Influence of solution conditions and polymer chemistry on the adsorption behaviour of anionic dispersants onto chalcocite in aqueous media

The adsorption behaviour of two polymeric dispersants (Cyquest 3223: sodium acrylate/acrylamide co-polymer and P80: sodium allyl sulfonate/maleic acid co-polymer) onto chalcocite mineral particles has been investigated as a function of solution pH (5, 7 and 9) and different oxidative environments. The dissociation of both polymers in aqueous solutions in the pH range 2–10 was quite similar, commencing at pH 2 and finishing at ∼pH 7, where the polymers became fully ionised, reflecting maximum negative charge. Strong pH-dependent adsorption onto negatively charged chalcocite at pH 7 and 9 was observed, the behaviour consistent with polymer binding through a chemical complexation mechanism. Furthermore, the plateau adsorption density was ∼80% greater under air or O2 gas saturation, than under N2 gas saturation and ∼25% higher for P80 than Cyquest 3223. Unlimited polymer adsorption propensity was displayed at pH 5, with no polymer remaining in solution irrespective of initial polymer concentration. The polymer adsorption behaviour is rationalized in terms of dissolved Cu(II) metal ion mediation. Both lower pH and stronger oxidative environment (oxygen or air saturation) facilitated chalcocite oxidation, Cu(II) leaching and hydrolysis at chalcocite particle–solution interface. These subsequently fostered Cu(II)-polymer (carboxylic acid and sulfonate groups) complexation and adsorption, the extent of which was greatly attenuated under weak dissolution conditions of N2 purging and high pH. Langmuirian polymer adsorption behaviour was displayed at pH 7 and 9, implying substantially homogeneous chalcocite surface adsorption sites.