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Batch flotation tests were carried out in a laboratory on ore containing platinum group metals, with the aim of determining how different milling methods affected flotation. In this study the comparison was made between the use of high pressure grinding rolls and conventional crushing combined with either wet or dry rod milling. The results showed that the combination of HPGR and dry milling produced the worst results, while conventional crushing and wet milling resulted in the highest grades and recoveries. These results are discussed in terms of the characteristics of the ores, their particle size distribution and the pulp chemistry., Batch flotation tests were carried out in a laboratory on ore containing platinum group metals, with the aim of determining how different milling methods affected flotation. In this study the comparison was made between the use of high pressure grinding rolls and conventional crushing combined with either wet or dry rod milling. The results showed that the combination of HPGR and dry milling produced the worst results, while conventional crushing and wet milling resulted in the highest grades and recoveries. These results are discussed in terms of the characteristics of the ores, their particle size distribution and the pulp chemistry.

Tests were carried out on a sulphide ore containing 12% sphalerite and a platinum-group metal ore containing 2% of base-metal sulphides which were subjected to crushing in a high-pressure grinding roll (HPGR) or a cone crusher followed by wet or dry milling and flotation. In the case of the sphalerite ore dry milling resulted in the highest Zn grades and recoveries, irrespective of the crushing process used, whereas a similar treatment for the PGE ore produced the poorest results. Both crushing methods produced a similar particle size distribution for the two ores. Use of the HPGR alone produced a finer product than the cone crusher. In the case of the base-metal sulphides the HPGR yielded percentage liberation values which were similar to those obtained with the cone crusher followed by milling. In the case of the PGE ore the HPGR significantly improved the percentage liberation of the platinum-group metals., Tests were carried out on a sulphide ore containing 12% sphalerite and a platinum-group metal ore containing 2% of base-metal sulphides which were subjected to crushing in a high-pressure grinding roll (HPGR) or a cone crusher followed by wet or dry milling and flotation. In the case of the sphalerite ore dry milling resulted in the highest Zn grades and recoveries, irrespective of the crushing process used, whereas a similar treatment for the PGE ore produced the poorest results. Both crushing methods produced a similar particle size distribution for the two ores. Use of the HPGR alone produced a finer product than the cone crusher. In the case of the base-metal sulphides the HPGR yielded percentage liberation values which were similar to those obtained with the cone crusher followed by milling. In the case of the PGE ore the HPGR significantly improved the percentage liberation of the platinum-group metals.

Batch flotation tests were carried out on a haematite-containing iron ore slimes sample from Sishen, South Africa, and the effects of grinding on flotation performance, the flotation response of various impurities in the sample and the feasibility of increasing metal recovery by re- floating tailings in a scavenger flotation step were investigated. Reverse cationic flotation was effective in rejecting impurities from the sample. The levels of impurities from a head grade assaying 6.4% SiO2, 2. 14% Al2O3, 0.402% K2O, 0.082% P and 0.194% TiO2 were reduced to 1.83% SiO2, 0.88% Al2O3, 0.095% K2O, 0.066% P and 0.174% TiO2 in the final concentrate at an Fe recovery of 74%. The flotation response of SiO2, Al2O3 and K2O was better than that of P and TiO2. Grinding to 80% smaller than about 49 micrometers was essential to produce an Fe concentrate grade of more than 67%. The grind size corresponded to about 80% liberation of haematite from the gangue minerals. Fe recoveries of up to 76% were obtained by re-floating the rougher tailings in a scavenger stage, with little effect on the final concentrate grade. Size-by-size Fe recovery data indicated that particles smaller than ten micrometers were mostly lost in the desliming stage prior to flotation, while some reported to the froth by entrainment. Some of the coarser haematite- gangue composite particles reported to the froth product by true flotation., Batch flotation tests were carried out on a haematite-containing iron ore slimes sample from Sishen, South Africa, and the effects of grinding on flotation performance, the flotation response of various impurities in the sample and the feasibility of increasing metal recovery by re- floating tailings in a scavenger flotation step were investigated. Reverse cationic flotation was effective in rejecting impurities from the sample. The levels of impurities from a head grade assaying 6.4% SiO2, 2. 14% Al2O3, 0.402% K2O, 0.082% P and 0.194% TiO2 were reduced to 1.83% SiO2, 0.88% Al2O3, 0.095% K2O, 0.066% P and 0.174% TiO2 in the final concentrate at an Fe recovery of 74%. The flotation response of SiO2, Al2O3 and K2O was better than that of P and TiO2. Grinding to 80% smaller than about 49 micrometers was essential to produce an Fe concentrate grade of more than 67%. The grind size corresponded to about 80% liberation of haematite from the gangue minerals. Fe recoveries of up to 76% were obtained by re-floating the rougher tailings in a scavenger stage, with little effect on the final concentrate grade. Size-by-size Fe recovery data indicated that particles smaller than ten micrometers were mostly lost in the desliming stage prior to flotation, while some reported to the froth by entrainment. Some of the coarser haematite- gangue composite particles reported to the froth product by true flotation.

