Competitive adsorption mechanisms of phosphorus species on montmorillonite-iron oxyhydroxide complexes

• Published in: Chemical geology 2025-01, Vol.672, p.122510, Article 122510
• Main Authors: Jia, Chonghao, Chi, Jialin, Fan, Yuke, Qin, Lihong, Ren, Tao, Putnis, Christine V., Zhang, Wenjun
• Format: Article
• Language: English
• Subjects: Competitive adsorption; DFS; iron oxyhydroxides; Montmorillonite; Phosphorus species
• ISSN: 0009-2541
• DOI: 10.1016/j.chemgeo.2024.122510

Phosphorus (P) biogeochemical cycle in subsurface environments is primarily mediated by various minerals. However, there is still unknown about the impact of iron (Fe) oxyhydroxides coexisting with clay on the fate of different P species. Here, the interfacial behavior for competitive adsorption of phytate and phosphate on montmorillonite-Fe oxyhydroxide (Mt-amFe) complexes was comprehensively investigated. The nucleation of amorphous Fe oxyhydroxides on montmorillonite contributes to the formation of Mt-amFe complexes and consequently the surface properties of clay are altered. Phytate is preferentially adsorbed on the complexes and the adsorption capacity for phytate is 5.8 times higher than that for P at a mass ratio of 1:1 during the competitive adsorption process. Moreover, during their competition adsorption on Mt-amFe, the interactions between Fe and clay generally tend to decrease the mass ratio of phytate and phosphate in aqueous phases, which is tightly associated with the risk of P contamination. As shown by solid characterization, the adsorption of P species is mainly attributed to inner-sphere complexation. To illustrate the thermodynamic mechanisms for the competitive adsorption effects, dynamic force spectroscopy was applied to quantify the immobilization of different species of P on Mt-amFe complexes, and the results show that phytate is more thermodynamically favorable for the complexation with minerals compared with that of phosphate. These findings can guide the prediction of P loss risk associated with the differences in P species in subsurface environments based on the analysis of mineral surface structures. [Display omitted] •The in situ deposition of Fe oxide on clay to form complexes was observed.•Phytate is preferentially adsorbed on Mt-amFe during competition with phosphate.•DFS was used to quantify the thermodynamic binding for competitive adsorption.•Phytate increases the risk of phosphorus loss following phosphate release.