[Preparation of Iron-improved Blue Algae Biochar and Its Co-adsorption Mechanism for Phosphorus in Surface Water]

To alleviate the problems of eutrophication and blue algae accumulation in water, biochar was prepared from blue algae dehydrated using polymerized ferrous sulfate(PFS) to absorb phosphate in water, and the biochar was activated using steam to adjust the pore structure. The preparation conditions of blue algae biochar were optimized using the response surface method. The optimal results were as follows:the dosage of PFS was 458 mg·L^-1, the carbonization temperature was 433℃, and the mass ratio of biochar precursor to steam was 1:11. Biochar without PFS(F₀H₁₁-433) and biochar with PFS(F₄₅₈H₁₁-433) were characterized using X-ray diffraction(XRD), Fourier-transform infrared spectroscopy(FTIR), zeta potential, and Raman spectra(Raman) were used to study whether blue algae biochar and PFS had a synergic effect on phosphate removal. The results showed that:compared with F₀H₁₁-433, iron oxide appeared on the surface, the zero point of charge(pH_pzc) increased from 4.41 to 6.19, and the disorder and defect degree of biochar was increased in F₄₅₈H₁₁-433. The pseudo-second-order model and Langmuir model were suitable for describing the adsorption process of F₄₅₈H₁₁-433, and the saturated adsorption capacity was 31.97 mg·g^-1. F₄₅₈H₁₁-433 had excellent phosphorus removal efficiency in actual lake water, and the residual phosphate content of effluent was less than 0.025 mg·L^-1. In the presence of several common anions, it still showed excellent selective adsorption. After five cycles, the phosphate removal of F₄₅₈H₁₁-433 still reached 75.78%, indicating that F₄₅₈H₁₁-433 had the characteristic of being renewable. Combined with the material characterization results before and after adsorption, the phosphorus removal mechanism of F₄₅₈H₁₁-433 mainly involved electrostatic attraction and ligand exchange.