Telluride minerals contribute 20-30% or more of the PGM present in South African Platreef ores and are considered to be slow-floating. The surface alteration and flotation behaviour of synthetic moncheite in the presence of pentlandite was examined to study whether oxidation products from grinding media and other minerals affected mineral surface composition and flotability. Tof-SIMS (time-of-flight secondary ion mass spectrometry) was used to characterise the mineral surface as well as the extent of alteration. Microflotation was employed to determine the hydrophobicity. Conditioning of moncheite in the presence of pentlandite reduced the flotation response of the +38 -106 micron fraction from more than 99% to 56%. This was due to pentlandite dissolution products forming overlayers on the mineral surfaces thereby inhibiting adsorption of collector. Further grinding of the samples, with and without pentlandite conditioning, showed a negative effect on recovery., Telluride minerals contribute 20-30% or more of the PGM present in South African Platreef ores and are considered to be slow-floating. The surface alteration and flotation behaviour of synthetic moncheite in the presence of pentlandite was examined to study whether oxidation products from grinding media and other minerals affected mineral surface composition and flotability. Tof-SIMS (time-of-flight secondary ion mass spectrometry) was used to characterise the mineral surface as well as the extent of alteration. Microflotation was employed to determine the hydrophobicity. Conditioning of moncheite in the presence of pentlandite reduced the flotation response of the +38 -106 micron fraction from more than 99% to 56%. This was due to pentlandite dissolution products forming overlayers on the mineral surfaces thereby inhibiting adsorption of collector. Further grinding of the samples, with and without pentlandite conditioning, showed a negative effect on recovery.

The results are presented of zeta potential and time-of-flight secondary ion mass spectrometry analysis of natural pyroxene from the Merensky Reef, South Africa, which showed that when pyroxene is exposed to Cu, Ni and/or Ca ions in solution at alkaline pH a surface reaction occurs between the pyroxene and the hydroxy species, in the case of Cu and Ni, or divalent Ca ions, which affects the floatability of the pyroxene. After exposure to Cu and Ni ions at pH 9, addition of sodium isobutyl xanthate resulted in the pyroxene floating readily. In the case of Cu, the activating effect of the adsorbed hydroxy species can be reduced by the addition of complexing amines prior to sodium isobutyl xanthate., The results are presented of zeta potential and time-of-flight secondary ion mass spectrometry analysis of natural pyroxene from the Merensky Reef, South Africa, which showed that when pyroxene is exposed to Cu, Ni and/or Ca ions in solution at alkaline pH a surface reaction occurs between the pyroxene and the hydroxy species, in the case of Cu and Ni, or divalent Ca ions, which affects the floatability of the pyroxene. After exposure to Cu and Ni ions at pH 9, addition of sodium isobutyl xanthate resulted in the pyroxene floating readily. In the case of Cu, the activating effect of the adsorbed hydroxy species can be reduced by the addition of complexing amines prior to sodium isobutyl xanthate.

