Steps in Recyling Processes

2800 words (11 pages) Essay in Engineering

18/05/20 Engineering Reference this

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Literature Review-

Key Processes involved in Recycling of LIBs –

There are many types of recycling processes of that are currently available for recycling of spent LIBs. The processes can be either mechanical or chemical. The primary focus of recycling is to recover highly valuable materials such as lithium and cobalt which are used in as active cathode materials. Moreover, recycling is also done because of the environmental issues that are caused by toxic materials inside the LIBs. There are four steps in recycling method – Pre-treatment, metal extraction, product recovery, and production preparation.

Figure-1: Four recycling steps for spent LIBs [1].

  1. Pre-treatment-

The first step in pre-treatment is sorting of spent batteries according to the sizes. The batteries having capacity less than 100Wh will be considered small batteries, whereas batteries above 100Wh will be considered big or large batteries [2]. The spent batteries of LIBs of EVs are much bigger than the consumer electronics and easily cross the threshold capacity of 100Wh as they are approximately 250Wh [2]. After sorting has happened and the capacity of the spent LIBs are determined, discharging of batteries are done to avoid any kind of combustion or short circuiting. The batteries are kept or immersed in a salt solution which is good method for discharging. When the discharging of batteries is done, the next step is to dismantle the spent LIBs either manually or by mechanical separation process. The motive behind this step is to separate plastic casings and the internal components of the battery such as cathode, anode and separator. Moreover, various other treatment methods are used to separate active cathode material from aluminium foil such as chemical, thermal, physical treatments [1].

  1. Metal extraction-

This step helps metallic components in active cathode materials to convert into a metal ion state or into an alloy, which further helps in separation of the components and recovering of these components as well (Anh Le Phuc). In the whole recycling process, metal extraction plays an important role. This step incudes two major processes which are used in recycling of spent LIBs – pyrometallurgical process and hydrometallurgical process.

  1. Pyrometallurgical Process-

It is also known as High-Temperature Metal Reclamation (HTMR) process. To melt the battery wastes, a furnace is used which helps in reaching high temperatures. This process allows valuable metallic components to be reduced and then recovering it in an alloy form [1], [4].

Figure-2: Pyrometallurgy process [3].

It consists of three steps for recycling-

  1. Mechanical Pre-treatments

The grinding machine helps in dismantling the batteries into smaller pieces, which increases the surface area during smelting and gives an insight to the materials inside the batteries. The plastic will stay afloat whereas the heavy metals will fall to the bottom.

  1. Smelting Reduction-

As mentioned above the battery waste is melted when kept in the furnace and along with that, increasing the temperature of the furnace subsequently over a period of time. In-order to separate the desired metals or materials from others, reducing agents such as coal, coke and waste carbon products are added. Slag is one of the by-products of this reduction step. It is further used as an additive in concrete or cement when composed of oxides [1], [4].

  1. Casting-

The molten metal is then cast into ingot moulds. The impurities in the moulds will rise to the top after some time and it will be scraped away, leaving the metal to cool [1], [4].

This process is very time efficient when compared to hydrometallurgy. However, it is not eco-friendly as it emits gases which are toxic and uses large amount of energy to melt battery waste.

  1. Hydrometallurgical Process-

This process involves leaching of battery waste by aqueous solutions. It is more environment friendly as compared to pyrometallurgy as it does not emit gases to the atmosphere. It also uses less energy since it operates near ambient temperature. The shortcoming of hydrometallurgical process is that the rate of reaction is slow, and acid is also required.

Figure-3: Hydrometallurgical process [3]

It consists four steps for recycling-

  1. Mechanical Pre-treatment-

This process remains same as mentioned above in pyrometallurgical process. The grinding machine helps in dismantling the batteries into smaller pieces, which increases the surface area during smelting and gives an insight to the materials inside the batteries. The plastic will stay afloat whereas the heavy metals will fall to the bottom

  1. Leaching-

In order to dissolve metal from other impurities, a particular leachate is selected. Metal salts in aqueous form will be present in the solution and the metal salts can be of different types.

