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Kinetics of chalcopyrite dissolution at pH 3

Institute of Earth Sciences "Jaume Almera" – CSIC, c/Lluís Solé i Sabarís, s/n, 08028 Barcelona, Spain

^* Corresponding author, e-mail: pacero{at}ija.csic.es

The management of mine wastes and the quantitative forecast of Acid Rock Drainage (ARD) generation have aroused widespread interest. In order to be coupled with gas and water flux models, chalcopyrite dissolution kinetics at pH 3, at temperatures from 25 to 70 °C and at variable dissolved oxygen concentrations was studied in flow-through experiments.

In the range of conditions under study, the rate of chalcopyrite dissolution is independent of the concentration of dissolved oxygen. This enables chalcopyrite to dissolve throughout the whole waste piles. The rise in temperature from 25 to 70 °C produces an increase of one order of magnitude in the chalcopyrite dissolution rate.

As a result of this study, the following expression for chalcopyrite dissolution rate was obtained:

where R_chalcopyrite is the chalcopyrite dissolution rate (molm^–2 s^–1), R is the gas constant (kJmol^–1 uK^–1) and T is the temperature (K).

In line with earlier studies carried out under different conditions, iron was released to solution preferentially over copper in all the experiments carried out. XPS examination of the samples showed that reacted surfaces were formed by phases enriched in sulfur and copper (relative to iron) compared with the initial, pristine chalcopyrite surface. However, these surface layers allow the progress of dissolution with out passivating the chalcopyrite surface. According to the apparent activation energy obtained (32±5 kJ mol^{– 1}) and to the lack of rate variation with stirring, the chalcopyrite dissolution rate seems to be controlled by surface reactions and is independent of the non-stoichiometric surface layer.

Key-words: chalcopyrite, dissolution kinetics, flow-through, sulfides.

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