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Wettability is an important property of powders in many applications such as inks and paints, the food and pharmaceutical industries, as well as flotation separation of mineral particles. It is known that the enthalpy of immersion is a useful method to quantify the hydrophobicity or wettability of a powder since it measures the heat evolved when water molecules interact with the powder surface. However, in the present investigation it was found that for the powders investigated, viz. the minerals, galena, quartz, pyrite, pyrrhotite, chalcopyrite, sphalerite, quartz and albite, an initial endotherm was repeatedly observed, and it was hypothesized that this may be due to the endothermic dissolution of ions from the minerals as a primary step. Various methods of supressing dissolution were investigated, from using saturated solutions of the minerals, to coating of the mineral surface with surfactant, to the use of a non-solvating wetting liquid. The last two of these procedures were found to be most successful in terms of inhibiting the presence of an endotherm. These results provide strong evidence to support the hypothesis that the endotherm is due to the dissolution of ions. In the case of using hexanol, a non-solvating wetting liquid, the resulting exothermic responses provide a relative scale of hydrophobicity values for different mineral surfaces even though it is not directly measuring the mineral-water interaction which is fundamental to the concept of hydrophobicity. The methodology was extended to the measurement of heats of immersion of binary mixtures of powders and extrapolated to predict the heat of immersion, and by extension the hydrophobicity, of the pure components. [Display omitted] • Heat of immersion in water is a very useful measure of powder surface wettability. • Minor dissolution of the powder in water can interfere with the immersion response. • Three methods of suppressing the dissolution response were investigated. • Successful suppression of the dissolution was achieved. • Methodology used to predict wettability of a pure mineral from a binary mixture. [ABSTRACT FROM AUTHOR]

• Microcalorimetry. • Enthalpy of immersion. • Enthalpy of adsorption. • Flotation. Microcalorimetry is an important experimental method to quantify the reactions occurring between a solid material and reagents adsorbing at the surface. In the case of flotation which is arguably the most important process used to beneficiate mineral ores the surface reactions occurring between water and reagents such as collectors are measured as the enthalpy of immersion or adsorption respectively using microcalorimetry. There is significant literature on the determination of such values in many solid–liquid systems. However, in the case of flotation, such measurements have mostly been carried out as microcalorimetric studies and no attempts have been made to relate the enthalpies measured to the ultimate flotation performance of the mineral under investigation. This paper reviews the literature in this regard and attempts to show how such measurements may be related to the flotation behaviour of the mineral. Such studies may have significant overall implications for flotation research. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to investigate the adsorption of guar gum onto talc, pyroxene, plagioclase, chromite and chalcopyrite and mixtures of talc with each of the other four minerals. These minerals commonly occur in the Merensky and UG2 ore bodies of the Bushveld Complex in South Africa, which is host to much of the world’s platinum group minerals (PGMs). Zeta potential measurements were conducted to establish differences in surface charge between a pH of 2 and 10. At pH 9, the pH of most PGM flotation operations, plagioclase had the most negative surface charge, followed by talc, chromite and pyroxene whose surface charges were very similar. Chalcopyrite had the least negative surface charge. On the basis of the observed surface charges and in terms of classical acid–base theory, guar was expected to have the strongest interaction with chalcopyrite and the weakest with plagioclase. Equilibrium adsorption studies confirmed that in a buffered solution, chalcopyrite had the highest affinity for guar, followed respectively by talc, chromite, pyroxene and plagioclase. Results of studies to evaluate the relative adsorption of each mineral in a mixture with talc showed that guar adsorbed preferentially onto chalcopyrite, pyroxene and chromite, in that order, rather than onto talc. Talc however, preferentially adsorbed guar when in a mixture with plagioclase. The ramifications of these findings for the operation of PGM flotation plants are discussed. [Copyright &y& Elsevier]

[Display omitted] • PAX adsorption and floatability of sperrylite increases with decreasing pH. • Poor collector adsorption at pH 9 may be due to preferential OH– adsorption. • At pH 3, PAX is co-adsorbed as metal xanthate in addition to dixanthogen. • Collector amount and dixanthogen presence on sperrylite govern its hydrophobicity. • Using NaClO to chemically control Eh reduces the floatability of sperrylite. There is evidence of a very weak interaction between sperrylite and xanthate collectors at pH 9, the typical pH used in PGM concentrators. This results in the mineral being hardly hydrophobic when exposed to such collectors. Xanthate collectors adsorb via an electrochemical mechanism which is dependent on pH and Eh. In this study, it was shown that potassium amyl xanthate (PAX) adsorption increases with decreasing pH, with 2.9x10−05 mol/m2 adsorbed at pH 3 compared to only 0.4x10−05 mol/m2 at pH 9. Furthermore, spectroscopic analyses performed in this study showed that PAX is adsorbed as dixanthogen at pH 3 whereas this species was not observed at pH 9. In addition to dixanthogen, the collector may be co-adsorbed as the metal xanthate on sperrylite. However, it is the specific presence of dixanthogen that ultimately strongly promotes the hydrophobicity of the mineral. The adsorption of the collector on sperrylite correlated well with the flotation recovery of this mineral. The microflotation recovery of sperrylite was improved from 22 % at pH 9 to 61 % at pH 3. On the other hand, the use of NaClO to chemically modify Eh was shown to result in excessive oxidation of sperrylite and/or resulted in a reaction between NaClO and PAX which in fact hindered the ability of the collector to impart hydrophobicity. This was found to have a detrimental effect on the floatability of sperrylite. Ultimately, this study provides evidence and insights into the floatability of sperrylite. [ABSTRACT FROM AUTHOR]

