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Two reagent systems in commercial use for recovering and upgrading oxide copper minerals into mineral concentrates are discussed. The surface of an oxide copper mineral such as malachite, azurite, cuprite or tenorite is sulphidised using sulphide ion, either from a manual dose of NaSH or Na2S using a trial-and-error approach and visual assessment of the resulting froth, or from a controlled-potential sulphidisation based on the addition of sulphidiser to a measured and controlled residual of sulphide ion in solution. The S2- ion is followed by a collector such as xanthate. Direct flotation of oxide copper minerals after the addition of a hydroxamate collector is presented as an alternative and the advantages of this technology over sulphidisation are considered in the laboratory and on an industrial scale. Ore-related factors such as slimes, clays and goethite contents that can affect copper flotation performance are given as well as a summary of laboratory test procedures for the flotation of oxide copper ores., Two reagent systems in commercial use for recovering and upgrading oxide copper minerals into mineral concentrates are discussed. The surface of an oxide copper mineral such as malachite, azurite, cuprite or tenorite is sulphidised using sulphide ion, either from a manual dose of NaSH or Na2S using a trial-and-error approach and visual assessment of the resulting froth, or from a controlled-potential sulphidisation based on the addition of sulphidiser to a measured and controlled residual of sulphide ion in solution. The S2- ion is followed by a collector such as xanthate. Direct flotation of oxide copper minerals after the addition of a hydroxamate collector is presented as an alternative and the advantages of this technology over sulphidisation are considered in the laboratory and on an industrial scale. Ore-related factors such as slimes, clays and goethite contents that can affect copper flotation performance are given as well as a summary of laboratory test procedures for the flotation of oxide copper ores.

Adsorption and flotation tests were used to investigate the application of the chelating hydroxamate collector Aero 6943 for the treatment of two types of residue. The first was a lime neutralisation sludge containing 6.5% Fe, 21.1% Ca, 0.1% Cu, 0.5% Zn, 0.05% Ni and 0.02% Pb. The hydroxamate was shown to be a selective collector for the flotation of ferric hydroxide from calcium sulphate, with gypsum containing 1.2% Fe being obtained as the non-float product. The second was a sulphatation roast/water leach residue containing 22.1% Pb, 15.3% Fe, 2.3% Zn and 33.3% Ca. Flotation resulted in a lead sulphate product containing 10-12% Fe., Adsorption and flotation tests were used to investigate the application of the chelating hydroxamate collector Aero 6943 for the treatment of two types of residue. The first was a lime neutralisation sludge containing 6.5% Fe, 21.1% Ca, 0.1% Cu, 0.5% Zn, 0.05% Ni and 0.02% Pb. The hydroxamate was shown to be a selective collector for the flotation of ferric hydroxide from calcium sulphate, with gypsum containing 1.2% Fe being obtained as the non-float product. The second was a sulphatation roast/water leach residue containing 22.1% Pb, 15.3% Fe, 2.3% Zn and 33.3% Ca. Flotation resulted in a lead sulphate product containing 10-12% Fe.

AM28 is a non-hazardous product which is used as a 10%-50% solution in dilute KOH and is a selective collector for oxide or oxidised base metal minerals and replaces conventional sulphidisation for oxide mineral flotation. At Radio Hill AM28 is used in conjunction with traditional sulphide collectors, which allows simultaneous flotation of oxide and sulphide minerals. The concentrator is currently configured to treat supergene Cu ore from the open pit. The sulphide minerals in the upper zone of the VMS type deposit are digenite and chalcocite, with lesser chalcopyrite and covellite. Oxide minerals include cuprite, with lesser malachite and azurite. Gangue minerals include quartz, talc and chlorite. Plant trials are described in which AM28 was stage added into the circuit at nominally 80 g/t. Plant data over three months showed that the Cu recovery increased consistently from about 50%-60% to above 70% when AM28 was added. The concentrate grade was consistent with and without AM28, at 22%-24% Cu., AM28 is a non-hazardous product which is used as a 10%-50% solution in dilute KOH and is a selective collector for oxide or oxidised base metal minerals and replaces conventional sulphidisation for oxide mineral flotation. At Radio Hill AM28 is used in conjunction with traditional sulphide collectors, which allows simultaneous flotation of oxide and sulphide minerals. The concentrator is currently configured to treat supergene Cu ore from the open pit. The sulphide minerals in the upper zone of the VMS type deposit are digenite and chalcocite, with lesser chalcopyrite and covellite. Oxide minerals include cuprite, with lesser malachite and azurite. Gangue minerals include quartz, talc and chlorite. Plant trials are described in which AM28 was stage added into the circuit at nominally 80 g/t. Plant data over three months showed that the Cu recovery increased consistently from about 50%-60% to above 70% when AM28 was added. The concentrate grade was consistent with and without AM28, at 22%-24% Cu.

The literature of chelating agents, whose specificity for metal ions was recognised and researched from the 1920s, is reviewed. Although a large number of agents have been examined over the years, if S-O compounds are excluded then the only commercially used chelating collector is hydroxamate, as metal hydroxamates are particularly stable. Within suitable pH ranges, the neutral hydroxamic acid molecule chemisorbs on mineral surfaces: good flotation is obtained in some systems with monolayer coverage of hydroxamate and in others even with partial coverage, but at pH 9 the hydroxamate ion co-adsorbs with the hydroxamic acid molecule to give multilayers of collector that result in excellent flotation. In some systems, hydrolysis of metal ions that have left their lattice sites in the mineral is crucial for flotation; surface reaction between metal ions/hydroxy complexes are very important in these systems. Flotation of chrysocolla and rhodonite, hubnerite and pyrolusite occurs in a pH region in which their contained metal ions hydrolyse to monohydroxy complexes. Adsorption and flotation can be enhanced by higher temperature, or by longer conditioning time with insoluble minerals such as haematite. Excellent flotation of calite is obtained in relatively acid media due to its solubility leading to formation and adsorption of calcium hydroxamate on its surface. Hydroxy oximes function well as collectors, giving a similar response to that obtained by octyl hydroxamate in the case of chrysocolla and cuprite., The literature of chelating agents, whose specificity for metal ions was recognised and researched from the 1920s, is reviewed. Although a large number of agents have been examined over the years, if S-O compounds are excluded then the only commercially used chelating collector is hydroxamate, as metal hydroxamates are particularly stable. Within suitable pH ranges, the neutral hydroxamic acid molecule chemisorbs on mineral surfaces: good flotation is obtained in some systems with monolayer coverage of hydroxamate and in others even with partial coverage, but at pH 9 the hydroxamate ion co-adsorbs with the hydroxamic acid molecule to give multilayers of collector that result in excellent flotation. In some systems, hydrolysis of metal ions that have left their lattice sites in the mineral is crucial for flotation; surface reaction between metal ions/hydroxy complexes are very important in these systems. Flotation of chrysocolla and rhodonite, hubnerite and pyrolusite occurs in a pH region in which their contained metal ions hydrolyse to monohydroxy complexes. Adsorption and flotation can be enhanced by higher temperature, or by longer conditioning time with insoluble minerals such as haematite. Excellent flotation of calite is obtained in relatively acid media due to its solubility leading to formation and adsorption of calcium hydroxamate on its surface. Hydroxy oximes function well as collectors, giving a similar response to that obtained by octyl hydroxamate in the case of chrysocolla and cuprite.

