Metal Sulfide Complexes and Clusters

Abstract

In this chapter we show that 1. Metal sulfide complexes and clusters enhance the solubility of metal sulfide minerals in natural aqueous systems, explaining the transport of metals in sulfidic solutions and driving the biology and ecology of some systems. 2. There is little or no evidence for the composition or structure of many of the metal sulfide complexes proposed in the geochemical and environmental literature. 3. Voltammetry appears to be a powerful tool in providing additional evidence about the composition of metal sulfide complexes and clusters which complements the increasing use of techniques such as UV-VIS, Raman and IR spectroscopy, EXAFS, XANES and mass spectrometry. 4. Many of the stability constants for metal sulfide complexes are very uncertain because of the lack of independent evidence for their existence. 5. Experimental measurements of metal sulfide complex stability constants is constrained by the lack of knowledge about the composition, structure and behavior of, often nanoparticulate, low temperature metal sulfide precipitates. 6. The competitive kinetics of metal sulfide complex and cluster formation in complicated natural sulfidic systems contributes to the distribution of metals in the environment. 7. The mechanisms of the formation of metal sulfide complexes and clusters provide basic information about the mechanism of formation of metal sulfide minerals and explain the stabilities and compositions of the complexes and clusters. 8. There appears to be a continuum between metal sulfide complexes, metal sulfide clusters and metal sulfide solids. 9. The nature of the first-formed metal sulfide mineral, which is often metastable, can be largely determined by the structure of the metal sulfide cluster in solution. The metal chemistry of anoxic systems is dominated by reactions with reduced sulfur species. These reduced sulfur systems presently characterize the Earth’s subsurface and are occasionally important in marine and freshwater systems. In the first half of Earth history, of course, the surface environments were …