Abstract: In the present study the effect of adding sodium di-ethyldithiophosphate (DTP) to sodium isobutyl xanthate (SIBX) as a co-collector in the flotation of a platinum group mineral (PGM) ore was studied with a view to investigating whether there was any evidence of a synergistic beneficial effect resulting from the use of the mixture. Flotation tests were carried out using single collectors as well as various mixtures of the collectors at different but constant total molar concentrations. Size-by-size analyses of the concentrates were carried out in all cases. After deconvoluting the results of the different flotation tests there was no conclusive evidence of a synergistic effect when using mixtures. The DTP was shown to cause an increase in the recovery of fine particles (<25μm) and this is ascribed to its effect on the behaviour of the froth phase. It was concluded that the effect of the addition of the DTP was to stabilise the froth phase and that this was a parallel reaction and not a result of any synergistic interaction between the SIBX and DTP. [Copyright &y& Elsevier]

Mineral surface oxidation, slimes coating and inadvertent activation can detrimentally affect flotation and the separation of sulphide minerals. Surface oxidation and slime coatings will reduce hydrophobicity and collector adsorption selectivity. Inadvertent activation of gangue minerals by metal ions is frequently suspected of playing a detrimental role in selective flotation. In this study, the floatability of a pentlandite–pyroxene system was investigated in synthetic process water at pH 6 and pH 9 using zeta potential, microflotation and time of flight secondary ion mass spectrometry (ToF-SIMS) techniques. The aim was to maximise pentlandite recovery and simultaneously minimise the percentage pyroxene reporting to the concentrate. The results obtained showed that inadvertent activation by heavy metal ions, Cu(II) and Ni(II), contributes significantly to the true flotation of pyroxene. The microflotation tests revealed that pyroxene rejection is greatly improved by the addition of diethylenetriamine (DETA) in combination with sodium polyphosphate, this being particularly noticeable at pH 6. The mechanism responsible for the observed selectivity is explained by the ability of DETA to deactivate Ni(II), Cu(II) and possibly other ions through formation of stable chelates. The addition of polyphosphate introduced a more negative surface charge onto the minerals investigated thus preventing the formation of valuable-gangue mineral aggregates. [Copyright &y& Elsevier]

Activation of sulphide minerals by copper sulphate is common practice on platinum group mineral (PGM) concentrators. However, the role of copper sulphate in the flotation of PGMs is still unclear especially in the case of those PGM ores which contain relatively low concentrations of sulphides. This study was conducted to determine, using electrochemical techniques, the effect which the presence of copper sulphate has on the surface reactions occurring between xanthate collectors and minerals which are representative of those treated in PGM concentrators. Specifically rest potential and cyclic voltammetry measurements were conducted on the minerals moncheite (PtTe 2 ) and cooperite (PtS) at pH 6, 8 and 10. The results were interpreted by relating them to previous reports using the same minerals which included micro-flotation and X-ray photoelectron spectroscopy (XPS) studies. Electrochemical interactions between cooperite and CuSO 4 were observed to be occurring at all the pHs considered, whereas no significant interactions were seen in the case of moncheite. In the presence of SEX as a collector, CuSO 4 was shown to inhibit the electrochemical interactions of xanthate with both the sulphide and telluride mineral surfaces and this is consistent with the observations reported previously on the negative effect of copper sulphate on the flotation of these minerals. [ABSTRACT FROM AUTHOR]

Abstract: The use of High Pressure Grinding Rollers (HPGR) has been widely reported to have major benefits in the treatment of minerals such as iron ore and diamonds. To date there have been few investigations into its use in the treatment of ores containing Platinum-Group Minerals (PGMs). HPGRs are known to reduce energy consumption and wear costs and improve the throughput in the circuit. In the present investigation the effect of the comparative use of HPGR and conventional crushing in combination with either dry or wet rod milling on the flotation of PGMs was studied using batch flotation. Previous studies of a base metal sulphide had shown that either HPGR or conventional crushing followed by dry milling produced the highest grades and recoveries (). However in the present study it was observed that a similar treatment of Platinum-Group Minerals produced the poorest results and the highest grades and recoveries were obtained for the case of conventional crushing in combination with wet milling. The HPGR showed no advantages in terms of flotation performance and dry milling produced particularly poor flotation results. The results were investigated further using various surface characterization techniques in order to determine the reason for the decrease in grades and recoveries of platinum when using dry milling and HPGR as opposed to the case for base metal sulphides. The feed and product samples were analysed using ToF-SIMS, XPS and MLA. The paper will propose reasons to explain the different flotation behaviour of the two ore types following the various comminution processes focusing on the surface characteristics of the ores, the particle size distribution and the pulp chemistry. [Copyright &y& Elsevier]