Phosphate Removal by Ca-Modified Magnetic Sludge Biochar Prepared by a One-Step Hydrothermal Method

The problem of phosphorus pollution and its resource utilization has been a source of general concern. The preparation of green, renewable, and non-secondary pollution adsorbents has become a research direction. In this paper, a one-step hydrothermal preparation method of Ca-modified magnetic sludge biochar (Ca-MSBC) is used for enhancing phosphate removal. The results show that the adsorption rate of phosphate by Ca-MSBC is mainly controlled by chemisorption but is also related to physical adsorption and an internal diffusion mechanism. The maximum phosphorus adsorption capacity of Ca-MSBC was 89.25 mg g−1 at 343 K (initial phosphate concentration 500 mg L−1). After nine cycles of adsorption experiments, the adsorption capacity of 70.16 mg g−1 was still high. In addition, coexisting ions Cl−, NO3−, SO42−, and CO32− have no significant effect on the adsorption properties of phosphate. XRD, FT-IR, VSM, XPS, and N2 adsorption/desorption isotherms showed that the mechanism of phosphate removal from water by Ca-MSBC was mainly the chemical precipitation reaction of phosphate and calcium. The results of this study indicate that Ca-MSBC has potential application and environmental value as a solid waste recycling material for environmental remediation.