Role of pH regulator on controlling the adsorption performance of LDHs type adsorbents toward Li+ from brines

Abstract

Aluminum-based lithium adsorbent is a kind of bilayer hydroxide. Due to its advantages such as environmental friendliness, simple elution process and good cycling stability, it is usually regarded as one of the most effective and practical solid Li⁺ collectors in brine. However, the adsorbent is limited by its low adsorption capacity and fragile intrinsic structure, and its long-term cycle adsorption in real brine is restricted. Up to now, the intercalation strategies of different anions are common methods to solve the above problems. Considering the importance of pH regulation during the precipitation process, different pH regulators were designed for pH regulation, and different anions were introduced for intercalation at the same time.

A detailed study was conducted on how the intercalation behavior of different anions affects the lithium extraction performance of aluminum-based adsorbents. The results show that the adsorption capacity of the prepared LDHs adsorbent depends on the pH regulators HCl (8.4 mg/g), H₂SO₄ (7.2 mg/g), HNO₃ (7.2 mg/g) and H₃PO₄ (4.4 mg/g). Among them, the adsorbent obtained by using H₂SO₄ as the pH regulator exhibited a capacity retention rate higher than 90 % after five desorption/adsorption cycles in real brine. The intercalation of highly negatively charged ions with larger ion radii significantly alters the interlayer spacing of the adsorbent. Although it does not contribute significantly to the adsorption capacity, it enhances the cycling stability of the adsorbent in real brine. This is attributed to the electrostatic interaction that makes the AlO₆ octahedral connection tighter, thereby improving the intrinsic structure of the adsorbent's anti-interference ability against high-concentration impurity ions from the outside. Based on the structure-performance relationship of adsorbents, the control mechanism of adsorbents was summarized, and the key factors for selecting pH regulators were preliminarily proposed. This research can provide theoretical and technical guidance for the configuration and preparation of highly efficient lithium adsorbents to effectively recover Li⁺ from various brine resources.