Efficient recovery of lithium from the reverse osmosis concentrate of shale gas wastewater treatment: Adsorption performance and mechanism of Al-doped manganese-based adsorbent particles prepared via hydrophilic modification

The growing demand for lithium in energy storage batteries has driven interest in extracting lithium from shale gas wastewater as a sustainable alternative to traditional mining. To address challenges such as high cycling loss of adsorbent powder and complex operational procedures, this study developed adsorbent spheres by pelletizing Al-modified H1.33Mn1.67O4 powder with polyvinyl chloride (PVC) as the skeleton material, and introducing cellulose acetate (CA) or Pluronic F127 as hydrophilic modifiers. CA-modified powder exhibited superior mechanical stability, internal porosity, and hydrophilicity. These properties reduced interference from organic matter and allowed a lithium adsorption capacity of 20.2 mg/g, surpassing the 18.8 mg/g capacity of unmodified PVC particles. Adsorption behavior followed the Freundlich isotherm model, while pseudo-second-order kinetics indicated that multi-step and multi-layer chemisorption governed lithium uptake. In fixed-bed filtration experiments, the optimal empty bed contact time (EBCT) was determined to be 40 min, leading to an adsorption saturation bed volume more than 40 times the empty bed volume. Desorption enrichment provided lithium concentrations of approximately 200 mg/L. The adsorbent maintained its adsorption capacity over 10 adsorption-desorption cycles, with manganese dissolution losses below 0.3 % and in some cases as low as 0.2 %. These findings confirm the durability and efficacy of the novel composite adsorbent in lithium recovery, offering a significant step toward more efficient and sustainable lithium extraction from treated shale gas wastewater.