An effective desilication method for a titanyl chloride (TiOCl 2) solution obtained by dissolving sodium titanate using concentrated hydrochloric acid was investigated in order to increase the purity of titania pigment and the productivity of the process. When the TiOCl 2 solution obtained by HCl leaching was used without desilication, clogging of the filtration system or precipitation of silica occurs. To overcome these disadvantages using a simple and efficient desilication method, the acidity, preservation temperature, and time elapsed after the preservation of TiOCl 2 solution were controlled. In the experiments, TiOCl 2 solutions produced using 57 M HCl solution were preserved at 274313 K for 5 days. When the acidity, preservation temperature, and time elapsed after preservation were increased, the removal efficiency of silica increased. The conditions for the concentration of silica below 1 mg/L and the removal of silica by gelation were determined. When the purified TiOCl 2 solution was hydrolyzed at 363 K, titanium dioxide with a purity of 99.699.9% was obtained. Therefore, the results of this study demonstrated a straightforward and effective desilication method for highly acidic TiOCl 2 solution.
Bipolar electrodialysis was used in a process of desalting a lithium sulfate solution, converting it to lithium hydroxide and sulfuric acid, and concentrating and recovering them. The effects of the experimental variables such as applied voltage, the concentration of electrode solution, the concentration of raw material solution, volume ratio, and impurity were confirmed. The optimum conditions were investigated by comparing the conversion(%) of lithium hydroxide and sulfuric acid, the process time, and energy consumption. As the applied voltage was increased, the energy consumption tended to increase, but the processing time decreased significantly. As the concentration of lithium sulfate in the raw material solution increased, the conversion(%) of lithium hydroxide decreased. As the concentration of lithium sulfate increased, the energy consumption did not increase linearly, and energy consumption increased significantly. When a raw material solution of 0.5 M Li<sub>2</sub>SO<sub>4</sub> or more is used in the bipolar electrodialysis process, an applied voltage of 25 V is preferable. As the applied voltage increased at a constant process time, the conversion(%) of LiOH and H<sub>2</sub>SO<sub>4</sub> increased. Regarding the effect of the electrode solution concentration, when a 5.0 wt% electrode solution was used rather than a 3.0 wt% electrode solution, energy consumption decreased by more than 10%. When the volume of the raw material solution was increased, the processing time required for desalting increased. By using a low concentration raw material solution, it was confirmed that it was simultaneously possible to recover and concentrate lithium hydroxide and sulfuric acid through volume ratio control. When the raw material solution contained Na as an impurity, it was converted to NaOH with a surface LiOH, and it was not possible to separate the lithium and sodium.
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