Recovery of Valuable Metals from Lithium-Ion Batteries (2)

Article Series / Chapter 2 Recycling of Waste Lithium-Ion Batteries There are two main reasons why great importance is attached to lithium-ion battery recycling processes. First, the materials used in battery production are recognized as strategic raw materials in Europe and worldwide. Second, as battery use increases daily, waste quantities are also growing exponentially. Battery and accumulator waste management raises environmental concerns. This is because toxic compounds contained in waste batteries and accumulators can harm water and soil if improperly disposed of, and release dioxin emissions into the air when incinerated. Toxicity in batteries generally stems from lead, mercury and cadmium. Additionally, other metals used in batteries such as zinc, copper, manganese, lithium and nickel can also pose environmental hazards. Alkaline and zinc-carbon batteries, due to their content of heavy metals such as mercury, zinc and manganese, emerge as waste requiring recovery (Bartolozzi, 1990). Once batteries reach the end of their service life and become waste, they retain economic value. However, when discarded into nature, they cause both economic and environmental problems. Lithium-ion batteries have different physical and chemical characteristics depending on their intended application. Because they do not contain harmful materials to humans and nature in their structure, unlike nickel-cadmium batteries, they become environmentally and economically friendly in a sense—after their service life ends, the materials constituting these batteries can be recovered and used to manufacture new batteries. To prevent environmental and economic damage, waste batteries can be recycled to avoid their harmful effects and recover valuable elements they contain, thereby preventing raw material and economic losses. Recycling is fundamentally a process that can be summarized by the principle "reduce, reuse, recycle," aimed at reducing and minimizing waste quantities. Recovery, on the other hand, is a concept defined as "separate collection at source, grouping, and conversion of reusable waste into other products or energy through physical and chemical methods," encompassing both "reuse and recycling" (Yavuz, et al., 2012). In previous periods, waste lithium-ion batteries, as in many parts of the world, were buried and disposed of in our country. However, today, through recycling operations, valuable materials constituting the battery are recovered and reused in battery production or secondary industries. The combined use of physical and chemical processes is necessary for recovering valuable metals from secondary sources. The most important objective in applying these processes is to prevent lithium-ion batteries from exploding during recycling operations, reduce by-products, and ensure adequate enrichment of lithium-ion batteries in the subsequent process. Following mechanical operations, materials are separated according to their physical behavior (conductivity, density or magnetic susceptibility). Thermal operations apply high temperatures in furnaces to separate electrode materials from organic compounds and produce steel-metallic alloys. However, during this process, toxic emissions from organic additives and carbon can occur. Chemical operations are processes performed for extraction and recovery of valuable metals in waste lithium-ion batteries and are divided into three groups: pyrometallurgical, hydrometallurgical and bioleaching. The pyrometallurgical process releases volatile organics under high-temperature oxidation conditions. Additionally, metals are reduced with carbon and melted. While valuable metals form alloys, slag forms in the other phase. However, this process has lagged behind hydrometallurgical processes due to industrial application costs, environmental concerns and high energy consumption. Hydrometallurgical processes involve leaching operations in acidic and alkaline environments, followed by extraction, precipitation and regeneration steps. This method is the most widely used for recovering valuable metals from waste lithium-ion batteries. This commercially widespread process enables high metal recovery and consumes significantly less energy. Through the bioleaching process, metals are dissolved using organic and inorganic acids produced by microorganism activities. This process provides low energy consumption and is environmentally friendly and low-cost. However, application of this process has remained experimental and has not been commercialized due to certain limitations such as long reaction times, low kinetic rates, unstable efficiency and microorganism cultivation requirements (Moazzam et al., 2021). Waste lithium-ion batteries that have been safely collected and stored must be discharged before recycling operations. The reason is the possibility of lithium-ion battery cells still possessing high energy capacity. For this reason, lithium-ion batteries are discharged using various methods. Discharged lithium-ion batteries are broken with the aid of a cutter (Figure 5). Subsequently, screening is performed to separate coarse and fine materials. Screening results in battery dust as undersized material and plastic, iron, copper and aluminum as oversized material. The characteristic properties of materials constituting lithium-ion batteries differ greatly from those of natural ore. When the same type of lithium-ion battery is considered, the quantity of material within it and the material type and physical properties