Thermodynamic Study On The Tungsten Extraction By Primary Amine And Aqueous Solution Of Tungsten And Molybdenum

Due to the lack of the theoretical basis of research on the process of tungstenextraction by primary amine and tungsten, molybdenum aqueous solution, a study onthe experiments and thermodynamic model of the tungsten extraction by primaryamine was carried out as well as the solubility model of the sodium tungstate andmolybdate. The following innovative results were obtained:(1) The liquid-liquid extraction equilibrium data were determined by performinga series of experiments at293.15K. The extraction reaction mechanism wasconfirmed to keep consistent when the tungsten concentration was below1g/L. Thena thermodynamic model for the extraction of tungsten by primary amine N1923wasdeveloped based on the extraction equilibrium data and the activity coefficientcalculated by Pitzer equations in aqueous and organic phase. The new model wassuccessfully used to predict the regularities of extraction efficiency along withequilibrium pH and initial N1923concentrations. Simultaneously，correspondingexperiments were carried out in order to verify the new model. The results indicatedthat the model could moderately predict this extraction system.(3) The Pitzer model for the extraction of tungsten by N1923was improved.Pitzer-Margules model and Pitzer-NRTL model for the extraction of tungsten byprimary amine N1923were established based on the activity coefficient calculatedby Margules and NRTL equations in organic phase, respectively. The AARD forthese two models were approximate and their predicted results were in consistentwith the improved Pitzer model. This demonstrated that the deviations of modelswere caused by the formation of isopolyanions in aqueous phase.(4) The solubility ofNa2WO42H2OandNa2MoO42H2Oin aqueoussolutions were measured using a dynamic method within the temperature range of293.15K to343.15K. A thermodynamic model for the solubility of sodiumtungstate or molybdate in sodium sulfate solutions was developed based onsolubility data. The corresponding AARD was0.3358%and0.7140%which showedthat the calculated data were in good agreement with the experimental values. Thenthe models were successfully used to calculate the solubility ofNa2WO42H2OandNa2MoO42H2Oin pure water and the results showed that the calculated data were in consistent with the experimental values. In addition, the solubility ofNa2MoO42H2Oin1.000molality of sodium sulfate was calculated by the modeland these calculated results agreed well with the experimental data. Furthermore, thetwo models were used to predict the solubility ofNa2WO42H2OandNa2MoO42H2OinNa2WO4-Na2MoO4-Na2S O4-H2O systems. These resultsof sodium tungstate calculated by the model agreed well to the experiment, whilethose of sodium molybdate deviated a little.