In this chapter, the use of Raman spectroscopy (RS) for studies of aqueous solutions is shown. This technique is mainly used for the characterization of solid samples, but presents numerous features permitting its use for the analysis of aqueous media. Indeed, it possesses all the advantages of optical methods (versatility, rapidity, contact-less non-destructive measurement, etc.), but also offers possibilities for in situ measurements. The Raman spectrum will be influenced by several parameters such as the solution concentration or its temperature-phase. Thus, the analysis of a set of aqueous solutions of different concentrations in a certain temperature range can permit the identification of the specific effect of salt and temperature. A proper analysis based on the follow-up of the specific peak areas or intensities can permit the determination of the salt concentration or the phase transition of the studied solution. The analysis can be focused on the salt direct effect on the spectrum, analysis of the salt signature itself, or on its indirect effect on the water signature. The method for the characterization of aqueous solutions of some salts is presented: elaboration of calibration curves and concentration determination. As an application example, a special attention is devoted to aqueous solutions that are used in the winter maintenance domain (solution of acetates, formates, or chlorides), which are very relevant examples of aqueous solution behavior. A specific analysis set to determine the solution solid-liquid phase transitions is presented as well as the thus-constructed phase diagram.
All over the world, winter maintenance is based on the application of the NaCl salt on roads, a product necessary for the elimination of slippery conditions. The quantities used for the salting operations are increasing with the development of the road network (in France, up to 2 million tons are applied each winter). This chapter will present the salt used as a deicer (its origin and chemical composition) and its chemical properties that are exploited for that purpose. Furthermore, an overview of the means of its transfer from the roads to the environment (soils and waters) as well as its impacts on these media will be presented, a special attention being devoted to the soil. The interactions of salt with other road pollutants and the treatment possibilities in the road pollution context will be discussed.
Part of the book: Salt in the Earth