Research On Solid-Liquid Equilibria Of Multi-systems Of High Salt Wastewater In Coal Chemical Industry

In recent years,coal chemical industry has become an important part of China’s energy and chemical industry.However,at the same time the environmental problems have become more and more serious,especially water resources and water environment issues have become the bottleneck restricting the development of coal chemical industry.Therefore,it is necessary to desalinate a large number of high-salt wastewater discharged from coal chemical process.The composition of high-salt wastewater from coal and chemical industry is complex.According to the content of each ion,it is summarized as Na+//Cl-,SO42-,NO3-,CO32--H2O water-salt system.The basis of the process of separating and extracting salt is the dissolution equilibrium relationship of various salts in the system,the study on the SLE and the physical and chemical properties of the solution is completed,and the resources of the liquid inorganic salts in the high salt water in the coal chemical process are developed in a targeted way.It is ofgreat significance that both is in theory and practice.The paper measure the SLE data and physico-chemical property(nD,η,p,pH)of liquid-phase of the quinary system’s subsystem(including five teanary systems and four quaternary systems at 313.15 K)with the method of isothermal dissolution.Draw the phase diagram,water diagram and physical-chemical properties of each system composition diagram.(1)The three simple ternary system Na+//Cl-,CO32--H2O、Na+//Cl-,NO3-H2O and Na+//NO3-,CO32--H2O phase diagrams all contain a co-saturation point,two single curves,three crystallization zones(two single salts,one co-saturated),No double salt exiated at these systems.The phase diagram of the complex ternary systems Na-//CO32-,SO42--H2O and Na+//SO42-,NO3--H2O have two co-saturation points,three invariant curves,five crystallization zones(three of which are single-salt crystallization zones,two co-saturated crystallization zones)and the two systems have separate salts(Na2CO·2Na2SO4 and NaNO3·Na2SO4·H2O),all of which belong to the saturated type I ternary system.(2)The simple quaternary system Na+//Cl-,NO3-,CO3 2--H2O includes one invariant point,three isothermal univariant curves and three single-salt crystallization zones(NaCl,Na2CO3·H2O and NaNO3).Two quaternary systems Na+//Cl-,SO42-,CO32--H20 and Na+//Cl-,SO42-,NO3--H20 at 313.15 K includes two invariant points,four crystallization zones and five isothermal univariant curves.There are no solid solutions in the two quaternary systems but there are duplicate salts,which belong to the more complex quaternary system.The Na+//C032-,SO42-,NO3--H2O system at 313.15 K has two invariant points,five crystallization zones and six isothermal univariant curves.Comprehensive analysis:The area of the crystallization is showed that Na2CO3-2Na2SO4>Na2SO4>NaCl>Na2CO3-H20>NaNO3·Na2SO4·H2O>NaNO3.Among them,Na2CO3·2Na2SO4 has the largest crystallization area.NaNO3 has the smallest crystallization area(least likely to precipitate).(3)Four quaternary systems were studied by translation method of phase equilibrium phase diagram at 313.15 K.Comparing the phase diagrams obtained by the previous experiments,the predicted phase diagrams are basically consistent with the experimentally drawn phase diagrams.The phase diagram of the quinary system Na+//Cl-,SO42-,NO3-,CO32--H20 was predicted by the translation method.It is predicted that the quinary system Na+//Cl-,SO42-,NO3-,CO32--H2O has two quinary system co-saturation points,seven isothermal univariant curves and six crystallization regions.(4)Based on the phase diagram application of water-salt system,combined with 313.15 K Na+//Cl-,SO42-,NO3--H2O quaternary system phase diagram,ternary system Na+//CO32-SO42--H20 phase diagram,the phase diagram analyzes the various stages of the isothermal evaporation process.The phase diagram theoretically optimizes the process of separating and extracting salt from the high-salt wastewater of coal chemical industry.The results obtained in this paper reveal the solubility and salt separation rule of various salt in the five-component system,which lays a theoretical foundation for the crystallization process of high salt-containing wastewater from coal chemical industry.