Phosphogypsum-Based Composite Cementitious Porous Filter Media: Performance Regulation and Phosphate Adsorption Mechanism

In this work, a high-dosage phosphogypsum (PG) composite cementitious system was fabricated via alkali activation, using 50 wt.% PG, 15 wt.% fly ash and 35 wt.% ordinary Portland cement. Redispersible polymer powder (RPP) was incorporated to improve matrix toughness, and animal protein foaming was employed to construct continuous mesoporous structures for water treatment. Key preparation parameters were optimized through single-factor experiments. The optimized porous filter media present a bulk density of 0.809 g/cm3, a 1 h water absorption rate of 39%, and a breakage and wear rate of 4.89%. In static adsorption tests with 40 mg/L simulated phosphate wastewater, the filter media achieve a phosphate-removal rate of 71.81% within 6 h, which is significantly superior to that of commercial sintered ceramsite (50.28%). Combined characterization using BET, SEM, XRD, XRF and FT-IR demonstrates that phosphate removal mainly relies on calcium-induced chemical precipitation, with mesoporous physical adsorption playing an auxiliary role. Leaching tests verify that all heavy metal leaching concentrations of the prepared filter media satisfy the GB 5085.3-2007 standard, while fluoride release can be detected under strong acid conditions. This polymer modification strategy facilitates large-scale PG solid waste disposal and eutrophic water remediation, providing a practical route for preparing low-cost polymer-inorganic porous filter media for water purification.