Study On Deep Fluoride And Phosphorus Removal Of Two High-salt Solutions

The high salt system has high concentration and complex components of various pollutants usually,among which the pollutants such as fluoride and phosphorus exist in various forms,which further increases the difficulty of removing flouride and phosphorus pollutants in the high salt system.In this paper,two high-salt systems of battery-grade manganese sulfate solution and the wastewater of Yunnan were selected to carry out the removal of flouride from manganese sulfate solution and the removal process of low-concentration fluoroborate,hypophosphate and phosphite.It is of great significance to explore the deep removal of fluoride and phosphorus in high-salt solution by economic means.The main research contents and results are as follows:（1）The simulated fluorinated manganese sulfate solution with 20%manganese sulfate mass fraction was taken as the research object,the two-stage adsorption method of homemade hydrated zirconia after coagulation of zirconium sulfate was used to deeply remove fluoride and adsorption mechanism was studied.1)In the coagulation stage,when the initial flouride concentration of the manganese sulfate solution was 100and 500 mg/L,respectively,the p H value of the coagulation was controlled to be 4.0,the temperature was 25°C,the standing time was 5min,zirconium sulfate was added for coagulation with the ratio of zirconium to fluoride substance is 2（n（Zr/F）=2）and the concentration of residual fluoride in filtrate is less than 10 mg/L,and the manganese loss rate is 0.53%and 5.30%,respectively.The high fluoride concentration coagulation directly realizes the deep fluoride removal,resulting in excessive manganese loss.2)The initial fluoride concentration in the adsorption stage was 50 mg/L,and the hydrated zirconia adsorbent was synthesized by the direct precipitation method.Under the adsorption conditions of p H=4.0,adsorbent dosage was 2 g/L,adsorption temperature was 20℃,and adsorption time was 6 h,the residual fluoride concentration in the manganese sulfate solution is 8.54 mg/L,there is no zirconium residue in the solution after adsorption.The adsorption of fluoride by hydrated zirconia conforms to the pseudo-second-order kinetic model,and the adsorption isotherm fits well with the Freundlich isotherm,the maximum theoretical adsorption capacity of fluoride ion by hydrated zirconia at 35℃is 77.64 mg/g.The adsorption of fluoride ions on hydrated zirconia is a spontaneous,endothermic and entropy-increasing process.Fourier transform infrared spectroscopy（FT-IR）and X-ray photoelectron spectroscopy（XPS）results show that fluoride ions is mainly removed by ion exchange with hydroxyl groups on hydrated zirconia.（2）Aiming at the possible existence of tetrafluoroborate and hypophosphite and phosphite in the wastewater of Yunnan,the simulated fluoroborate wastewater and simulated wastewater containing hypophosphite and phosphite were taken as the objects.The research was carried out according to the ideas of polyaluminum chloride（PAC）decomposition-coagulation defluorination and calcium hypochlorite oxidation-precipitation phosphorus removal.1)The initial concentration of BF₄^-in the simulated wastewater was 2.05 mmol/L（fluoride concentration was 155.78 mg/L）,the p H of decomposition was 4.0,and the decomposition rate of BF₄^-is 99.86%at 25℃for 10 h with the addition of 8.74 g/L PAC.Adjust the p H of the decomposed solution to7.0 for coagulation to remove fluoride,and the residual fluoride concentration in the filtrate is 0.76 mg/L.2)Hypophosphite and phosphite with an initial phosphorus concentration of 10 mg/L（calculated as total phosphorus）were treated respectively.At p H=3.0 and 25℃,the addition amount of calcium hypochlorite in hypophosphite and phosphite simulated wastewater were 300 mg/L and 150 mg/L,and the oxidation time were 8 h and 4 h,respectively,and adjust the p H of the solution after oxidation to 11.0,the total phosphorus concentration in the filtrate is lower than 0.1 mg/L.The above process conditions can treat hypophosphite and phosphite simulated wastewater with a total phosphorus concentration of 1 mg/L to below 0.1 mg/L 3)For the actual wastewater with high fluoride and high phosphorus of Yunnan（fluoride concentration is 1480.52 mg/L,total phosphorus concentration is 1497.15mg/L,conductivity is 62.54 m S/cm）,According to the small-scale treatment process of adding Ca O for preliminary phosphorus and fluorine removal after Ca（Cl O）₂ oxidation treatment,continuing to add Ca O for deep phosphorus removal,and adding PAC for deep fluorine removal,the total phosphorus concentration of the effluent is 0.1 mg/L,and the fluorine concentration is 0.45 mg/L,which meets the requirements of fluoride concentration≤1 mg/L and total phosphorus concentration≤0.1mg/L in"Surface Water Environmental Quality Standard".