Adsorption Of As(?) And Cr(?) On Modified Lanthanide And Cerium Rare Earth Nanomaterials

With the rapid development of modern industry,the treatment of heavy metal pollution in water has become the focus of the world.New rare earth materials La-3and Ce-Mn@9CNTs were prepared to removed As???and Cr???.The chemical composition and morphology of the La-3 and Ce-Mn@9CNTs were analyzed by a series of characterizations and the effects of various factors on the adsorption of As???and Cr???on La-3 and Ce-Mn@9CNTs were investigated.In addition,the adsorption mechanism of As???and Cr???was revealed by adsorption kinetics,adsorption isotherm and adsorption thermodynamics and the following conclusions are drawn.:La-3 and Ce-Mn@9CNTs were prepared by coprecipitation.XRD showed that La-3 was consisted of pure La₂O₃,and the peak of Ce-Mn@9CNTs indicated that MnO₂ was amorphous.SEM showed that La-3 was a disc-like nanoparticle and Ce-Mn@9CNTs consisted of CNTs covered with small flocs.La-3 and Ce-Mn@9CNTs possessed typical mesoporous structures with the specific surface areas of 19.0 and 242.1 m²/g respectively.Results showed that the optimum pH for As???adsorption by La-3 was between5 and 9.The removal rate of As???by Ce-Mn@9CNTs remained between 62.1%and 74.4%,rarely affected by pH.The adsorption processes of As???by La-3 and Ce-Mn@9CNTs were inner layer adsorption.The removal efficiency of Cr???adsorpted by La-3 and Ce-Mn@9CNTs exhibited higher under acidic conditions,they reached 80.2%and 87.4%respectively when the pH was 3.OH^-competed with Cr???for adsorption sites,resulting in a sharp decrease in Cr???removal efficiency under alkaline conditions.The pseudo-second-order kinetics model can better simulate the adsorption of As???and Cr???on La-3 and Ce-Mn@9CNTs,which meaned that they were chemical adsorption processes.Besides,they also conformed to Langmuir adsorption isotherm model,indicating that the adsorption were single layer adsorption on uniform interfaces.The adsorption thermodynamics showed that the adsorption of As???and Cr???by La-3 and Ce-Mn@9CNTs were spontaneous endothermic reaction.The removal of As???by La-3 mainly due to the formation of monodentate or bidentate complexes by the reaction of La-OH on La-3 surface with As???.The adsorption of As???by Ce-Mn@9CNTs existed redox effect which As???was oxidized to easily adsorbed As?V?by Ce?IV?,Mn?IV?and Mn???on the surface of Ce-Mn@9CNTs.As a result of the dissolution of manganese oxides,part of Mn?II?and As?V?were released into the solution again and finally re-adsorbed.The mechanism of the Cr???removal by La-3 and Ce-Mn@9CNTs can be summarized as follows:under acidic conditions,the positively charged adsorbents binded to the negatively charged Cr???by electrostatic interaction.In addition,the presence of-OH on the surface of La-3 and Ce-Mn@9CNTs participated in the Cr???adsorption process.Part of M-OH on the surface of adsorbent was replaced by Cr???,which formed Cr-O bond and thus removed Cr???from solution.