The effect of tartrate on the mild leaching of low-grade polymetallic complex chalcopyrite ore in acidic ferric chloride solution

Abstract

The mild leaching of low-grade polymetallic complex chalcopyrite ore (LPCCO) is of great significance, but is limited by the passive film. In this work, the leaching of LPCCO at atmospheric pressure and 298–358 K in the ferric chloride solutions (pH = 0) without and with tartrate was studied. The reasons why tartrate improves the leaching/dissolution were further investigated by electrochemical characterizations and surface analyses. Results showed that in 15 h and 358 K, the Cu extraction rate increased to 95.2% from 81.6% after the addition of tartrate. The electrochemical study results indicated that tartrate had significant effects on OCP, the anodic peak (A₁) of LPCCO dissolution, current crossing loop related to oscillation/re-activation, resistances of charge transfer (CT) across solution-film and film-LPCCO interfaces, measure of the non-ideality of capacitor related to the roughness of passive film, and polarization current. XPS results suggested that tartrate decreased Cu²⁺ and Pb(II) contents and increased S⁰ content in residues. Additionally, SEM-EDS signified severer LPCCO dissolution when the tartrate was present. A mechanism of LPCCO dissolution was proposed. Tartrate/tartaric captures metal ions by complexation of two –COO⁻, which facilitate CT, and possibly, incidentally takes S⁰ away by the organic terminal (–CH) attacking S⁰. As the tartrate complex departs from the surface, S⁰ is pushed away by the resetting of –OH. The released S⁰ is forced to deposit on the adjacent point and heaps together. This work provides insights into the leaching behavior of LPCCO and the great potential of tartrate.