Effect of Low Molecular Weight Organic Anions on Adsorption of Potassium by Variable Charge Soils

Abstract

Low‐molecular‐weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes. In the present paper, the effect of the anions of four LMW organic acids on the adsorption of potassium (K) by two variable charge soils was investigated. The results showed that the presence of organic anions led to an increase in K adsorption. The ability of organic anions to induce K adsorption followed the order: citrate>malate>malonate≈oxalate>acetate. The adsorption of K induced by organic anions increased with the increases in pH and the concentration of the anions. Both Langmuir and Freundlish equations can be used to describe the adsorption of K by variable charge soils in the presence of organic anions. Adsorption of ions is a direct consequence of carrying of surface charge for soils. Recent works have shown that the presence of organic anions led to an increase in negative surface charge and a decrease in positive surface charge of variable charge soils. The results indicated that the extents of the effect of different organic anions on adsorption of K and surface charge were generally of the same order. Therefore, it can be considered that the main reason for the adsorption of K induced by organic anions is the increase in net negative surface charge caused by the adsorption of the anions on the soils.