A closed-loop sodium glutamate system for leaching of lead sulfate in spent lead-acid batteries

Leaching of PbSO4 is one of the key steps of waste lead paste via hydrometallurgical process, but its low efficiency and high cost of reagents need to be improved. Sodium glutamate was used as a leaching reagent to leach PbSO4 from waste lead paste for the first time. Through the coordination reaction between sodium glutamate (Glu) and PbSO4, the leaching ratio of PbSO4 could reach nearly 100 %. The Glu-containing species mainly exist in the form of HGlu- in the leaching solution, and Pb(2+ )could combine with the carboxylic groups and the amine group from HGlu- to form a ternary ring chelate with a stable binding energy of -7.5416 eV. Furthermore, the rate-limiting step of PbSO4 leaching by sodium glutamate was the internal diffusion. Then, high-purity PbCO3 (99.9896 %) could be obtained from the Glu-Pb solution by using sodium carbonate, and sodium glutamate was regenerated simultaneously. Finally, the effectiveness and stability of the process were verified by sodium glutamate recirculation process, and the PbSO4 leaching ratio from waste lead paste remained at above 97.31 % within 10 round of recirculation. These findings achieved the high efficiency recovery of waste lead paste, deep purification of impurities and recycling of leaching agents under mild conditions.