In this study, we synthesized composite metal modified biochar using fruit shell biochar impregnated with ferric chloride and potassium permanganate. We investigated its potential to adsorb phosphorus at low concentrations. Results show that the adsorption of low-concentration phosphorus by Fe and Mn modified biochar was significantly better than by non-modified biochar. SEM and FT-IR spectra indicate that iron and manganese oxides or iron hydroxides might be present on the surface of Fe and Mn modified biochar. When the phosphorus concentration is 0.5 mg·L-1 at a temperature is 298 K and solid-to-liquid ratio (mg:L) of 500, the adsorption capacity of modified biochar is 0.96 mg·g-1. When the pH of the solution is 4 to 10, a higher removal rate and adsorption capacity are realized. The biochar equilibrium data were fitted to the Freundlich equation, which indicated that the adsorption was a multimolecular layer adsorption. Adsorption thermodynamics studies showed that ΔGθ < 0, ΔHθ > 0, and ΔSθ > 0, indicating that the adsorption was a spontaneous, with positive entropy, and an endothermic process. The adsorption reached equilibrium after 60 min, and the adsorption kinetics followed a pseudo-second-order model. This research provides basic data for the removal of low-concentration phosphorus from a water body and sewage treatment plant.
Keywords: adsorption; biochar; composite metal modified; ferric chloride; low concentration phosphorus; potassium permanganate.