Phosphate concentration and association as revealed by sequential extraction and microprobe analysis. The case of sediments from two Argentinean dams

ORONÁ, C.; BORGNINO, L.; MAINE, M.A.; AVENA, M.

Carmona, España

Simposio; 4th International Symposium on Phosphate in Sediments; 2003

This article reports the general characteristics of the sediments of two Argentinean reservoirs, which are used for water supply. The chemical composition, granulometry and surface area are presented together with a study of phosphate association by combining sequential extraction and microprobe analyses. In general, the sediments of both reservoirs have similar characteristics. Coarse-grained material prevails at the river mouths and fine-grained material is dominant in the central areas or near the dams. There is a very good correlation between the surface area of the sediments and the clay fraction, which contains phyllosilicates and fine-grained metal hydroxides. The mapping with the microprobe reveals that Ca- and P-rich material is present at the river mouths but very scarce, if exists, in the central areas of the reservoirs. Both, sequential extraction and microprobe analyses indicate that phosphate is associated to the surface of aluminum and iron oxides as well as to the surface of phyllosilicates. Since phyllosilicates are very inefficient in binding phosphate, it seems that this anion is bound to their basal surfaces due to the presence of coating aluminum, iron and calcium cations, which constitute very active sites for phosphate adsorption. The presence of these coating in the studied sediments is evidenced by the high iron content found on mica surfaces and clay aggregates