Electroassisted leaching of black mass solids from Ni–Cd batteries for metal recovery: Investigation of transport and transfer phenomena coupled to reactions

• Combined electroassisted leaching to electrodeposition is achieved in one cell.
• Ni–Cd waste form spent batteries can be converted to Ni salts and metal Cd.
• Evaluation of the various transport rates allows identification of the controlling step.
• Transport of ions through porous materials in the cell has been simply modelled.

Combined leaching of solid wastes to electrodeposition can be an attractive technique for their optimal beneficiation. In most investigations in the area, results are given in terms of energy consumption and selectivity, without thorough analysis of the rates of the various processes involved. The present investigation deals with the significance of transport and transfer phenomena involved in relation to reaction processes, in a cell combining electroassisted leaching to electrodeposition in view to designing treatment processes of manufactured wares after their end of life. The case of the so-called black mass of used Ni–Cd batteries has been considered here, for the separate productions of nickel salts and metal cadmium. First, leaching of the various hydroxides contained in the black mass has been studied either upon addition of acid or by electrochemical generation of H+ at the anode. Moreover, transport of the metal cations produced from the anode compartment to the cathode through the cloth acting as the separator has been investigated through a simple description of transport phenomena. Comparison and discussion of the various transport or reaction rates could show that ion transport through the porous separator could represent the rate-determining step.