Closed-loop extraction of precious metals from e-waste via NH₄HCO₃ desulfurization and secondary lead smelting

This study presents a novel, eco-friendly metallurgical process that integrates battery recycling with e-waste precious metal extraction in a single closed-loop system. The method uniquely combines ammonium bicarbonate-based desulfurization of spent lead-acid battery paste, secondary lead (Pb) smelting, and Parkes process refining for precious metals extraction. Ammonium bicarbonate (NH₄HCO₃) achieved a sulfur removal efficiency of up to 97%, which is comparable to or higher than many conventional reagents such as NaOH and Na₂CO₃, under similar conditions. The desulfurized paste was then smelted (with coal as reductant and soda ash flux) to produce high-purity lead metal (∼98-99% Pb), which served as a liquid collector for gold, silver, and palladium from e-waste. Subsequently, the Parkes process (zinc alloying) was applied to selectively separate these precious metals into a Zn-rich phase. The integrated process was validated under various conditions; XRF analyses and theoretical modeling confirmed consistent extraction of lead and precious metals. For the first time, this work demonstrates a continuous closed-loop Pb metallurgy route capable of simultaneously processing battery waste and e-waste. The results show that the process is scalable, adaptable to different feedstocks, and efficient in both sulfur removal and precious metal extraction offering a practical, sustainable alternative to conventional fragmented or chemical-intensive recycling methods.