Degree of Al-Si order in K-feldspar and its effect on K-feldspar’s dissolution

the effect of Al-Si ordering on K-feldspar’s dissolution

Abstract

Dissolution or alteration of feldspars is controlled by many factors such as the crystal structure (e.g., Al/Si ordering), temperature, pH, surface area, organic acids, chemical affinity, and precipitation of secondary minerals. The effects of Al/Si ordering (i.e., the degree of Al/Si order) on the percentage of feldspar dissolution (i.e., the extent of feldspar alteration) have not been studied. In this study, the degree of Al/Si order of different types of K-feldspars (eleven specimens including one sanidine sample, five orthoclase samples and five microcline samples) were investigated and determined by both X-ray powder diffraction (XRPD) and Fourier transform infrared spectra (FTIR) method. Further dissolution experiments of K-feldspar samples were operated under the hydrothermal condition for exploring the effects of Al/Si ordering on their dissolution. The degree of Al/Si order between XRPD and FTIR shows a good positive correlation (Pearson’s R =0.94726). The degree of Al/Si order is slightly positively correlated with the percentage of K-feldspars dissolution, and this presents a useful guide for people who are going to utilize K-feldspar as the fertilizer using a hydrothermal alkaline method and try to pick up those samples including orthoclase or microcline from an economic view point.