Review of metal sulphide precipitation

Although there have been numerous studies on metal sulphide precipitation, the research field as a whole is not well integrated. This paper reviews the disparate areas of study into metal sulphide precipitation in an attempt to summarise the current work, as well as to suggest potential for future consolidation in the field. The review encompasses (1) fundamental studies into metal sulphide precipitation, which usually focus on mechanisms and are carried out at very low (micromolar) concentrations; (2) applied studies focussing on metal removal and reaction kinetics (mostly via the aqueous phase); (3) studies that focus on the solid phase and address the crystallization kinetics of the formed particles; (4) studies into precipitation of metal sulphide nanocrystals and lastly. (5) applications of metal sulphide precipitation to effluent treatment processes such as Acid Mine Drainage (AMD) treatment as well as industrial hydrometallurgical processes. The review found that, besides lack of integration between the fundamental and applied areas of study, the applied studies have often used flawed methods to evaluate the efficiency of the metal sulphide precipitation process. Applying classical crystallization theory has also not been entirely successful because of the sparingly soluble nature of the systems. The studies that investigate nanocrystal formation tend to focus mostly on recipes and characterization of the formed particles. The industrial and effluent treatment studies form another area of research that stands relatively isolated from its more scientific counterparts. One of the key insights obtained from the summary of these disparate areas of work is that the level of scientific understanding in each of the fields is vastly different. The fundamental studies into mechanistic aspects of metal sulphide precipitation are far advanced of the other areas. However, they are restricted to very low concentrations, which are of limited value in most process-based hydrometallurgical applications. Most of the applied studies are still at a relatively empirical level, with the findings being highly system-dependent. Truly generic findings are still to be realised in these areas. Developing robust measurement techniques to be able to collect consistent data and thus model the simultaneous nucleation, growth, aggregation and attrition of the nano to micro scale particles is one of the challenges in the field. Understanding and characterising the complex aqueous chemistry, taking into account multiple sulphide and metal species interactions, is another. It is proposed that, by integrating the different priorities of the various study areas (chemistry, reaction mechanisms, crystallization mechanisms, particle characterization and industrial applications) the research field as a whole would benefit. (C) 2010 Elsevier B.V. All rights reserved.