Direct and selective extraction of precious metal molybdenum from solid matrices using supercritical carbon dioxide

Sustainable separation and purification strategies for transition metal molybdenum, enlisted as a critical mineral owing to its vast industrial applications and limited natural resources, from secondary resources are of paramount importance. Directed towards this aim, this is the first report of direct, mineral acid-free Mo recovery from solid matrices by supercritical carbon dioxide extraction using alpha benzoin oxime (ABO) and pentadecafluoro-n-octanoic acid (HPFOA) as complexing agents. Efficient (>90%) Mo recovery was achieved under optimised conditions (323 K, 200 atm, in situ complexation mode) by eliminating any high-temperature treatment and harsh acid/base leaching steps. Additionally, high removal efficiencies were obtained for other metal ions, namely, U (>91%) from the U–Mo blend matrix relevant to fission moly applications and V (∼100%), Al (>88%), and Ni (>91%) from the simulated spent catalyst matrix. Further insight into the Mo-complex in the SC CO₂ extract was obtained by UV-vis spectrophotometry, FTIR and electrometric investigations. Mo oxalate precipitation from a compact SC CO₂ extract was also demonstrated. This study, therefore, addresses the challenge of developing a simple, efficient and selective method for the recovery of Mo from various solid matrices.