title: Lithium Extraction via Mechanochemical Treatment of End-of-Life Glass-Ceramics and Lithium Silicate Minerals
Creators: name: Necke, Tobias
Publisher: name: UNSPECIFIED
Year: 2024

description: Owing to recent trends in e-mobility, lithium is in high demand resulting in increased global production and record prices for lithium ores and compounds. Accordingly, many efforts are being made to maintain supply by exploiting primary resources around the world, while effective lithium recycling from secondary sources is still lacking. Concerning primary pegmatite ores, the current state of industrial technology necessitates energy intense high-temperature pretreatments to increase the reactivity of the refractory lithium minerals prior to leaching. Moreover, these routes are focused only on the low but economically relevant lithium content, disregarding the main components Al and Si, leading to large quantities of leaching residues. In addition to primary lithium minerals, a similar chemical assemblage of elements is found in secondary raw materials, such as Li₂O-Al₂O₃-SiO₂ glass-ceramics (LAS), which can be seen as an untapped urban source of lithium found in significant quantities in discarded electrical appliances. Although the recycling of these devices is already established, large quantities of valuable lithium are lost on this disposal route, as recycling has so far only concentrated on recovering the transition metals while neglecting the glass-ceramic sections. Encouraged by these circumstances, the present dissertation investigated a holistic approach that attempts to utilize the entire chemical inventory of the feedstock materials, leading to various value-added by-products during extraction and downstream hydrometallurgical treatments on the way to a pure lithium compound. For this study, a LAS glass-ceramic plate from an end-of-life cooktop and naturally occurring lithium silicate minerals such as lepidolite, spodumene and petalite were selected as source materials for alkaline mechanochemical studies, focusing on lithium extraction without thermal pretreatments.
The first section addresses the experimental investigations of the LAS samples, leading to efficient decomposition of the lithium-containing β-quartz phase under alkaline conditions, while lithium was significantly enriched in the leach liquor. Optimal experimental parameters were identified at a NaOH concentration, a rotational speed and a ball-to-powder ratio of 7 mol/L, 600 rpm and 50:1 g/g respectively, resulting in a substantial extraction of up to 92.4 %. In addition to leaching, the entire feedstock was transformed into different zeolite frameworks as a function of NaOH concentration.
In the second section, the findings from the investigations of LAS samples were transferred to the three most common lithium silicate minerals lepidolite, spodumene and petalite. In these studies, petalite was identified to be significantly more compatible with the chosen mechanochemical approach compared to spodumene or lepidolite. This resulted in a considerable lithium extraction of up to 84.9 %, while in parallel a nearly complete conversion of petalite into a sodalite zeolite was achieved. The significantly higher reactivity of petalite under mechanochemical conditions was associated with specific features in its crystal structure, such as the less dense atomic packing and the pronounced activation of cleavage planes along the lithium sites during ball milling.
Unavoidably, as a side effect of alkaline leaching, parts of the silicon from the starting materials went into solution during the mechanochemical experiments, necessitating desilication as an intermediate step prior to lithium precipitation. CaO proved to be an effective agent leading to high desilication rates for LAS- and petalite-based solutions, while the lithium content remained unaffected in both cases. Upon purification of the solution by desilication, lithium was precipitated by adding moderate amounts of phosphoric acid, permitting the formation of sparingly soluble Li₃PO₄ at specific P:Li ratios. In a final step, the obtained Li₃PO₄ was further treated with Ca(OH)₂, resulting in the precipitation of hydroxyapatite Ca₅(PO₄)₃OH and the formation of lithium hydroxide LiOH·H₂O in solution, which can be crystallized to a pure phase after filtration. In addition, Ca-silicate phases, formed during the desilication of the enriched solution, as well as apatite, resulting from the transformation procedure, are regarded as value-added byproducts as they offer specific applications and thus correspond to the holistic approach.
The leaching residues obtained during mechanochemical treatments of LAS or petalite samples revealed comparable high specific surface areas, and consisted mainly of sodalite and/or LTN zeolites, renowned for their special properties in molecular sieving or selective adsorption. Accordingly, these byproducts were investigated as potential adsorbents in a side study, demonstrating excellent sorption performance for divalent heavy metal ions in synthetic wastewater samples.