Research On Precipitation-Adsorption Combined Process For Treatment Of Industrial Fluorinated Wastewater

With the extensive use of fluorine resources in industry,a large amount of fluorinated wastewater will inevitably be produced,which will bring certain harm to human health and the quality of process products.In this paper,the simulated fluorinated wastewater is treated by the precipitation-adsorption combined process,and the feasibility of applying it to the actual industrial fluorine-containing wastewater treatment is explored.Firstly,the precipitation method was used to remove high concentration of fluoride ions in industrial wastewater,and the fluoride removal effects of different calcium sources and coagulants were studied.The results showed that Ca Cl₂ had the best fluorine removal effect,followed by Ca（OH）₂,and finally Ca O.When Ca Cl₂ is used as calcium source,the concentration of F^-in the simulated fluorine-containing solution can be reduced from 1000 mg/L to8.8 mg/L by controlling the mass ratio of calcium to fluoride to be 1.2:1 and p H=4～10.When Ca（OH）₂ is used as calcium source,the mass ratio of calcium to fluorine is controlled to be 1.6:1,p H=2～6,the concentration of F^-in the same solution can be reduced to 35.6 mg/L,while Ca O has a poor defluorination effect.When the fluorine concentration increases,the fluorine removal rate of Ca（OH）₂ and Ca O decreases slightly.The fluoride removal effect of coagulants PAC,PFS and PAFC is not much different.When the dosage is 0.4 g/L,the F^-concentration can be reduced to about 6.0～7.0 mg/L,and the coagulant is conducive to solid-liquid separation.,the precipitation was complete between 25 and 30 min.The coagulation aid PAM further shortens the precipitation time.When its dosage is 10～15 mg/L and p H=6～10,the precipitation time is 3～6 min.The coagulation orthogonal experiment results show that the influence of p H,PAC and PAM on the fluoride removal effect is p H>PAM>PAC,and the optimal level of each factor is:p H=6,C（PAC）=0.6 g·L^-1,C（PAM）=6 mg·L^-1.Then,the adsorption method is further selected to remove the lower concentration of fluoride ions in the industrial wastewater.In this paper,a carbon-based adsorbent loaded with ceria was successfully synthesized by a one-step impregnation method.First,by comparing the fluoride removal performance and cost of four kinds of carriers:coconut shell activated carbon,columnar activated carbon,activated alumina balls,and zeolite,it is determined that coconut shell activated carbon is the best carrier,and the optimal preparation process of the adsorbent is optimized as follows:The concentration of cerium salt is 0.1 mol/L,n(H₂O₂:Ce³⁺)=1:2,the ratio of the carrier mass to the volume of the cerium-containing loading solution（solid-liquid ratio）is 5 g/50 m L,and the loading time is 12 h.The fluoride removal experiment was carried out with the adsorbent prepared under this process.The results showed that:adding 3 g adsorbent to 100 m L of simulated wastewater with p H=2 and fluorine content of 10 mg/L,the reaction was performed for 90 min,and the fluoride ion concentration was reduced to 0.18mg/L,the removal rate is as high as 98.2%.In the simulated wastewater,the order of the influence of different anions on the fluorine removal rate is:Cl^-<NO₃^-<SO₄^2-<PO₄^3-,and the order of the influence of different cations on the fluorine removal rate is:Ni²⁺<Na⁺<Fe³⁺.The adsorption process was an endothermic reaction with a maximum saturation capacity of 2.0 mg/g.The adsorption process conformed to Langmuir adsorption isotherm model and pseudo-second-order kinetic model.In addition,the regeneration cycle experiment of the adsorbent found that the adsorbent still had a 70%removal rate for fluoride ions after being continuously regenerated and used for 5 times in the environment of p H=2.The loading mechanism of cerium salt was explored by ICP,XPS,FTIR,etc.The results showed that cerium was mainly loaded on the carrier in the form of Ce（OH）₄ and Ce O₂.During the adsorption process,the dissolution rate of cerium was only 0.28%.The removal of fluoride ions is the result of the combined action of ion exchange.Finally,when using the precipitation-adsorption combined process to treat the actual wastewater with an initial fluorine concentration of 697.1 mg/L,after adding 0.7 g/L Ca Cl₂,0.1 g/L PAC,and 0.003 g/L PAM,the fluorine concentration dropped to 9.1 mg/L,the removal rate was 98.7%,and after being adsorbed by the adsorbent for 90 min,the fluoride ion concentration dropped to 0.50 mg/L,the fluorine removal rate was 94.5%,and the total removal rate of the combined process reached 99.9%,which meets the requirements of fluorine-containing wastewater.Process the request.The precipitation-adsorption combined treatment process explored in this paper provides a direction for advanced treatment of industrial fluorine-containing wastewater.