Extractability and dissolution kinetics of pure and soil-added synthesizedaluminium hydroxy sulphate minerals

Citation
J. Prietzel et C. Hirsch, Extractability and dissolution kinetics of pure and soil-added synthesizedaluminium hydroxy sulphate minerals, EUR J SO SC, 49(4), 1998, pp. 669-681
Citations number
34
Categorie Soggetti
Agriculture/Agronomy
Journal title
EUROPEAN JOURNAL OF SOIL SCIENCE
ISSN journal
13510754 → ACNP
Volume
49
Issue
4
Year of publication
1998
Pages
669 - 681
Database
ISI
SICI code
1351-0754(199812)49:4<669:EADKOP>2.0.ZU;2-C
Abstract
Various extractants used in current analytical procedures for the fractiona tion 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 sy nthesized and aged in the laboratory at 20 degrees C and 50 degrees C. The dissolution kinetics at 20 degrees C of these Al hydroxy sulphates in deion ized water, 0.02 M HCl and 0.02 M 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 th e reagents used increased in the order H2O less than or equal to 0.016 M KH 2PO4 << 0.02 M HCI approximate to acidic NH4 oxalate approximate to 0.5 M N aHCO3 < Na2CO3/NaHCO3 < 0.1 M NH4F < 0.5 M NH4F < 0.05 M NaOH less than or equal to 0.05 M LiOH. In Al hydroxy sulphate-containing soils, inorganic S is probably underestimated and ester sulphate S overestimated, if the inorg anic S pool is assessed by extraction with KH2PO4, Ca(H2PO4)(2) or NaHCO3 s olutions. The dissolution of all studied Al hydroxy sulphates, particularly that of K and Na alunite, in H2O and 0.02M HCl is strongly delayed by kine tic restraints. Thus it seems unlikely that Al3+ or SO42- activities in soi l solutions are strictly regulated by precipitation/dissolution equilibria of these minerals except for horizons with extraordinarily slow seepage wat er movement.