Potassium release from muscovite and phlogopite as influenced by selected organic acids

Low molecular weight carboxylic acids (LMW) play an important role in improving the bioavailability of soil nutrients. Nonexchangeable soil K, trapped between the interlayers of clay minerals, is an important source of K for plants in many soils. The objectives of this study were to determine the effect of selected LMW organic acids on the release of K from micaceous minerals and to investigate the resulting mineralogical changes. A laboratory dissolution study was carried out using a completely randomized design with three replicates. Muscovite and phlogopite (< 60 μm size) were reacted with 0, 500, 2000 and 4000 μM solutions of oxalic, citric and malic acids for a period of 5 hours to 120 days. The amount of K released to the solution was determined with flame photometer. The rate of K release varied with the type of organic acids and also the kind of mica. Citric acid solution with a concentration of 4000 μM was able to release more K from minerals. The higher the concentration of organic acid, the higher the amount of K released. The amount of K released from minerals was in the order of phlogopite>muscovite. The kinetics of non-exchangeable K release from minerals consisted of two phases, the first phase was relatively rapid and then it had a constant rate untile the end of experiment. Strongly coordinating LMW carboxylic acids enhance the mineral dissolution and weathering reactions through the detachment of surface complexes into solution. There was not any XRD detectable changes in minerals reacted with organic acids up to 4 months.