Fang Xia

Mineral carbonation offers permanent and safe disposal of anthropogenic CO2. Well distributed and abundant resources of serpentine minerals and natural weathering of these mineral to stable and environmentally benign carbonates favour the exploitation of these minerals as the most suitable raw material for mineral carbonation. However, slow dissolution kinetics are impeding the large scale implementation of mineral carbonation. Heat treatment of serpentine minerals results in enhanced reactivity for subsequent carbonation processes at the expense of an additional energy penalty4. Heat treatment of these minerals results in the removal of structurally bound hydroxyl groups which leads to partial amorphisation of the structure and enhanced reactivity. Therefore, understanding the role of the mineralogical changes during dehydroxylation and determination of activation energy (Ea) is crucial for providing an energy efficient solution for commercialisation of mineral carbonation...

The formation of arsenian pyrite has been studied experimentally by hydrothermal reactions of either pyrite or pyrrhotite with arsenic-bearing fluids. Both pyrite and pyrrhotite were transformed to arsenian pyrite retaining the overall morphology of the starting grains but distinct kinetic and textural features were observed. Pyrite was transformed to dense arsenian pyrite with diffused arsenic distribution at the phase boundary; the transformation rate increases with increasing temperature, suggesting that the incorporation of As was controlled by solid-state diffusion processes. By contrast, pyrrhotite was transformed to a mixture of porous arsenian pyrite and arsenian marcasite with zonation textures; the newly formed arsenian pyrite/marcasite was separated from the unreacted pyrrhotite by gaps of tens of microns. Also, the transformation rate decreases with increasing temperature. These are typical characteristics of pseudomorphic coupled dissolution-reprecipitation replacement reactions. Elemental distribution revealed a negative correlation between S and As distributions, suggesting the substitution of As for S during arsenian pyrite formation. Therefore, arsenian pyrite can form by dissolution-reprecipitation during pyrite crystallization from a solution or by later solid-state diffusion of arsenic into the pyrite structure. The textures formed are similar to natural examples, suggesting that the same mechanisms may dominate in the formation of natural arsenian pyrites.