remain constant. In this case, parameters in recycling processes applied to the same type of batteries are quite clear. However, considering all lithium-ion battery types, due to differences in their chemical composition, recycling processes can vary for each battery type. Cathode and anode electrodes contain active cathode materials and graphite on aluminum and copper foils. In the crushing circuit, cutting, crushing and grinding effects cause graphite and battery dust to fall from the electrodes. However, as a result of these effects, the dimensions of metallic foils can be reduced to a certain size. With screening performed at an appropriate size, aluminum and copper foils do not mix with battery dust. This condition prevents difficulties that may arise in hydrometallurgical processes. Following the crushing and screening circuit, coarse material (aluminum, copper, plastic and iron) is removed from the top of the screen, while graphite and battery dust are collected together as fine material from below the screen. The oversized material is then sent first to a magnetic separator and then to an air separator, from which iron is first obtained, followed by plastic and electrode materials. The most important point in lithium-ion battery recycling is the recovery of battery dust. The reason is that all globally strategic elements are present here (graphite, lithium, cobalt). Battery dust is called black mass. There are numerous laboratory and industrial-scale studies for the recycling of this black mass. However, the general topic of these recycling processes is metallurgical processes. Pyrometallurgy, hydrometallurgy (leaching) and electrometallurgy are the final stages of recycling operations. The vast majority of lithium-ion battery recycling processes applied worldwide are hydrometallurgical processes. As a result of pyrometallurgical processes, valuable materials in battery dust are obtained as metallic and alloy forms. However, both the cost and the need for many processes for reuse place pyrometallurgical processes in the background. Nevertheless, hydrometallurgical processes are quite widespread, and metal salts obtained as products can be directly reused in battery production through simple operations. In mechanical separation methods applied in battery recovery, separation is achieved by exploiting different properties of metals such as density, conductivity and magnetic properties. Thermal processes are generally combined with the production of steel, iron-manganese alloys or other metallic alloys. In mechanical-chemical processes, the crushing method combined with acid leaching at room temperature enables easy separation of cobalt and lithium. In the dissolution process, organic agents are used to dissolve materials present in the anode and cathode, separating LiCoO2 from its bound structure and achieving effective recovery (Xu et al., 2008). Hydrometallurgical processes consist of several steps. In the first step, metallic values are brought into solution. In the second step, recovery operations are performed from the solution. Sometimes desired purity or selectivity may not be met, and a final additional operation may be required. In such cases, higher purity products can be obtained through electrometallurgical processes (Alver et al., 2016). Different solvents and different parameters are applied in leaching operations. The reason is the chemical composition of the active cathode material from the cathode. As is known, there are many types of active cathode materials. In this case, the type and quantity of metal ions to be brought into solution directly affect the process (Jha et al., 2013). In the recovery of metals with high economic value found in Li-ion batteries such as Li, Co, Ni and Mn, pyro-hydrometallurgical processes come to the fore, while metals such as Cu, Al and Fe can be recovered through physical or mechanical methods. Graphite, which has high carbon content, receives little attention from the battery recycling industry and is mostly lost during recycling. Separating graphite also facilitates recovery of other metals during dissolution. Graphite can be separated from reduced-size anode and cathode materials through flotation methods after thermal and chemical pretreatment. In the black mass, both graphite and metal oxides containing Li show excellent flotability because their surfaces are coated with organic binders such as polyvinylidene fluoride (PVDF). For this reason, direct flotation of black material results in weak selectivity between graphite and Ni, Co and Mn. Thermal treatments such as pyrolysis or roasting have proven to be effective approaches for reducing the effect of organic binder coatings before flotation (Yang et al., 2021). Environmentally compatible management of waste batteries and prevention of ecological imbalance require fulfillment of obligations regarding collection, recovery and disposal of waste batteries. Batteries, recognized as strategic raw materials due to their critical element content, can be recycled through the application of ore dressing and enrichment methods.   Research Assistant Zeynep Üçerler İstanbul Teknik Üniversitesi Faculty of Mines, Department of Ore Preparation Engineering Research Assistant Nazlım İlkyaz Dinç İstanbul Teknik Üniversitesi Faculty of Mines, Department of Ore Preparation Engineering Associate Professor Fırat Burat İstanbul Teknik Üniversitesi Faculty of Mines, Department of Ore Preparation Engineering   References Akkuş, N. (2011, January). 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