Leaching of waste battery paste components. Part 2: Leaching and desulphurisation of PbSO4 by citric acid and sodium citrate solution

In this study, as part of developing a new process that can avoid both smelting and electro-winning, citric acid based reagents were reacted with PbSO4, in aqueous media for achieving lead recovery simultaneously with desulphurisation. PbSO4 is the main component in a spent battery paste (accounting for nearly 50% by weight). Recovery of the two oxides PbO and PbO2, which together account for the remaining 50% of the paste, has been discussed in Part 1 in a separate paper. Leaching of PbSO4 with a solution containing C6H5Na3O7·2H2O alone was neither effective in removing the sulphate or in synthesising uncontaminated lead citrate. When both C6H5Na3O7·2H2O and C6H8O7·H2O reagents were used together, it was possible to achieve effective recovery of lead precursor as lead citrate while simultaneously removing sulphur as Na2SO4. The lead citrate product was characterised by SEM and XRD analysis. Conditions for achieving a recovery of 99% of the lead precursor crystallites have been experimentally deduced by varying the concentrations of various reagents, time and temperature of the reaction, and the starting ratio of solid to liquid.