Alkaline gelatinised cassia tora and locust bean gums as talc depressants: Adsorption and thermochemical aspect

Talc is a gangue mineral of most platinum group metals and base metal ores commonly found in the Southern African mineral repository. It is naturally hydrophobic, and invariably, the depression of talc is paramount and challenging in the flotation of these ores. This paper introduced alkaline gelatinised cassia tora gum (CTG) and locust bean gum (LBG) as novel talc depressants. The adsorption densities, thermochemical properties, and talc depression of these depressants were studied using adsorption, zeta potential and microflotation studies. Talc flotability in the absence of the depressant was 89%, which implied that the talc used in this study was naturally floatable. Adsorption studies revealed that CTG yielded the highest talc adsorption density, followed by LBG and carboxymethyl cellulose (CMC), and their adsorption densities were 5.8 mg/m², 4.6 mg/m² and 3.5 mg/m², respectively. PGM flotation occurs at pH 9. Therefore, the zeta potential results at this pH were given more attention in the present study. The zeta potentials at pH 9 were −5.75 mV for LBG and CTG and −15 mV for CMC. In addition, the percentage of talc depression achieved in the microflotation studies decreased in the order of LBG > CTG > CMC; their respective values were 72% > 56% > 51%. Therefore, the zeta potential values agree with the adsorption and microflotation results observed in this study, i.e. LBG and CTG depressed talc more effectively than CMC. Finally, bench flotation results revealed that LBG had the greatest effect on talc depression at 100 g/t; while, CTG had the greatest effect on talc depression at 25 g/t. Thus, these results agreed with thermodynamic theory, viz. a low molecular weight polymer is effective at low dosages where the surface is unsaturated. In contrast, a high molecular weight polymer is effective at high dosages because there is enough quantity to cover the surface adequately.