Abstract
Previous studies speculate that hydroxo species present in flotation pulps at pH > 9, particularly those of polyvalent cations, selectively adsorb onto gangue minerals. Such species supposedly enhance the depressive action of carboxymethyl cellulose (CMC) onto gangue via an acid-base interaction between the positively charged mineral surface and the negatively charged CMC molecule. Thus, the hydrophilicity of gangue minerals is enhanced, preventing the dilution of the concentrate. However, as there is little evidence to support these claims for complex process waters of increasing ionic strength, it is important to investigate. Adsorption data and mineral surface charge analyses provide a fundamental understanding of how electrolytes and their ionic strengths affect gangue mineral-depressant adsorption. It is strongly anticipated that decoupling these effects will allow process operators to tailor their process water quality needs towards best flotation operating regimes and, in the long run, effect closed water circuits. Thus, using talc as a proxy for naturally floatable gangue common in sulfidic Cu–Ni–PGM ores, this work investigates the influence of the ionic strength of process water on the adsorption of CMC onto talc for a perspective on how saline water in sulfidic ores would affect the behavior and therefore management of floatable gangue. In the presence of CMC, the microflotation results showed that the rate of talc recovery decreased with increasing ionic strength of process water. Increases in ionic strength resulted in an increase in the adsorption of CMC onto talc. Talc particles proved to have been more coagulated at higher ionic strength since the settling time decreased with increasing ionic strength. Furthermore, the zeta potential of talc particles became less negative at higher ionic strengths of process water. It is thus proposed that increases in the ionic strength of process water increased the zeta potential of talc particles, enhancing the adsorption of CMC onto talc. This in turn created a more coagulated nature on talc particles, increasing their hydrophilicity and thereby retarding floatability.
Highlights
The phenomenon of gangue depression in mineral flotation is of critical importance as regards the attainment of a required concentrate grade
In the absence of carboxymethyl cellulose (CMC), the recovery of talc increased with increasing ionic strength of Synthetic plant waters (SPW)
CMC was adsorbed onto the mineral surface as the ionic strength of SPW increased
Summary
The phenomenon of gangue depression in mineral flotation is of critical importance as regards the attainment of a required concentrate grade. The depressant of choice has to have a high selectivity for the targeted gangue minerals. This would prevent gangue from reporting to the concentrate without inadvertently depressing the value bearing mineral. The chemistry of the environment regulates the manner in which gangue depression occurs. In sulfidic Cu–Ni–Pt ore flotation, polysaccharides are used to depress naturally floatable gangue which may, in the case of Merensky ores, exist as talc (the most problematic issue) [1]. Two widely used polysaccharides in the South African context are carboxymethyl cellulose (CMC) and modified guar gum.
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