  1. Chemical Treatments-

Solvent extraction which is a type of chemical treatment which is executed to separate the main metal from other metals. Special chemicals are mixed in order to carry out solvent extraction process. The special chemicals tend to have higher solubility with specific type of metals. Therefore, separation of main aqueous metal from the solution [1], [4].

  1. Metal recovery process-

The meta solution undergoes electrolysis which is a metal recovery process. In this the current is applied to excite the chemical reaction and therefore, metal is recovered [1], [4].

3.     Product recovery –

Lithium, cobalt and nickel are some of the resulting products from the metal extraction step. Therefore, the main aim of this step is to separate and recover the valuable metals efficiently. Chemical precipitation and solvent extraction are the widely used separation techniques. The products in hydrometallurgy are usually separated by leaching process whereas the pyrometallurgy method requires acid dissolution. The technique used for separating metallic compounds based on different solubilities in two immiscible liquids in termed as solvent extraction. Whereas, the chemical precipitation is a chemical technique which uses specific reagent that can precipitate metallic ions while leaving undesired substances in the aqueous solution.

4.    Product Preparation –

For further actions the products are purified and prepared, this is main purpose of this step. The products are transformed into solid state after being purified, crystallised, dewatered and oxidised. The further actions of solid-state valuable components can be commercial sales as construction material and synthesis of new active cathode material.

Other Key Processes

Industrial processes are based on hydrometallurgical and pyrometallurgical processes or a combination of both. Industrial processes such as Umicore, Toxco and Inmetco are well known and include the mechanism of above mentioned two processes or a combination of both. Out of these three recycling processes Umicore industrial process is the one which is used most commonly. This process is explained below-:

  1. Umicore Process –

The most common industrial process for recycling LIBs and NiMH batteries is Umicore process. This process is a combination of both hydrometallurgical and pyrometallurgical process and does not include pre-treatment of the batteries. The aim of this process is to recover valuable metals such as Cu, Co and Ni. It also recycles Li and other rare elements from slag fraction process. In order to reduce the mechanical pre-treatment, Isa smelt furnace is used. This furnace has three different temperature zones when in operation –

Figure-4: Umicore recycling process [6].

  • The top pre-heating zone- in order to evaporate the battery electrolytes, the temperature of the furnace is kept below 3000C. By keeping the temperature low at the start, the risk of combustion of dangerous chemicals in electrolyte reduces [5].
  • The middle pyrolyzing zone – the temperature in this zone is kept around 7000C as this helps in removing the plastics of spent battery [5].
  • The bottom smelting zone – this zone helps in separating the battery components into alloy phase and slag by keeping the temperature between 1200 to 14000C. The alloy phase mainly constitutes of Cu, Co, Ni and Fe alloys, whereas slag constitutes of some metal oxides as well as lithium oxides. The slag is then sold as construction material whereas alloys undergo hydrometallurgical process [5].

Nickel and Cobalt are recovered in the form of Nickel hydroxide (Ni(OH)2) and cobalt chloride (CoCl2), respectively. A new cathode material is produced such as lithium cobalt oxide (LCO), when cobalt chloride is oxidised and burnt with LiCO3. The major advantage of this process is that there is no pre-treatment of the spent batteries. The other advantage could recovery of valuable metallic components such as nickel and cobalt. (Anh Le Phuc)

The other processes such as Toxco process which is also a method of recycling process of spent LIBs is based on hydrometallurgy. INMETCO process is based on pyrometallurgical process.

