Phosphate-iron interactions and their role in the inhibition of schwertmannite precipitation

Research output: Contribution to conferenceAbstractAcademic

Abstract

The iron(III) phosphate mineral schwertmannite has shown potential for the removal of oxyanions such as phosphate and arsenate through their adsorption [1,2] and incorporation into the schwertmannite structure [3]. Here we have used dynamic light scattering (DLS) to explore the inhibitory effect of mM concentrations of phosphate on the nucleation dynamics of schwertmannite at different temperatures. Our experiments show that for ferric chloride solutions, the solution species are dominated by hydrated Fe3+ ions and some Fe-chloride complexes based on UV-Vis spectra. When sulphate or phosphate is added to the solution new ion pairs between Fe and these oxyanions are also present in the UV-Vis spectra. However, when phosphate and sulphate are present together a new solution species forms that is no longer measurable with the UV-Vis spectrometer due to its high adsorption. Dynamic light scattering experiments demonstrate that in ferric chloride solutions no particles can be measured, unless the solution is left for several hours at temperatures of 60 °C. Here the nucleation of an Fe-hydroxide was observed as a change in the system behavior, where scattering particles were observed and began to grow. In contrast, iron sulphate solutions that are supersaturated with respect to schwertmannite show the presence of particles immediately at the start of the experiment, even at room temperature. In this system there is a sudden change in the scattering behaviour in the solution, which correlates with the nucleation of schwertmannite and its subsequent growth before eventually settling in out of the solution. The time before nucleation decreased with increasing temperatures.
In the presence of phosphate, particles present at the beginning of the experiment increased their stability in correlation with increasing phosphate concentrations. At the highest phosphate concentrations, which have the longest time prior to nucleation, these particles are even observed to slowly grow. After nucleation of schwertmannite, particle growth was characterized by a much faster rate until the particles began to settle from the solution. The growth rate after nucleation decreased, whereas the induction time increased with increasing phosphate concentration. A higher retardation of the nucleation time was still observed when temperature is decreased at the same phosphate concentration. Phosphate likely alters the system dynamics through direct interactions with the iron(III) as evident even at the ion pair level in UV-Vis spectroscopy measurements and the incorporation of phosphate into the schwertmannite structure based on X-ray diffraction analysis.
References
1. Eskandarpour et al. 2007 ISIJ International 47, pp. 563.
2. Burton et al. Environmental Science and Technology, 43, 9202.
3. Regenspurg & Peiffer 2005 Applied Geochemistry, 20, pp. 1226.

Original languageEnglish
Publication statusPublished - 2023
EventGranada-Münster Discussion Meeting 10 - Münster, Germany
Duration: 29 Nov 20231 Dec 2023

Conference

ConferenceGranada-Münster Discussion Meeting 10
Country/TerritoryGermany
CityMünster
Period29/11/231/12/23

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