Acceleration and retardation of silicate weathering due to organic substances

The influence of organic substances on the weathering processes of feldspar-rich material were investigated with experiments using salicylic, tartaric and citric acids and pyrocatechol violet. The dissolution processes of feldspar-rich rocks is affected by the acids mentioned above after an initial adsorption of the respective organic ligand at the mineral surface resulting in an increase in the dissolution rates. Complex-forming organic ligands cause significantly higher concentrations of dissolved Al and a change of the Al/Si-ratio in the solution. In the range between pH 4.5 and pH 6 the ratio is equal to that of the feldspar, indicating a congruent dissolution process. The blocking of reactive surface sites with stable mineral-organic complexes (chemisorption) is shown by the experiments with pyrocatechol violet.