Key problem areas –

With the advancement in technologies in battery arena, comes some issues which need to be addressed or solved amicably. There has been ever increase in number of LIBs produced every year from small to big size and varying in power outputs. The increasing numbers are due to increase in demands of consumer electronics, EVs and ESSs. However, with increase in number LIB batteries, also comes the increasing number of spent LIBs every year. This is due to the problem that only 5% of the batteries are recycled currently [7]. It clearly indicates that the current recycling processes are not able to handle the large quantity of spent LIBs or are not sufficient to recycle them properly.

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Landfilling being a conventional method used to be an option of treating spent LIBs. However, the batteries pose a serious threat because they contain toxic material as well as there are risks for both humans and environment. Landfill could have been an option if the number of spent LIBs were under control. But, with the 25 billion LIBs to be produced by 2020 only by china [1], gives an indication that other recycling processes will be required to great extent. Also, LIB global market is estimated to be approximately $32 billion by 2020 [8].

  • Critical stage of the metals-

The cathode of LIB consists of valuable metal such as lithium, cobalt and nickel. All the three metals are valuable as they are used across other variety of applications. Out of the three cobalt has the highest commercial price and therefore its necessary to recycle it and reuse it for new LIBs or other applications. However, cobalt and lithium are in a critical state of supply risk. This is so because cobalt is by product of nickel and copper mining process. Moreover, 65% of cobalt comes from Mid-Africa [1], which is a highly unpredictable area due to high corruption rate and also politically instable. They can anytime stop or cause scarcity of cobalt supplies. Following cobalt, lithium has also entered critical area only because of ever increasing demand of LIBs [9].

  • Key issues in processes-

Hydrometallurgy and pyrometallurgy are the two key recycling processes for the spent LIBs. They both have advantages and disadvantages. Hydrometallurgy as mentioned above is used commonly because of its high metal recovery rate and product purity along with low energy consumption. However, the main disadvantage is that high consumption of chemicals for recycling processes. Whereas, pyrometallurgy is not eco-friendly, has high energy usage, high metal loss rate and also produces toxic gases.

The other processes such Umicore, Toxco and Inmetco processes are key players in the market but they also do have some issues. The recovery rate of valuable metals is low and the slag which is sold as construction materials at low prices, still contains high level of unrecovered metals. Therefore, improving the quality of recycled products will increase profits and more investments will be made in the recycling process of spent LIBs.

  • Issues in Australia-

Developed nations must come forward and help in promoting the recycling process of spent LIBs. But, country like Australia lags when it comes to recycling process. Australia achieves 6% of recycling rate which when compared to their united nations partners such as the European unions achieve almost 45% which has been their target [10]. The main reasons behind this could be poor monitoring by government, poor or lack of recycling infrastructure and low waste volumes. In addition to that Australia is expected to have waste of spent LIBs from 3,400 tonnes in 2016 to 120,000 tonnes in 2035 [11]. Moreover, every year around 8,000 tonnes of handheld batteries land up in landfill [12]. But out of those only lead acid, mercury and silver batteries are mostly recycled, as stated by Australian Battery Recycling Initiative (ABRI).

The other shortcoming of Australian recycling process is that all the spent batteries of Automotive SLI and Industrial are reprocessed whereas handheld batteries end up in landfill. The secondary batteries such lithium, nickel and cobalt are handheld batteries and are not considered in recycling program. Australia however exports these batteries overseas as they are not able to recycle them internally. Some of the batteries can have hazardous material and cannot be processed overseas, this can be termed as illegal exports as well. However, these exporting processes is looked well by the Australian government. 

  • Battery materials are toxic-

Batteries and battery materials are toxic and can cause serious damage to humans as well as environment. Some metals such as lead, mercury and cadmium are highly toxic to nature. Once they are dumped in the landfill, they have the tendency to contaminate the soil and water, thus damaging the ecosystem. Mental health problems and organ damage are some of the issues caused when these above-mentioned metals are inhaled or ingested. Foetuses of pregnant women are most vulnerable to these metals as it can cause some deformity. Nickel may not be so harmful to humans or their organs, but they are toxic to plants and it might reduce their growth rate.

References –

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