Organic Acids as Agents of Chemical Weathering of Silicate Minerals

Abstract

IN geologic weathering systems, organic acids such as fulvic and humic acids from humus or soil microorganisms decompose minerals dominantly by reacting with polyvalent cations in minerals to form water-soluble or -insoluble metallo-organic complexes (or chelates). Whether the complexes are soluble or insoluble is controlled primarily by the structures of ligands and relative stabilities of the complexes in relation to pH and Eh in the systems1–5. We report the results of the laboratory dissolution of common silicate minerals at room temperature in dilute and in 0.01 M, organic acids which contain such functional groups as carboxyl, hydroxy—and amino—which occur in soil acids and Other organic acids of geologic and pedologie systems. The systems fall into two categories: first, weakly complexing—acetic (monocarboxylic aliphatic) and aspartic (dicarboxylic amino aliphatic); and second, strongly complexing—citric (hydroxy, tricarboxylic aliphatic), tartaric (dihydroxy aliphatic), salicylic (monohydroxy aromatic) and tannic (commonly a mixture of aliphatic and polyhydroxy carboxylic acids).