution as lixiviant and iron powder or granular activated carbon as carrier material. Using iron powder over 97 wt% of Pb and Zn were extracted to the solution phase, but only Pb was recovered by cementation from the iron powder harvested from the pulp by magnetic separation, leaving behind Zn ions in the solution phase. Single-metal adsorption experiments with granular activated carbon gave 85% Pb and 88% Zn recovery, and 60% Pb and 70% Zn in the multi-metal experiments. The leaching test conducted on the Fe- treated residue showed that the solubilisation of Pb was suppressed to a value well below that defined as safe for landfill disposal., A carrier-in-pulp method is proposed to extract and recover heavy metals from melted fly ash. A carrier material, which recovers extracted metals from the aqueous phase, is added simultaneously with fly ash to leaching solutions and is harvested from the pulp by physical separation methods such as magnetic separation or sieving. Shaking flask experiments were conducted under various conditions using NaCl solution as lixiviant and iron powder or granular activated carbon as carrier material. Using iron powder over 97 wt% of Pb and Zn were extracted to the solution phase, but only Pb was recovered by cementation from the iron powder harvested from the pulp by magnetic separation, leaving behind Zn ions in the solution phase. Single-metal adsorption experiments with granular activated carbon gave 85% Pb and 88% Zn recovery, and 60% Pb and 70% Zn in the multi-metal experiments. The leaching test conducted on the Fe- treated residue showed that the solubilisation of Pb was suppressed to a value well below that defined as safe for landfill disposal.

Carrier-microencapsulation (CME) suppresses both the floatability and oxidation of pyrite by coating the pyrite particles with a thin layer of metal oxide or hydroxide using catechol solution as a carrier combined with metal ions. The layer converts the pyrite surface from hydrophobic to hydrophilic and acts as a protective coating against oxidation. Studies have been carried out to demonstrate the effect of CME using Si-catechol complex to suppress the pyrite floatability. The bubble pick-up experiments showed that attachment of pyrite particles to air bubble is suppressed by the CME treatment at pH 4-10, Si-catechol complex concentration over 0.5 mol m3 and treatment time within 2 min. Hallimond tube flotation experiments showed that the pyrite floatability is suppressed by the CME treatment even in the presence of typical flotation collectors such as kerosene and xanthate. SEM-EDX analysis confirmed that Si was present on the pyrite surface treated by the Si-catechol complex, implying that the SiO2 or Si(OH4) layer formed by the CME treatment converting the pyrite surface from hydrophobic to hydrophilic., Carrier-microencapsulation (CME) suppresses both the floatability and oxidation of pyrite by coating the pyrite particles with a thin layer of metal oxide or hydroxide using catechol solution as a carrier combined with metal ions. The layer converts the pyrite surface from hydrophobic to hydrophilic and acts as a protective coating against oxidation. Studies have been carried out to demonstrate the effect of CME using Si-catechol complex to suppress the pyrite floatability. The bubble pick-up experiments showed that attachment of pyrite particles to air bubble is suppressed by the CME treatment at pH 4-10, Si-catechol complex concentration over 0.5 mol m3 and treatment time within 2 min. Hallimond tube flotation experiments showed that the pyrite floatability is suppressed by the CME treatment even in the presence of typical flotation collectors such as kerosene and xanthate. SEM-EDX analysis confirmed that Si was present on the pyrite surface treated by the Si-catechol complex, implying that the SiO2 or Si(OH4) layer formed by the CME treatment converting the pyrite surface from hydrophobic to hydrophilic.

