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Dissolution, adsorption and phase transformation in the fluorapatite-goethite system

Author:
  • Asa Bengtsson
  • Malin Lindegren
  • Staffan Sjoberg
  • Per Persson
Publishing year: 2007
Language: English
Pages: 2016-2028
Publication/Series: Applied Geochemistry
Volume: 22
Document type: Journal article
Publisher: Elsevier
Additional info: 9

Abstract english

An aqueous system containing fluorapatite (Ca-5(PO4)(3)F), (FAP) and varying amounts of goethite (alpha-FeOOH) has been investigated. Batch experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to monitor the dissolution products of FAP, as well as the adsorption, and phase transformation of phosphate at the goethite surface over a period of 129 days. The results show that the presence of goethite increases dissolution of FAP, mainly due to the high affinity of phosphate for the goethite surface: Ca-5(PO4)(3)F(s)+3 FeOH+ (3 + 3n)H+<-> 3 FeHnPO4(n-2)-"+3H(2)O+5Ca(2+) + F-. Besides monitoring the pH changes associated with this reaction, the concentrations of Ca2+ and fluoride were determined. Furthermore, the amount of phosphate adsorbed was quantified from ATR-FTIR spectra. In addition to adsorbed phosphate, phase transformations of goethite into a Fe phosphate phase (FePO4(s)) are seen in the samples with relatively high phosphate to goethite ratios (excess phosphate to available surface sites) equilibrated for 15-129 days. An equilibrium model that takes into account (i) FAP dissolution, (ii) solution complexation, (iii) surface complexation of phosphate species onto goethite and (iv) possible phase transformation Ca-5(PO4)(3)F-CaF2 and FeOOH-FePO4 was designed. This model-was found to be in very good agreement with experimental observations and could thus be used to give qualitative and quantitative information about goethite promoted dissolution of FAP under other pH conditions than those studied in the present work. (C) 2007 Elsevier Ltd. All rights reserved.

Keywords

  • Earth and Related Environmental Sciences

Other

Published
  • ISSN: 0883-2927
Per Persson
E-mail: per [dot] persson [at] biol [dot] lu [dot] se

Professor

MEMEG

+46 46 222 17 96

+46 70 266 38 79

E-C350

50

Professor

Centre for Environmental and Climate Research (CEC)

+46 46 222 17 96

+46 70 266 38 79

D350

Ekologihuset, Sölvegatan 37, Lund

50