Addition of carboxylic acids modifies phosphate sorption on soil and boehmite surfaces: A solution chemistry and XANES spectroscopy study

• Published in: Journal of colloid and interface science Vol. 330; no. 1; pp. 51 - 59
• Main Authors: Schefe, C.R., Kappen, P., Zuin, L., Pigram, P.J., Christensen, C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.02.2009; Elsevier
• Subjects: Alumina; Aluminium; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Organic acids; Phosphate fertiliser; Soft X-rays; Surface physical chemistry; Synchrotron; XANES; Phosphate fertiliser; XANES; Aluminium; Synchrotron; Alumina; Organic acids; Soft X-rays; Phosphates; Binary compound; XANES spectrometry; Acidification; Fluorescence; X ray; Carboxylic acid; Synchrotrons; Dicarboxylic acid; Structure; Aluminium hydroxide; Binding; Phosphorus; Dissolution; Sorption; Soils; Chemistry; Oxalic acid; Adsorption; Solid phase; X ray absorption; Electrons
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2008.10.044

Soil acidification is a globally significant agricultural issue, as the plant availability of phosphorus (P) is decreased through increased P sorption onto aluminium (Al) hydroxides and other solid phase binding sites. X-ray absorption near edge structure (XANES) spectroscopy generated new information on the speciation of Al and P in the presence of carboxylic acids on soil and boehmite ( γ-AlOOH) surfaces. XANES spectra were acquired in the soft X-ray regime at the P and Al L 2 , 3 -edges, and the Al K-edge, respectively. Adding oxalic acid to soil enhanced Al dissolution and exposed previously occluded soil P, while hydroxybenzoic and coumaric acids did not compete with P for surface binding sites. Boehmite strongly adsorbed carboxylic acids in the absence of applied phosphorus. However, when P was applied with carboxylic acids, the carboxylics were unable to compete with P for binding, especially hydroxybenzoic and coumaric acids. Using XANES in both total electron yield and fluorescence yield modes provided valuable information on both surface and near-surface processes of P and Al due to different information depths. The Al K-edge XANES provided baseline information on the solid-phase matrix. XANES in total electron yield mode and at the P L-edge shows promise for speciation of elements on soil surfaces due to enhanced sensitivity for speciation of surface-adsorbed species compared to the commonly used P K-edge XANES. Addition of oxalic acid to soil may displace chemisorbed phosphate from Al binding sites on soil surfaces, also potentially removing Al from the surface and exposing previously-bound soil P.