Study of the Hydrated Structure of KCl and NaCl Mixed Solutions Using X-ray Diffraction and Raman Spectroscopy

Research on the hydrated structure of KCl and NaCl mixed solutions with a concentration range between 0 and 26% was conducted using X-ray diffraction and Raman spectroscopy at 25 degrees C. Their reduced structure functions, F(Q), and reduced pair distribution functions, G(r), obtained from X-ray diffraction indicate that compared with Na+, the hydration numbers and shell radii of the hydrated K+. ions are larger. This explains why the solubility of NaCl is higher than that of KCl at 25 degrees C. According to the Raman spectroscopy, the tetrahedral hydrogen bonds of water molecules will be destroyed with the increase in KCl concentration and the decrease in NaCl concentration. The extent of the bond destruction has systematic variations; for example, increasing at first and then decreasing. These results show that the destruction of the hydrogen bond structure resulting from Na+ is more serious than from K. Also, with the appropriate K+ content in the NaCl solution, Na+ will behave as a structure breaker instead of a structure maker, which enhances the destructiveness of the solution structure.