Selective depression of copper-activated pyrite by oxalic acid: Implications for enhanced chalcopyrite–pyrite separation

The selective separation of pyrite (FeS₂) and chalcopyrite (CuFeS₂) in flotation processes poses significant challenges due to the activation of the pyrite surfaces by copper ions dissolved from associated copper sulfide minerals. This study proposes oxalic acid as an environment-friendly reagent to inhibit the copper-induced activation of pyrite. Chalcopyrite was used as a model mineral to evaluate the selectivity of oxalic acid treatment. The flotation experiments demonstrated that oxalic acid reduced the flotation recovery of copper-activated pyrite from 58 % to 16 % at pH 9 while exerting no discernible effect on chalcopyrite flotation. Further tests using artificial mixtures of chalcopyrite and pyrite confirmed the ability of oxalic acid to selectively separate chalcopyrite from copper-activated pyrite under mildly alkaline conditions, improving the separation efficiency from 30 % to 78 % with the addition of 15 kg/t (0.55 mM) oxalic acid at pH 9. The mechanism underlying this selectivity was investigated using infrared spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The results revealed that oxalic acid reacts with copper ions to form copper oxalate, which effectively prevents copper deposition on the pyrite surface. This reaction inhibits pyrite activation and suppresses the adsorption of xanthate collectors. These findings highlight the potential of oxalic acid as a sustainable reagent for enhancing the selectivity and efficiency of chalcopyrite–pyrite separation in flotation processes.