The benefits are discussed of hydroxamate (AHX) based collectors compared with traditional tall oil fatty acids to float Ti and Fe based coloured impurity minerals in the treatment of kaolin resources. Recent advances are reviewed in the manufacture and formulation of modified AHX products that offer more economical alternatives and process options to provide high purity kaolin clay products for speciality applications on the basis of cost-performance criteria. The flotation performance of a series of newly developed formulations is described., The benefits are discussed of hydroxamate (AHX) based collectors compared with traditional tall oil fatty acids to float Ti and Fe based coloured impurity minerals in the treatment of kaolin resources. Recent advances are reviewed in the manufacture and formulation of modified AHX products that offer more economical alternatives and process options to provide high purity kaolin clay products for speciality applications on the basis of cost-performance criteria. The flotation performance of a series of newly developed formulations is described.

The papers presented are intended to highlight a significant advance in chemical use in each of a number of different mineral processing unit operations. The book is in three main sections: Dispersion and flocculation (6 papers); Selective processing (4 papers); and Microbiological control (3 papers). Topics include the role of polymers in dispersion stability, the synthesis of new polymeric surfactants and dispersants, the role of colloidal interactions in determining rheology, polymeric dispersants for very fine calcium carbonate slurries, the non-polymeric charge stabiliser or micro-dispersant AMP-95, pigment dispersion, selective flocculation of kaolinite, adsorption sites on unrefined and ball-milled kaolin, simulating water molecules at mineral surfaces, modified hydroxamate collectors for kaolin, implications of the Biocidal Products Directive, options for controlling microbiological problems in mineral slurries, and solving microbiological problems in the pigment slurry industry. There is a subject index., The papers presented are intended to highlight a significant advance in chemical use in each of a number of different mineral processing unit operations. The book is in three main sections: Dispersion and flocculation (6 papers); Selective processing (4 papers); and Microbiological control (3 papers). Topics include the role of polymers in dispersion stability, the synthesis of new polymeric surfactants and dispersants, the role of colloidal interactions in determining rheology, polymeric dispersants for very fine calcium carbonate slurries, the non-polymeric charge stabiliser or micro-dispersant AMP-95, pigment dispersion, selective flocculation of kaolinite, adsorption sites on unrefined and ball-milled kaolin, simulating water molecules at mineral surfaces, modified hydroxamate collectors for kaolin, implications of the Biocidal Products Directive, options for controlling microbiological problems in mineral slurries, and solving microbiological problems in the pigment slurry industry. There is a subject index.

The goal in kaolin flotation circuits is to remove coloured impurities to result in a product of acceptable brightness. Kaolin flotation originated with a novel carrier flotation process, and carrierless techniques were subsequently developed. The collector chemistry used to beneficiate kaolin is based on fatty acids, and recently hydroxamates have been successfully used. Discussion is presented of ultraflotation (carrier flotation), the ECCI (English China Clay International) carrierless process, the Ti removal and extraction process (TREP), and hydroxamate flotation. There are still many technological challenges to be addressed, including the variable response of kaolins from different sources, high conditioning energy requirements, low flotation solids and higher Fe removal., The goal in kaolin flotation circuits is to remove coloured impurities to result in a product of acceptable brightness. Kaolin flotation originated with a novel carrier flotation process, and carrierless techniques were subsequently developed. The collector chemistry used to beneficiate kaolin is based on fatty acids, and recently hydroxamates have been successfully used. Discussion is presented of ultraflotation (carrier flotation), the ECCI (English China Clay International) carrierless process, the Ti removal and extraction process (TREP), and hydroxamate flotation. There are still many technological challenges to be addressed, including the variable response of kaolins from different sources, high conditioning energy requirements, low flotation solids and higher Fe removal.

The Aluminium de Grece refinery has been processing Greek diasporic bauxite since 1964. The plant has five primary mud settlers, four flat bottomed and one conical bottomed, which operate on starch-based flocculants. The maximum overflow rate has been around 0.6 m3/h/m2, corresponding to 50 kg/h/m2 mud throughput. To get additional washing stages and reduce mud residence time, several synthetic flocculant strategies were investigated. The target overflow rate was 1.2 m3/h/m2. During industrial tests, the target was exceeded with hydroxamate, both with and without starch. With polyacrylamide and starch, it was difficult to control both clarity and rake torque. Hydroxamate dosage was progressively optimised and operation with only two settlers is being considered., The Aluminium de Grece refinery has been processing Greek diasporic bauxite since 1964. The plant has five primary mud settlers, four flat bottomed and one conical bottomed, which operate on starch-based flocculants. The maximum overflow rate has been around 0.6 m3/h/m2, corresponding to 50 kg/h/m2 mud throughput. To get additional washing stages and reduce mud residence time, several synthetic flocculant strategies were investigated. The target overflow rate was 1.2 m3/h/m2. During industrial tests, the target was exceeded with hydroxamate, both with and without starch. With polyacrylamide and starch, it was difficult to control both clarity and rake torque. Hydroxamate dosage was progressively optimised and operation with only two settlers is being considered.