Melting has become a popular pretreatment method for municipal solid waste (MSW) incineration residues in Japan. Although the method is effective in stabilizing the hazardous organic substances such as dioxin in the residue, it concentrates the heavy metals such as Zn, Pb, Cu, and Cd in a newly formed fly ash which is also known as melting fly ash. Melting fly ash is classified as a hazardous waste because of the leaching potential of these heavy metals in landfill environments. Extraction and recovery of these metals seem to be more environmentally and economically attractive than disposing the material to landfill after immobilization process. This study proposes a Carrier-in-Pulp (CIP) method as a new hydrometallurgical route to reject and recover heavy metals from fly ash before landfilling. In this method, a carrier material which recovers the extracted metals is added simultaneously with fly ash to leaching solutions and is harvested from the pulp by physical separation method like magnetic separation or sieving. To demonstrate the effect of CIP method, shaking flask experiments for melting fly ash were conducted under various conditions using NaCl solution as lixiviant and iron powder or granular activated carbon as carrier materials.In the CIP method using iron powder, more than 97 wt% of Pb, Zn, Cu, and Cd, were extracted from the ash to the solution phase. However, the iron powder which was harvested from the pulp by magnetic separation, recovered only Pb and Cu (more than 94%) through cementation, leaving behind Zn and Cd ions in the solution phase. Due to this problem, granular activated carbon was used as an alternative carrier material. The CIP method using activated carbon extracted more than 90% of Zn, Pb, Cu, and Cd from the ash. The carbon granules were separated from the pulp through sieving. The results showed that activated carbon was superior to the iron powder since it was able to recover the extracted heavy metals from the ash through adsorpt

Pyrite coexisting with copper sulphide minerals such as chalcopyrite is separated by flotation as tailings and is oxidised in tailings dams, resulting in the formation of acid mine drainage. To suppress both the flotability and the oxidation of pyrite, a carrier micro-encapsulation process has been developed in which an organic carrier combined with Ti is used to form a thin TiO2 layer on the surface of the pyrite. Ground pyrite samples were treated with a Ti-catechol complex solution under various conditions. Bubble pick-up and flotation experiments showed that the characteristics of the pyrite changed from hydrophobic to hydrophilic, even in the presence of xanthate as a flotation collector. Oxidation tests using 0.02 kmol/m3 HNO3 showed that Fe release was suppressed by the treatment due to the formation of a TiO2 coating., Pyrite coexisting with copper sulphide minerals such as chalcopyrite is separated by flotation as tailings and is oxidised in tailings dams, resulting in the formation of acid mine drainage. To suppress both the flotability and the oxidation of pyrite, a carrier micro-encapsulation process has been developed in which an organic carrier combined with Ti is used to form a thin TiO2 layer on the surface of the pyrite. Ground pyrite samples were treated with a Ti-catechol complex solution under various conditions. Bubble pick-up and flotation experiments showed that the characteristics of the pyrite changed from hydrophobic to hydrophilic, even in the presence of xanthate as a flotation collector. Oxidation tests using 0.02 kmol/m3 HNO3 showed that Fe release was suppressed by the treatment due to the formation of a TiO2 coating.

Leaching tests using chloride media and ferric ions as oxidant were performed to investigate the relationship between the leaching rate of Cu from chalcopyrite and the oxidation-reduction potential. A zone of high leaching rates was found where Cu and Fe concentrations increased sharply; leaching reached a maximum at low oxidation-reduction potentials where ferrous ions were more concentrated than ferric ions., Leaching tests using chloride media and ferric ions as oxidant were performed to investigate the relationship between the leaching rate of Cu from chalcopyrite and the oxidation-reduction potential. A zone of high leaching rates was found where Cu and Fe concentrations increased sharply; leaching reached a maximum at low oxidation-reduction potentials where ferrous ions were more concentrated than ferric ions.

The results of shaking flask leaching experiments showed that leaching rate of chalcopyrite was determined by the normalised redox potential, a function of Cu2+, Fe2+ and Fe3+ concentrations. The results of the column leaching experiments showed that the control of the normalised redox potential improved copper extraction from chalcopyrite., The results of shaking flask leaching experiments showed that leaching rate of chalcopyrite was determined by the normalised redox potential, a function of Cu2+, Fe2+ and Fe3+ concentrations. The results of the column leaching experiments showed that the control of the normalised redox potential improved copper extraction from chalcopyrite.

