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Recycling Lead acid batteries –a paradigm for recycling in a circular economy.

Recycling Lead acid Batteries 

– A Paradigm for recycling in a circular economy

In this blog we will be looking at recycling lead acid batteries as a model for the energy storage industry. We are all aware of the concept and benefit of a circular economy. The most critical part of that, is having not only recycling processes for used goods, but also an established, safe infrastructure for collection and transport of the scrap materials. With the burgeoning use of batteries for many commercial and industrial applications, notably electric vehicles and Energy Storage Systems, there is increasing concern over the sourcing of battery raw materials and the recyclability of those batteries. It is fairly obvious that their recyclability and the availability of raw materials for their manufacture are inextricably linked. There are several electrochemical storage technologies which currently represent the majority of battery manufacturers and use in the world today.

Worldwide battery market
Figure 1. Proportion of different battery chemistries sold worldwide as a function of MWh

Fig. 1 shows the approximate split by global MWh sales of the different types of batteries produced annually. Clearly lead acid and lithium-ion battery are two technologies that dominate the current battery markets. Equally clear, is the very rapid growth rate of li-ion batteries, and there are concerns about this growth rate. One is the lack of a commercial recycling process for lithium batteries which may result in end of life disposal problems. The other is that there may be insufficient materials to manufacture batteries for the growing demand. The two are inextricably linked and in this blog, we will be looking at how lead acid chemistry could be a model for recycling of all types of electrochemical storage systems.

One of the virtues that distinguishes lead acid chemistry, is its age. Because of this we have developed methods of recycling and reusing all of the constructional materials, to the extent that we can claim almost a 100% recovery rate of the complete battery. This impressive statistic is not just a function of the mechanical and chemical methods used for breaking, classification and refining of the materials, it is also about having a collection and distribution network. The process of lead melting and refining has been known to humans for several thousands of years. However, the very attributes of lead, which favour recycling, i.e. low melting point and lack of reactivity, are those attributes which reduce its electrochemical activity and therefore its energy density. This recyclability is a major factor in the acceptance of lead as a constructional material for batteries; this is despite its known toxicity. It is the toxicity which is currently of concern, both for battery manufacturers and battery recyclers. For this reason, alternative methods to the traditional polluting pyrometallurgical techniques are being developed. These methods rely on dissolution of the battery active material in solvents, then extracting the lead in a variety of chemical forms. We will discuss the pros and cons of both approaches in the next blog and give a view on their relative merits. But for this instance, we are concentrating on the lead acid technology and the recycling infrastructure and methods currently in use. At this point it would be useful to briefly cover the general principles of recycling in order to appreciate the hurdles which need to be overcome to effectively and commercially recycle all battery types.

A general definition of recycling would be:

  • “The action or process of converting waste into useable materials.”
  • This definition can be further refined and split into two streams: open and closed loop recycling.
Standard Recycling Models
Figure 2. Standard recycling models showing closed and open loop recycling models

Fig. 2 gives the general principles of both types. Closed loop means that the materials recovered are reused in their original purpose, such as waste glass bottles being recycled into more glass bottles. Open loop recycling is the repurposing of the recovered materials into a different, and probably single use before finally ending up as unusable waste. An example of this would be the incineration of domestic waste to provide local heating to a shopping mall. The by-products, largely gases such as NOx, SOx and CO2,would be considered pollutants. Any solid by-products would also be unusable waste, ending up in landfill.

Whilst the definitions of recycling given above are fine for discussion purposes, we would need to add one word: “economically” between converting and waste, in order to have a financially viable process. This is important. Without this key factor, no business would take on the laborious, expensive processes needed to collect and transport the waste, as well as the cost and expense of extracting and recovering the required materials. As a general principle there is little doubt that it is technically possible to recover and recycle almost anything from every manufactured component on Earth. The technology and know-how exist. The problem is, how much does it cost?

With these principle in mind we can look specifically into recycling of batteries. Fig. 3,  is a schematic diagram, illustrating the circular, official recycling practice for lead acid batteries.

Circular economy recycling credentials of lead acid batteries
Figure 3. Circular economy recycling credentials of lead acid batteries

From this it is evident that there is a well established and informed route from manufacture to disposal and recovery of lead acid batteries. There are collection points where the original retailer or private and public recycling points have used batteries returned by the consumer for the specific purpose of recycling into new batteries. One thing to note is that the transportation of used batteries requires proper containment due to their hazardous nature. These procedures and working practices refer to the official recycling organizations which consist of collection and delivery companies, retail organizations, lead smelters and refiners (often called recyclers), which are held together by the glue of legislation and regulation for the collection, storage and transport of hazardous materials. However, as is widely recognized there is also the informal sector which recycles lead acid batteries outside of the expensive legal constraints of the official routes.

Whilst this situation is known to exist in countries such as Africa, India and South America, it is believed that more industrially developed nations typified by Europe would not have recourse to informal elements within this closed loop process. If so we should have near 100% recycling efficiency within European countries.

Recycling Efficiency for Lead acid batteries
Figure 4. Recycling efficiency for lead acid batteries in European Nations

Unfortunately, this is not the case, and Fig. 4 shows the status of recycling for the majority of Europe. Here we can see that only 8 out of 30 countries achieved better than 90% recycling efficiency in 2018, with only 4 countries reaching or close to reaching a 100% recovery and recycling rate. However, there are many factors behind these statistics, including reporting criteria and the moving target of matching current annual sales levels, with battery life and the amount of scrap available from previous years’ sales. The movement and distribution of scrap batteries in Europe can sometimes, despite legislation, still occur through informal and sorry to say, illegal means. This is particularly true when demand is high and supply is short.

