Preparation and characterization of a novel active sediment capping material (geopolymer) for inhibiting phosphate releasing from sediment

In situ remediation of sediment can effectively control the release of phosphate in sediment and improve water eutrophication. The essential question of this remediation techniques lies in the development of stable, high-efficiency, low-cost and easily available active sediment capping materials. This study synthesised a novel sediment capping material using bulk solid waste, and phosphate inhibition mechanism of the materials was explored. Results indicated that GSCM was prepared under the conditions of NaOH concentration of 3 M, hydrothermal temperature of 160℃, hydrothermal time of 36 h and the mass ratio of 40 wt% SS to 60 wt% FA. The result of batch adsorption and compressive strength test suggested that phosphate adsorption capacity and compressive strength of GSCM were 2.15 mg/g and 24.20 MPa, respectively. The characterization result showed that GSCM was composed of sodium zeolite, riversideite, grossular and fayalite, exhibiting a uniformly distributed slit mesoporous structure. The in-situ inhibition efficiency of GSCM to P ranged from 76.65 % to 86.72 %, exceeding that of commercial zeolite. The in-situ inhibition mechanism was controlled by sodium zeolite and riversideite, and concluded by the following:1) Substitution between [SiO₄] tetrahedra (within the sodium zeolite structure), -OH (on the surface of materials) and [PO₄], 2) Coordination of [PO₄] tetrahedra with Al active site within the sodium zeolite structure, 3) Precipitation reaction between phosphate and slow-release of Ca²⁺ from the riversideite.