Weathering of Silicate Minerals by Humic Acids: II. Nature of Cation Solubilisation from Hornblende and Biotite and Characteristics of the Residual Products
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Abstract:
The present study aims at understanding how humic acids (HAs) (extracted from Entisol, Alfisol and Mollisol) affect and transform primary silicate minerals, viz., hornblende (inosilicate) and biotite (phyllosilicate), and aid in nutrient release therefrom. The focus is on the kinetics of dissolution and the alterations brought about in the products formed after treatment with HA. The kinetic curves exhibit alternate crests and troughs pointing to alternate solubilisation and precipitation. Structural difference between the two primary silicates lead to differential release of cations. The contrast between the minerals is more pronounced when the altered products are compared. While hornblende shows drastic changes including reduction in Fe2+/3+ and Ca2+ and enrichment in Si4+, Al3+ and Mg2+, biotite is almost minimally altered. XRD(X ray diffraction) studies indicate the disappearance/attenuation of many prominent bands of hornblende in the weathered residues with several new crystalline phases. Biotite, however, is only slightly altered with the formation of a few new phases. IR studies suggest deposition of HA on the surfaces of both biotite and hornblende but such deposition is far more prominent with hornblende.Keywords:
Hornblende
Silicate minerals
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