La-activated biochar addition improves phosphorus adsorption performance in soil: Competitive adsorption dominated by organic phosphorus

To investigate the adsorption properties of La-activated biochar for pollutants in a binary coexistence system.

La was impregnated with walnut shells to prepare biochar and orthophosphate (OP) and inositol hexaphosphate (IHP) were adsorbed in the composite system.

At the same concentration (75 mg L⁻¹), the overall phosphorus adsorption performance of biochar treatment (CK + BC) was considerably better than that of gypsum (CK + GP) and zeolite (CK + ZP). The maximum adsorption capacities of OP and IHP were 0.52 and 1.29 mg g⁻¹, respectively. In the binary coexistence system, there is a competition among phosphorus species because of the number of adsorption sites on the surface of adsorbents and the blockage effect of pores. The fitting results of the adsorption kinetics and adsorption isotherm model show that the adsorption of phosphorus species is primarily controlled by chemical action.

The adsorption mechanism may include electrostatic attraction, ligand exchange, precipitation, and complexation.