Browsing by Author "Jeza, Sabelo Acceptance"

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    Integrated development and optimisation of an organic acid-based hydrometallurgical process for treatment of spent lithium-ion batteries (LIBs)
    (Stellenbosch : Stellenbosch University, 2022-04) Jeza, Sabelo Acceptance; Akdogan, Guven; Dorfling, Christie; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: Lithium-ion batteries (LIBs) are the heart of some of the latest technological devices but these batteries become harmful waste at the end of their life. At present, the use of organic acid-based hydrometallurgy processing of spent LIBs is the most promising alternative route to pyrometallurgical processing in terms of economic feasibility and environmental impact. This study aimed to develop an integrated and optimised organic acid-based hydrometallurgical process for the treatment of LIBs to recover metals at end-of-life. This was achieved by conducting leaching, precipitation and solvent extraction batch experiments in a specific order, followed by flowsheet modelling using experimentally obtained values and techno-economic analysis to assess potential feasibility. Citric acid was selected as the organic acid with which to leach LIBs at a constant temperature of 95 °C, while stirring at 750 rpm, with a S/L ratio of 20 g/L and 2 vol. % H2O2. The effect of lixiviant concentration (0.75 M, 1 M, 1.5 M, 2 M and 3 M) on metal equilibrium extraction was also investigated. The concentration of 0.75 M resulted in equilibrium metal extraction of 94.3% Li, 95.1% Co, 96.2% Mn and 95.7% Ni after 1 hour. Ni was the first metal to be recovered through precipitation from a leachate solution using 0.07 M dimethyl glyoxime (DMG) at a pH of 6, followed by the solvent extraction of Mn using 10% D2EHPA at an O/A ratio of 3 and a pH of 5. Mn was stripped from the organic phase using 0.5 M H2SO4 at an O/A ratio of 1.33 followed by hydroxide precipitation. The aqueous phase from Mn solvent extraction mainly consisted of Co which was precipitated using NaOH at a pH of 13.5. Four process products were recovered: Ni(OH)2 with more than 99.5% purity and 62.7% Ni recovery; Mn(OH)2 with 89% purity and 90.2% recovery; Li2SO4 with 97% purity and 57.3% Li recovery and cobalt hydroxide based product (Co(OH)2) with 68 % purity and 71.4% Co recovery. A feed rate of 868 tonnes per year was used for the flowsheet modelling, based on the South African context in terms of expected LIBs waste, and this resulted in an estimated annual revenue of R190 023 414. The estimated capital expenditure was R162 920 270 and the operating expenditure was R88 148 631. An NPV value of R241 272 740 over a 10-year investment period was discounted at 11.11%, equivalent to a 67.95% IRR, which implies that the process would be profitable upon implementation.