Study on the structure of aqueous potassium chloride solutions using the X-ray diffraction and Raman spectroscopy methods

• The KCl solution was tested by laboratory and synchrotron X-ray, and Raman spectroscopy.
• The reconstructive laboratory X-ray source is competent for testing KCl solution structure.
• Below 1.00% (include 1.00%), the structure of KCl solution was unchanged.
• Above 15.00% (include 15.00%), the structure change of KCl solution was obvious.

Many researchers have studied potassium chloride aqueous solutions, whereas, for the tests were carried out at different conditions, the results with diverse concentrations were not comparable. In this study, the structure of aqueous potassium chloride solutions were determined by X-ray diffraction (both using the synchrotron beam line and laboratory X-ray source) and Raman spectroscopy. Potassium chloride solutions at the concentrations ranging from 0.07% to 26.00% were systematically tested through these methods. For the solutions studied, a semi quantitative structural analysis was performed at the level of the reduced pair distribution functions (RPDFs) deduced from X-ray diffraction diagrams. The structure features can be seen directly from the RPDFs, which show systematic variations with the increase of the solutions. According to the results, when the concentration was above 15.00%, characteristic peak of K+–Cl− contact ion pairs was observed in the RPDFs at 3.15 Å, and their contributions became more and more significant with the increase of the concentrations. Furthermore, O–H bond lengths in water molecules are stretched with the increase of the concentration. Raman spectroscopy was carried out to support the conclusion that the hydrogen bonds in the aqueous solutions were disrupted with the increase of the potassium chloride concentration.

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