Theoretical analysis of crystallization of sodium sulphate for sulphate saline soil containing chloride

Concerning the salt heaving within the sulphate salty soil, it is characterized by the crystallization of sodium sulphate. Specifically, the mirabilite (Na₂SO₄·10H₂O) can be precipitated directly from the saturated sodium sulfate solution under some conditions, and the solid volume of salt crystal consequently increases 4.18 times, which finally results in large salt heaving. By collecting experimental data, a static model is established to describe the soluble properties of sodium sulphate, which can be employed to analyze the crystal amount of sodium sulphate in soil. Using this model, the crystallization of sodium sulphate is analyzed and calculated in the cooling process. At the same time, the influences of salt content, water content, concentration of sodium chloride and soil initial temperature on crystallization are discussed. It is found that the critical values for salt content and water content exist for the crystallization of sodium sulphate. The influences of sodium chloride on crystallization of sodium sulphate depend on the coupled effects of salt content and water content. In case of the favorable combination, the crystallization in soil can be restrained by addition of sodium chloride. Contrarily, the sodium chloride can accelerate the crystallization of sodium sulphate. The crystal amount of sodium sulphate depends on the environment temperature seriously, and partial sodium sulfate is crystallized if the initial temperature of soil is low, which reduces the crystallization in further cooling process.