The optimum conditions for Mn2+ removal from acid mine drainage were studied. Experiments were carried out to investigate the effects of pH, coexisting metal ions and S2- (as Na2S) concentration on MnS formation from Mn2+ solutions. The amount of Mn removed decreased with decreasing pH. Zn2+ or Fe2+ coexisting in the solutions consumed S2- by forming ZnS or FeS, and this inhibited Mn removal. A high molar ratio of S2- to Mn2+ concentrations was required to form manganese sulphides. Experiments using the sulphate-reducing bacteria Desulphovibrio desulphuricans (ATCC 7757) were carried out at 37 degrees C, pH 5-7 and in the absence of coexisting ions to investigate the effects of Mn2+ concentration on the activity of the bacteria in modified ATCC 1249 media containing 100-600 g/m3 Mn2+. In the solutions initially containing 100 and 200 g/m3 Mn2+, Mn concentration decreased to less than 10g/m3, the maximum contaminant level for environmental water quality in Japan. X-ray diffraction and an X-ray fluorescence spectroscopy analysis showed that the precipitate formed during Mn removal in the bioreactor was a metastable gamma-manganese sulphide., The optimum conditions for Mn2+ removal from acid mine drainage were studied. Experiments were carried out to investigate the effects of pH, coexisting metal ions and S2- (as Na2S) concentration on MnS formation from Mn2+ solutions. The amount of Mn removed decreased with decreasing pH. Zn2+ or Fe2+ coexisting in the solutions consumed S2- by forming ZnS or FeS, and this inhibited Mn removal. A high molar ratio of S2- to Mn2+ concentrations was required to form manganese sulphides. Experiments using the sulphate-reducing bacteria Desulphovibrio desulphuricans (ATCC 7757) were carried out at 37 degrees C, pH 5-7 and in the absence of coexisting ions to investigate the effects of Mn2+ concentration on the activity of the bacteria in modified ATCC 1249 media containing 100-600 g/m3 Mn2+. In the solutions initially containing 100 and 200 g/m3 Mn2+, Mn concentration decreased to less than 10g/m3, the maximum contaminant level for environmental water quality in Japan. X-ray diffraction and an X-ray fluorescence spectroscopy analysis showed that the precipitate formed during Mn removal in the bioreactor was a metastable gamma-manganese sulphide.

Although it is generally accepted that ferric ions are a strong oxidant for chalcopyrite whereas ferrous ions contribute to the leaching only as the oxidant's source, experiments have shown that 0-0.1 mol/l of ferrous ions can leach chalcopyrite more effectively than 0-0.1 mol/l of ferric ions in sulphuric acid solutions in air at ambient temperature. The oxidation of chalcopyrite by dissolved oxygen was promoted by the ferrous ions but suppressed by the ferric ions, resulting in a larger amount of Cu being extracted by the ferrous ions. Thiobacillus ferrooxidans suppressed ferrous-promoted leaching at around pH 2 by consuming the promoter ferrous ions, but bacterial action was inhibited when the initial pH was less than 1.35., Although it is generally accepted that ferric ions are a strong oxidant for chalcopyrite whereas ferrous ions contribute to the leaching only as the oxidant's source, experiments have shown that 0-0.1 mol/l of ferrous ions can leach chalcopyrite more effectively than 0-0.1 mol/l of ferric ions in sulphuric acid solutions in air at ambient temperature. The oxidation of chalcopyrite by dissolved oxygen was promoted by the ferrous ions but suppressed by the ferric ions, resulting in a larger amount of Cu being extracted by the ferrous ions. Thiobacillus ferrooxidans suppressed ferrous-promoted leaching at around pH 2 by consuming the promoter ferrous ions, but bacterial action was inhibited when the initial pH was less than 1.35.

The effects of six surfactants on bacterial leaching of chalcopyrite by Thiobacillus ferrooxidans were investigated without nutrient mineral salts such as ammonium sulphate. The chalcopyrite and sphalerite concentrate contained 27.0% Cu and 8.6% Zn. The adhesion of cells on the mineral surface was depressed by adding Tween20 and the cell numbers in the liquid phase increased with increasing addition. When adding 20-50 g/m3 of Tween20, ferrous ions were rapidly oxidised to ferric ions by Thiobacillus ferrooxidans and the ferric concentration became high. As more Tween20 was added, the main reactions of the indirect leaching mechanism were depressed and the amount of copper extraction decreased. The leaching behaviour with Tween40, Tween60, and Brij35 was similar. Tween80 and Tween85, however, have unsaturated bondings and they strongly suppressed the chemical leaching of chalcopyrite with ferric ions, with the maximum value of copper extracted being lower than with the other surfactants., The effects of six surfactants on bacterial leaching of chalcopyrite by Thiobacillus ferrooxidans were investigated without nutrient mineral salts such as ammonium sulphate. The chalcopyrite and sphalerite concentrate contained 27.0% Cu and 8.6% Zn. The adhesion of cells on the mineral surface was depressed by adding Tween20 and the cell numbers in the liquid phase increased with increasing addition. When adding 20-50 g/m3 of Tween20, ferrous ions were rapidly oxidised to ferric ions by Thiobacillus ferrooxidans and the ferric concentration became high. As more Tween20 was added, the main reactions of the indirect leaching mechanism were depressed and the amount of copper extraction decreased. The leaching behaviour with Tween40, Tween60, and Brij35 was similar. Tween80 and Tween85, however, have unsaturated bondings and they strongly suppressed the chemical leaching of chalcopyrite with ferric ions, with the maximum value of copper extracted being lower than with the other surfactants.