Detailed studies carried out on samples of varying mineralogy showed that they differ significantly in their flotation behaviour. Flotation kinetics was found to play an important role in the recovery of various copper minerals. Hallimond tube and batch flotation experiments indicated the superiority of alkyl hydroxamate over xanthate for the flotation of oxidised ores. The high oxide ore sample containing 23% chalcopyrite, 40% chalcocite, 25% malachite, and 10% cuprite, showed significant improvement in kinetics using a 50:50 combination of xanthate and hydroxamate., Detailed studies carried out on samples of varying mineralogy showed that they differ significantly in their flotation behaviour. Flotation kinetics was found to play an important role in the recovery of various copper minerals. Hallimond tube and batch flotation experiments indicated the superiority of alkyl hydroxamate over xanthate for the flotation of oxidised ores. The high oxide ore sample containing 23% chalcopyrite, 40% chalcocite, 25% malachite, and 10% cuprite, showed significant improvement in kinetics using a 50:50 combination of xanthate and hydroxamate.

Four ore types are found: chalcopyritic, tarnished chalcopyritic, secondary sulphides and high oxide and were used to investigate two techniques, sulphidisation and the addition of a chelating auxiliary agent, which can enhance the flotation of mixed ores. An increase in the xanthate dosage caused a significant improvement in the flotation kinetics of secondary sulphides but not malachite. Sulphidisation-flotation was found to be most effective in the sulphide ion electrode potential range of -500 to -600 mV. Alternatively the flotation kinetics of oxidised ores could also be enhanced using a xanthate-hydroxamate reagent combination., Four ore types are found: chalcopyritic, tarnished chalcopyritic, secondary sulphides and high oxide and were used to investigate two techniques, sulphidisation and the addition of a chelating auxiliary agent, which can enhance the flotation of mixed ores. An increase in the xanthate dosage caused a significant improvement in the flotation kinetics of secondary sulphides but not malachite. Sulphidisation-flotation was found to be most effective in the sulphide ion electrode potential range of -500 to -600 mV. Alternatively the flotation kinetics of oxidised ores could also be enhanced using a xanthate-hydroxamate reagent combination.

The industrial uses of Y are reviewed and the results are presented of an investigation into the pre-concentration of xenotime with the objective of reducing the costs of further processing stages for Y production. Tests were carried out on a xenotime and zircon concentrate sample obtained from the non- conducting product of the electrostatic separator at the Pitinga mine in Amazonas, Brazil. Microflotation experiments were performed in a modified Hallimond tube in the presence of a commercial hydroxamate collector and sodium silicate, calcium lignin sulphonate, starch, amylopectin and quebracho as depressants. Optimum selectivity was obtained using sodium silicate and starch, with xenotime recoveries of 93.9% and 96.5%, respectively, being achieved., The industrial uses of Y are reviewed and the results are presented of an investigation into the pre-concentration of xenotime with the objective of reducing the costs of further processing stages for Y production. Tests were carried out on a xenotime and zircon concentrate sample obtained from the non- conducting product of the electrostatic separator at the Pitinga mine in Amazonas, Brazil. Microflotation experiments were performed in a modified Hallimond tube in the presence of a commercial hydroxamate collector and sodium silicate, calcium lignin sulphonate, starch, amylopectin and quebracho as depressants. Optimum selectivity was obtained using sodium silicate and starch, with xenotime recoveries of 93.9% and 96.5%, respectively, being achieved.

The proceedings are presented in three volumes, comprising vols.8-10 of the journal Mineral Processing and Extractive Metallurgy Review. Topics range from overviews through theoretical and laboratory to plant studies and from mineral processing through hydro-, electro- and pyrometallurgy to process technology and modelling, covering ferrous, non- ferrous, rare-earth and nuclear metals. The first volume includes papers on Cu in situ leaching, extractive metallurgy, peroxygen reagents in hydrometallurgy, electrogenerated gas bubbles in flotation, leaching processes, decomposition mechanisms, Cu SX-EW, high-purity Al via electrochemical model of electrolysis, controlled adsorption of surfactant and polymer-surfactant mixtures, bioprocessing Au, rare earth separation/purification, leaching Cu sulphides and mattes in oxygenated chlorides/sulphates, pyrite removal in coal flotation, emerging technologies in hydrometallurgy, electrochemistry of pyrite flotation with/without K-octyl hydroxamate, and top-submerged lancing (Sirosmelt) technology in smelting complex materials. The second volume includes papers on mathematical modelling in materials processing, removal of fine particles by liquid beds, Ag and Cu dissolution from alloys, WC-Co by direct reduction carburisation, spent fuel reprocessing in France, Pt recovery from analytical residues, roasting of Ni garnierites, fixing heavy metals in clay/sludge at high temperatures and pressures, flotation of fluorite from cassiterite, measuring flow and interpolar resistance in advanced Hall-Heroult cells, chemical metallurgy in the vapour phase - plasma-assisted deposition, NiCl2 vapourisation kinetics/diffusion, chromite beneficiation and agglomeration in Turkey, pyrometallurgical preconcentration of Cu, Ni and Co from Ghatsila copper converter slag, pressure leaching sphalerite-galena-chalcopyrite-silver concentrate in H2SO4+O2 solution, design of gas fluidised beds, mining and processing Turkish borates, As in Au processing, The proceedings are presented in three volumes, comprising vols.8-10 of the journal Mineral Processing and Extractive Metallurgy Review. Topics range from overviews through theoretical and laboratory to plant studies and from mineral processing through hydro-, electro- and pyrometallurgy to process technology and modelling, covering ferrous, non- ferrous, rare-earth and nuclear metals. The first volume includes papers on Cu in situ leaching, extractive metallurgy, peroxygen reagents in hydrometallurgy, electrogenerated gas bubbles in flotation, leaching processes, decomposition mechanisms, Cu SX-EW, high-purity Al via electrochemical model of electrolysis, controlled adsorption of surfactant and polymer-surfactant mixtures, bioprocessing Au, rare earth separation/purification, leaching Cu sulphides and mattes in oxygenated chlorides/sulphates, pyrite removal in coal flotation, emerging technologies in hydrometallurgy, electrochemistry of pyrite flotation with/without K-octyl hydroxamate, and top-submerged lancing (Sirosmelt) technology in smelting complex materials. The second volume includes papers on mathematical modelling in materials processing, removal of fine particles by liquid beds, Ag and Cu dissolution from alloys, WC-Co by direct reduction carburisation, spent fuel reprocessing in France, Pt recovery from analytical residues, roasting of Ni garnierites, fixing heavy metals in clay/sludge at high temperatures and pressures, flotation of fluorite from cassiterite, measuring flow and interpolar resistance in advanced Hall-Heroult cells, chemical metallurgy in the vapour phase - plasma-assisted deposition, NiCl2 vapourisation kinetics/diffusion, chromite beneficiation and agglomeration in Turkey, pyrometallurgical preconcentration of Cu, Ni and Co from Ghatsila copper converter slag, pressure leaching sphalerite-galena-chalcopyrite-silver concentrate in H2SO4+O2 solution, design of gas fluidised beds, mining and processing Turkish borates, As in Au processing

