P. J. Harris

The effect of chemical composition and molecular weight of polysaccharide depressants on the flotation of talc

Abstract Polysaccharide reagents are frequently used in the mineral processing industry to improve the grade of the concentrate by depressing the naturally floatable gangue. A microflotation study showed that at an ionic strength of 10 −3 M KNO 3 , the dosage, molecular weight, and chemical composition of polysaccharide depressants affect their depressing action on talc. Viscosity readings for four carboxymethylcellulose (CMC) reagents and three modified guar gum reagents are reported, and estimates of the molecular weight of the CMCs are calculated. The natural floatability of talc was diminished when guar-based polymers were added to the system. Moreover, the depression of talc was increased as the guar molecular weight was increased. Strong depression of talc was achieved at a relatively low guar dosage; higher dosages did not further increase this depression. At 10 −3 M KNO 3 , the CMCs were ineffective depressants of talc. No systematic change in talc depression for differing molecular weight CMCs was observed. A small increase in depression was observed when the concentration of CMC was increased. A mechanism is proposed for the polymer–talc interactions based on these preliminary studies and information from similar studies in literature.

Frother characterisation using dynamic surface tension measurements

There is as yet no accepted method of predicting flotation frother performance in plant processes based on laboratory scale characterisation techniques. This paper investigates the use of dynamic surface tension, using the maximum bubble pressure method, as a means of evaluating frother performance. The method has been refined to facilitate measurement at high bubble rates, an important criterion with respect to the analysis of small, fast adsorbing molecules at low concentration such as flotation frothers. An adsorption model is presented, which has been used to elucidate the role of frothers with respect to bubble size in a flotation cell, based on the correlation of model parameters to physical frother characteristics. The potential for the application of dynamic surface tension to the performance of the froth phase in a flotation system is also discussed.

The flotation behaviour of chromite with respect to the beneficiation of UG2 ore

Abstract The UG2 reef of the Bushveld Igneous Complex in South Africa is a valuable source of platinum group metals (PGMs) that is beneficiated by flotation. Chromite is one of the main gangue consituents of UG2 ore and it is essential that the amount of chromite reporting to the concentrate during flotation be minimised since it is detrimental to the subsequent smelting operations. It is generally considered that chromite is naturally hydrophilic and only reports to the concentrate by entrainment. However, it is possible that, under certain conditions, the chromite can be activated by the typical reagent suite used in the flotation of UG2 ore, rendering it hydrophobic and amenable to true flotation. The aim of this work was to investigate the effect of copper sulphate and the collectors, sodium isobutyl xanthate and dithiophosphate on the flotability of chromite in a microflotation cell. The effect of copper sulphate on the zeta potential of chromite was also determined. It was found that collectors alone have an insignificant effect on the flotation of chromite whereas, in the presence of copper sulphate recoveries of above 60% were observed in mildly acid to mildly alkaline solutions decreasing 20% at a pH value of 10. The extent of activation depended on the copper sulphate dosage. Zeta potential measurements showed that, above pH 4 copper species were adsorbed on the chromite and between pH 5 and 9 the adsorption lead to charge reversal of the chromite particles to positive values. The speciation programme, MINTEQA2, was used to predict the copper species present over the pH range used. It was postulated that the activation is due to the adsorption of copper hydroxide species at the chromite surface, which then act as sites for collector adsorption.

The use of electrochemical measurements in the flotation of a platinum group minerals (PGM) bearing ore

Abstract Electrochemical potential is considered an important parameter for controlling the recovery and selectivity of sulphide minerals during flotation. The aim of this work was to use mineral potential measurements to gain an understanding of respective mineral flotation performance in the processing of a platinum group mineral (PGM) bearing ore, whilst manipulating the chemical conditions in the pulp. Sulphide mineral potentials were logged during the conditioning stage of the flotation tests. Varying the milling environment and conditioning pH affected the chemical conditions in the pulp. At any condition the mixed potential of the mineral electrodes varied, spanning a range of approximately 100 mV, and increased as follows: pyrrhotite, pentlandite, chalcopyrite, pyrite and platinum. The addition of CuSO 4 caused the potential to increase, whilst the addition of xanthate caused to the potential to decrease. The magnitude of the changes in potential for the various mineral electrodes on reagent addition was not the same and followed the recovery trend of the minerals viz. chalcopyrite>pentlandite>pyrrhotite. Chalcopyrite recovery was unaffected by differences in milling media and conditioning. Pyrrhotite flotation was inhibited when the ore was milled in the plant circuit even though the mixed potentials were similar to those measured in laboratory milled pulps. This was presumably due to excessive oxidation in the grinding and classification circuits of the plant. Acid conditioning improved the recovery of pyrrhotite through cleaning the mineral surface from hydrophilic iron oxy/sulphoxy species and also showed an enhanced reaction with xanthate. Pyrrhotite flotation was only slightly inhibited when its mixed potential was below the equilibrium potential for dixanthogen formation.