A short and low-carbon approach for spent lead paste recycling via (NH₄)₂SO₄-NH₃·H₂O suspension electrolysis: lead phases conversion

Abstract

Spent lead paste (SLP) presents a major recycling challenge in lead-acid battery treatment due to its insoluble lead compounds. This study develops an innovative and environmentally sustainable approach by integrating (NH₄)₂SO₄-NH₃·H₂O with suspension electrolysis, effectively converting poorly soluble PbSO₄ into soluble [Pb(NH₃)₄]²⁺ complexes. The electrolytic conversion mechanisms of SLP components are systematically elucidated, revealing four distinct transformation pathways: 1) metallic Pb undergoes complete dissolution as [Pb(NH₃)₄]²⁺ complexes followed by cathodic reduction to elemental lead; 2) PbO₂ increases after suspension electrolysis since part of PbO is oxidized; 3) PbO demonstrates dual behavior, with 45.74% undergoing anodic oxidation to PbO₂ while the remainder (54.26%) participates in cathodic electrodeposition; 4) PbSO₄ exhibits triple conversion routes, including: 1) 32.98% transformation through intermediate (NH₄)Pb(OH)SO₄ formation followed by anodic conversion to PbO·PbSO₄, 2) 21.36% direct cathodic reduction to metallic lead, and 3) the residual fraction maintaining soluble [Pb(NH₃)₄]²⁺ speciation in the electrolyte. The optimized process achieves exceptional current efficiency (95.49%) and lead recovery (45.67%), with anode residues comprising 67.58% PbO₂ and 32.42% PbO·PbSO₄. Remarkably, this process exhibits significant economic and environmental advantages, with recycling 1 kg of SLP through the (NH₄)₂SO₄-NH₃·H₂O suspension electrolysis process resulting in a net profit of 0.3466 USD and a reduction in carbon emissions of 119.758 kg CO₂ eq., offering dual advantages of environmental and economic benefits. This work provides fundamental insights into lead phase conversion during suspension electrolysis while presenting a practical, effective solution for battery recycling industries.

Graphical abstract

Keywords

Spent lead paste (SLP) / Suspension electrolysis / Phases conversion / Metallic lead / Cost-effective

Highlight

	● Successful SLP recycling is achieved via (NH4)2SO4-NH3·H2O electrolysis.
	● Lead phases conversion during the suspension electrolysis is elucidated.
	● The process is cost-effective and environmentally friendly.

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