Phosphate Removal by Surface-Modified Ceramsite Derived from the Synergistic Use of Multiple Solid Wastes

To address the dual challenges of aqueous phosphate pollution and the resource utilization of petrochemical solid wastes, this study proposes a novel closed-loop “waste-to-waste” strategy. This approach innovatively integrates multiple solid wastes (including oily sludge and petroleum hydrocarbon-contaminated soil) into a porous ceramic matrix and utilizes lanthanum recovered from spent catalysts for surface modification, successfully fabricating an optimized adsorbent—lanthanum-modified ceramsite (BC@La). Under the conditions of pH 6, an adsorbent dosage of 1 g/L, and a temperature of 318 K, BC@La achieved a maximum phosphate adsorption capacity of 2.56 mg/g, corresponding to 128.0 mg of phosphorus per gram of La. Kinetic and isotherm analyses revealed that the adsorption process followed the pseudo-second-order model and fitted well with the Langmuir isotherm, consistent with monolayer chemisorption. Thermodynamic studies further indicated that the adsorption was spontaneous and endothermic. The primary adsorption mechanism was attributed to the precipitation of lanthanum phosphate (LaPO4). This study not only demonstrates a high-performance adsorbent but also provides a sustainable strategy for the synergistic utilization of industrial solid wastes.