Flotation and leaching were investigated as possible processing routes for improving PGE recovery from an oxidised platinum-group metal (PGM) ore from the Mimosa mine (Zimbabwe). Different flotation reagent schemes and lixiviants were evaluated and their PGE extraction response measured. The maximum PGE flotation recovery achieved using sulphide co-collector schemes was 55.1% 3E (Pt, Pd, and Au). Application of the hydroxamate oxide collector improved the flotation recovery to 74.7% 3E. The superior PGE recoveries achieved with hydroxamates is probably due to their ability to form complexes with base metals such as iron. Direct leaching of oxidic PGE ore using different acids yielded relatively low PGE extractions. Leaching in hydrochloric acid gave extractions of 36.6% Pt and 8.8% Pd, nitric acid had extractions of 34.5% Pt and 7.1% Pd. The best leaching results were obtained using aqua regia, with extractions of 48% Pt and 24.5% Pd. In view of the low PGE extractions obtained by leaching run-of-mine ore, it was considered more promising to leach the concentrate as a way of further upgrading it. Concentrate leaching using sulphuric acid gave recoveries of 73.3% Cu, 82.9% Ni, and 8.1% Fe., Flotation and leaching were investigated as possible processing routes for improving PGE recovery from an oxidised platinum-group metal (PGM) ore from the Mimosa mine (Zimbabwe). Different flotation reagent schemes and lixiviants were evaluated and their PGE extraction response measured. The maximum PGE flotation recovery achieved using sulphide co-collector schemes was 55.1% 3E (Pt, Pd, and Au). Application of the hydroxamate oxide collector improved the flotation recovery to 74.7% 3E. The superior PGE recoveries achieved with hydroxamates is probably due to their ability to form complexes with base metals such as iron. Direct leaching of oxidic PGE ore using different acids yielded relatively low PGE extractions. Leaching in hydrochloric acid gave extractions of 36.6% Pt and 8.8% Pd, nitric acid had extractions of 34.5% Pt and 7.1% Pd. The best leaching results were obtained using aqua regia, with extractions of 48% Pt and 24.5% Pd. In view of the low PGE extractions obtained by leaching run-of-mine ore, it was considered more promising to leach the concentrate as a way of further upgrading it. Concentrate leaching using sulphuric acid gave recoveries of 73.3% Cu, 82.9% Ni, and 8.1% Fe.

The design and development of selective flotation collectors has been the key to the remarkable success of flotation in beneficiating complex, difficult-to-process ores. Sustained research efforts in the field over the past hundred years have led to delineating the scientific basis of selective mineral flotation in terms of the crystal chemistry and the surface and colloid chemistry of minerals including their solubility, and the aqueous solution chemistry of added reagents. It is now well-established that the electrical double-layer theory (EDL) is the most powerful means of quantifying the relative strength of mineral-reagent interactions in the case of nonsulphide minerals. The utility and the power of the EDL in delineating the science underlying selective mineral flotation is illustrated with the help of a few examples taken from the authors' own work, in particular on the selective flotation of rare-earth minerals (bastnaesite) from associated semisoluble minerals (barite and calcite) using alkyl hydroxamate collectors and the flotation separation of lithium-containing minerals (spodumene) from associated alumino-silicate minerals with oleate (fatty acids). Both of these mineral separation systems are of contemporary research interest and of immense value to the industry today. Recent advances in utilising molecular modelling computations, particularly in the context of quantifying the effect of crystal chemistry and the relative distribution of adsorption sites available on mineral cleavage planes, are also reviewed., The design and development of selective flotation collectors has been the key to the remarkable success of flotation in beneficiating complex, difficult-to-process ores. Sustained research efforts in the field over the past hundred years have led to delineating the scientific basis of selective mineral flotation in terms of the crystal chemistry and the surface and colloid chemistry of minerals including their solubility, and the aqueous solution chemistry of added reagents. It is now well-established that the electrical double-layer theory (EDL) is the most powerful means of quantifying the relative strength of mineral-reagent interactions in the case of nonsulphide minerals. The utility and the power of the EDL in delineating the science underlying selective mineral flotation is illustrated with the help of a few examples taken from the authors' own work, in particular on the selective flotation of rare-earth minerals (bastnaesite) from associated semisoluble minerals (barite and calcite) using alkyl hydroxamate collectors and the flotation separation of lithium-containing minerals (spodumene) from associated alumino-silicate minerals with oleate (fatty acids). Both of these mineral separation systems are of contemporary research interest and of immense value to the industry today. Recent advances in utilising molecular modelling computations, particularly in the context of quantifying the effect of crystal chemistry and the relative distribution of adsorption sites available on mineral cleavage planes, are also reviewed.

