Abstract
ABSTRACT Two selective chemical 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. Chemical analysis shows that CA is more effective in removing iron from Ultisol, and OX extracts it more efficiently from Andisols. 6 K 57 Fe-Mossbauer data indicate 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. INTRODUCTION Selective chemical dissolution treatments are useful, and in many circumstances essential, laboratory procedures in order to improve the mineralogical analysis of soil samples. However, no chemical extractive solution, whatever the chemical dissolution mechanism, is expected to completely dissolve certain groups of chemically related minerals, while leaving unaffected the other species. In soils, iron (oxyhydr)oxides very often occur as a continuum of inter-related mineral forms or assemblages of strongly cemented multiphase grains in heterogeneous systems, of a wide range of degree of crystallinity.Cornell and Schwertmann
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