Floatability of chalcopyrite and molybdenite in the presence of lignosulfonates. Part I. Adsorption studies

The adsorption of six lignosulfonates on molybdenite and chalcopyrite was studied through direct adsorption measurements and size exclusion chromatography at natural pH (5.0–5.5) and pH 11. The tests were carried out using different reagents for pH adjustments, i.e., potassium hydroxide (KOH), lime (CaO), and sodium carbonate (soda ash – Na2CO3). In the case of chalcopyrite, all the tests were performed in the presence of potassium ethyl xanthate – a chalcopyrite collector – added ahead of lignosulfonates. Overall, lignosulfonates give higher adsorption densities on chalcopyrite than on molybdenite. The adsorption density on both minerals was a function of not only the pH but also of the type of pH modifier used. Additions of lime enhanced lignosulfonate adsorption at higher pH but the adsorption of lignosulfonates dramatically decreased when soda ash or KOH were used for pH control. For all the lignosulfonates tested, higher molecular weight fractions tended to preferentially adsorb over lower molecular weight components. The results also indicated that electrostatic forces and chemical interactions between the anionic polyelectrolytes and metal-hydroxy sites on the mineral surfaces largely controlled the adsorption process.