Doctoral Degrees (Chemical Engineering)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/323

Browse

Browsing Doctoral Degrees (Chemical Engineering) by browse.metadata.advisor "Akdogan, Guven"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Comparing the environmental impact of different hydrometallurgical processes for the recycling of lithium-ion batteries using a life cycle assessment approach
    (Stellenbosch : Stellenbosch University, 2024-03) Maritz, Roelof Frederick; Dorfling, Christie; Akdogan, Guven; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
    ENGLISH ABSTRACT: Lithium-ion batteries (LIBs) have become commonplace for everyday use in consumer electronics. These batteries have also gained a lot of popularity recently for usage in larger scale application such as electric vehicles (EV). The LIB market is projected to grow from 700 GWh in 2022 to 4.7 TWh in 2030 (Fleischmann et al., 2023). The consequence of this rapidly increasing demand for LIBs is the formation of a fast-growing end-of-life (EOL) LIB waste stream. This waste stream includes valuable metals such as lithium, cobalt, nickel, and manganese to potentially be recycled, thus providing benefits in terms of waste management and income from the sale of these recovered metals. There is thus a clear need for EOL LIB recycling and a necessity to find out what is the best process technology available to recycle EOL LIBs. Traditionally LIBs have been recycled using pyrometallurgy, but the recent industry focus has shifted towards alternative process technologies such as hydrometallurgy. There is, however, no clear consensus on how these hydrometallurgical flowsheets should be arranged. As such, the purpose of this study was to compare the environmental impacts of implementing different hydrometallurgical process flowsheets designed for the recovery of metals from EOL LIBs. This comparative environmental study was performed using the life cycle assessment (LCA) framework and considered the use of three lixiviants (hydrochloric-, sulphuric-, and citric acid) alongside the use of three flowsheet options (sequential metal precipitation, mixed metal precipitation, and hybrid sequential precipitation - solvent extraction systems). Lastly, the process was modelled based on a mixed feed of LiCoO2, LiFePO4, and NMC111 batteries. The potential environmental impacts of mineral acid-based processes were found to generally be lower than that of organic acid-based processes by 18 to 61 percentage points. Furthermore, mixed metal precipitation provided the greatest environmental benefit of the flowsheet options considered by 46 to 117 percentage points when compared to the closest competitor. The LCA system was subsequently subjected to multivariate uncertainty analysis and a discernability analysis regarding process feed sensitivity which served to confirm the trends already observed. The LCA system was also subjected to a weak point analysis, where the consumption of NaOH and electricity were listed as the main concerns for process improvement. The process solutions recommended to address both weak points involve the integration of membrane technology and antisolvent crystallisation. Furthermore, the LCA system was compared for a South African and a European context, where it was determined that South Africa’s overreliance on hard coal for energy generation is the main difference between the two regions. Finally, the hydrometallurgical EOL LIB recycling processes were subjected to an additional LCA study regarding the use of recycled metals for resynthesizing NMC cathode materials. This additional study showed that integrating the sequential precipitation recycling process with solid-state synthesis of NMC622 cathode could save up to 70% on energy consumption during cathode synthesis. Meanwhile, integrating the mixed NMC precipitation recycling process with the solid-state synthesis of NMC622 cathode could reduce the environmental impact of NMC cathode production by up to 67%.
  • Thumbnail Image
    Item
    Selective recovery of metals from citric acid leach solutions during the recycling of lithium-ion batteries
    (Stellenbosch : Stellenbosch University, 2022-04) Punt, Tiaan; Akdogan, Guven; Bradshaw, Steven Martin; van Wyk, Andries Pieter; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: Recycling has become an imperative part of the lithium-ion battery (LIB) life cycle due to growing demand for energy storage in applications like electric vehicles and renewable energy technologies, as well as government legislations requiring the recycling of LIBs to reduce environmentally harmful waste. LIB recycling processes must therefore aim to provide a secondary source for strategically scarce metals, like lithium and cobalt, while seeking to reduce the environmental impact of LIB waste. This project aimed to develop a hydrometallurgical process based on environmentally-friendly reagents to recover manganese, lithium, cobalt, and nickel in separate product streams from end-of-life lithium-ion batteries. Organic acids are effective lixiviants in hydrometallurgical recovery of metals from scrap LIBs, having the added benefit of being more environmentally benign than mineral acids. Among these organic acids, citric acid exhibits similar extraction performance when compared to mineral acids. Leaching LiCoO2 (LCO) and LiNixMnyCozO2 (NMC) cathode powder following dismantling and aluminium removal with 1.5M citric acid, 2 vol.% H2O2 at 95°C and 20 g/L for 20 minutes, achieved 93% Al, 90% Co, 96% Li, 94% Mn, and 94% Ni dissolution, confirming citric acid’s performance as lixiviant. A combination of solvent extraction and precipitation technologies was then used to sequentially separate cobalt, lithium, manganese, and nickel from the citric acid leach solution. A diverse range organic extractants, namely: Versatic 10, Cyanex 272, PC-88A, D2EHPA, LIX 84-IC, LIX 984N-C, TBP, Alamine 308, Alamine 336, and Aliquat 336TG was screened to determine which metals can be selectively separated from the citrate leach solution. It was concluded that manganese and residual aluminium are best separated from the PLS under strong acidic conditions with D2EHPA, after which lithium can be separated under weak acidic conditions with D2EHPA in a second subsequent extraction. The cobalt and nickel were separated poorly by the organic extractants and would thus be separated by precipitation from the lithium extraction raffinate. The first separation of manganese and trace aluminium was optimized with 12 vol.% D2EHPA in kerosene at a pH of 2.5 and O/A ratio of 2 when using 3 counter current stages, which separated 99.9% Mn and 80% Al from the PLS. The co-extraction of other metals under optimum conditions was determined to be 7.7% Co, 12.1% Li, and 4.9% Ni. Comparable stripping performance was achieved with sulphuric acid and citric acid from the loaded organic and thus citric acid was chosen as stripping agent. Optimal stripping of the aluminium and manganese loaded organic was achieved with 1.5M citric acid at an A/O ratio of 2, where 78% Mn and 20% Al was stripped in a single stage. The novel second, sequential extraction separated 93.6% Li to a reversible 3rd phase under weak acidic conditions where the optimal lithium separation was achieved with 23 vol.% D2EHPA in kerosene at a pH 5.5 and O/A ratio of 4 with 3 counter-current stages. The co-extraction during the optimum lithium separation included 6.6% Co and Ni. The lithium loaded 3rd phase and diluent emulsion was selectively stripped with 1.5M citric acid and an A/O ratio of 1 to recover 71% Li with 24% Co and Ni in one stage. Optimal nickel precipitation from the lithium extraction raffinate using DMG was achieved with a Ni/DMG ratio of 0.2 at a pH of 8, which enabled 98.5% Ni precipitation with 20% Co co-precipitation. The final effluent from the process had a 96.1 wt.% cobalt purity (metal basis) in the aqueous phase. This hydrometallurgical process was therefore capable of effectively separating the LIB metals from an organic acid PLS to individual metal product streams.