Recovery of critical battery metals from cobalt-rich deep-sea polymetallic nodules: Selective carbothermal reduction based on kinetics

Metal recovery from deep-sea polymetallic nodules (DPN) is a promising option to ensure the future supply of critical battery metals due to terrestrial resource constraints. In this study, the leaching efficiency of Mn and critical metals (Co, Ni, and Cu) that hosted in the crystal lattice of Mn(IV) mineral is significantly enhanced by selective carbothermal reduction. The reduction kinetics of Mn(IV) is consistent with the CO gas diffusion-controlled mechanism, and the kinetic equation can be expressed as 1 -23 R -(1 -R)23 = 0.024e-10.06 RT center dot t. Under the optimal conditions of 600 degrees C, 60 min, and 3 wt% carbon addition, 61.54 % of Mn(IV) minerals are reduced to Mn(II) and the rest was converted to Mn(III), while the leachable metal oxides (CoO, NiO, and CuO) are hardly reduced, therefore, the leaching efficiency of Co and Mn increased from 8.18 % and 5.12-98.03 % and 96.23 %, respectively. In order to limit the leaching of the impurities Fe and Al, high-pressure acid leaching was carried out after selective carbothermal reduction, and the leaching parameters were optimized to 160 degrees C, H2SO4/DPN 0.77 wt%, and leaching for 4 h with a liquid/solid ratio of 5:1 mL/g. As a result, only 2.35 % Fe and 3.34 % Al were leached, and the leaching efficiencies of Co, Ni, Mn and Cu were 98.47 %, 95.72 %, 97.24 % and 94.99 %, respectively.