Study on multivariate salt phase equilibrium relationship of high-salt wastewater under the influence of organic impurities in evaporation process

The small amount of organic impurities in the pre-treated saline wastewater will affect the original solubility of the saline wastewater, which is one of the key issues that restrict the evaporation of saline wastewater with near-zero discharge under the working condition. We have investigated the solid-liquid phase equilibrium relationship under typical organic impurities in falling film evaporation tubes with different parameters. Results show the phase diagram of Na⁺, Mg²⁺//Cl^--H₂O in the presence of organic impurities belongs to the phase diagram of a simple system. The phase diagram contains a co-saturation point, two single-variable curves and four crystallization zones. In addition, the overall change in the solubility of the ternary system of Na⁺, Mg²⁺//Cl^--H₂O under organic impurities was not significant with the increase in temperature. However, the solubility of MgCl₂ was more affected by temperature and increased by 5.67% when the temperature increased from 303.15 K to 373.15 K. This study provides a theoretical basis for rational control of salt scaling in the evaporation process of coal chemical industry. It is important to ensure the efficient operation of the evaporator, realize the recycling of inorganic salt products, and ultimately achieve the goal of 'near-zero discharge'.