| Layered double hydroxides（LDHs）as a layered bimetallic hydroxide had a large specific surface area and a special layered structure.The interlayer anion exchangeability and structural memory effect of LDHs enabled LDHs to maintained good adsorption capacity in wastewater treatment.In the recent year,the adsorption activity of LDHs prepared by chemical method in the adsorption of pollutants is lower than that of the original preparation in actual wastewater treatment process.At the same time,chemical production of LDHs will consume the metal salt,bringing secondary pollution,which will undoubtedly increase the cost of wastewater treatment.Therefore,to solve the above defects,this thesis proposes to use electric flocculation method to generated LDHs to adsorbed various pollutant in-situ.In this study,Zn/Al layered double hydroxides（Zn/Al-LDHs）were generated in situ by controlling the addition of metal cations and the types of plates in the process of electric flocculation.The adsorption capacity of Zn/Al-LDHs on methyl orange（MO）and anionic pollutant fluoride ions（F-）was investigated by in-situ generation of Zn/Al-LDHs in different systems.The results were based on Zn/Al molar ratio,current density,initial p H value and reaction time,explored the optimal experimental parameters for Zn/Al-LDHs to absorb MO and F-.The experiment was easy to operated and the process is simple.The in-situ production of Zn/Al-LDHs by EC（Electrocoagulation）was studied for adsorption and separation of MO in wastewater.It was found that in the EC system,with the Zn as anode and Al3+added in externally,the MO removal rate of in-situ Zn/Al-LDHs produced by electrocoagulation could reached 99.3±0.30%under the best experimental parameters.Different Zn/Al molar ratio will affect MO removal rate.With the increase of the initial p H value of the solution,the removal rate of MO increased gradually,but when the solution is too alkaline,the removal rate of MO decreased.In the EC system with Al as anode and Zn2+added externally,the removal rate of MO by in-situ Zn/Al-LDHs can reached 96.2±0.85%under the best experimental parameters.It was found that the difference of Zn/Al molar ratio can affected the removal rate of MO.The removal rate of MO increased with the increase of p H value,and when the solution is too alkaline,the removal rate of MO is also high.In the EC system with Zn as anode and Al as cathode and periodic exchange of anode and cathode,the MO removal rate of Zn/Al-LDHs produced in situ by electrocoagulation can reached 97.5±0.85%under the best experimental parameters.It was found that the different Zn/Al molar ratio also resulted in different removal rate of MO.When the initial p H value of the solution is low,the removal rate of MO is high.With the increase of the initial p H value,the MO removal rate up first and then down.Finally,the substances generated by electrocoagulation in situ under the best experimental parameters in different systems were collected after adsorption and treatment of MO.The collected substances were characterized by XRD,SEM and FT-IR,and the results showed that Zn/Al-LDHs was the main phase of products generated in solution.The in-situ production of Zn/Al-LDHs by EC was studied for adsorption and separation of F-in wastewater.It was found that in the EC system with Al as anode and Zn2+added externally,the removal rate of F-by in-situ Zn/Al-LDHs produced by electrocoagulation could reached 92.1±1.1%under the best experimental parameters.Different Zn/Al molar ratio will affect the removal rate of F-.The increase of current density will improve the removal rate of F-,but the current density too high will inhibited the removal of F-.With the increase of initial p H value of solution,the removal rate of F-gradually increased,but too high initial p H value of solution would reduce the removal rate of F-.In the EC system with Zn as anode and Al as cathode and periodic exchange of anode and cathode,the removal rate of F-by in-situ Zn/Al-LDHs can reached 95.1±1.15%under the best experimental parameters.It is found that different Zn/Al molar ratio can affect the removal rate of F-.The removal rate of F-varies with the initial p H of the solution.In a certain range,the increase of the initial p H of the solution will improved the removal rate of F-,but the strong alkaline environment had negative effects to the adsorption and removal of F-.Finally,the substances generated by electrocoagulation in situ under the best experimental parameters in different systems were collected after adsorption and treatment of F-.The collected substances were characterized by XRD,SEM and FT-IR,and the results showed that Zn/Al-LDHs was the main phase of products generated in solution. |
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