INFLUENCE OF IMPURITIES ON DISSOLUTION BEHAVIOR OF SODIUM SULFATE IN COAL CHEMICAL INDUSTRY SALINE WASTEWATER
The study on the influence of typical impurities in saline wastewater on the crystalline properties of sodium sulfate is beneficial for optimizing the sodium sulfate crystallization process and promoting the value-added utilization of sodium sulfate.Taking the sodium sulfate waste impurities system in the coal chemical industry as the research object,this study used OLI and COSMO-RS to investigate the effects of temperature,typical inorganic impurity ions,and organic impurities on the solubility,solvation,and interactions of sodium sulfate.The results indicate that the solubility behavior of sodium sulfate is controlled by the polarity of impurities,the solvation capacity of Na+and SO42-,the concentration of impurities,and the common ion effect,with polarity exerting the strongest influence.Calcium ions(Ca2+),ammonium ions(NH4+),potassium ions(K+),bicarbonate ions(HCO3-),fluoride ions(F-),and nitrate ions(NO3-)are with less polarity than Na+and SO42-,and they promote the crystallization of sodium sulfate.Among these,cations promote the crystallization of sodium sulfate through the common ion effect,while anions promote it through both the common ion effect and weakening the solvation of Na+and SO42-.Magnesium ions(Mg2+)and carbonate ions(CO32-)promote the dissolution of sodium sulfate.Magnesium ions enhance the solvation of Na+and SO42-,thus promoting the dissolution of sodium sulfate,while carbonate ions promote the dissolution of sodium sulfate through their strong polarity.Removing Mg2+and CO32-from saline wastewater is a necessary measure to promote the crystallization of sodium sulfate.At low concentrations,organic impurities promote the crystallization of Na2SO4 by weakening the interaction between Na+and SO42-.Calcium ions and fluoride ions not only significantly increase the freezing crystallization time of sodium sulfate,but also generate new substances with sodium sulfate.Related theoretical research provides theoretical support for the utilization of sodium sulfate waste salt.
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