This week’s seminar was given by Dr Ola Hekselman of the Department of Materials. The talk was on her work developing a low-energy, low-temperature, environmentally friendly alternative to the traditional methods for recycling of lead-acid batteries.
Lead-acid batteries (LABs) have one of the highest recycling rates of commercial products around the world today, with rates exceeding even commonly known items, such as glass or paper. Recycling of lead-acid batteries is one of the great success stories of the recycling industry with nearly 100% of battery components able to be recovered and reused.
A surprising success story
There are several reasons contributing to this success. Firstly, lead-acid batteries are the most popular power supply for automotive industry and demand for them continues to grow, even with an increasing number of hybrid and electric vehicles. They remain ‘the’ energy storage device for the 12V internal electronics that control SRS, power steering or lighting in both conventional and state-of-the-art hybrid or fully electric vehicles. With industrial forecasts predicting 2 billion vehicles on the roads worldwide by 2035 and new emerging applications, such as grid-scale energy storage, LABs are expected to remain a dominant battery technology for the foreseeable future.
Moreover, lead maintains its properties regardless of number of recycling cycles. Production of the secondary lead is cheaper than extraction of lead from metal ores. However, use of lead is not without problems and limitations.
The main risk associated with LABs is the toxicity of lead. It is a highly poisonous material, affecting all organs in the body and often causing irreversible health outcomes. The nervous system is particularly susceptible to toxic effects of lead, with young children being at a greater risk of poisoning. Long-term exposure to lead can be associated with cognitive impairment, behavioural problems, lower IQ, increased societal violence and lower life expectancy. Hence, it is of vital importance that contamination of the environment is minimised by implementing an effective recycling system of lead.
Currently, the industrial recycling of lead is dominated by pyrometallurgical processing. Used lead-acid batteries are firstly separated into individual components: plastic cases, electrolyte and used lead grids and lead paste.
Plastics are crushed, melted and pelletised to be used in the manufacture of new cases and covers; battery acid may be either neutralised or converted to sodium sulphate and used as a detergent component; whereas lead grids are separated from lead paste and passed directly for refining to remove alloy impurities.
Lead paste, a mixture of PbSO4, PbO, PbO2 and metallic Pb, is treated with alkali carbonates or hydroxides to convert PbSO4 to PbCO3 and Pb(OH)2, followed by smelting of the entire mixture to obtain metallic lead. De-sulphurisation step helps to mitigate formation of off-gases containing sulphur, which significantly reduces air pollution. Smelting step is a high-temperature process, typically operating at 1100-1300 ˚C, where reduction to metallic lead is achieved by carbothermic reaction with carbonaceous fuels as reducing agents. Subsequently, the metallic lead is refined with metallic lead grids.
Numerous industry standards and environmental legislation regulate handling and disposal of used lead-acid batteries, resulting in almost 100% recycling rates of spent lead-acid batteries in the US and EU and creating continuous closed loop economies.
While rates of lead exposure and release are carefully controlled in those markets, in low- and middle-income countries they can be considerably higher, due to a combination of minimal regulation and less adherence to safer recycling processes. Recent reports by Pure Earth and Blacksmith Institute estimate that human exposure to lead comes primarily from informal recycling of lead-acid batteries, making it the most polluting industrial process in the world and resulting in 9 million Disability-Adjusted Life Years (DALYs) and 594,000 deaths in 2015 globally.
A bright future
While the success of LAB recycling is encouraging, it is clear that significant improvements can be made in both energy consumption and exposure minimisation. My research focuses on developing new low-temperature chemical and electrochemical technologies for lead recycling via solution-based processing. I use deep eutectic solvents (DES), which are considered the next-generation of ionic liquids, because of their relative low cost, ease of handling, low environmental impact and, most importantly, their ability to dissolve a wide range of inorganic compounds – including oxides. These technologies will not only have a lower overall energy demand but will also significantly reduce lead-to-air emissions.
Currently, we are focussing on the most suitable DES for use in large-scale processes and the total process modelling to optimise performance and energy-efficiency of our technology. We will be then working with our industrial partner to understand the impact on their business and workflows. I think that with the correct technologies we can maintain the almost 100% recycling rate while dramatically reducing environmental impacts of the process.
Dr Ola Hekselman
Dr Hekselman is a Research Associate in the Department of Materials at Imperial College London. Ola earned her PhD at the University of St Andrews, developing novel electrolytes for Li- and Na-ion batteries.
Before joining RELAB project in December 2017, she investigated chemical and electrochemical degradation processes in solid-state Li-ion batteries at Imperial College London and mechanism of ion transport in polymer electrolytes at the University of Oxford.
Currently, Ola is focused on recycling of lead-acid batteries; developing environmentally-friendly alternatives for lead recovery and analysing life-cycle of these batteries in low- and middle-income countries.