Studies On The Ion-Exchange Kinetics Characteristic Correlating With The 200 T/A Mid-Experiment Of Extracting Potassium Nitrate From Seawater

The 200 t/a mid-experimentation of extracting potassium nitrate from seawater, a key subject of science and technology in the tenth five-year plan of our country, was one of the important contents of research on the new technology of extracting potassium vitriol and potassium nitrate from seawater and bittern. The purpose on this study was to research the ion-exchange kinetics characteristic correlating with the mid-experimentation on the basis of the production of extracting potassium nitrate from seawater. It mainly included two facets: One was the effect of different filling height of zeolite on the adsorption and elution of K⁺, the other was the characteristic on internal diffusion at different stirring speeds, ion-exchange temperatures and concentrations of NH4NO3. This subject could afford theoretical dependence to some extent for optimizing technological parameters, advancing the ion-exchange velocity of zeolite, reducing the diluted eluting solution.Through the study on the effect of different filling height on K⁺ adsorption, the adsorption curves was protracted, and the effects of different filling height on the adsorption rate of K⁺ in seawater and the adsorption quantity of clinoptilolite were analysed. The results of adsorption experiment indicated that the filling height of adsorption columniation was better to exceed 4m. Through research on effect of different filling height on K⁺ elution, The elution curves of K⁺ was protracted, and the effects on the K⁺ peak value of elution curves and the average concentration of enrichment potassium solution were compared. The elution experiment results suggested that the effect on elution was enhanced to some extent with the increasing of the zeolite height. The fluxion resistance at different filling height was also measured.The kinetics characteristic of the internal diffusion in clinoptilolite was studied through method of whisking in reaction flask. On the trial conditions, the results proved that different stirring speed hardly affect the velocity of K⁺-NH₄⁺ ion exchange. The effect of altering ion-exchange temperature and concentration of NH4NO3 on internal diffusion in clinoptilolite indicated that the velocity of K⁺-NH₄⁺ ion exchange was gradually enhanced with the increasing of temperature and the concentration of NH4NO3. The experiment data were disposed by the theory of shrinking-core model, and we could found the rules above similarly. Further more, the control mechanism of K⁺-NH₄⁺ ion-exchange was particle diffusion control on this trial condition. The apparent diffusion velocity coefficients and the effective diffusion coefficients of NH4NO3 at different ion-exchange temperature and different concentration of NH4NO3 were calculated. The effective diffusion coefficients augmented with the increasing of the ion-exchange temperature and the descending of the concentration of NH4NO3. On the basis, the internal diffusion kinetics model on K⁺-NH₄⁺ ion exchange was deduced.