Study On Fluoride Removal By Enhanced Electrosorption With Zirconia Based Three-Dimensional Anode

The nation-wide distribution of high-fluorine raw water is a serious problem in our country, which can cause severe diseases as people drink it for a long-term. The present technology has showed some removal effects for fluorine in raw water, but there are still some defects in these techniques, such as secondary pollution and high operating costs. So it is important to develop a kind of clean technology which is characterized as low energy consumption during fluorine removal process.In this thesis, a unipolar three-dimensional electrode was developed when combining the electrical conductivity material and effective fluorine chemical absorbent, which not only has high electrical conductivity to promote the migration of fluorine anions, but also has an increased high adsorption capacity for fluorine anions due to the enhancement effects of electric filed.After comparing the fluorine removal efficiency with different electrical conductivity material and different fluorine chemical absorbent, Hydrous Zirconium oxide was regarded as the best active constituent in the three-dimensional granular electrode, and the graphite with 5% carbon nanotube was the best conductive constituent, the mass ratio of these two constituents is 8:2. This fluorine removal efficiency of the three-dimensional granular electrode based on the above prescription is as follows: the static saturated adsorption capacity reach 37.79mg/g at 25℃; the effluent concentration of fluorine can be reduced to 0.39 mg/L after 72h-operation of electric absorption dynamic reactor, which is far lower than upper limit value of 1.00mg/L for the fluoride concentration in drinking water stipulated in the National Hygienic Standard for Drinking Water(GB5749-2006), and the dynamic adsorption capacity of fluorine is 4.72mg/g; the efficiency of enhanced electro-sorption fluorine removal with 5 V adscititious electric field intensity was increased to 8.51% compared with that without adscititious electric field intensity. Electrosorption dynamic reactor with self-made hydroxyl zirconium oxide as the three-dimensional electrode particles was employed to purify drinking-water contaminated by excessive fluoride. The results showed that the optimum structure parameters for this dynamic reactor with the nafion 117 membrane as the diaphragm was 20cm height of packed bed, and 4cm electrode distance. Furthermore, the fluoride removal efficiency was increased by either increasing the voltage or decreasing the inflow velocity and the pH value within a certain range. The optimal operation conditions gained in this study were voltage of 7V, inflow velocity of 4ml/min and acid pH value.Both lye elution and electrode short circuit were selected to regenerate the three-dimensional granular electrode with absorption saturated. The results showed that the elution rate is the highest with 0.01mol/L sodium hydroxide, and reach 83.09%. Electric current was generated when both the main anode and cathode were reverse connected, the concentration of fluorine in effluent water increased,and the percentage of regeneration was 23%.Based on the experimental results, pilot dynamic reactor was made to treat the raw water with high concentration of fluorine which is from Qinghe county in Hebei province. During 223h running, fluorine concentration in effluent is lower than 1.00mg/L, and the dynamic adsorption capacity of fluorine reached 5.03mg/g.