Influence of Sorbed Hydroxyl and Sulfate on Neutralization of Soil Acidity1
- A. Mehlich2
Soils of varying clay mineral characteristics were treated with anion-exchange resin to obtain systems containing either sorbed OH- or SO42-. They were then equilibrated with Ca(OH)2, and the neutralization of acidity consisting of permanent charge (Hp), variable charge (Hv) and anion-exchange (Han, principally SO42- absorbed) evaluated. The order of neutralization was Hp (consisting principally of Al3+ except in the case of the muck) first, followed virtually simultaneously by Hv and Han. Sorbed SO42- resulted in more strongly acidic systems. Hv is postulated to arise from covalently-bonded H of aquo groups in the coordination sphere of hydrated Al (or possibly Fe3+ atoms). The source of Han is postulated to be acid radicals substituted for OH groups, likewise in the coordination sphere of Al and Fe3+ associated with clay surfaces or in hydrous oxide crystals. The magnitude of Han, the soil acidity due to sorbed acid radical anions, may be an appreciable part of the total acidity of Red-Yellow Podzolic and Reddish-Brown Lateritic soils.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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