Role of Variable Charge Soils of Removing Phosphate From Water Body Through Adsorption

An experiment was conducted to study P adsorption capacity of four kinds of variable charge soils in water,using the one-batch method and soil-column leaching method.Results show that the variable charge soils were very strong in P adsorption capacity,displaying an order of Oxisol(Kunming)>Ultisol(Liuzhou) ≈ Oxisol(Xuwen)>Ultisol(Yingtan),which is the same as the ones for content of free Fe/Al oxides in the soils.This suggested that Fe/Al oxides in the soils were a major factor affecting adsorption of phosphate.Desorption of pre-adsorbed phosphate from the soils in 0.01 mol·L^-1 NaNO₃ solution was found to be insignificant and normally less than 10% of the adsorbed phosphate.However,citric acid induced desorption of pre-adsorbed phosphate from the soils.The findings suggested that phosphate was adsorbed by the variable charge soils mainly through non-electrostatic adsorption mechanism.The results of the leaching experiment show that given that phosphorus concentration of the leachate is 0.4 mg·L^-1,the amounts of phosphate adsorbed by Oxisol(Kunming),Ultisol(Liuzhou),Oxisol(Xuwen) and Ultisol(Yingtan) reached as high as 1 792,1 536,1 408 and 1 280 mg·kg^-1,respectively.Therefore,the variable charge soils,especially the soils high in Fe/Al oxide content,may potentially be employed as P adsorbent to remove phosphate from water bodies.