In-situ Raman Spectroscopy Study On Salt-water System

The composition of the water-salt system reflects the material composition and physicochemical conditions when the system is formed.Through qualitative and quan-titative analysis,the development and utilization of Salt Lake resources can be acceler-ated.Component analysis has always been a major difficulty in research.There are many methods for analyzing water-salt systems.Among them,laser Raman spectros-copy is a simple and fast non-destructive detection method.Compared with other con-ventional methods,it can easily and quickly obtain the specific information of mole-cules and chemical groups in the system without damaging the sample.Under the above background,this paper combined Raman spectroscopy to conduct a systematic study on water-salt system.Firstly,the Raman spectra of sodium sulfate,potassium sulfate and ammonium sulfate in anhydrous and hydrated states were detected.By comparing different sulfates,it was found that the Raman wavenumber behaves differently in the solid state because the internal SO₄^2-vibration mode of the sulfate is different.The change in wavenumber shift was indirectly affected by the cation radius,showing cation dependence;when it was dissolved in water,the cation dependence disappeared,and the sulfate solutions all had similar peak shapes.Secondly,a Raman spectrometer was used to establish a method for quantitatively detecting the concentration of sodium sulfate solution.In the process of quantifying a high-concentration solution,a calibration can be used to determine the sulfate concen-tration.Then,the effects of the normalization method and different indicators on the performance of the Raman sensor during the quantitative process of dilute solutions were discussed.Experimental sensitivity and accuracy depend on the choice of these methods and indicators.Next,the in-situ Raman spectroscopy was used to detect the cooling and crystalli-zation process of sodium sulfate system in the water-salt system.The effect of end tem-perature and cooling rate on the system crystallization was explored.It was found that the metastable sodium sulfate heptahydrate preferentially spontaneously crystallized during the cooling and crystallization process.Prior to this,there is no relevant literature to study the cooling and crystallization process of sodium sulfate system by in-situ Ra-man technique.Finally,by adding anhydrous sodium sulfate solids with different solid content and particle size to the saturated sodium sulfate solution,the factors and laws affecting the characteristic peak intensity in the process of solid quantification by Raman were ex-plored.