Nanometer-sized nickel and cobalt doped forsterite synthesis for investigating critical element recovery from mafic and ultramafic rocks

Abstract

A synthesis method for nanosized forsterite (Mg₂SiO₄) doped with varying concentrations of Ni and Co has been developed to support studies of carbonation-based extraction and separation of Ni and Co from mafic and ultramafic rocks. The protocol expands upon an existing sol–gel/surfactant method and is demonstrated for doping levels of 5% and 25% of Ni or Co. Variables such as metal reagents, surfactant ratios, and calcination procedures were optimized to achieve high specific surface areas and small particle sizes while minimizing secondary phase formation. Particle sizes ranged from 29 to 83 nm, and specific surface areas were between 11 and 32 m² g⁻¹. Metal oxide impurities were minimal, appearing only in undoped and 25% Ni-doped samples at 0.6 wt% or less. Ni and Co were only detected in the +II oxidation state and partitioned predominantly in the M1 cation site of the forsterite crystal structure. Doped nanosized forsterites prepared with this method will enable in situ experiments that can track, at the molecular scale, the fate of Ni and Co during carbonation reactions and thus provide a knowledge base for improving metal extraction and separation technologies.