Adsorption of Acid Phosphatase on Minerals and Soil Colloids in Presence of Citrate and Phosphate

The aim of this work was to study the influence of phosphate and citrate, which are common inorganic and organic anions in soils, on the adsorption of acid phosphatase by kaolin, goethite and the colloids separated from yellow-brown soil (YBS) and latosol (LS) in central-south China. The YBS colloid has the major clay mineral composition of 1.4 nm mineral, illite and kaolinite while the LS colloid mainly contains kaolinite and oxides. The adsorption isotherm of acid phosphatase on the examined soil colloids and minerals fitted to the Langmuir model. The amount of enzyme adsorbed in the absence of ligands was in the order of YBS colloid > LS colloid > kaolin ≈goethite. In the presence of phosphate or citrate, the amounts of the enzyme adsorbed followed the sequence YBS colloid > kaolin > LS colloid > goethite. The presence of ligands also decreased the binding energy between the enzyme and soil colloids or minerals. With the increase of ligand concentration from 10 mmol L-1 to 400 m mol L-1, different be