The oxidation of pyrite results in the formation of acid mine drainage containing heavy metals. A carrier-micro-encapsulation (CME) method is described to prevent oxidation in which an organic agent is used as an in- situ carrier to transport Ti from Ti minerals to the pyrite surface through an aqueous phase. The organic carrier is then decomposed and a Ti(OH)4 or TiO2 film is formed on the pyrite surface as a protective coating. Shaking-flask leaching experiments were carried out on ground pyrite at 298 K in air for 25 days in the presence or absence of anatase using catechol (1,2-dihydroxybenzene) as the organic carrier. The amounts of Fe and S extracted from the pyrite were lower in the presence of TiO2 and catechol, indicating that CME is effective in suppressing oxidation. The Ti concentration in solution initially increased and then decreased. Ti and O were present on the pyrite surface and oxidation of catechol occurred on the pyrite electrode., The oxidation of pyrite results in the formation of acid mine drainage containing heavy metals. A carrier-micro-encapsulation (CME) method is described to prevent oxidation in which an organic agent is used as an in- situ carrier to transport Ti from Ti minerals to the pyrite surface through an aqueous phase. The organic carrier is then decomposed and a Ti(OH)4 or TiO2 film is formed on the pyrite surface as a protective coating. Shaking-flask leaching experiments were carried out on ground pyrite at 298 K in air for 25 days in the presence or absence of anatase using catechol (1,2-dihydroxybenzene) as the organic carrier. The amounts of Fe and S extracted from the pyrite were lower in the presence of TiO2 and catechol, indicating that CME is effective in suppressing oxidation. The Ti concentration in solution initially increased and then decreased. Ti and O were present on the pyrite surface and oxidation of catechol occurred on the pyrite electrode.

Agglomeration tests were performed under various conditions. It was found that the porosity decrease was closely related to the formation and growth of agglomerates. There was a critical Os value (the ratio of volume of bridging liquid to void volume) beyond which the total number of agglomerates decreased rapidly. The size of the agglomerates is governed by a balance between the cohesive force of the agglomerates and the destructive force in the agitation field., Agglomeration tests were performed under various conditions. It was found that the porosity decrease was closely related to the formation and growth of agglomerates. There was a critical Os value (the ratio of volume of bridging liquid to void volume) beyond which the total number of agglomerates decreased rapidly. The size of the agglomerates is governed by a balance between the cohesive force of the agglomerates and the destructive force in the agitation field.

Agglomeration in liquid is a promising method for mineral and materials processing, fuel beneficiation and waste treatment. Fine particles suspended in a liquid are agglomerated by the addition of a second immiscible liquid or bridging liquid, which wets them preferentially under appropriate agitation conditions. Recent fundamental studies and applications are reviewed., Agglomeration in liquid is a promising method for mineral and materials processing, fuel beneficiation and waste treatment. Fine particles suspended in a liquid are agglomerated by the addition of a second immiscible liquid or bridging liquid, which wets them preferentially under appropriate agitation conditions. Recent fundamental studies and applications are reviewed.

