AMMONIUM OXALATE AND CITRATE-ASCORBATE AS SELECTIVE CHEMICAL AGENTS FOR THE MINERALOGICAL ANALYSIS OF CLAY FRACTIONS OF AN ULTISOLAND ANDISOLS FROM SOUTHERN CHILE

Two selective chemieal treatments consisting of mixtures of (i) oxalic acid - ammonium oxalate at pH 3 (OX) and (ii) sodium citrate - ascorbic acid at pH 6 (CA) were used to selectively remove minerals from clay fractions of four volcanic soils: one from an Ultisol and three Andisols, of the southern Chile. Chemieal analysis shows that CA is more effective in removing iron from Ultisol, and OX extracts it more efficiently from Andisols. 6 K 57Fe-M6ssbauer data indícate that OX tends to remove all magnetically ordered species with low hyperfine fields; CA has no clear effect on the removal of those or the identified iron oxides in these volcanic soil materials