Effect of nanoparticles on kinetics release and fractionation of phosphorus

In this study, we examined the effect of nanoparticles (Al2O3 and TiO2) on kinetics release, fractionation and speciation of phosphorus (P) in some calcareous soils of western Iran. The maximum (average of five soils) (40.3 mg kg(-1)) and the minimum (10.5 mg kg(-1)) P were released by control soils and soils plus 3% TiO2, respectively. Pseudo second-order model described well P release. In order to predict and model the effects of NPs on P release, surface complexation model in PHREEQC program was used. The model could simulate the P release very well in all soils. After P release, the percentage of organic matter and sulphide-P fraction increased markedly following NPs addition, while carbonated-P fraction remained the most dominant fraction in all soils. In the initial stage of P release the solution samples in all soils and treatments were saturated with respect to strengite, and undersaturated with respect to other phosphate minerals. At the end of P release, all solutions were saturated with respect to hydroxyapatite and strengite and undersaturated with respect to other phosphate minerals. These results reflected that the NPs caused immobilization of P in soils and reduced the bioavailable P, thus, reducing their environment risk.