Experimental results are presented which show that ions such as Cu and Ni, when present in the pulp, are able to adsorb onto the surfaces of the two gangue minerals pyroxene and feldspar during the flotation of platinum group minerals, especially at alkaline pH values when the metals adsorb predominantly as hydroxy species. The gangue minerals are prone to float when subsequently exposed to collector molecules such as xanthates. The xanthate concentration on the surface is a function of the metal concentration. Copper hydroxy species from the surface of the gangue can be removed with the complexing agent diethylenetriamine., Experimental results are presented which show that ions such as Cu and Ni, when present in the pulp, are able to adsorb onto the surfaces of the two gangue minerals pyroxene and feldspar during the flotation of platinum group minerals, especially at alkaline pH values when the metals adsorb predominantly as hydroxy species. The gangue minerals are prone to float when subsequently exposed to collector molecules such as xanthates. The xanthate concentration on the surface is a function of the metal concentration. Copper hydroxy species from the surface of the gangue can be removed with the complexing agent diethylenetriamine.

The minerals moncheite ((Pt,Pd)(Bi,Te)2 and PtTe2) and merenskyite ((Pd,Pt)(Bi,Te)2 and PdTe2), contribute 20%-45% of the PGMs present in the Platreef ore in the northern limb of the Bushveld Complex, South Africa. There is evidence that these minerals report to the tailings, and an investigation was carried out to determine their flotation behaviour and to relate this to their surface characteristics. Microflotation tests were carried out using sodium isobutyl xanthate as collector and copper sulphate as activator. Cu activation of both moncheite and merenskyite samples reduced the flotation response compared with xanthate on its own. Xanthate added alone was adsorbed on the mineral surfaces at a higher concentration than the Cu-activated minerals. Oxidation of the minerals had a negative effect on the flotation performance of the Pt and Pd bismuth telluride samples but not the Pt and Pd telluride samples. Finer grinding reduced recoveries. Increasing the calcium ion concentration from 80 to 500 ppm in the synthetic water did not negatively affect the flotation response of the PdTe2 mineral., The minerals moncheite ((Pt,Pd)(Bi,Te)2 and PtTe2) and merenskyite ((Pd,Pt)(Bi,Te)2 and PdTe2), contribute 20%-45% of the PGMs present in the Platreef ore in the northern limb of the Bushveld Complex, South Africa. There is evidence that these minerals report to the tailings, and an investigation was carried out to determine their flotation behaviour and to relate this to their surface characteristics. Microflotation tests were carried out using sodium isobutyl xanthate as collector and copper sulphate as activator. Cu activation of both moncheite and merenskyite samples reduced the flotation response compared with xanthate on its own. Xanthate added alone was adsorbed on the mineral surfaces at a higher concentration than the Cu-activated minerals. Oxidation of the minerals had a negative effect on the flotation performance of the Pt and Pd bismuth telluride samples but not the Pt and Pd telluride samples. Finer grinding reduced recoveries. Increasing the calcium ion concentration from 80 to 500 ppm in the synthetic water did not negatively affect the flotation response of the PdTe2 mineral.

