The role of sodium chloride on surface properties of chalcopyrite leached with ferric sulphate.

Abstract

Leaching of chalcopyrite in oxidizing conditions usually results in low copper extraction due to mineral passivation. It has been proposed that sodium chloride has a positive effect on chalcopyrite dissolution increasing copper extraction. Aiming to bring further insight into this topic, the present work seeks to evaluate the influence of sodium chloride on the leaching of chalcopyrite focusing on surface area and porosity of the reaction products formed during leaching. A finely ground (d50=5.5 μm) chalcopyrite concentrate assaying 25.2% iron, 30.9% sulphur and 27.5% copper was leached in oxygenated ferric sulphate solutions at atmospheric pressure and 95 °C. It has been observed that although sodium chloride favoured natrojarosite precipitation, which reduced the total iron concentration during leaching, copper extractions as high as 91% were accomplished as compared to 45% copper extraction in the absence of NaCl. It is suggested that sodium chloride reduces chalcopyrite passivation and complexes Cu (I) ions adding a second redox couple to the system. Furthermore, morphologic characterization of the reaction products performed by SEM analyses as well as specific surface area and porosity measurements have confirmed that NaCl increases surface area and porosity of the product layer, which explains the high copper extractions observed in the presence of the salt.