New paper on co-precipitation of silicon with iron and interactions with phosphorus

Friday, January 19, 2024

A new paper published in the journal Chemosphere presents the results of experiments looking at the interactions and competition between dissolved phosphorus and silicon (mostly found in the forms of the anions phosphate and silicate) during the precipitation of iron(III) oxyhydroxides as a result of iron(II) oxidation. The paper’s first author, Lu Huang, is a former ERG PhD student. Her co-authors are ERG members Chris T. Parsons, Stephanie Slowinski and Philippe Van Cappellen.

The study used batch experiments where anoxic solutions containing dissolved iron(II) different amounts of dissolved silicon (DSi), dissolved phosphorus (DP), and therefore different DP:DSi ratios were exposed to oxygen to encourage iron(II) oxidation. Along with the iron(II) oxidation and associated formation of solid iron(III) oxyhydroxides, DP and DSi were removed from the solution due to co-precipitation with or adsorption to the iron(III) oxyhydroxides. The results of the experiments showed that DP is more easily incorporated into the iron(III) oxyhydroxides than DSi, meaning that less DSi is removed by co-precipitation or adsorption during iron(II) oxidation in the presence of higher DP:DSi ratios. This finding has implications for sediment-water interfaces where oxygen concentration gradients exist. At these interfaces, anoxic porewater often diffuses up, encountering oxygen, promoting iron(II) oxidation. In these environments, higher DP:DSi ratios will likely result in less DSi removal in iron(III) oxyhydroxides and more DSi recycling from sediments to overlying surface waters. The results highlight the importance of sediment chemical reactions and interactions in controlling biogeochemical exchanges at sediment-water interfaces.

The published paper is open access and can be found online: "Co-precipitation of iron and silicon: Reaction kinetics, elemental ratios and the influence of phosphorus."