Study on the purification mechanisms of black and odorous water bodies using hydroxyapatite prepared from...

Putty powder-based hydroxyapatite (P-HAP) was synthesized hydrothermally from high-calcium waste putty powder as the calcium source and characterized by XRD, FTIR, SEM, EDS, BET, and zeta potential analyses. The effects of P-HAP dosage and pH on the adsorption of Mn²⁺, Fe²⁺, COD, and NH₃-N from black and odorous wastewater were investigated. At a dosage of 1.6 g/L and pH = 10 (C_Fe²⁺ = 10 mg/L, C_Mn²⁺ = 100 mg/L, C_COD = 50 mg/L, C_NH3-_N = 50 mg/L, 25 °C), the maximum adsorption capacities were 61.24, 6.25, 21.00, and 21.86 mg/g for Mn²⁺, Fe²⁺, COD, and NH₃-N, respectively; the adsorption efficiencies of Fe²⁺ and COD reached 100% and 67.18%. At a dosage of 4 g/L and pH = 7, under the same conditions, the adsorption efficiencies for Mn²⁺ and NH₃-N reached 100% and 73.92%, respectively. The adsorption conformed to the pseudo-second-order kinetics and the Freundlich isotherm models, indicating multilayer heterogeneous surface chemical adsorption. The adsorption mechanisms primarily involve complexation reactions and ion exchange. A quantitative model for predicting dosage was also established. This provides a new approach for the resource utilization of waste putty powder, also for the efficient, low-cost, and environmentally friendly treatment of black and odorous water bodies.