Separation And Extraction Of Na₂SO₄?Na₂S₂O₃ And NaSCN In The Aqueous Solution

There are a certain amount of Na2SO4,Na2S2O3 and NaSCN in the coking desulfurizing waste liquid.They are valuable materials in the industry area.To separate and extract Na2SO4,Na2S2O3 and NaSCN which existing in the aqueous solution,this paper made a lot of research.The main contents and achievements were summarized as following:(1)Phase equilibria of the ternary salt-water systems(Na2SO4-Na2S2O3-H2O,Na2S2O3-NaSCN-H2O,Na2SO4-NaSCN-H2O)and quaternary salt-water system(Na2SO4-Na2S2O3-NaSCN-H2O)at 40 0C were studied by the isothermal dissolution equilibrium method.The equilibrium solid phases were determined by X-ray spectroscopy.The ternary phase diagram and quaternary phase diagram were drawn in this paper.According to the results of the experiments,there is no double salt or solid solution formed.Therefore,the systems all belong to simple types;the phase diagrams of the ternary systems have one invariant point and two univariant curves at the boundary of two crystallization fields respectively;the phase diagram of quaternary salt-water system suggests that Na2SO4 has larger crystallization area,Na2S2O3 and NaSCN have very small crystallization area;the experimental results suggest that an increase of the Na2S2O3 and NaSCN concentration is accompanied by an obvious decrease of the solubility of Na2SO4.(2)Through the simulation of Na2SO4,Na2S2O3 and NaSCN contents in the coking desulfurizing waste liquid,According to the phase diagram of quaternary salt-water system,this paper determined the crystallization order of Na2SO4,NaSCN and Na2S2O3 when it was evaporated;on the basis of the salting out order,the extraction proce ss of separating this three kind of salts is that Na2SO4 was derived first,then Na2S2O3 and NaSCN was separated;it is needed that adding Na2SO4 crystal and Na2S2O3 crystal to solution when separate Na2S2O3 and NaSCN.When the evaporation temperature at 80?90? and the cooling rate at 3?5?/h,the recovery rate and purity of Na2SO4,Na2S2O3 and NaSCN are relatively higher,the recovery rate of this three kind of salts can reach about 75%,66%,66%respectively,the crystal purity can reach about 98%,90%,98%respectively.