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

Abstract

Lead–acid batteries are important to modern society because of their wide usage and low cost. The primary source for production of new lead–acid batteries is from recycling spent lead–acid batteries. In spent lead–acid batteries, lead is primarily present as lead pastes. In lead pastes, the dominant component is lead sulfate (PbSO4, mineral name anglesite) and lead oxide sulfate (PbO•PbSO4, mineral name lanarkite), which accounts for more than 60% of lead pastes. In the recycling process for lead–acid batteries, the desulphurization of lead sulfate is the key part to the overall process. In this work, the thermodynamic constraints for desulphurization via the hydrometallurgical route for recycling lead pastes are presented. The thermodynamic constraints are established according to the thermodynamic model that is applicable and important to recycling of lead pastes via hydrometallurgical routes in high ionic strength solutions that are expected to be in industrial processes. The thermodynamic database is based on the Pitzer equations for calculations of activity coefficients of aqueous species. The desulphurization of lead sulfates represented by PbSO4 can be achieved through the following routes. (1) conversion to lead oxalate in oxalate-bearing solutions; (2) conversion to lead monoxide in alkaline solutions; and (3) conversion to lead carbonate in carbonate solutions. Among the above three routes, the conversion to lead oxalate is environmentally friendly and has a strong thermodynamic driving force. Oxalate-bearing solutions such as oxalic acid and potassium oxalate solutions will provide high activities of oxalate that are many orders of magnitude higher than those required for conversion of anglesite or lanarkite to lead oxalate, in accordance with the thermodynamic model established for the oxalate system. An additional advantage of the oxalate conversion route is that no additional reductant is needed to reduce lead dioxide to lead oxide or lead sulfate, as there is a strong thermodynamic force to convert lead dioxide directly to lead oxalate. As lanarkite is an important sulfate-bearing phase in lead pastes, this study evaluates the solubility constant for lanarkite regarding the following reaction, based on the solubility data, PbO•PbSO4 + 2H+ ⇌ 2Pb2+ + SO42− + H2O(l).

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].…”

Renewal of Lead Battery Electrodes Using a Plasma—Chemical Processing Method

“…The main steps in recycling of Pb-type batteries are: collecting batteries and transporting them to a recycling facility, separating battery components, melting and refining lead components, washing plastic components, then crushing or melting them, cleaning and treating the sulfuric acid electrolyte, and waste treatment and disposal. Currently, about 98% of Pb batteries are recycled by utilizing their products or using them as secondary raw materials in circular economy processes [2,3,[25][26][27]. As was already mentioned, the Pb charging processes are stopped by the formation of various compounds on the surface of the electrodes.…”