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Extractability and dissolution kinetics of pure and soil‐added synthesized aluminium hydroxy sulphate minerals
Author(s) -
PRIETZEL J.,
HIRSCH C.
Publication year - 1998
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1046/j.1365-2389.1998.4940669.x
Subject(s) - alunite , dissolution , chemistry , nuclear chemistry , precipitation , fractionation , jarosite , inorganic chemistry , geology , chromatography , hydrothermal circulation , organic chemistry , physics , seismology , meteorology
Summary Various extractants used in current analytical procedures for the fractionation of sulphur (S) in soils were compared with respect to their ability to dissolve Al hydroxy sulphate minerals of defined composition (basaluminite, K alunite, mixtures of basaluminite and Na alunite). The minerals were synthesized and aged in the laboratory at 20°C and 50°C. The dissolution kinetics at 20°C of these Al hydroxy sulphates in deionized water, 0.02M HCl and 0.02M NaOH were also investigated. The dissolution stability of the Al hydroxy sulphate minerals increased in the order basaluminite < K alunite < Na alunite. The dissolving power of the reagents used increased in the order H 2 O ≤ 0.016M KH 2 PO 4 ≪ 0.02M HCl ≈ acidic NH 4 oxalate ≈ 0.5M NaHCO 3 < Na 2 CO 3 /NaHCO 3 < 0.1M NH 4 F < 0.5M NH 4 F < 0.05M NaOH ≤ 0.05M LiOH. In Al hydroxy sulphate‐containing soils, inorganic S is probably understimated and ester sulphate S overestimated, if the inorganic S pool is assessed by extraction with KH 2 PO 4 , Ca(H 2 PO 4 ) 2 or NaHCO 3 solutions. The dissolution of all studied Al hydroxy sulphates, particularly that of K and Na alunite, in H 2 O and 0.02 M HCl is strongly delayed by kinetic restraints. Thus it seems unlikely that Al 3+ or SO 2− 4 activites in soil solutions are strictly regulated by precipitation/dissolution equilibria of these minerals except for horizons with extraordinarily slow seepage water movement.