This brings up the next point, which is confusion over the often-quoted statistic, that lead acid batteries are almost 100% recycled. This is true when we are talking about the amount of recovery of battery materials from the process, not the total amount of batteries recycled. This means that nearly all the plastic, lead and acid in the battery ends up as feedstock for more batteries. In some cases, it can include feedstock for other materials, such as sulphuric acid being used to make fertilizer. In any event it is not technically possible to recover 100% of anything, as some losses will inevitably occur, albeit small losses of less than 1%. The diversion of sulphuric acid to other uses as mentioned also means that the recovery procedures do not completely meet the circular model which is happily portrayed in the websites of lead organizations and recycling companies. We need also to add into this the inevitable toxic emissions and waste (slag) which can be generated by pyrometallurgical methods of lead acid battery recycling.

To understand the recycling rates, any losses in the processes and any waste generated, we need to examine both the materials in a lead acid battery and also the chemistry and engineering principle of the recovery processes. Fig. 5 is a schematic diagram of the recovery process used in lead acid battery recycling.

Figure 5. Processing route for collected lead acid battery scrap
Figure 5. Processing route for collected lead acid battery scrap

In this case it is the current pyrometallurgical methods, which so far are the only commercially available processes. The diagram shows 4 basic stages after collection and delivery to the recycling site. These are:

  1. Battery breaking and segregation. The battery scrap is put into a hammer mill to be broken, then separated into basic lead bearing paste, metallic grid granules, plastic bits and acid components, Fig. 6.
Lead acid battery scrap starting to be processed at a recycling plant
Figure 6. Lead acid battery scrap starting to be processed at a recycling plant
  1. Desulfurization. The paste or leady active material is treated with soda ash to remove the sulfur.
  1. Smelting (blast or reverberatory) furnace. The desulfated paste is then smelted in a blast or reverberatory furnace to reduce the leady compounds to soft or hard lead bullion, depending on the composition of the scrap and the intended final product, Fig. 7.
Reverberatory furnace used for lead acid battery active material recycling
Figure 7. Reverberatory furnace used for lead acid battery active material recycling
  1. Refining the lead bullion. The most common method is calcining to produce either soft (pure) lead or hard (alloy) lead.

This diagram throws up some interesting points. Along with the recycled components as products, there is also the problem of emissions at various process stages. These are generally atmospheric and effluent emissions of gases (COx, SOx, NOx), lead bearing dusts and effluent water containing contaminants such as sulphur and lead. These emissions are governed by national and local standards in every country where lead recycling is practiced. Modern levels are very small and contamination of air, land and water are generally a problem of the past in the regulated formal sector. However, this is not true of the informal sector which, according to the WHO, has been, and still is, responsible for significant land contamination and raised blood lead levels in some cities and villages. In addition to this pollution there is the ongoing problem of how to deal with the slag produced from smelting which can be as high as 3% of the scrap processed. Both of these problems are the subject of constant R&D and solutions which are currently being developed. These will be reported on in more detail in a later blog, but for now they can be categorized as new processes which replace the smelting with dissolution of the active material paste fraction. This modification removes the slag problem and makes the process cheaper and more environmentally friendly. Another development in the pyrometallurgical process, is the recovery of metallic contaminants from the waste slag which can make this waste fraction suitable for land or road fill projects.

Two examples of these dissolution processes are the patented technologies of Aurelius and Citrecycle. Both of these companies have a process which uses citric acid as the solvent for dissolving the leady paste before recovering it a variety of lead compounds for further treatment.

Schematic comparing two dissolution routes to lead acid battery active material recycling
Figure 8. Schematic comparing two dissolution routes to lead acid battery active material recycling

Fig. 8 is a flow diagram which compares both of these processes. From the diagram it can be seen that the battery scrap is still broken and segregated as with the conventional method, but the smelting and desulfurization process is missing. There is a sale-able product, the dried lead citrate which can be sold on to the formal sector for further processing under controlled and regulated conditions. It has been proposed that this type of process could be adopted in modular form, under local authority control, by the current informal recycling sector. It would have the dual benefit of not only preventing lead contamination and blood poisoning, but also draw the informal recyclers into the control of the formal recycling sector.

Lead acid batteries are the most recycled commodity on the planet, Fig. 9.

The lead acid battery recycling sector is indeed a model for a circular economy and could be taken as a first stage blueprint from which various iterations could be derived which are suitable for different battery chemistries. However, there are challenges centered around the toxicity of lead and the control of emissions and waste products from the current pyrometallurgical recycling methods. Managing the informal sector which does not fulfill the legal requirements laid down by national and local governments when collecting, storing and processing scrap batteries, needs to be improved. However, new cheaper and more environmentally friendly processes, designed to address the pollution and safety issues, are nearing commercial availability.

With these methods, which are safer and less polluting, the goal to produce four-nines soft lead from battery scrap will be achievable. Global economics and politics affect the supply of material and lead used in battery manufacture. Complete recycling of all internally generated battery scrap, using methods which produce less CO2, remove slag and minimize pollution, is the way forward. Whilst the present situation of lead acid battery recycling may be the current exemplar, the industry still strives to improve to make all of its processes cleaner, safer and more environmentally friendly. The new technologies which hope to achieve this goal could be a significant step forward, and Microtex as always, will be at the forefront of accurately informing its customers and partners of the latest battery technology developments which directly affect us all.

Dr Mike McDonagh, Chief Technical Officer - Microtex

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