Significant PGM losses may occur due to the poor floatability of arsenides of the platinum group elements which contribute around 21% of those present in Platreef ore from the Bushveld Complex, South Africa. The surface characteristics and flotation behaviour were investigated of synthetic sperrylite (PtAs2) and palladoarsenide (Pd2As). The results showed that both can be recovered by flotation in the presence of xanthate alone, and the addition of copper sulphate as activator resulted in a slight decrease in recovery. A sperrylite sample synthesised using a short initial thermal treatment floated well in the presence of xanthate, while a sample synthesised for a longer period floated poorly irrespective of the reagent suite used. The former sample exhibited many Pt blebs while the latter was more homogeneous. The latter sample when crushed to below 38 micrometres showed increased recovery, possibly due to the exposure of the Pt blebs., Significant PGM losses may occur due to the poor floatability of arsenides of the platinum group elements which contribute around 21% of those present in Platreef ore from the Bushveld Complex, South Africa. The surface characteristics and flotation behaviour were investigated of synthetic sperrylite (PtAs2) and palladoarsenide (Pd2As). The results showed that both can be recovered by flotation in the presence of xanthate alone, and the addition of copper sulphate as activator resulted in a slight decrease in recovery. A sperrylite sample synthesised using a short initial thermal treatment floated well in the presence of xanthate, while a sample synthesised for a longer period floated poorly irrespective of the reagent suite used. The former sample exhibited many Pt blebs while the latter was more homogeneous. The latter sample when crushed to below 38 micrometres showed increased recovery, possibly due to the exposure of the Pt blebs.

A study was carried out into a mainly pentlandite-pyroxene system using zeta potential, microflotation and time of flight secondary ion mass spectrometry techniques. The results showed that inadvertent activation by heavy metal ions, Cu (II) and Ni (II), or their hydroxy forms depending on the pH of the pulp, occurs on the pyroxene and that this contributes significantly to the true flotation of pyroxene. It is possible to manage this inadvertent activation of the gangue mineral by using amines such as EDA, DETA and TETA. EDTA is not effective and this is explained in relation to the equilibrium concentrations of the various species present in solution. The adsorption of Cu, which exists as a hydroxy species at pH 9, on the pyroxene is also discussed., A study was carried out into a mainly pentlandite-pyroxene system using zeta potential, microflotation and time of flight secondary ion mass spectrometry techniques. The results showed that inadvertent activation by heavy metal ions, Cu (II) and Ni (II), or their hydroxy forms depending on the pH of the pulp, occurs on the pyroxene and that this contributes significantly to the true flotation of pyroxene. It is possible to manage this inadvertent activation of the gangue mineral by using amines such as EDA, DETA and TETA. EDTA is not effective and this is explained in relation to the equilibrium concentrations of the various species present in solution. The adsorption of Cu, which exists as a hydroxy species at pH 9, on the pyroxene is also discussed.

The major loss of base metals in beneficiation of Merensky Reef ore in South Africa occurs during separation of the siliceous gangue from platinum-group and base-metal sulphides by selective flotation. Zeta potential, time-of-flight secondary ion mass spectroscopy and X-ray photoelectron spectroscopy data have shown that pyroxene becomes Cu-activated in the presence of copper sulphate and is floated when xanthate ions are added. Flotation and surface analysis data revealed that pyroxene could also be inadvertently activated by Ni(II) ions, which would result in a higher pyroxene recovery and thus lower selectivity. In the presence of ethylenediamine (EDA) the concentration of Cu(II) and Ni(II) ions found on pyroxene and pentlandite surfaces was significantly reduced, the effect being more predominant with pyroxene. The removal mechanism involves the formation of soluble stable metal-EDS chelates and their dissolution., The major loss of base metals in beneficiation of Merensky Reef ore in South Africa occurs during separation of the siliceous gangue from platinum-group and base-metal sulphides by selective flotation. Zeta potential, time-of-flight secondary ion mass spectroscopy and X-ray photoelectron spectroscopy data have shown that pyroxene becomes Cu-activated in the presence of copper sulphate and is floated when xanthate ions are added. Flotation and surface analysis data revealed that pyroxene could also be inadvertently activated by Ni(II) ions, which would result in a higher pyroxene recovery and thus lower selectivity. In the presence of ethylenediamine (EDA) the concentration of Cu(II) and Ni(II) ions found on pyroxene and pentlandite surfaces was significantly reduced, the effect being more predominant with pyroxene. The removal mechanism involves the formation of soluble stable metal-EDS chelates and their dissolution.