Study On The Treatment Of High Concentration Brine Containing Na~+ By Salting-out Crystallization

At present,the coal chemical industry commonly uses concentrated solidification of landfill for the treatment of high concentration of brine.Coal chemical wastewater contains abundant inorganic salt resources.Separating the salt from the wastewater not only can treat the high concentration of salt water harmlessly,but also can use of inorganic salt.In this paper,we used the salting-out crystallization to separate Na₂SO₄ and NaCl from coal chemical sodium wastewater concentrated by membrane.The first part of this paper,we tested several solvents,such as methanol,ethanol,acetone,acetonitrile,diethylamine and ionic liquid,respectively.We found that the solubilities of Na₂SO₄ and NaCl decreased with the increased of the content of solvent.Comparing the change of the two kinds of sodium salt’s solubility under the effect of different solvents,finding that the effect:methanol>ethanol>acetone>diethylamine>acetonitrile>Tetrafluoroborate ionic liquids.When the solvent was methanol,20 ℃,alcohol:water（volume ratio）was 3:7,the decrease of the sodium salt’s solubilities were the largest indicating the effect was the best,and the precipitation rate of sodium sulfate was 90%.On the basis of above work,we studied the influence of the factors such as time,temperature,rotational speed,initial concentration of solution and the amount of solute in solution.The results showed that the dissolution time,temperature and rotational speed had little effect on the crystal size,and had no effect on the precipitation rate of Na₂SO₄.We found the precipitation rate of Na₂SO₄ increased with the increase of the initial Na₂SO₄ concentration in the solution.A real coal chemical wastewater was separated by salting-out crystallization,and the results showed that when the ratio of methanol to water is 1:1,the precipitation rate of Na₂SO₄ was 94%,and the purity was about 99%.The third part of this paper used the equilibrium method to determine the solubility of Na₂SO₄ at the temperature 288.15 K-303.15 K in the NaCl-water-methanol system.The results showed that the solubility of NaSO₄ decreased with the increase of the content of NaC]and methanol in the solution,and increased with the increase of the temperature.Then we used the electrolyte NRTL model to correlate the solubility data,and a satisfactory agreement was found between the calculated and experimental data points.Additionally,we got the correlated binary NRTL parameters between the five kinds of particles in the solution,which provided the theoretical basis for predicting the solubility of NaSO₄ in each system.