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The effect of lignosulfonates on the floatability of molybdenite and chalcopyrite Ansari, Anita

Abstract

The applicability of six lignosulfonates as selective depressants in chalcopyritemolybdenite separation was assessed by means of modified Hallimond tube flotation tests, supplemented by adsorption studies to determine the magnitude of lignosulfonatemineral interactions. Flotation and adsorption tests were performed as a function of pH using different pH modifiers, i.e. lime, potassium hydroxide (KOH) and soda ash. Size exclusion chromatograms (SEC) were generated to determine which molecular weight fractions of the lignosulfonates were actually adsorbing onto the surfaces of the minerals. The depression of chalcopyrite flotation by lignosulfonates was found to be related to the presence of physically adsorbed xanthate and the availability of metallic sites on the mineral surface. Once the physically adsorbed xanthate was removed from the surface, the depression of the mineral was possible only when lignosulfonates adsorbed onto the mineral. The adsorption process was enhanced by the presence of positively charged metallic sites on the mineral surface. The activating role of calcium ions introduced by lime for lignosulfonate adsorption was demonstrated. The depression of molybdenite flotation was a function of pH. Good flotation of molybdenite was observed only under neutral / weakly acidic pH values, and the addition of all lignosulfonates resulted in the complete depression of molybdenite flotation. As in the case of chalcopyrite, pH adjustments using KOH and soda ash decreased the adsorption of lignosulfonates, which strongly suggests that the lignosulfonate adsorption process was controlled by electrostatic repulsion between the anionic polyelectrolytes and the negatively charged mineral surface. When lime was used as a pH modifier, the adsorption density dramatically increased due to the presence of calcium species in solution. The SEC data indicated that higher molecular weight fractions of lignosulfonates preferentially interact with mineral surfaces. Overall, the results suggest that it is possible to selectively float chalcopyrite from molybdenite by depressing molybdenite. This can be achieved over a wide pH range provided that a pH modifier other than lime is used for pH control. It is suggested that this process option be used in a cleaner flotation stage where pulp dilution and the use of flotation columns could greatly enhance the selectivity of the process.

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