PNNL

Abstract

Ni and Co are critical elements needed for modern technologies, and a better understanding of the ability of Mg-based minerals to incorporate these elements would benefit strategy development for Ni and Co extraction and recovery from mafic and ultramafic deposits. In this work, we performed density functional theory calculations of six Mg-based minerals (brucite (Mg(OH)2), magnesite (MgCO3), nesquehonite (MgCO3?3H2O), lansfordite (MgCO3?5H2O), artinite (Mg2CO3(OH)2?3H2O), and hydromagnesite (Mg5(CO3)4(OH)2?4H2O)) in combination with ab initio thermodynamics to explore the pH2O–pCO2 conditions at the Mg-based minerals were predicted to be thermodynamically stable and to quantify the Gibbs free energy of Ni and Co substitutions at Mg sites. Phase diagrams of the relative thermodynamic stability of the Mg-based minerals agreed with previous theoretical work and experimental observations. Among the six Mg-based minerals, brucite and magnesite were predicted to have the lowest Ni and Co substitution free energies. An analysis of the effect of temperature indicated that, at low temperature (335 K), magnesite more favorably incorporated Ni and Co. Between 100 K and 335 K, Ni was predicted to preferentially substitute for Mg in brucite and Co for Mg in magnesite. Insights gained in this work could therefore help select experimental conditions that either promote or inhibit incorporation of these critical elements into Mg-based mineral phases.