Development of an environmentally friendly lithium-ion battery recycling process

Thesis (MEng)--Stellenbosch University, 2019.ENGLISH ABSTRACT: The main aim of this work was to evaluate the technical feasibility of using organic acids as lixiviants for Co, Li and Ni recovery from lithium-ion batteries (LIBs) and to recover the metals from the resulting pregnant leach solution (PLS). Batch leaching tests to investigate the effects of H2O2 addition, temperature and acid concentration on metal dissolution were performed in a glass jacketed reactor with 300 ml working volume, using citric acid and DL-malic acid as lixiviants. Initial tests to investigate the effects of H2O2 addition indicated that it speeds up the leaching kinetics, hence it was included in successive leaching tests. Leaching tests were performed to investigate the effect of temperature and acid concentration on metal dissolution. Temperature levels of 30℃, 60℃ and 95℃ were used and acid concentration levels of 1 M, 1.25M and 1.5 M were used, with the H2O2 concentration and pulp density being kept constant at 2 % v/v and 20g/L, respectively. Results revealed that the performances of both acids were almost similar with over 95% metal dissolution within 30 minutes, using 1.5M citric acid and 1M DL-malic acid in the presence of 2% v/v H2O2 at 95℃ and 20g/L pulp density. After considering the cost of each acid, citric acid was selected as the more suitable lixiviant and was used in successive tests. Batch solvent extraction tests were performed, with the aim of separating Mn and Al from Co, Li and Ni in the PLS, using D2EHPA as extractant in kerosene diluent. The following variables at the given levels were investigated: D2EHPA concentration (10% v/v and 20% v/v), pH (2.5, 3.0 and 3.5) and organic/aqueous phase ratio (O/A) (1, 2, 3, 4, and 5). The best separation results were obtained using 10% v/v D2EHPA at pH 2.5 and organic phase/aqueous phase O/A ratio 5, where 94% Mn was extracted within 15 minutes, with 47% Al, 7% Co, 9% Li and 3% Ni co-extraction, in one stage. The McCabe-Thiele method was employed under the optimum conditions and it predicted that over 99% Mn can be extracted in two stages. This was verified experimentally and 99% Mn and 89% Al were extracted in two stages, with 13% Co, 17% Li and 6% Ni co-extraction. Metal precipitation tests were carried out at 50℃, 60℃, 70℃ and 80℃ using NaH2PO4 as precipitating agent. The results revealed that the solubility of Li3PO4 decreases with temperature increase, while the solubilities of Co3(PO4)2, Mn3(PO4)2 and Ni3(PO4)2 were not affected, in the investigated temperature range. Five scenarios for the recovery of metals from solution were considered and the proposed separation order in each scenario was experimentally investigated. For each scenario a flowsheet was constructed and mass balances were performed. Comparisons were made based on the mass balances, and the flowsheet in scenario four was selected as the most efficient one. It involves Mn and Al extraction from PLS using D2EHPA, followed by phosphate precipitation at 50℃ (targeting Co and Ni) and subsequent phosphate precipitation at 80℃ (targeting Li). This yields three products: a 93% pure Mn product, a Co-Ni product with 42 wt. % Co and 57 wt. % Ni and a Li product with 89 wt. % Li.AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie werk was om die tegniese uitvoerbaarheid van die gebruik van organiese sure as loogmiddels vir Co, Li en Ni-herwinning uit lithium-ion batterye (LIBs) te evalueer en om die metale van die resulterende pregnant loogsifoplossing (PLS) te herwin. Lotlogingstoetse om die effek van H2O2-aanvulling, temperatuur en suurkonsentrasie op metaaldissolusie te ondersoek, is uitgevoer in ʼn glasomhulselreaktor met 300 ml werkende volume, deur sitroensuur en DL-appelsuur as loogmiddels te gebruik. Aanvanklike toetse om die effek van H2O2-aanvulling te ondersoek, het gewys dat dit die loging-kinetika versnel, en is dit dus ingesluit in opeenvolgende logingstoetse. Logingstoetse is uitgevoer om die effek van temperatuur en suurkonsentrasie op metaaldissolusie te ondersoek. Temperatuurvlakke van 30 °C, 60 °C en 95 °C is gebruik en suurkonsentrasievlakke van 1 M, 1.25 M en 1.5 M is gebruik, met die H2O2-konsentrasie en pulpdigtheid wat konstant gehou is by 2% v/v en 20 g/L, onderskeidelik. Resultate het bekendgemaak dat die doeltreffendheid van beide sure amper soortgelyk was met meer as 95% metaaldissolusie binne 30 minute, deur 1.5 M sitroensuur en 1 M DL-appelsuur te gebruik in die teenwoordigheid van 2% v/v H2O2 by 95 °C en 20 g/L pulpdigtheid. Nadat die kostes van elke suur in ag geneem is, is sitroensuur gekies as die meer gepaste loogmiddel en is in opeenvolgende toetse gebruik. Lotoplosmiddelekstraksietoetse is uitgevoer, met die doel om Mn en Al van Co, Li en Ni in die PLS te skei, deur D2EHPA as ekstraheermiddel in keroseenverdunner te gebruik. Die volgende veranderlikes by die gegewe vlakke is ondersoek: D2EHPA-konsentrasie (10% v/v en 20% v/v), pH (2.5, 3.0 en 3.5) en organiese/waterige-verhouding (1, 2, 3, 4 en 5). Die beste skeiding resultate is verkry deur 10% v/v D2EHPA by pH 2.5 en O/A-verhouding 5 te gebruik, waar 94% Mn binne 15 minute geëkstraheer is, met 47% Al, 7% Co, 9% Li en 3% Ni koëkstrahering in een stadium. Die McCabe-Thiele-metode is gebruik met die optimale kondisies en dit het beraam dat meer as 99% Mn in twee stadia geëkstraheer kan word. Dis eksperimenteel geverifieer, en 99% Mn en 89% Al is geëktraheer in twee stadia, met 13% Co, 17% Li en 6% Ni koëkstrahering. Metaal presipitasietoetse is uitgevoer by 50 °C, 60 °C, 70 °C en 80 °C deur NaH2PO4 as neerslagmiddel te gebruik. Die resultate het bekendgemaak dat die oplosbaarheid van Li3PO4 afneem met temperatuur wat toeneem, terwyl die oplosbaarheid van CO3(PO4)2, Mn3(PO4)2 en Ni3(PO4)2 nie geaffekteer is in die temperatuurbestek wat ondersoek is nie. Vyf scenario’s vir die herwinning van metale uit oplossing is oorweeg en die voorgestelde skeidingsorde in elke scenario is eksperimenteel ondersoek. Vir elke scenario is ʼn vloeidiagram saamgestel en massabalanse is uitgevoer. Vergelykings is gemaak gebaseer op die massabalanse, en die vloeidiagram in scenario vier is gekies as die mees doeltreffende een. Dit sluit in Mn en Al ekstrahering uit PLS deur D2EHPA te gebruik, gevolg deur fosfaatneerslag by 50 °C (gerig op Co en Ni) en daaropvolgende fosfaatneerslag by 80 °C (gerig op Li). Hierdie lewer ʼn opbrengs van drie produkte: ʼn 93% suiwer Mn-produk, ʼn Co-Ni-produk met 42 wt. % Co en 57 wt. % Ni, en ʼn Li-produk met 89 wt. % Li