Desorption mechanisms of phosphate from ferrihydrite and goethite surfaces

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Desorption mechanisms of phosphate from ferrihydrite and goethite surfaces. / Krumina, Lelde; Kenney, Janice P L; Loring, John S.; Persson, Per.

In: Chemical Geology, Vol. 427, 01.06.2016, p. 54-64.

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Krumina, Lelde ; Kenney, Janice P L ; Loring, John S. ; Persson, Per. / Desorption mechanisms of phosphate from ferrihydrite and goethite surfaces. In: Chemical Geology. 2016 ; Vol. 427. pp. 54-64.

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TY - JOUR

T1 - Desorption mechanisms of phosphate from ferrihydrite and goethite surfaces

AU - Krumina, Lelde

AU - Kenney, Janice P L

AU - Loring, John S.

AU - Persson, Per

PY - 2016/6/1

Y1 - 2016/6/1

N2 - The fate of phosphate in the environment is governed by reactions at particle surfaces. These adsorption and desorption reactions display biphasic kinetics involving an initial rapid reaction followed by a substantially slower one extending over long time periods. In this study we have investigated the molecular mechanisms of desorption kinetics of phosphate from ferrihydrite and goethite nanoparticles in the absence of competing ligands. Desorption was studied by means of in-situ infrared (IR) spectroscopy over a wide pH range and a time period of 24 h. The spectroscopic data sets were subjected to multivariate curve resolution alternating least squares (MCR-ALS), which enabled the resolution of surface species characterized by unique IR spectra together with their corresponding kinetic profiles. The desorption results showed the typical biphasic behavior and that increasing positive surface charge of ferrihydrite and goethite slowed down desorption of the negatively charged phosphate ions. Moreover, diprotonated phosphate desorbed faster than monoprotonated phosphate at a given pH. At circumneutral pH values desorption from ferrihydrite was substantially faster as compared to goethite, and this could be ascribed to electrostatic effects and differences in charging between ferrihydrite and goethite. The collective desorption results were explained by a model, consisting of a series monodentate phosphate surface complexes in different protonation states, in conjunction with a description that accounts for the electrostatic effects on desorption kinetics at charged mineral-water interfaces. The fast and slow desorption followed directly from this model and indicated that biphasic kinetics can be caused by a single phosphate surface complex as a result of decreasing surface coverage along with the lateral repulsive interactions between adsorbed phosphate groups. Hence, in contrast to previous models our study has shown that biphasic desorption kinetics do not have to involve several different structural complexes related to either weak and strong sites or a distribution of phosphate between external surfaces and mineral pores.

AB - The fate of phosphate in the environment is governed by reactions at particle surfaces. These adsorption and desorption reactions display biphasic kinetics involving an initial rapid reaction followed by a substantially slower one extending over long time periods. In this study we have investigated the molecular mechanisms of desorption kinetics of phosphate from ferrihydrite and goethite nanoparticles in the absence of competing ligands. Desorption was studied by means of in-situ infrared (IR) spectroscopy over a wide pH range and a time period of 24 h. The spectroscopic data sets were subjected to multivariate curve resolution alternating least squares (MCR-ALS), which enabled the resolution of surface species characterized by unique IR spectra together with their corresponding kinetic profiles. The desorption results showed the typical biphasic behavior and that increasing positive surface charge of ferrihydrite and goethite slowed down desorption of the negatively charged phosphate ions. Moreover, diprotonated phosphate desorbed faster than monoprotonated phosphate at a given pH. At circumneutral pH values desorption from ferrihydrite was substantially faster as compared to goethite, and this could be ascribed to electrostatic effects and differences in charging between ferrihydrite and goethite. The collective desorption results were explained by a model, consisting of a series monodentate phosphate surface complexes in different protonation states, in conjunction with a description that accounts for the electrostatic effects on desorption kinetics at charged mineral-water interfaces. The fast and slow desorption followed directly from this model and indicated that biphasic kinetics can be caused by a single phosphate surface complex as a result of decreasing surface coverage along with the lateral repulsive interactions between adsorbed phosphate groups. Hence, in contrast to previous models our study has shown that biphasic desorption kinetics do not have to involve several different structural complexes related to either weak and strong sites or a distribution of phosphate between external surfaces and mineral pores.

KW - Desorption

KW - Electrostatic interactions

KW - Ferrihydrite

KW - Goethite

KW - Infrared spectroscopy

KW - MCR-ALS

KW - Phosphate

UR - http://www.scopus.com/inward/record.url?scp=84958998993&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2016.02.016

DO - 10.1016/j.chemgeo.2016.02.016

M3 - Article

VL - 427

SP - 54

EP - 64

JO - Chemical Geology (Isotopic Geoscience) Section

T2 - Chemical Geology (Isotopic Geoscience) Section

JF - Chemical Geology (Isotopic Geoscience) Section

SN - 0009-2541

ER -