Study On The Chloride Removal From Wastewater By Magnesium-Aluminum Layered Oxide(Mg-Al LDO)

The accumulation of chloride ions(Cl~-)will accelerate the salinization of soil,corrode industrial production pipelines,and endanger human health.Its increasing threat to the ecological environment,production and life forces researchers to continue to explore environmentally friendly and efficient removal technologies.The application of layered double hydroxide/oxide(LDHs/LDOs)in water treatment is attracting increasing attention.Firstly,magnesium-aluminum layered hydroxides(Mg-Al LDH)was prepared by co-precipitation method,and magnesium-aluminum layered oxides(Mg-Al LDO)were obtained after calcination in this paper.The basic properties and structure of materials are characterized.The synthesized Mg-Al LDO was utilized for the elimination of Cl~-in wastewater.The effects of calcination temperature,calcination time,adsorbent dosage,Cl~-initial concentration,contact time,and adsorption temperature on the Cl~-removal performance of the material was investigated.The mechanism of Cl~-removal was discussed by means of XRD,FT-IR,BET,SEM,Zeta potential,XPS and other characterization methods.Secondly,based on the Response Surface Methodology,the interactive effects of environmental factors on the Clremoval were discussed.The removal process of Cl~-was optimized,which were applied to the removal of high-concentration Cl~-in actual wastewater and to guide the practical industrial operation.The main conclusions of this paper are as follows:When the calcination temperature is 480 ℃,the calcination time is 3 h,the dosage of Mg-Al LDO is 2 g,and the contact time is 13 h,more than 97% of the Cl~-could be eliminated.The Mg-Al LDO could be regenerated and reused by calcination.The removal efficiency was greater than 90% even after 11 regeneration cycles.The removal process of Cl~-from water by Mg-Al LDO conformed to the pseudo-secondorder kinetic model and the Freundlich model.Intraparticle diffusion is the main ratecontrolling step of this adsorption process.The characterization analysis of the material before and after adsorption indicated that the reconstruction of the material hydroxide and the ion exchange between the residual NO3-and Cl~-are the reasons for the removal of Cl~-.The results of the response surface methodology show that the ion molar ratio(A)and the quadratic term of the calcination temperature(B2)have a very significant influence on the Cl~-removal ratio(P<0.0001);the interaction between the calcination time(B)and the contact time(C)affects the response value to be significant.The order of the influence degree of each factor on Cl~-removal rate is A > B > C.The optimal process for Cl~-removal by Mg-Al LDO is obtained by the fitting model optimization analysis as follows: the ion molar ratio is 5.9,the calcination temperature is 480 ℃,and the contact time is 9.2 h.The predicted value of Cl~-removal is 93.70%.The deviation between the optimization results and the verification test results is 0.82%,indicating that the predicted value is good,the model can reflect the process more accurately,and the obtained optimization process has practical guiding significance.Under the conditions of calcination temperature of 480 ℃ and contact time of 8 h,the Cl~-removal rates of Mg-Al LDO in seawater and desulfurized gypsum wastewater can reach 93.47% and 91.57% respectively,after the fourth-stage reaction.Mg-Al LDO can effectively remove the Cl~-from practical wastewater.XRD and FT-IR characterization results show that the material has restored the unique layered structure of double metal hydroxides,and also has a certain removal effect on SO42-and CO32-in actual wastewater.It can be concluded that the Mg-Al LDO has good anion removal in actual wastewater and a certain application prospect.