Elucidating the mechanisms determining the availability of phosphate by application of biochars from different parent materials

The consortium of minerals and organic matter notably alters and affects minerals' surface characteristics and nutrients providence. Organic matter such as biochar can modify the availability status of macronutrients like phosphorus (P). Despite some investigation, the adsorption/desorption of P with pure iron (hydr)oxides and the probable mechanisms involved are still unknown. In the present study, the goethite/hematite or goethite–biochar/hematite–biochar complexes were prepared, and a batch experiment with different P concentrations, time spell, pH, and ionic strength is performed to evaluate the sorption characteristics of P. The results of our study suggest that the P adsorption on mineral surface decreased with the increasing pH. Furthermore, the coexistence of biochar and minerals significantly inhibits P adsorption on the minerals surface. The results of Languimner and Freundlich's equations signify that the biochar–minerals complexes have heterogeneous adsorption sites and the presence of biochar reduces P adsorption on minerals surface. Among four biochars including peanut straw biochar (PC (B1)), rice straw biochar (RC (B2)), canola straw biochar (CC (B3)), and soybean straw biochar (SC (B4)), PC was more effective than other biochars to inhibit P adsorption on minerals surfaces. Graphical abstract