The degree of surface hydrolysis of the minerals was measured by the deviation of the pH value from that of the ionic equivalence point. Two flotation agents were used. Flotation of barite with DAA was affected by surface hydrolysis, but flotation using SDS was not, showing the latter is adsorbed chemically. For calcite, both DAA and SDS flotation is affected by surface hydrolysis. The flotation behaviour of scheelite with DAA and SDS as a function of pH value was closely related to variation in the zeta potential., The degree of surface hydrolysis of the minerals was measured by the deviation of the pH value from that of the ionic equivalence point. Two flotation agents were used. Flotation of barite with DAA was affected by surface hydrolysis, but flotation using SDS was not, showing the latter is adsorbed chemically. For calcite, both DAA and SDS flotation is affected by surface hydrolysis. The flotation behaviour of scheelite with DAA and SDS as a function of pH value was closely related to variation in the zeta potential.

Leaching rates of chalcopyrite in sulphuric acid solutions depend on a redox potential determined by the activity ratio of ferric to ferrous ions, and is faster below a critical value called the critical potential. The paper reviews recent studies on the redox potential dependence of the leaching in the presence of activated carbon, silver ions, and bismuth ions as leaching catalysts. Leaching experiments show that all three increased the critical potential and expended the critical region where rapid copper extraction occurs. A proposed model assumes the formation of intermediate Cu2S by chalcopyrite reduction and its subsequent oxidation at low redox potentials. The leaching catalysts remove the hydrogen sulphide formed by chalcopyrite reduction, and this enhances the intermediate Cu2S formation and increases the critical potential corresponding to the redox potential., Leaching rates of chalcopyrite in sulphuric acid solutions depend on a redox potential determined by the activity ratio of ferric to ferrous ions, and is faster below a critical value called the critical potential. The paper reviews recent studies on the redox potential dependence of the leaching in the presence of activated carbon, silver ions, and bismuth ions as leaching catalysts. Leaching experiments show that all three increased the critical potential and expended the critical region where rapid copper extraction occurs. A proposed model assumes the formation of intermediate Cu2S by chalcopyrite reduction and its subsequent oxidation at low redox potentials. The leaching catalysts remove the hydrogen sulphide formed by chalcopyrite reduction, and this enhances the intermediate Cu2S formation and increases the critical potential corresponding to the redox potential.

Semi-batch flask leaching tests and circulated column leaching tests were used to investigate the effect of redox potential of the leach solutions on chalcopyrite leaching, and the results evaluated using a reaction model which assumed the formation of Cu2S as an intermediate product. Flask leaching tests of a chalcopyrite concentrate achieved approximately 99% copper extraction at a suitable range as predicted by the model. A practical method of control of the redox potential during leaching of low-grade copper ore containing mainly chalcopyrite is proposed; rougher bulk concentrates containing pyrite blended as a redox buffer proved very effective in column leaching of low-grade copper ore., Semi-batch flask leaching tests and circulated column leaching tests were used to investigate the effect of redox potential of the leach solutions on chalcopyrite leaching, and the results evaluated using a reaction model which assumed the formation of Cu2S as an intermediate product. Flask leaching tests of a chalcopyrite concentrate achieved approximately 99% copper extraction at a suitable range as predicted by the model. A practical method of control of the redox potential during leaching of low-grade copper ore containing mainly chalcopyrite is proposed; rougher bulk concentrates containing pyrite blended as a redox buffer proved very effective in column leaching of low-grade copper ore.

The noise emission of particles suspended in a liquid medium and agitated in a stirred vessel was studied experimentally. High-frequency noise signals exhibited changes corresponding to those in the size and number of particles. An increase in size or number of beads increases noise event rate, energy rate, oscillation rate, relative energy and frequency power spectra. The fundamental frequencies of vibration were estimated. The calculated frequencies of vibration arising from bead-wall and bead-bead impacts is in good agreement with the measured frequencies. An empirical relation between the relative energy of the noise and the diameter and number of particles was also derived. Liquid agglomeration techniques were used to produce zirconia microspheres with diameters less than 500 microns. A monitoring system that utilises changes in turbidity of the suspension and noise emitted during the agglomeration process was developed to produce agglomerates with the desired properties. The technical feasibility of online monitoring of the agglomerate diameter was demonstrated by measuring the relative energy of the noise and laser attenuation., The noise emission of particles suspended in a liquid medium and agitated in a stirred vessel was studied experimentally. High-frequency noise signals exhibited changes corresponding to those in the size and number of particles. An increase in size or number of beads increases noise event rate, energy rate, oscillation rate, relative energy and frequency power spectra. The fundamental frequencies of vibration were estimated. The calculated frequencies of vibration arising from bead-wall and bead-bead impacts is in good agreement with the measured frequencies. An empirical relation between the relative energy of the noise and the diameter and number of particles was also derived. Liquid agglomeration techniques were used to produce zirconia microspheres with diameters less than 500 microns. A monitoring system that utilises changes in turbidity of the suspension and noise emitted during the agglomeration process was developed to produce agglomerates with the desired properties. The technical feasibility of online monitoring of the agglomerate diameter was demonstrated by measuring the relative energy of the noise and laser attenuation.

