Evaluation of a Titanium-Based Adsorbent for Lithium Extraction from Various Brines: Applicability and Mechanism Insights

This study investigated the applicability, underlying mechanisms, and countermeasures for using a titanium-based adsorbent in lithium extraction from different types of brine. First, the effect of brine pH on the adsorption performance of the titanium-based adsorbent was tested; when the pH decreased from 11.8 to 1.8, the equilibrium Li+ adsorption capacity sharply dropped from 21.9 to 0.9 mg/g due to the significantly negative effect of H+. Second, the adsorbent‘s performance was tested with different types of salt lake brine and mother liquor from lithium precipitation. The equilibrium adsorption capacity ranged from 15 to 21 mg/g for carbonate-type brine, sodium sulfate-type brine, and mother liquor but was only 5–7 mg/g for magnesium sulfate-type and chloride-type brine; moreover, the lithium recovery rate could not be significantly improved by increasing the amount of the adsorbent. The main reason was that the former three brines contain large amounts of bicarbonate and/or carbonate ions, which acted as acid buffers, resulting in a minimal pH decrease during adsorption. To improve the applicability of the adsorbent for magnesium sulfate-type brine and chloride-type brine, the effects of different acid buffers were investigated. With the introduction of acid buffer NaHCO3, the pH of magnesium sulfate-type brine at adsorption equilibrium increased from 3.3 to 6.8, and the adsorption capacity increased from 6.4 to 16.2 mg/g, indicating that acid buffer can significantly improve the applicability of a titanium-based adsorbent. The key to determining the suitable acid buffers for regulating the brine pH lies in their reactivity with the brine. Finally, an electrolysis-based technological route was proposed to improve the applicability of a titanium-based adsorbent. This method can also increase the pH of the brine, thereby significantly enhancing the adsorption performance for chloride- and magnesium sulfate-type brine. This study provides valuable insights for industrial applications of titanium-based adsorbents.