Test results indicate that under the synergistic action of the combined collector, a copper concentrate of 26% Cu grade, with 80% recovery, can be produced from an ore containing malachite and pseudomalachite, and a concentrate of 25% Cu, with a recovery of 85%, from a highly siliceous pelitic copper oxide ore. The collector has successfully floated a siliceous Cu-Fe intergrowth oxidised ore containing silver and gold to produce a 36% Cu concentrate and an Ag-rich Au concentrate containing 340g/ton Ag and 108g/ton Au., Test results indicate that under the synergistic action of the combined collector, a copper concentrate of 26% Cu grade, with 80% recovery, can be produced from an ore containing malachite and pseudomalachite, and a concentrate of 25% Cu, with a recovery of 85%, from a highly siliceous pelitic copper oxide ore. The collector has successfully floated a siliceous Cu-Fe intergrowth oxidised ore containing silver and gold to produce a 36% Cu concentrate and an Ag-rich Au concentrate containing 340g/ton Ag and 108g/ton Au.

A kaolin clay from northern Brazil, containing coloured impurities of iron oxides and of TiO2 including iron-stained anatase, has been treated by flotation using the collector alkylhydroxamate R6973, which does not require activators. About 90% of the sample particles were finer than 2 microns. It was possible to reduce the TiO2 content from 1.9% to approximately 1% at 70-76% weight recovery. Selective flocculation can achieve a TiO2 content of 0.8% at 56% weight recovery., A kaolin clay from northern Brazil, containing coloured impurities of iron oxides and of TiO2 including iron-stained anatase, has been treated by flotation using the collector alkylhydroxamate R6973, which does not require activators. About 90% of the sample particles were finer than 2 microns. It was possible to reduce the TiO2 content from 1.9% to approximately 1% at 70-76% weight recovery. Selective flocculation can achieve a TiO2 content of 0.8% at 56% weight recovery.

Modified hydroxamate collectors have been developed for the removal by reverse flotation of discolouring impurities from kaolin. Unlike the conventional tall oil collector, they do not require activation of the metal ion and they have better performance than the current hydroxamate collector used - Aero Promoter 6493. Flotation tests were carried out on fine-grained hard and coarse-grained soft Georgia kaolins. Generally the new collectors S-8704 and S-8706 had higher activity, easier handling, improved stability, and could have improved frothing quality. In full-scale column flotation plant trials, S-8706 showed better performance in flotation of a soft kaolin than AP 6493., Modified hydroxamate collectors have been developed for the removal by reverse flotation of discolouring impurities from kaolin. Unlike the conventional tall oil collector, they do not require activation of the metal ion and they have better performance than the current hydroxamate collector used - Aero Promoter 6493. Flotation tests were carried out on fine-grained hard and coarse-grained soft Georgia kaolins. Generally the new collectors S-8704 and S-8706 had higher activity, easier handling, improved stability, and could have improved frothing quality. In full-scale column flotation plant trials, S-8706 showed better performance in flotation of a soft kaolin than AP 6493.

A critical analysis of the available information and data, based on several case studies, flotation testing and microscopic analysis, indicates that alkyl hydroxamates can effectively recover well-defined Cu oxide minerals, such as malachite, cuprite, tenorite, azurite, atacamite and high-Cu chrysocolla, without sulphidisation or activation. However, certain species which report as acid-soluble in chemical assays cannot be recovered. These include Cu-bearing goethite (often misidentified as cuprite), finely disseminated cuprite and low-Cu chrysocolla. Mineralogical characterisation by microscopic and microprobe analysis must therefore be carried out prior to flotation testing. Alkyl hydroxamates offer a simple and attractive alternative to sulphidisation-flotation, with no special controls needed, flexibility of addition point and ease of handling., A critical analysis of the available information and data, based on several case studies, flotation testing and microscopic analysis, indicates that alkyl hydroxamates can effectively recover well-defined Cu oxide minerals, such as malachite, cuprite, tenorite, azurite, atacamite and high-Cu chrysocolla, without sulphidisation or activation. However, certain species which report as acid-soluble in chemical assays cannot be recovered. These include Cu-bearing goethite (often misidentified as cuprite), finely disseminated cuprite and low-Cu chrysocolla. Mineralogical characterisation by microscopic and microprobe analysis must therefore be carried out prior to flotation testing. Alkyl hydroxamates offer a simple and attractive alternative to sulphidisation-flotation, with no special controls needed, flexibility of addition point and ease of handling.

The reagents studied for the flotation of treated slag were sodium oleate, hydroxamate, dodecyl amido-methyl phosphonic acid, sodium fluorosilicate and sodium silicate. It was shown that perovskite can be effectively separated from Ti-rich diopside, titanaugite and spinel in weak acid pulp using hydroxamate as collector, sodium silicate as depressant and sulphuric acid as regulator. An investigation into the chemical mechanism of reagent attachment to the mineral surface found that the different flotabilities of perovskite and titanaugite resulted from different distribution densities, location and activation of Ca and Ti particles on the crystal surfaces. A decrease in zeta potential of perovskite with increased hydroxamate dosage indicated that it was adsorbed on the mineral surface and the bonding was confirmed by the infrared spectra., The reagents studied for the flotation of treated slag were sodium oleate, hydroxamate, dodecyl amido-methyl phosphonic acid, sodium fluorosilicate and sodium silicate. It was shown that perovskite can be effectively separated from Ti-rich diopside, titanaugite and spinel in weak acid pulp using hydroxamate as collector, sodium silicate as depressant and sulphuric acid as regulator. An investigation into the chemical mechanism of reagent attachment to the mineral surface found that the different flotabilities of perovskite and titanaugite resulted from different distribution densities, location and activation of Ca and Ti particles on the crystal surfaces. A decrease in zeta potential of perovskite with increased hydroxamate dosage indicated that it was adsorbed on the mineral surface and the bonding was confirmed by the infrared spectra.