An investigation of gold distribution in mill products at the Iranian plant showed that on average 44% of gold is routinely recovered as a by-product in the copper concentrate, while the remainder is lost to tailings. Gold distribution and modes of occurrence in ore and mill products were studied by back-scattered electron imaging of samples and by secondary ion mass spectroscopy of individual sulphide grains. The mineralogical distribution of gold revealed by microbeam techniques was combined with the results of metallurgical testwork including sizing, heavy media separation and diagnostic leaching tests. The results suggested that, while there is some gold in solid solution or as colloids in the sulphides, visible gold is the principle form of occurrence., An investigation of gold distribution in mill products at the Iranian plant showed that on average 44% of gold is routinely recovered as a by-product in the copper concentrate, while the remainder is lost to tailings. Gold distribution and modes of occurrence in ore and mill products were studied by back-scattered electron imaging of samples and by secondary ion mass spectroscopy of individual sulphide grains. The mineralogical distribution of gold revealed by microbeam techniques was combined with the results of metallurgical testwork including sizing, heavy media separation and diagnostic leaching tests. The results suggested that, while there is some gold in solid solution or as colloids in the sulphides, visible gold is the principle form of occurrence.

Operators at the zinc cleaning operation at Toyoha, Japan, had an initial strategy for controlling concentrate grade by adjusting air flow rate. The fuzzy controller was developed based on this main rule of thumb and limiting rules for the tailings grade were added. A more stable and higher grade was obtained using the fuzzy controller and total recovery was also satisfactory. Reagent consumption was reduced., Operators at the zinc cleaning operation at Toyoha, Japan, had an initial strategy for controlling concentrate grade by adjusting air flow rate. The fuzzy controller was developed based on this main rule of thumb and limiting rules for the tailings grade were added. A more stable and higher grade was obtained using the fuzzy controller and total recovery was also satisfactory. Reagent consumption was reduced.

Column leaching experiments were carried out on two chalcopyrite concentrates agglomerated on supporting particles using H2SO4 solutions under various conditions. The results were compared with those obtained in shaking flask leaching experiments. Solution composition, co-existing minerals such as pyrite and the presence of Fe-oxidising bacteria affected the dissolution of chalcopyrite, resulting in a significant variation in the Cu extraction fraction vs. time plots. The Cu extraction rate from unit surface area of chalcopyrite could be determined simply from a previously proposed normalised redox potential which is a function of the ferric, ferrous and cupric ion concentrations. The Cu extraction rate vs. normalised potential plot for the column leaching data fitted well with the plot obtained in shaking flask experiments. The Cu extraction rate has a maximum at normalised potentials of 0.4-0.5. The results suggest that the normalised potential may be used to assess and optimise chalcopyrite leaching using different methods and under various conditions., Column leaching experiments were carried out on two chalcopyrite concentrates agglomerated on supporting particles using H2SO4 solutions under various conditions. The results were compared with those obtained in shaking flask leaching experiments. Solution composition, co-existing minerals such as pyrite and the presence of Fe-oxidising bacteria affected the dissolution of chalcopyrite, resulting in a significant variation in the Cu extraction fraction vs. time plots. The Cu extraction rate from unit surface area of chalcopyrite could be determined simply from a previously proposed normalised redox potential which is a function of the ferric, ferrous and cupric ion concentrations. The Cu extraction rate vs. normalised potential plot for the column leaching data fitted well with the plot obtained in shaking flask experiments. The Cu extraction rate has a maximum at normalised potentials of 0.4-0.5. The results suggest that the normalised potential may be used to assess and optimise chalcopyrite leaching using different methods and under various conditions.