Abstract

Size fractions 149-297 μm of olivine, augite, muscovite, labradorite, and microcline were dissolved in distilled water, CCVcharged water, weakly complexing acids (0.01 M acetic or aspartic) or strongly complexing acids (salicylic or tartaric acid) for up to 21 days. Dissolved Si, Al, Fe, Mg, Ca, K, and Na, and pH and conductivity were determined in the centrifuged solutions.

Solubilities of Si, Al, Fe, Ca, and Mg were higher in organic acids than in H2O or CO2-charged water. Solubility of Al and Fe is enhanced presumably by complexing as respective salicylates and tartrates. Relatively high solubility of Al with respect to Si appears to be significant.

Congruency (or incongruency) of dissolution with respect to Si was estimated by comparing: (1) the ratio of the mole fraction of Si dissolved to the mole fraction of another ion (Al, Mg, for example) dissolved, with (2) the ratio of the Si to the other ion as contained in the solid mineral. Si and Al in augite dissolved essentially congruently in salicylic and tartaric acids; Al dissolved proportionately more than Si from microcline in all the organic acids. Calculated depths of dissolution ranged from 120 to 3000 Å inward from the surfaces of mineral particles.

Since the organic acids used are representative of components of humic acid and lignitic acids, they illustrate possible effects of organic acids in geological and pedological weathering. When Al is moved congruently with (or in excess of) Si in solution, field results such as podsolization, transfer of Al to Al-rich minerals (as bauxite under lignite in Arkansas), or recombination with Si to yield kaolin minerals (as in German kaolins via the Moorverwitterung process) may be attributed to dominant dissolution effects of organic acids.

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