Abstract:

 Preparation of calcium-modified biochar (Ca−BC) using corn stover biochar (BC) as raw material and calcium chloride (CaCl₂) as modifier. The changes in morphological composition of biochar before and after modification were compared, and the effect of Ca−BC on the phosphate adsorption and the role of different pH for it were explored. Meanwhile, investigated the effect of Ca−BC on various forms of phosphorus in the substrate, to clarify the effect of Ca−BC on the control of phosphorus in the water body and the substrate. The results showed: (1) compared with BC, Ca−BC had a denser pore structure, larger specific surface area, and more adsorption sites and oxygen−containing functional groups. Under neutral conditions, Ca−BC prepared at a CaCl₂ concentration of 1.0mol·L⁻¹ had the best adsorption effect on phosphate, at which time the removal rate of phosphate could reach 88.3%, which was nearly 3 times higher removal rate than BC. (2) The adsorption process of Ca−BC on phosphate conformed to the quasi−primary, quasi−secondary kinetic model and Langmuir isothermal adsorption model, which was mainly determined by single−molecule adsorption and influenced by both diffusion and chemisorption, and the theoretical maximum adsorption amount reaches 15.6mol·L⁻¹. (3) Addition of Ca−BC to the substrate, the proportion of exchange phosphorus (Ex−P), organic phosphorus (Org−P), and calcium−bound phosphorus (Ca−P) decreased from 0.5% to 0.3%, 22.6% to 19.4%, and 39.1% to 41.5%. Therefore, the addition of Ca−BC can promote the morphological transformation of substrate phosphorus, resulting in a decrease in the proportion of potentially reactive phosphorus and an increase in the proportion of stable state phosphorus, reducing the risk of substrate phosphorus release.

Key words: Biochar, Calcium modification, Phosphate, Adsorption, Sediment phosphorus