Effect of pH on desulphurization of spent lead paste via hydrometallurgical process

The effect of pH was investigated in a hydrometallurgical method for recycling spent lead-acid batteries with citric acid. The pH in this novel procedure was adjusted with a cheap and conveniently available alkalescent reagent-ammonia. The desulphurization efficiency of spent lead paste could be increased dramatically up to 99 wft at a weaker acidic pH of 5.5, compared with only 20 wt% without pH adjustment using a fixed leaching at more acidic pH of 2.1 for the duration time of 180 min. The mechanism of the improvement of desulphurization efficiency at adjusted weaker acidic pH was proposed as the demolition of the core-shell structure. The dissolution of lead citrate (shell) will make the lead sulphate particles (core) released and available to react. The chemical formula of the lead citrate product was either Pb(C6H5O7)center dot H2O at more acidic pH of 3.3, or Pb3(C6H5O7)(2)center dot 3H(2)O at weaker acidic pH of 5.5 and 6.2. The pH value will also notably affect the final concentrations of the main impurities in the obtained lead citrate products. A more acidic pH was more favorable for the elimination of the main impurities such as Fe, Ba, Sb, Cu, Zn and Al, by forming soluble species that remained in the leaching solution, which results in cleaner solid lead citrate products. This study has emphasized the availability of pH as a key factor in a novel hydrometallurgical route for recycling spent lead acid batteries. (C) 2016 Elsevier B.V. All rights reserved.