Goal and Scope Definition
The goal of this study is to quantify the environmental impact of the hydrometallurgical and hybrid recycling processes for the LIBs and determine the greener option out of the two processes under study. The findings of this study can be useful to the end-of-life vehicle handling practitioners who intend to set up a recycling plant for the LIBs.
The functional unit for the study is one tonne of EoL LIBs. The functions of the product system in scope are pyrometallurgical and hydrometallurgical recycling processes. The reference flow is determined by the mass of the materials present in the LIB. In this study, we define the boundary by considering only the recycling phase in the EoL (disposal) stage of the battery life cycle. Figure 3 shows a typical battery treatment system with different phases.
The battery is collected and around 40% of the weight is recovered from dismantling that includes disassembly of components like cathode, anode, casing, frame, cables etc. Fluids like electrolytes are also drained separately. This is followed by a recovery which includes reuse and remanufacturing. The parts that are obtained from disassembly can be either reused or remanufactured depending on their age and state of repair. Post this, the rest of the battery is shredded and separated for recycling. Magnetic and eddy current separation is used to remove ferrous and non-ferrous materials respectively. Further manual sorting is performed to segregate Automotive Shredder Residue (ASR) fractions that include plastic, glass, rubber, fibre, foam and dirt. The remaining light and heavy ASR fractions are incinerated for energy recovery where it is burned in an incinerator at a high temperature to recover energy in the form of heat. Finally, the unusable waste from recycling, reuse, remanufacturing and energy recovery operations go through an audit to target for zero landfill assessment and future material substitution before landfill.
Hydrometallurgical Recycling Process
Leaching is the process of extracting substances from a solid by dissolving them in a liquid, either naturally or through an industrial process. Here, H2SO4 (sulphuric acid) and H2O2 (hydrogen peroxide) are used as leaching agents. Lithium cobalt oxide (LiCoO2) reacts with H2SO4 and H2O2 to form Li2SO4 (lithium sulphate), CoSO4 (cobalt sulphate), H2O (water) and oxygen (O2). The reaction is,
2LiCoO2 (s) + 3H2SO4 + H2O2 → Li2SO4 + 2CoSO4 + 4H2O + O2 (g) (1)
From the stoichiometry, we determine that 9.08 kg of LiCoO2 will require 13.64 kg of H2SO4 and 1.58 kg of H2O2. The mass of Li2SO4 and CoSO4 produced will be 5.1 kg and 14.37 kg respectively.
Similarly, the reactions for LiNiO2 (lithium nickel oxide) and LiMnO2 (lithium manganese oxide) are consistent with reaction (1). Here, NiSO4 (nickel sulphate) and MnSO4 (manganese sulphate) are produced instead of CoSO4 and the rest of the products are the same as (1).
Cu (copper) reacts with H2SO4 and H2O2 to form CuSO4 (copper sulphate) and H2O,
Cu (s) + H2SO4 + H2O2 → CuSO4 + 2H2O (2)
Copper cementation reaction is governed by the following reaction,
Fe (s) + Cu2+ → Fe2+ + Cu (s) (3)
In the above Fe (iron) exists as iron powder and the mass of Cu present in the battery is 11.14 kg. Based on the stoichiometry, we determine the mass of H2SO4, H2O2 required and CuSO4 produced to be 17.18 kg, 5.96 kg and 27.97 kg respectively.
Precipitation is the creation of a solid phase when the concentration of a salt exceeds its solubility in a solution. CoSO4 obtained in reaction (1) is precipitated using NaOH (sodium hydroxide) and the reaction is,
CoSO4 + 2NaOH → Co(OH)2 (s) + Na2SO4 (4)
From reaction (1), we find that the mass of CoSO4 is 14.37 kg and from stoichiometry, we determine the mass of NaOH required is 7.42 kg. The mass of Co(OH)2 (cobalt hydroxide) and Na2SO4 (sodium sulphate) produced will be 8.62 kg and 13.17 kg respectively. Similarly, NiSO4 and MnSO4 are precipitated using K2CO3 (potassium carbonate) and Na2S (sodium sulphide) respectively.
The precipitation reactions of Fe2(SO4)3 (ferric sulphate) and Al(NO3)3 (aluminium nitrate) in the presence of water and sodium hydroxide is,
Fe2(SO4)3 + 4H2O → 2FeO.OH (s) + 3H2SO4 (5)
From the stoichiometry, we determine the mass of H2O, FeO.OH (ferric oxy-hydroxide) and H2SO4 to be 17.46 kg, 43.1 kg and 71.31 kg respectively.
Al(NO3)3 + 3NaOH → Al(OH)3 (s) + 3NaNO3 (6)
From the stoichiometry, we determine the mass of NaOH, Al(OH)3 (aluminium hydroxide) and NaNO3 (sodium nitrate) to be 37.52 kg, 24.39 kg and 79.73 kg respectively.
