Selective Adsorption of Various Phosphorus Species Coexistence in Water-Soluble Ammonium Polyphosphate on Goethite : Experimental Investigation and Molecular Dynamic Simulation

The geochemical processes of polyphosphates (poly-Ps) is important for phosphorus (P) management and environmental protection. Water-soluble ammonium polyphosphate (APP, (NH 4 ) n+2 P n O 3n+1 , n<20) containing various P species has been increasingly used as an alternative P-fertilizer. The various P species coexistence and the chelation of poly-Ps to mental would trigger the competitive adsorption of P and affect the adsorption intensity of APP on goethite, compared to single orthophosphate (P 1 ) . P adsorption behaviors of APP1 with two P species (n=1-2) and APP2 with seven P species (n=1-7) on goethite were investigated via bath experiments in comparison to the traditional P-fertilizer of ammonium phosphate (MAP, NH 4 H 2 PO 4 ). Co-adsorption of P 1 and pyrophosphate (P 2 ) on goethite was investigated by molecular dynamic simulation (MDS). The more Fe 3+ dissolved from goethite due to the chelation of poly-Ps in APP as a bridge and contributed to the stronger APP adsorption compared with MAP. Ion chromatography and spectral analysis showed P 1 and P 2 in APP were mainly selectively adsorbed by goethite via mainly forming mono- and non-protonated bidentate complexes. The goethite preferentially adsorbed P 1 , but increased the adsorption for poly-Ps at higher APP concentration. MDS showed that goethite strongly adsorbed P 2 and the P 1 pre-adsorbed on gothite could be replaced by P 2 with increasing P 2 concentration. The results develop new insights regarding the selective adsorption of various P species coexistence in goethite-rich environments