Characteristics of Films on the Surface of Sea Sand and Effects on the Dissolution of Chloride

Abstract

In this study, the effects of the specimen preparation method, temperature, and duration of the extraction step for the determination of the water-soluble chloride content of sea sand were investigated. The results demonstrated that increasing the heating temperature and duration promoted the dissolution of chloride, where the maximum value was obtained at 80°C and 60 min. Hot water extraction (80°C/60 min) could eliminate the effects of different specimen preparation methods on the final test results. Therefore, a new method was developed with drying at a temperature of 110 ± 5°C and hot water extraction at a temperature of 80°C for 60 min. The suitability of the new method for determining the water-soluble chloride content of sea sand was verified by testing the extracted specimens again. The results indicated that the chloride in sea sand dissolved fully with the new method, and thus it is suitable for testing the water-soluble chloride content of sea sand. Finally, the organic and inorganic compositions of the film adsorbed on the surface of sea sand were studied based on thermogravimetric analysis, inductively coupled plasma atomic emission spectrometry, ion chromatography, and total organic carbon measurements. The results indicated that a layer of substance (a multi-substance film) was adsorbed onto the surface of sea sand. This layer comprised inorganic salts (such as Cl–, Na+, Mg2+, SO42–, and Ca2+) and organic compounds, which were related to the composition of sea water. The multi-substance film greatly affected the dissolution and diffusion of chloride in the sea sand. Hot water extraction accelerated the dissolution of the film and increased the test results in terms of the water-soluble chloride contents.