Flotation testing was carried out at a laboratory scale using staged addition of various hydroxamates. From the results, it was inferred that chemisorption of hydroxamate species on the haematite surface takes place, possibly involving both the undissociated hydroxamic acid and hydroxamate ion, as maximum recovery occurred close to the pKa of the hydroxamic acid. A specular haematite ore containing 40% Fe and 42.5% SiO2 gave the highest iron grades in concentrate at pH 6, in contrast to published data which suggested pH 9 as the optimum value for processing. Using octyl hydroxamate in four stage additions of 50 g/t at pH 6, a rougher concentrate assaying 67% Fe was obtained with 51% recovery. For lower-grade concentrates still meeting the 60% Fe requirement for pigment-grade micaceous iron oxide, iron recoveries of 80% were possible with stage additions of 50 g/t octyl hydroxamate in the pH range 6-8., Flotation testing was carried out at a laboratory scale using staged addition of various hydroxamates. From the results, it was inferred that chemisorption of hydroxamate species on the haematite surface takes place, possibly involving both the undissociated hydroxamic acid and hydroxamate ion, as maximum recovery occurred close to the pKa of the hydroxamic acid. A specular haematite ore containing 40% Fe and 42.5% SiO2 gave the highest iron grades in concentrate at pH 6, in contrast to published data which suggested pH 9 as the optimum value for processing. Using octyl hydroxamate in four stage additions of 50 g/t at pH 6, a rougher concentrate assaying 67% Fe was obtained with 51% recovery. For lower-grade concentrates still meeting the 60% Fe requirement for pigment-grade micaceous iron oxide, iron recoveries of 80% were possible with stage additions of 50 g/t octyl hydroxamate in the pH range 6-8.

Oleoyl sarcosine was compared with hydroxamate and potassium oleate for its ability to remove Ti minerals (mainly rutile with some sphene) from a feldspar ore before and after dry magnetic separation. For the size fraction 0.2-2.0 mm, a non-magnetic concentrate was produced with 88.3 wt% feldspar, 0.105% TiO2 and 0.095% Fe2O3. Floated with oleoyl sarcosine under optimum conditions, this gave rise to a feldspar concentrate assaying 0.036% TiO2 and 0.090% Fe2O3, with 89.7% of the remaining TiO2 recovered to TiO2 concentrates but little reduction in the micaceous Fe2O3 content of the feldspar product beyond that already achieved by magnetic separation. Optimum grades and recoveries were obtained by increasing the solids content of the pulps to 30 wt%. Oleoyl sarcosine had fast kinetics and required six times lower collector dosages than either hydroxamate, which was very selective but highly expensive, or potassium oleate., Oleoyl sarcosine was compared with hydroxamate and potassium oleate for its ability to remove Ti minerals (mainly rutile with some sphene) from a feldspar ore before and after dry magnetic separation. For the size fraction 0.2-2.0 mm, a non-magnetic concentrate was produced with 88.3 wt% feldspar, 0.105% TiO2 and 0.095% Fe2O3. Floated with oleoyl sarcosine under optimum conditions, this gave rise to a feldspar concentrate assaying 0.036% TiO2 and 0.090% Fe2O3, with 89.7% of the remaining TiO2 recovered to TiO2 concentrates but little reduction in the micaceous Fe2O3 content of the feldspar product beyond that already achieved by magnetic separation. Optimum grades and recoveries were obtained by increasing the solids content of the pulps to 30 wt%. Oleoyl sarcosine had fast kinetics and required six times lower collector dosages than either hydroxamate, which was very selective but highly expensive, or potassium oleate.

Turkish feldspars contain rutile and occasionally sphene as the major source of Ti minerals, with Fe originating from micas. Studies were carried out of the use of a conventional collector, potassium oleate, and new collectors, oleoyl sarcosine and hydroxamate, in the flotation of TiO2 impurities. Results showed that for similar performances, only 200 g/t of oleoyl sarcosine was required whereas potassium oleate needed 1 000 g/t. Staged collector addition improved the quality of the feldspar concentrate for all the collectors. Optimum grades and recoveries were obtained by increasing wt% solids to 42% for oleoyl sarcosine and 28% for hydroxamate. Under optimum conditions, oleoyl sarcosine produced a concentrate assaying 0.039% TiO2 with 84.2% TiO2 recovery in a single stage while hydroxamate gave a concentrate of 0.037% TiO2 with 86.5% recovery using four-stage collector addition., Turkish feldspars contain rutile and occasionally sphene as the major source of Ti minerals, with Fe originating from micas. Studies were carried out of the use of a conventional collector, potassium oleate, and new collectors, oleoyl sarcosine and hydroxamate, in the flotation of TiO2 impurities. Results showed that for similar performances, only 200 g/t of oleoyl sarcosine was required whereas potassium oleate needed 1 000 g/t. Staged collector addition improved the quality of the feldspar concentrate for all the collectors. Optimum grades and recoveries were obtained by increasing wt% solids to 42% for oleoyl sarcosine and 28% for hydroxamate. Under optimum conditions, oleoyl sarcosine produced a concentrate assaying 0.039% TiO2 with 84.2% TiO2 recovery in a single stage while hydroxamate gave a concentrate of 0.037% TiO2 with 86.5% recovery using four-stage collector addition.

The Minto mine in Yukon, Canada, processes a high-grade Cu-Au deposit. The ore is from a primary copper sulphide deposit with separate additional deposits of copper oxides. Laboratory studies were carried out of the flotation of a blended ore containing 70 wt% sulphide ore and 30wt% oxide ore. The copper sulphides were bornite and chalcopyrite and the oxides were malachite and minor azurite. The results showed that the use of n-octyl hydroxamates in conjunction with traditional sulphide collectors could be used to recover copper sulphides and oxides simultaneously. The copper sulphide recovery did not decrease when compared with the treatment of the sulphide ore alone. The rougher scavenger Cu recovery was as high as 95.5% and was higher than that obtained using only xanthate after controlled potential sulphidisation., The Minto mine in Yukon, Canada, processes a high-grade Cu-Au deposit. The ore is from a primary copper sulphide deposit with separate additional deposits of copper oxides. Laboratory studies were carried out of the flotation of a blended ore containing 70 wt% sulphide ore and 30wt% oxide ore. The copper sulphides were bornite and chalcopyrite and the oxides were malachite and minor azurite. The results showed that the use of n-octyl hydroxamates in conjunction with traditional sulphide collectors could be used to recover copper sulphides and oxides simultaneously. The copper sulphide recovery did not decrease when compared with the treatment of the sulphide ore alone. The rougher scavenger Cu recovery was as high as 95.5% and was higher than that obtained using only xanthate after controlled potential sulphidisation.

