A Facile and Environmentally Friendly Approach for Lead Recovery from Lead Sulfate Residue via Mechanochemical Reduction: Phase Transformation and Reaction Mechanism

Abstract

Lead sulfate residue (LSR) is an important secondary lead resource also categorized as a hazardous waste, which has gained great attention in clean and sustainable utilization technology due to the shortage of primary resources and environmental pollution. The current methods for LSR treatment involve a potential environmental risk including emission of SO x gas and generation of waste acids and alkali. Herein, an environmentally friendly method is proposed for treating LSR, by which lead was reduced under ambient conditions via mechanical ball milling using iron powder as the reductant. The phase transformation of lead was analyzed by X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectrometry, Fourier transform infrared, and X-ray photoelectron spectroscopy, revealing that the reduction time, rotation speed, mass ratio of ball to material (B/M), and iron powder dosage positively influenced the reduction of lead sulfate. The highest lead sulfate reduction efficiency of 99.9% was obtained under optimum conditions: rotation speed of 300 rpm, reduction time of 2 h, B/M of 15 g/g, and 1.5 times the theoretical dosage of iron powder. The generated ferrous sulfate was subsequently removed by water washing, and excess iron powder was separated by melting, accompanied by metallic lead produced with a high purity of 99.2%. This process is simple and environmentally friendly, showing good potential for industrial application.

Recycling of Lead Pastes from Spent Lead–Acid Batteries: Thermodynamic Constraints for Desulphurization

“…The reductants that have been used in hydrometallurgical routes include lead sulfide [3] and glucose [35]. Iron powder is also used as a reductant in mechanochemical reduction of lead dioxide [11]. In the mechanochemical reduction process, lead dioxide was reduced under ambient conditions via mechanical ball milling using iron powder as a reductant.…”

“…The Gibbs free energy change ( 0 298.15 r G Δ ) for the above reaction is 28.40 kJ•mol −1 , calculated from the thermodynamic properties from [27] for the respective species in Reaction (11). The positive Gibbs free energy change for Reaction (15) suggests that there is no thermodynamic driving force for lead dioxide to be decomposed into lead monoxide.…”

“…This is because the decomposition of lead sulfates is energy-intensive, as it requires high temperatures exceeding 1000 • C [7,8], and the decomposition process using coal or coke as the fuel produces many gaseous and solid pollutants, such as lead fume as well as dilute SO 2 gas streams [7][8][9]. Therefore, in order to prevent the above environmental and health problems as well as the energy-intensive problem, lead sulfates must be desulphurized first [10,11]. In the hydrometallurgical recycling process for lead-acid batteries, there are three desulphurization processes of lead pastes with oxalate, carbonate, and alkaline solutions.…”

Issues Concerning Manufacture and Recycling of Lead

“…Lead contents separated from the polymer case of the battery, the porous glass matt or other separator and sulfuric acid, are metal lead from the grid and interconnecting flags and the remaining paste from the electrodes, containing lead oxide, led granules and, most significantly, lead sulfate. In the modern environmentally sound approach, lead sulfate has to be first desulfurized in a hydrometallurgical process [41][42][43].…”