Purification Effects And Mechanisms Of Cr(Ⅵ)Removal By LDHs Modified Maifanites

Although the maifanites are used as the common materials in field of water treatment,they are facing the problems of low adsorption capacity and the saturation adsorption when applied in the field of wastewater treatment,especially in treating the wastewater containing heavy metal.Additionally,layered double hydroxides（LDHs）has excellent adsorption ability and larger specific surface area,however it will cause the blockage problems and difficulties in separating the liquid/solid in the later process owing to its powdery state when used in practical constructed wetlands（CWs）.Hence,our research is intended to coat the LDHs on the maifanite to assemble the CWs,and carry out the study on Cr（VI）removal rates and mechanisms,in order to extend the scope of application of maifanite and LDHs and improve the Cr（VI）removal performance.Through co-precipitation method,four kinds of LDHs（ZnAl-LDHs,ZnFe-LDHs,MgAl-LDHs and MgFe-LDHs）were synthesized under alkaline condition and in-situ coated on the surface of maifanite.The prepared LDHs modified maifanites were characterized by scanning electron microscope（SEM）and energy dispersive spectroscopy（EDS）.Then,LDHs-modified and original maifanites were placed into the customized experimental columns respectively,as experimental group which were utilized to explore the purification performance of Cr（VI）with control group.After purification experiments,batch tests of isothermal adsorption,desorption and kinetic adsorption were designed to elucidate the adsorption mechanisms of LDHs-modified and original maifanites.Meanwhile,through a series of microbial experiments,including measuring enzymatic activity and EPS contents,and the high-throughput sequencing technology,the structure composition and relative abundance of microflora could be revealed in lab-scale CWs.According to the research results,the surface of maifanites became coarser with layer,flake or flocculent materials as shown in the SEM images of LDHs modified maifanites and meanwhile,the EDS data demonstrated that the chemical composition on the surface have been altered owing to the LDHs coating way,which provided some useful evidences to confirm successful coating of LDHs on the surface of maifanites.From the results of purification experiments,the Cr（VI）removal performance of all LDHs modified maifanites were superior to that of the original maifanites.Additionally,the results of isothermal adsorption tests showed that the maximum theoretical adsorption capacities of all LDHs-modified maifanites were higher than that of original maifanites,especially ZnAl-LDHs modified maifanites.Moreover,the adsorption types of all kinds of maifanites were classified into the monolayer adsorption.The results of kinetic adsorption tests displayed that the predominant adsorption type of maifanites was transferred from the weaker physical adsorption to more stable chemical adsorption at initial concentration of 1 and 4 mg?L^-1 due to the LDHs coating way.Eventually,from the results of microbial experiments,the enzymetic activities and EPS contents were improved for the simulated CWs filled with LDHs-modified maifinites.Moreover,the microbial diversities and the relative abundance of microorganisms tolerating Cr（VI）were also increased on the surface of maifanites to certain extent because of LDHs coating way.