Study of chalcopyrite leaching from a copper concentrate with hydrogen peroxide in aqueous ethylene glycol media

The use of polar aqueous solvents, such as acetone, methanol and ethylene glycol, together with hydrogen peroxide and sulfuric acid solutions, have been shown to increase chalcopyrite dissolution. However, the reason for this improvement is not clear, especially in the case of ethylene glycol. The objective of the present study is to investigate the nature of chalcopyrite leaching, with and without the presence of ethylene glycol (EG), and to understand the role of this polar solvent in the modification of the characteristic behavior involved. For this purpose, a relatively pure chalcopyrite concentrate was leached at 20 degrees C and atmospheric pressure (79 kPa, Mexico City) with hydrogen peroxide in aqueous sulfuric acid solutions, with and without EG. The results showed that, in the absence of EG, the decomposition of 99% of the initial hydrogen peroxide in 24 h, was catalyzed by the Fe2+, Fe3+ and Cu2+ ions (Fenton reagents) present as a consequence of the leach itself. Furthermore, after the first six hours, the copper and iron dissolution effectively ceased (44 and 37%, respectively). In contrast, in the presence of EG, the H2O2 consumption was minimal (similar to 16%) in the same time period and mostly due to the oxidation reactions. The final extractions for copper and iron were 90 and 71%, with an ascendant tendency. It was suggested that hydroxyradicals, product of the Fenton-type reactions, are the driving force for peroxide decomposition and, these were shown to be absent in solutions containing ethylene glycol. Chalcopyrite dissolution kinetics in the presence of ethylene glycol, are well described by the reaction-controlled shrinking particle model. The kinetic expression is a first order function of the hydrogen peroxide concentration and is not dependent on the H+ concentration, although peroxide decomposition slightly increased at higher pH values. The reaction controlling the dissolution process was determined to be the conversion of the chalcopyritic sulfide to elemental sulfur; this was followed by its oxidation to sulfate, although apparently did not affect the leaching kinetics. (C) 2017 Elsevier B.V. All rights reserved.