Abstract

The recrystallization of copper sulphate from aqueous solution represents an important unit operation in copper mining and recovery and there is significant current interest, on environmental grounds, to the use of sea water as an alternative crystallisation solvent. Hence, the effect of sodium chloride on the shape, size, composition and growth kinetics of copper sulphate pentahydrate crystals is assessed and compared with results using freshwater in order to understand the effect of the principal ions present in brine (Na+ and Cl-) on the crystallisation process. The cooling rate and sodium chloride concentration are observed to have an effect in the crystal shape and size of the copper sulphate crystals albeit the purity of crystals is not significantly affected by the sodium chloride concentration used. Analysis of the crystal growth kinetics of copper sulphate in the supersaturation range from 0.682 to 0.787, and from 0.348 to 0.458 in aqueous and brine solvent, respectively, reveals a significant dependence on the growth environment, in which the growth of the {1-1 0} and {1-1-1} faces of crystals grown in aqueous solutions is consistent with the power law and BCF mechanisms (R-2 of 99.5% and 96%, respectively). In contrast for crystals grown in brine the results suggest that both the {1-1 0} and {1-1-1} faces grow via the BCF mechanism (R-2 of 99.5% and 96%, respectively). This difference in the face-specific growth mechanisms, in the different crystallisation media, is evidenced in the crystal shape revealing slightly more elongated crystals in aqueous solutions.