Study On Fluoride Removal Technology Of High Fluoride Zinc Sulfate Solution

In the process of zinc hydrometallurgy, most zinc plants have to deal with excess fluoride in their process liquors. In view of the deficiencies of applied fluoride removing methods from zinc sulfate solution, on the basis of consulting a large amount of relevant literatures and laboratory tests, a new approach of fluoride removal from high fluorine zinc sulfate solution by the modified calcium carbonate induced crystallization (MCCIC) is proposed in this paper. The method takes modified CaCO3 as the fluoride removal agent, and CaF2 as the crystal seed to remove fluoride by induced crystallization. This thesis focuses on the application of the method and its influencing factors to carry out a systematic experimental study. With this method, the open circuit problem of the fluorine from the zinc smelting system was solved. Basides, to obtaine the better process parameters, parameter optimization experiments were carried out.In the experiment, the fluoride removal tests of pure water, pure zinc sulfate solution and tail gas absorption solution etc.fluorine containing system were studied. The test results show that this method is suitable for the removal of fluoride from the pure water, pure zinc sulfate system and tail gas absorption solution etc. various system. The effect of coexisting ions in the actual zinc sulfate solution on the MCCIC was explored. Results show that Mg2+ is the main factor that affecting the depth of fluoride removal. A higher concentration of Mg2+ in solution will result a lower removal ratio of fluoride. While the effect of Mn2+, Fe2+ have not an appreciable effect to the fluoride removal. The specific process conditions for the removal of fluoride by MCCIC were studied. The optimal process conditions of MCCIC are optimized as follows:temperature is 70 ℃, reaction time is 45min, pH is 4.0-5.0, the addition amount of calcium carbonate is 2 times of the theoretical value and the addition amount of crystal seed is 6g/L and fluoride slag can be used as crystal seed return process. To an actual rotary kiln tail gas absorption liquid with a high fluoride concentration was studied. Experiments show that under the optimal process conditions, fluoride concentration can be decreased to 99.59mg/L from 1011.20mg/L, and the fluoride removal rate is 90.15%. In addition, a higher concentration of initial F- in solution will result a higher removal ratio of fluoride.Various experiments, which are discussed in this paper, colifirm that the MCCIC method studied in this paper successfully solve the problem of fluorine open circulation in high fluorine and low magnesium zinc sulfate solution. Compared with other fluoride removal process, it has the advantages of short process, simple process, good treatment effect and low cost per unit. It has a good application prospects.