Analytical Sciences

A Method for Determining the Composition of Aqueous Highly Concentrated Salt Mixture Solutions by Attenuated Total-Reflectance IR Spectrometry

Naohito YOSHIKAWA*, Hisakuni SATO** and Haruhiko OHYA**

*Sea Water Science Research Laboratory, The Salt Industry Center of Japan, 4-13-20, Sakawa, Odawara, 256-0816, Japan
**Department of Material Science and Chemical Engineering, Faculty of Engineering, Yokohama National University, Tokiwadai, Hodogaya, Yokohama, 240-0067, Japan

In the table-salt manufacturing process, the mother liquid and the concentrated brine in a crystallizer are highly concen-trated salt-mixture solutions comprising NaCl, MgCl2, KCl and CaCl2, and a determination of their concentrations plays an important role. A method is proposed to determine the concentration of each component in the mother liquid and the concentrated brine using the absorbance change relative to the water absorption at six wave numbers by attenuated total-reflectance IR (ATR-IR) spectrometry; an experimental confirmation can be used to accurately determine the composi-tion. In particular, for MgCl2, whose spectral change is larger than that of the other components, its concentration can be quantitatively determined with an accuracy nearly equal to that of a chemical analysis. (Keywords: Attenuated total-reflectance IR, composition analysis, aqueous salt-mixture solution, water absorption)

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