Primary amine-functionalized HTO/CMC/PVA composite films: Highly selective lithium adsorption and applications in complex lithium-containing systems

Rapid global new energy development fuels explosive lithium demand, with efficient purification of salt lake brine and battery leachate a research hotspot. Liquid-phase lithium recovery is severely hindered by coexisting metal ions with ionic radii similar to lithium, leading to high system complexity. Although powdered H₂TiO₃ (HTO) lithium ion sieves have inherent advantages of stable structure and excellent adsorption capacity, they face critical technical bottlenecks including low solid-liquid separation efficiency and easy co-adsorption by high-valence interfering ions. To solve these problems, this study modified polyacrylamide (PAM) through Hofmann degradation reaction to introduce primary amine groups, and further compounded modified PAM with carboxymethylcellulose (CMC) and polyvinyl alcohol (PVA) to prepare an HTO-loaded CMC/PVA/PAM composite adsorption film. The film forms a dense cross-linked network via intermolecular hydrogen bonds among the three polymers, fundamentally solving the solid-liquid separation issue of powdered HTO. In an alkaline adsorption environment (pH < 10.5), primary amine groups on modified PAM are protonated to form positive charge sites, which exert the Donnan exclusion effect through electrostatic repulsion to effectively inhibit co-adsorption of magnesium, cobalt, manganese and nickel ions, raising the lithium selective separation efficiency of HTO/CPP2 by nearly twofold compared with HTO/CP. The film showed outstanding specific adsorption performance in actual Da Qaidam Salt Lake water samples and waste battery residue leachate, with good cycling stability that retains 91.3% of the initial adsorption capacity after six cycles. This research thus provides a novel and feasible technical solution for the integrated green extraction of high-purity lithium from two typical complex lithium-containing systems.