PNNL

Abstract

Mafic and ultramafic rocks are comprised of divalent metal silicates that can have concentrations of Ni and Co in the hundreds to thousands of ppm. High surface area model silicate minerals doped with Ni and Co are needed to support fundamental in situ research to optimize metal extraction from these rocks. We report the synthesis of nanosized undoped, 5% Ni-, 25% Ni-, 5% Co-, and 25% Co-doped forsterite (Mg2SiO4) that expands on an existing sol-gel/surfactant method for pure forsterite to incorporate the Ni or Co. Metal reagents, surfactant ratios, and calcination procedures were optimized to synthesize the doped forsterites with high surface area while minimizing formation of secondary phases. Characterization by XRD indicated crystallite sizes of 29 – 83 nm with a strong preference for Ni and Co to partition to the M1 cation sites of the forsterite crystal structure. Metal oxide impurities were only present in undoped and 25% Ni-doped minerals at 0.6 wt. % or less. SEM demonstrated sizes consistent with XRD but with some particle fusion. UV-Vis, IR, XPS and STEM EDX analyses were used to evaluate the purity of the doped forsterites, and atomic level HAADF TEM indicates preferential partitioning of Ni and Co into the M1 cation sites, consistent with XRD. This synthesis methodology will enable in situ experiments that can track the fate of Ni and Co at laboratory timescales for metal extraction technologies.