Preparation Of Mn-Zr Adsorbents And Mechanism Of Defluorination

In this present study,a new adsorbent for the fluoride removal is prepared by Mn and Zr,based on the basis of the research of Zakir Hussain.The main objective of the study is to develop an effective adsorbent for the defluoridation with high adsorption capacity and wide application range.The experimental content is specifically shown below:?1?Mn-Zr composite adsorbent for the defluoridation was prepared through co-precipitation method and its defluoridation capacity was investigated.In this experiment,Zr?NO₃?₄·5H₂O and MnSO₄·H₂O were used to prepare the mixed solution in the molar ratio of 1:1.The aqueous ammonia was used as the precipitating agent and the pH of the titration's end was controlled at 10±0.2.The obtained precipitate was centrifuged,washed and then dried,after which it was calcined in a muffle furnace at 400^oC for 2 h to achieve the Mn-Zr composite adsorbent.The effects of pH on the defluoridation capacity of Mn-Zr composite adsorbent were studied as well as the adsorption kinetics and thermodynamics.The results show that when the adsorbent concentration and initial fluoride concentration are 2.0 g·L^-1and 10 mg·L^-1 respectively,the adsorption capacity of Mn-Zr composite adsorbent for fluoride is above 4.6 mg·g^-1 at 25 ^oC at a broad pH range?2-10?and the corresponding equilibrated time is about 120 min.?2?Mn-Zr composite adsorbent was further modified,in which Mn-Zr-Et composite adsorbent was synthesized through sol-gel method.The adsorption capacity of Mn-Zr-Et composite adsorbent for fluoride was studied in a batch system.Zr?NO3?4·5H2O and MnSO4·H2O were also used for the preparation of Mn-Zr-Et composite adsorbent.In this scenario,ethanol and deionized water were used as the solvent for the zirconium salt and manganese salt respectively.The zirconium and manganese salts were mixed to achieve the homogeneous sol.The sol was aged for 12 h at the room temperature for obtaining the white gel.After the gel was centrifuged,washed and then dried,the Mn-Zr-Et composite adsorbent was achieved.A batch study was conducted for investigating the defluoridation capacity of Mn-Zr-Et composite adsorbent.The results indicate that when the adsorbent concentration and initial fluoride concentration are 1.5 g·L^-1and 10 mg·L^-1 respectively,the adsorption capacity of Mn-Zr-Et composite adsorbent for fluoride ranges from 6.4-6.5 mg g^-1 at 25 ^oC at a broad pH range?2-11?.The equilibrated time is within 10 min when the initial fluoride concentrations are 10,30 and 50 mg·L^-1.The coexisting ions(i.e.HPO₄^2-and CO₃^2-)have great effects on the defluoridation capacity of Mn-Zr-Et composite when the initial concentrations of such anions are 500 mg·L^-1.Moreover,0.1 M Na2CO3 and NaOH solutions could well desorb the fluoride-containing Mn-Zr-Et composite.?3?Mn-Zr-Et composite was characterized by XRD,FTIR,FESEM,XPS,etc.Besides,the effects of pH on the concentrations of SO₄^2-,Zr⁴⁺and Mn²⁺ions in the treated fluoride solution were explored.The results show that the coordination reaction between Zr?IV?and CH₃CH₂OH may occur during the preparation of Mn-Zr-Et composite adsorbent while a large number of sulfate groups exist on the adsorbent surface.The prepared Mn-Zr-Et composite is amorphous with amorphous structure.In the fluoride adsorption process,the hydroxyl groups are involved in the reaction for adsorbing fluoride.Simultaneously,SO₄^2-ions on the adsorbent surface may have ion-exchange with fluoride ions.In addition,fluoride ions may react with the Zr-O group.The zirconium ions may not be greatly released during the fluoride adsorption and were insignificantly affected by pH.As for manganese ions,they are stably released at the initial pH range of 2-11.To sum up,the Mn-Zr-Et composite adsorbent for the defluoridation was successfully prepared.The advantages of the adsorbent include fast adsorption rate,application at wide pH range and anti-coexisting ion interference.The study has theoretical guidance for the following practical application and provides new ideas for solving the fluoride pollution in drinking water from the origin.