The use is discussed of polyacrylate and hydroxamate flocculants to aid solid-liquid separation of bauxite residue from pregnant liquor in the Bayer process. A study was carried out of bauxite residue flocculation using a focused-beam reflectance measurement probe to monitor aggregate dimensions. The main difference between polyacrylate and hydroxamate flocculation was the way the aggregates developed post-shear, with hydroxamate flocculation exhibiting a greater degree of post-shear flocculation. Polyacrylate aggregates were more dense and shear-resistant, whereas the hydroxamate aggregates exhibited greater fines capture and lower solids in the supernatant. The solids remaining in the supernatant after flocculation differed, with the polyacrylate system having more coarse particles within the solid and the hydroxamate system having finer and more Fe-rich particles. The results are discussed in relation to the different ways in which each polymer adsorbs on to the residue material., The use is discussed of polyacrylate and hydroxamate flocculants to aid solid-liquid separation of bauxite residue from pregnant liquor in the Bayer process. A study was carried out of bauxite residue flocculation using a focused-beam reflectance measurement probe to monitor aggregate dimensions. The main difference between polyacrylate and hydroxamate flocculation was the way the aggregates developed post-shear, with hydroxamate flocculation exhibiting a greater degree of post-shear flocculation. Polyacrylate aggregates were more dense and shear-resistant, whereas the hydroxamate aggregates exhibited greater fines capture and lower solids in the supernatant. The solids remaining in the supernatant after flocculation differed, with the polyacrylate system having more coarse particles within the solid and the hydroxamate system having finer and more Fe-rich particles. The results are discussed in relation to the different ways in which each polymer adsorbs on to the residue material.

A model system was used to investigate the interaction between carbonate mineral and octanohydroxamate collector. Bastnaesite (Ce) is the most important rare earth mineral that has been the dominant rare earth source since the 1960s. In this study, a synthetic cerium carbonate thin film on a calcite (the most common gangue mineral occurring with rare earth minerals) substrate was formed for a surface interaction investigation. The cerium carbonate thin film system was characterised using Raman spectroscopy, atomic force microscopy and magnetic atomic force microscopy. An adsorption study between the model compound and hydroxamate was also conducted. The study established the utility of using atomic force microscopy and magnetic atomic force microscopy to investigate the mineral surface interaction. Weak adsorption on the thin film surface was observed after 5 hours and 24 hours of conditioning and the hydroxamate adsorption became evident after 72 hours of conditioning. The adsorption studies for cerium carbonate and calcite also demonstrated that hydroxamate is selective for bastnaesite over Ca. (Authors.), A model system was used to investigate the interaction between carbonate mineral and octanohydroxamate collector. Bastnaesite (Ce) is the most important rare earth mineral that has been the dominant rare earth source since the 1960s. In this study, a synthetic cerium carbonate thin film on a calcite (the most common gangue mineral occurring with rare earth minerals) substrate was formed for a surface interaction investigation. The cerium carbonate thin film system was characterised using Raman spectroscopy, atomic force microscopy and magnetic atomic force microscopy. An adsorption study between the model compound and hydroxamate was also conducted. The study established the utility of using atomic force microscopy and magnetic atomic force microscopy to investigate the mineral surface interaction. Weak adsorption on the thin film surface was observed after 5 hours and 24 hours of conditioning and the hydroxamate adsorption became evident after 72 hours of conditioning. The adsorption studies for cerium carbonate and calcite also demonstrated that hydroxamate is selective for bastnaesite over Ca. (Authors.)

This is the last in a series of papers addressing the by-product potential of light rare-earth elements (LREE: La, Ce, Nd) and rare metals (Sn, Nb, W) within the St Austell kaolin deposits, UK. Previous results have shown that heavy minerals are pre-concentrated in the micaceous residue which displays relatively high light REE content (around 170 ppm) hosted by monazite. A combined gravity/flotation concentration flowsheet, starting with classification of the residue into 3 size fractions (+150 micrometres, 150-53 micrometres and -53 micrometres) was developed. This study presents the results of beneficiation of the clay-rich -53 micrometre size fraction by flotation using sodium oleate and hydroxamate as collectors and compares them with results obtained with a Falcon ultra-fine concentrator. The effect of dispersant addition during de-sliming operations on flotation efficiency was also investigated. The light REE grade in the floated product obtained with sodium oleate increased from 3 370 ppm to 5 350 ppm and recovery from 30% to 80% with dispersant, which is attributed to clay coating. Saturation tests performed on the Falcon ultrafine concentrator show a positive effect of desliming on separation performance which produces higher light rare earth elements grades and recoveries. Comparison of flotation performance and Falcon ultra fine concentrator of monazite to previous results obtained with the Falcon semi-batch gravity concentrator on the unscreened raw residue clearly shows that flotation of the fine residue is more efficient than the Falcon ultrafine concentrator and Falcon semi-batch gravity concentrator. Indeed the Falcon ultrafine concentrator produced high recoveries (87-95%) but with almost no enrichment (1.3-1.4 ratios) whereas the Falcon semi-batch gravity concentration of unscreened residue produced higher grades (up to 0.6% LREE) but with low recoveries (17-22%). This study has shown that light REE can be recovered with simple two-stage operations, This is the last in a series of papers addressing the by-product potential of light rare-earth elements (LREE: La, Ce, Nd) and rare metals (Sn, Nb, W) within the St Austell kaolin deposits, UK. Previous results have shown that heavy minerals are pre-concentrated in the micaceous residue which displays relatively high light REE content (around 170 ppm) hosted by monazite. A combined gravity/flotation concentration flowsheet, starting with classification of the residue into 3 size fractions (+150 micrometres, 150-53 micrometres and -53 micrometres) was developed. This study presents the results of beneficiation of the clay-rich -53 micrometre size fraction by flotation using sodium oleate and hydroxamate as collectors and compares them with results obtained with a Falcon ultra-fine concentrator. The effect of dispersant addition during de-sliming operations on flotation efficiency was also investigated. The light REE grade in the floated product obtained with sodium oleate increased from 3 370 ppm to 5 350 ppm and recovery from 30% to 80% with dispersant, which is attributed to clay coating. Saturation tests performed on the Falcon ultrafine concentrator show a positive effect of desliming on separation performance which produces higher light rare earth elements grades and recoveries. Comparison of flotation performance and Falcon ultra fine concentrator of monazite to previous results obtained with the Falcon semi-batch gravity concentrator on the unscreened raw residue clearly shows that flotation of the fine residue is more efficient than the Falcon ultrafine concentrator and Falcon semi-batch gravity concentrator. Indeed the Falcon ultrafine concentrator produced high recoveries (87-95%) but with almost no enrichment (1.3-1.4 ratios) whereas the Falcon semi-batch gravity concentration of unscreened residue produced higher grades (up to 0.6% LREE) but with low recoveries (17-22%). This study has shown that light REE can be recovered with simple two-stage operations

