The role of silicate-solubilizing microorganisms on potassium release kinetics from K-bearing minerals

In this study a factorial experiment in a completely randomized design performed in order to compare the kinetics of potassium (K) release from feldspar, illite and phlogopite in presence of microbial inoculation. The first factor involved microbial inoculation (bacteria, fungi and control), the second factor was K mineral types (feldspar, illite and phlogopite) and the third factor was incubation time (1, 2, 4, 8, 12, 16, 24, 32, 48, and 64 hours). The results showed that microbial inoculation caused an increase in potassium release and soluble-K (Ksol) which in samples inoculated with bacteria and fungi increased 92.3 and 92.8 percent in comparison to control, respectively. Mineral type showed significant impact on the kinetics of potassium release, potassium release from phlogopite was 1.11 and 1.13 times higher than feldspar and illite, respectively. The maximum reduction of pH and the highest increase of soluble-K, was observed in phlogopite treatment which was inoculated with fungi. pH amount in this treatment was decreased 2.69 unit and Ksol was increased 7.38 unit compared to the control. Among the kinetic models which were fitted, according to R2 and SEE, kinetics of potassium release was described with ellovich, power function, first order and parabolic diffusion equations satisfactorily. Among these four equations, the power function equation was detected as the best model for data fitting. Significantly inverse correlation (r = -0.83**) was observed between Ksol and pH. Therefore, the presence of silicate solubilizing microorganisms increase the rate of potassium release from K- bearing minerals.