Lead Acid Battery Recycling

This project on the design of energy-reducing, economically competitive, electro-hydrometallurgical strategies for recycling spent lead-acid batteries is part of a multi-disciplinary project between teams from the Departments of Chemical Engineering and Materials. The Electrochemical Engineering group is focusing on the scale up strategy and design of electrochemical reactors to assess key processing considerations that will impact the techno-economic modelling and overall process viability.

 Introduction

Lead-acid batteries are used in almost all the billion vehicles, in shipping and in building back-up power supplies worldwide, accounting for a global industry worth ca. 30 G£; 99 % of those batteries in Europe and USA are recycled. Normally, spent lead-acid batteries are recycled via a pyrometallurgical process. The use of coke as a reducing agent as well as oil or gas for inputting thermal energy causes significant CO2 and other emissions which result in significant environmental impact. Current practices in the UK metal industry are classified as energy intensive industries and account for 40% of the UK’s carbon emissions from businesses and the public sector. Consequently, they are susceptible to policies aimed at moderating climate change, potentially making the UK Electrical and Electronic Engineering industries sector uncompetitive with the rest of the world, particularly as there is no common global standard to reduce carbon emissions coupled with high and rising energy costs. Hence, novel, more energy-efficient and environmentally-benign processes are being developed and deployed for material recovery from spent lead-acid batteries; e.g. electro-hydrometallurgical processes using aqueous solutions or prospectively, ionic liquids, for dissolution of lead compounds/oxide(s) and subsequent electrodeposition of lead and possibly lead dioxide.

 Principles of Operation of Lead-Acid Battery Recycling

Battery Recycling Operation Principles

The high demand of lead-acid batteries due the increasing number of automotive vehicles and the increasingly stringent environmental regulations fuel the need to design improved processes for battery production and lead recycling to minimise environmental impact. Commonly, lead from spent lead-acid batteries are smelted to produce lead bullion which is further refined to produce soft lead suitable for battery production. The figure above shows a typical pyrometallurgical process involving battery breaking, desulfurisation (eq. 1), smelting (eq. 2 and 3) and refining to produce the final lead product.

(1)   PbSO4 + Na2CO3  Na2SO4 and PbCO3

(2)   PbCO3 PbO + CO2 (>550 oC)

(3)   2PbO + C  2Pb + CO2 (>1200 oC)

Compared to the smelting process, hydrometallurgical and electrochemical technologies have been proposed and developed for some of the following attractive characteristics:

  • High selectively as electrochemical deposition is selective for the metal of interest and results in highly quality metal production
  • Reduced waste production as only small amounts of chemicals and reactants are used in the process
  • Typical waste products include O2 and H2 which are acceptable gaseous emissions
  • Ambient working conditions which are free from dust emissions typically found in pyrometallurgical smelters

Hence offering significant energy and environmental benefits