Study On The Phase Behavior Of MNO₃ (M=Na,K,Rb,Cs) In A Polyhydric Alcohol-water Mixed Solvent

Adding an organic solvent to an aqueous salt solution normally decreases the solubility of salt in the original.solution.This new phase separation technique can be widely used in biochemistry,biochemical industry,cell biology,and many other fields.So these systems play an important role in many industrial applications.The investigation of the solubility and the related physical-chemical propoerties of the systems will not only enrich the chemisry of these systems,but also provide a reliable basis for the construction of the new thermodynamic model.Moreover,the result will be useful for the design of the separation and purification method of the salts.Therefore,but also it can offer a reliable theoretical and guidance for the purification technology of inorganic salts.The equilibrium solubilities of alkali metal nitrates in the mixed solvents of polyhydric alcohol-water were studied by the density-refractive index method using a self-made microdevice.The density and refractive index of the saturated and unsaturated solutions were also determined.The experimental data were correlated by the related equations.The main content and results of this paper are as follows:1.The equilibrium solubility,density and refractive index of the teranay systems of alkali metal nitrates+polyhydric alcohol+water were determined at the temperatures 288.15,298.15,308,15 and 318.15 K.The polyhydric alcohol are ethylene glycol,1,2-propanediol and glycerin.The alkali metal include sodium,potassium,rubidium and cesium.2.For the saturated systems,all the systems are a single solid-liquid equilibrium.That is,there is no two liquid phase exist.The solubility for the saturated solutions were found to decrease with an increase of the concentration of polyhydric alcohol.And the higher the temperature,the larger the solubility.For the density curves,different trends are observed.For ethylene glycol and 1,2-propanediol,the variation tendency of the density curve are very similar as the solubility curve except that the systems containing KNO3.For systems with KNO3,the density curves at the different temperatures are intersected.However,the densities increased with the increasing of glycerin in themixed solvent.Then,the,refractive index for the systems all increased with the increasing the content of polyhydric alcohol in the mixed solvent.And the refractive index curves have a interaction at the four temperatures except for NaNO3+polyhydric alcohol+H2O systems.3.For the unsaturated systems,the effect of the ratio of polyhydric alcohol to water and the temperature were taken into account.The density and refractive index all increased with the increase of the ratio of polyhydric alcohol to water,and with the increase of the content of the salts.However,the higher the temperature,the lower the density and refractive is.4.The solubility,density and refractive index of the saturated system were correlated by the equation Y=A+Bw1+Cw12+Dw,3.The data(refractive index and density)of the unsaturated solution were related by the equation Y-(A0+A1w1+A2W2+A3w1w2+A4w2w12)xexp[A5(w1/w3)+A6(w1/w3)2].According to the standard deviations,the above-mentioned equations are suitable for our research systems.5.The comparision of the experimental results of the saturated systems suggest that the more hydroxy number in the polyhydric alcohol,the higher solubility,density and refractive are.On the other hand,the solubility and density can be differed for ethylene glycol and 1,2-propanediol systems.While,the refractive index almost overlapped for the two alcohol with the same number hydroxy group.Moreover,the salting out ratio is not temperature-sensitive.And the lager solubility of the salts in the polyhydric alcohol,the lower salting out ratio present.