Lithium sulphate obtained during the leaching of LiCoO2, LiNiO2 and LiMnO2 is further precipitated using K2CO3 and the reaction is,
Li2SO4 + K2CO3 → Li2CO3 + K2SO4 (7)
The mass of Li2SO4 is found to be 15.26 kg and based on the stoichiometry, we determine the mass of K2CO3, Li2CO3 (lithium carbonate) and K2SO4 (potassium sulphate) to be 19.16 kg, 10.21 kg and 24.03 kg respectively.
Table 1 below presents the complete life cycle inventory data required for the hydrometallurgical recycling process. The data includes the battery composition, amount of electricity and process water.
In Table 1, the mass is listed for the composition of one battery. However, for the LCA, we have quantified the impact considering one tonne of battery materials.
Table 1
Inventory Data for Hydrometallurgical Recycling Process
Inputs |
Component | Composition | Amount | Unit |
Cathode | Lithium | 1.97 | Kg |
Cobalt | 5.5 | Kg |
Nickel | 5.5 | Kg |
Manganese | 5.07 | Kg |
Oxygen | 8.8 | Kg |
Anode | Graphite | 19.74 | Kg |
Casing | Steel | 28.06 | Kg |
Electrolyte | Ethylene carbonate | 14.46 | Kg |
Lithium hexafluorophosphate | 1.61 | Kg |
Cables | Copper | 1.83 | Kg |
Aluminium | 0.197 | Kg |
Steel | 1.001 | Kg |
Frame | Steel | 1.001 | Kg |
Plastic | 15.087 | Kg |
Foil | Aluminium | 5.499 | Kg |
Copper | 9.306 | Kg |
Cell case | Aluminium | 2.961 | Kg |
Separator | Polyethene | 7.6 | Kg |
Leaching agent | Hydrogen peroxide | 10.69 | Kg |
Sulphuric acid | 58.03 | Kg |
Precipitating agent | Sodium sulphide | 7.19 | Kg |
Sodium hydroxide | 44.94 | Kg |
Potassium carbonate | 32 | Kg |
Process water | 17.46 | Kg |
Electricity | | 19.6 | Kwh |
Process water | | 0.1 | Cubic metre |
Outputs |
Product output | Cobalt hydroxide | 8.62 | Kg |
Nickel carbonate | 11.04 | Kg |
Manganese (II) sulphide | 8.01 | Kg |
Copper | 11.14 | Kg |
Iron (III) oxide-hydroxide | 43.1 | Kg |
Aluminium hydroxide | 24.39 | Kg |
Lithium carbonate | 10.21 | Kg |
Emissions to water | Sodium sulphate | 63.5 | Kg |
Sulphuric acid | 71.31 | Kg |
Sodium nitrate | 79.73 | Kg |
Hybrid Recycling Process
The Pyrometallurgical process can be used only for recycling cobalt (Co), nickel (Ni), copper (Cu), iron (Fe) and the remaining elements like lithium (Li), manganese (Mn) and aluminium (Al) coming out as slag which needs to be further processed by the hydrometallurgical process.
The reaction of LiCoO2 (lithium cobalt oxide) with coke (C) as the reducing agent to form Li, Co and CO2 (carbon-di-oxide) is as follows,
LiCoO2 + C → Li + Co + CO2 (g) (8)
Similar reactions follow for LiNiO2. The reduction reactions of CuO (copper (II) oxide) and Fe2O3 (iron (III) oxide) are,
2CuO + C → 2Cu + CO2 (g) (9)
2Fe2O3 (s) + 3C (s) → 4Fe (s) + 3CO2 (g) (10)
We determine the total mass of the reducing agent required to be 29.51 kg. We use the higher heating value of carbon which is 32.8 MJ/kg to obtain 967.93 MJ energy of coke. The mass of slag forming agent (limestone) is assumed to be the same as that of coke which is 29.51 kg.
The mass of the outputs in the chemical reactions was obtained by theoretical calculations since it was not possible to get the field or experimental data for the reaction yields. We have taken the typical composition of inputs from the literature and calculated the lower bounds of the environmental impacts assuming ideal conditions (i.e. 100% conversion rate). However, in reality, the conversion rate will not be 100% and the impact will be higher due to loss factor or percentage. The paper aims to give an estimate of the lower bound impact to the practitioners if they intend to set up battery recycling plants. In reality, the same steps can be followed to determine the reaction yield by performing the experiments. The contribution of this paper is to perform a feasibility study through LCA inventory analysis and quantifying the environmental impact. The methodology development along with the theoretical contribution and stepwise LCA approach has been the main objective of this paper. Though it is a theoretical study, this research has been performed by consulting experts from chemical engineering and potential users of such batteries from automotive engineering.