The Characteristics And Impact Factors Of Organic Phosphorus Adsorption On Iron Oxides

Organic Phosphorus (OPS) constitutes large fraction of the total P pool and they can be utilized by primary producers. The interaction of OPS with iron oxides is important in controlling the mobility, transformation and bioavailability of phosphorus in the environment. Three OPS, adenosine monophosphate (AMP, C10H14N5O7P), adenosine triphosphate (ATP, C10H14N5O13P3), and Glucose 6-phosphate (G6P, C6H13O9P), which characterized as different chemical structure and molecular sizes, and KH2PO4 (Pi) were used as adsorbates to investigate the kinetics and isotherm adsorption characteristics on the hematite and goethite. In addition, we investigated the effect of environment factors such as pH, temperature and LMWOAs (oxalate, malate and citrate) on the adsorption process of OPs on both iron oxides. Meanwhile, the techniques of powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and the BET surface area analyzer were also used to explore and analyze the adsorption mechanisms of OPs on iron oxides.This work is helpful to provide supporting evidence to understand the interface processes of OPs on iron oxides. The main conclusions are as follows:1. The results showed that all curves of sorption kinetics presented similar characteristics, showing a fast adsorption and then followed by a slower process. The surface speciation of the P compounds on goethite are dominated by bidentate complexes, there may be coexistence of bidentate complex and three-dimensional precipitate at hematite surface. On each mineral, the order of the adsorption density and initial sorption rate for P compounds are listed as Pi> AMP> G6P> ATP.2. The adsorption isotherms results showed that the molecular size and structure of P-compounds, as well as the crystallinity and structure of the sorbent, influenced their adsorption behavior on iron oxides. The order of the maximum amounts (Qm) of P compounds are as follows:Pi> G6P> AMP> ATP. For each P compound, the Qm decrease with increasing crystallinity of the minerals, hematite< goethite. The affinity constant kL reflected the binding stability between sorbate and sorbent. The results showed that the KL of P-compounds to iron oxides with the order of ATP> Pi> AMP> G6P.3. The results showed that pH presented negative effects on the adsorption of P-compounds on both hematite and goethite. Moreover, the adsorption density of P compound on iron minerals increased with the temperature increasing, indicating the endothermic and spontaneous of the adsorption process.4. Low molecular weight organic acid (LMWOAs) suppress the adsorption of P compounds on iron oxides. This inhibitory effects were affected by the chemical structure and molecular size:citrate> malate≈oxalate. And the efficiency of the LMWOAs for P sorption on hematite were more significant than on goethite.