The Study Of Separation And Purification Of Iodine From Kelp Leaching Liquid

Ocean is known as “iodine bank” of the nature, it has been a trend of extracting iodine from seawater or seaweed. Using kelp leaching liquid as raw materials, the method of solvent extraction and activated carbon adsorption used for extracting iodine was studied in the thesis respectively. Oxidation rate, extraction rate and the distribution ratio were as inspection index in the process of solvent extraction to optimize the extraction process conditions. Adsorption rate was as inspection index in the activated carbon adsorption process to optimize the adsorption process conditions. The mass transfer kinetics of extraction process was studied by the Lews cell method.Iodine ion concentration was determined by the oxidation-reduction titration method in the process of the test, the national standard was referenced. The standard curve of determining iodine was drawn by the ultraviolet spectrophotometry method. The experimental condition was that2mL1.0mol/L sulfuric acid solution,3mL10g/L potassium iodide solution and5drops5g/L starch solution were added into5mL potassium iodate standard solution, then chromogenic time was10min.The optimal process conditions of the extraction process were concluded by single factor test and orthogonal test: the raw material liquid was acidized to pH1.5,0.01g/20mL sodium nitrite was added, the phase ratio was1:3, the temperature was55℃, the stirring speed was500r/min, the reaction time was25min, extraction rate was98.7%by level7countercurrent extraction. The countercurrent extraction series concluded by test was consistent with theoretical series by McGabe-Thiele graphic method. The optimal process condition of back extraction was the temperature35℃, the stirring speed500r/min and the back extraction time8min.The optimal process conditions of the activated carbon adsorption were activated carbon0.14g/100mL, the stirring speed600r/min, the adsorption temperature25℃and the adsorption time50min. The conclusion of elevated temperature was not conducive to the adsorption process was drawn by isothermal adsorption test, which was consistent with the conclusions of single factor experiment. The optimal process condition of desorption was temperature30℃, stirring speed500r/min and desorption time160min.The conclusion was drawn by extracting the preliminary study of thermodynamics: the reaction enthalpy change was11.89kJ/mol, the reaction entropy change was71.38J/(mol·K), the free energy was less than0. The reaction of extraction iodine was spontaneous, and temperature rising favours extraction.The effect of initial concentration of raw material liquid, stirring intensity, cross-sectional area and temperature on the extraction rate and mass transfer process was researched by the Lews cell method, and the conclusions were as follows: the process of extracting iodine belonged to diffusion control model, rate equation R0.0001I22, activation energy of extraction2.19kJ/mol, the relationship between stirring speed and mass transfer coefficient and between temperature and mass transfer coefficient were gained.