In this study the effects and mechanism of lead ions influence on wolframite flotation with benzohydroxamic acid (BHA) were studied through micro-flotation, adsorption experiments, zeta potential measurements, logarithmic concentration diagram, and X-ray photoelectron spectroscopy. It was observed that lead ions could significantly enhance the recovery of wolframite in flotation and adsorption density of collector BHA onto the wolframite surface. The results showed that Pb existed in the forms of lead ion, monohydric lead, and lead hydroxide at the water-wolframite interface respectively, at three pH ranges. They increased the zeta potential of wolframite. However, the zeta potential of wolframite was still negative, resulting in repulsive electrostatic force to anionic collector BHA. Combining with XPS spectra, it revealed the chemisorption of BHA onto the wolframite surface. In addition, PbO or Pb(OH)2 was observed on the wolframite surface due to the reaction between lead ions and wolframite. These reaction products increased the adsorption site of BHA on the wolframite surface because Pb hydroxamate was found on the wolframite surface. (Authors.), In this study the effects and mechanism of lead ions influence on wolframite flotation with benzohydroxamic acid (BHA) were studied through micro-flotation, adsorption experiments, zeta potential measurements, logarithmic concentration diagram, and X-ray photoelectron spectroscopy. It was observed that lead ions could significantly enhance the recovery of wolframite in flotation and adsorption density of collector BHA onto the wolframite surface. The results showed that Pb existed in the forms of lead ion, monohydric lead, and lead hydroxide at the water-wolframite interface respectively, at three pH ranges. They increased the zeta potential of wolframite. However, the zeta potential of wolframite was still negative, resulting in repulsive electrostatic force to anionic collector BHA. Combining with XPS spectra, it revealed the chemisorption of BHA onto the wolframite surface. In addition, PbO or Pb(OH)2 was observed on the wolframite surface due to the reaction between lead ions and wolframite. These reaction products increased the adsorption site of BHA on the wolframite surface because Pb hydroxamate was found on the wolframite surface. (Authors.)

The CNDO/M method was used to calculate the molecules of hydroximic acid, its ions and copper hydroxamate and to find a reduced model of hydroximic ion adsorption on copper oxide or sulphide minerals. The results show that two structures, RCOHNOH (hydroximic acid) and RCONHOH (hydroxamic acid) can coexist. Either of them can form a five-ring complex of similar structure with metallic ions. The hydroxamate ion is a good collector in the flotation of copper oxides; the adsorption reaction between hydroximic ions and copper oxides is stronger than between hydroximic ions and copper sulphides., The CNDO/M method was used to calculate the molecules of hydroximic acid, its ions and copper hydroxamate and to find a reduced model of hydroximic ion adsorption on copper oxide or sulphide minerals. The results show that two structures, RCOHNOH (hydroximic acid) and RCONHOH (hydroxamic acid) can coexist. Either of them can form a five-ring complex of similar structure with metallic ions. The hydroxamate ion is a good collector in the flotation of copper oxides; the adsorption reaction between hydroximic ions and copper oxides is stronger than between hydroximic ions and copper sulphides.

A critical review is presented of the use of chelating reagents (hydroxamates) in flotation. A series of experiments have been performed using an experimental commercial hydroxamate as collector. Bench-scale studies used two different ores and studies in a microflotation cell used several mineral combinations. It was concluded that the selectivity of minerals flotation with hydroxamates depends on a balance between the solubility of the mineral and the stability of the complex formed with the cation in the lattice. A favourable condition for the selective utilisation of hydroxamates as collectors is visualised if the mineral to be floated is the most soluble in the system and the chelate formed between the cation in the lattice and hydroxamate is the most stable., A critical review is presented of the use of chelating reagents (hydroxamates) in flotation. A series of experiments have been performed using an experimental commercial hydroxamate as collector. Bench-scale studies used two different ores and studies in a microflotation cell used several mineral combinations. It was concluded that the selectivity of minerals flotation with hydroxamates depends on a balance between the solubility of the mineral and the stability of the complex formed with the cation in the lattice. A favourable condition for the selective utilisation of hydroxamates as collectors is visualised if the mineral to be floated is the most soluble in the system and the chelate formed between the cation in the lattice and hydroxamate is the most stable.

A monazite ore from Sao Goncalo do Sapucai was studied using a commercial hydroxamate and sodium oleate as collectors and sodium metasilicate as depressant. Microflotation experiments proved to be an effective indicator of the best collector/depressant ratio for bench scale tests. Results showed that it was possible with both collectors to produce a high purity cleaner monazite concentrate (greater than 60% RE2O3). The concentrations of collector and depressant must be well defined to prevent a significant increase in the flotation of gangue minerals such as ilmenite, zircon and rutile, causing contamination of the monazite concentrate., A monazite ore from Sao Goncalo do Sapucai was studied using a commercial hydroxamate and sodium oleate as collectors and sodium metasilicate as depressant. Microflotation experiments proved to be an effective indicator of the best collector/depressant ratio for bench scale tests. Results showed that it was possible with both collectors to produce a high purity cleaner monazite concentrate (greater than 60% RE2O3). The concentrations of collector and depressant must be well defined to prevent a significant increase in the flotation of gangue minerals such as ilmenite, zircon and rutile, causing contamination of the monazite concentrate.