Alary, K.;Babre, D.;Caner, L.;Feder, F.;Szwarc, M.;Naudan, M.;Bourgeon, G.

Université de Poitiers, IC2MP-Hydr ASA UMR 7285, F-86 022 Poitiers (France);CIRAD, UPR Recyclage et risque, 18 524 Dakar (Sénégal);CIRAD, UPR Recyclage et risque, F-97 408 Saint-Denis La Réunion (France);CIRAD, US Analyse, F-34 398 Montpellier (France);CIRAD, UPR Recyclage et risque, F-34 398 Montpellier (France)

allophane;andosols;clay content;mineralogy

The possibilities of combining the dissolution of short-range-order minerals (SROMs) like allophane and imogolite, by ammonium oxalate and a particle size distribution analysis performed by the pipette method were investigated by tests on a soil sample from Reunion, a volcanic island located in the Indian Ocean, having a large SROMs content. The need to work with moist soil samples was again emphasized because the microaggregates formed during air-drying are resistant to the reagent. The SROM content increased, but irregularly, with the number of dissolutions by ammonium oxalate: 334 and 470 mg g^-1 of SROMs were dissolved after one and three dissolutions respectively. Six successive dissolutions with ammonium oxalate on the same soil sample showed that 89% of the sum of oxides extracted by the 6 dissolutions were extracted by the first dissolution (mean 304 mg g^-1). A compromise needs to be found between the total removal of SROMs by large quantities of ammonium oxalate and the preservation of clay minerals, which were unexpectedly dissolved by this reagent. These tests enabled a description of the clay assemblage of the soil (gibbsite, smectite, and traces of kaolinite) in an area where such information was lacking due to the difficulties encountered in recuperation of the clay fraction.