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Lithium (Li) is considered a strategic element whose use has significantly expanded. Its current high demand is due to its use in lithium ion batteries for portable electronic devices, whose manufacture and market are extensively growing every day. These days there is a great concern about the final disposal of these batteries. Therefore, the possibility of developing new methodologies to recycle their components is of great importance, both commercially and environmentally. This paper presents results regarding important operational variables for the dissolution of the lithium and cobalt mixed-oxide (LiCoO 2 ) cathodes from spent lithium ion batteries (LIBs) with hydrofluoric acid. The recovery and synthesis of Co and Li compounds were also investigated. The dissolution parameters studied were: temperature, reaction time, solid-liquid ratio, stirring speed, and concentration of HF. The investigated recovery parameters included: pH, temperature, and time with and without stirring. The final precipitation of lithium fluoride was also examined. The results indicate that an increase in the HF concentration, temperature, and reaction time favors the leaching reaction of the LiCoO 2 . Dissolutions were close to 60%, at 75 • C and 120 min with a HF concentration of 25% (v/v). The recovery of Co and Li were 98% and 80%, respectively, with purities higher than 94%. Co and Li compounds, such as Co 3 O 4 and LiF, were synthesized. Furthermore, it was possible to almost completely eliminate the F − ions as CaF 2 .

Herein is presented the results of a study on the hydrometallurgic extraction and recovery of aluminum and silicon by leaching of kaolinitic clays with HF. The studied extraction parameters were: temperature, reaction time, solid/liquid ratio, concentration, and precipitating agent mass. In the leaching process, mineral dissolutions near 100% were obtained when working at 348 K, solid/liquid ratio 2% w/v, HF 12% v/v, for 120 minutes. The HF leach liquor generated from the dissolution of kaolinitic clays contains H 2 SiF 6 and H 3 AlF 6 . Studies were conducted to recover the two valuable fluorides as K 2 SiF 6 and Na 3 AlF 6 by precipitation with alkaline salts from the leach liquor. Phases of precipitated fluorides were identified by XRD and surface morphology by SEM. The purity of the K 2 SiF 6 precipitate was 98.8%, whereas for Na 3 AlF 6 , it was 89.3%. Also, both synthesized solids are of high commercial value due to their industrial applications.

This work describes the development of a new process for the recovery of Li, Al and Si along with the proposal of a flow sheet for the precipitation of those metals. The developed process is comprised of lepidolite acid digestion with hydrofluoric acid, and the subsequent precipitation of the metals present in the leach liquor. The leaching operational parameters studied were: reaction time, temperature and HF concentration. The experimental results indicate that the optimal conditions to achieve a Li extraction higher than 90% were: solid-liquid ratio, 1.82% (w/v); temperature, 123 • C; HF concentration, 7% (v/v); stirring speed, 330 rpm; and reaction time, 120 min. Al and Si can be recovered as Na 3 AlF 6 and K 2 SiF 6 . LiF was separated from the leach liquor during water evaporation, with recovery values of 92%.

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