Adsorption Efficiency And Mechanism Of Modified Fe-Mn-Cu Composite Metal Oxide For Arsenic In Water

In the past decades,Arsenic?As?pollution has become an important environmental issueall over the world.It has caused great harm to the natural environment and human health.Now As pollution has threatened the development of the world because of its acute toxicity and carcinogenicity.Therefore,in order to minimize the negative effects of As pollution,it is of crucial importance to develop feasible and economical technologies for the removal of excess As from drinking water.Compared with other water treatment technologies,the adsorption process is an efficient and economical method with respect to removing As from drinking water,and many researches have been conducted on the development of advanced adsorbents for As removal.Therefore,in order to attain a high-efficiency and low-cost adsorbent for As removal from As-contaminated water,a novel Fe-Mn-Cu ternary oxide?FMCTO?was fabricated through a one-step simultaneous oxidation and co-precipitation method.This study explored the effect and the mechanism of FMCTO on arsenic removal.In addition,we also evaluated the effect of FMCTO in actual application.?1?Batch adsorption results showed that the best composition of FMCTO is in a molar ratio of Fe/Mn/Cu=3:1:1.The adsorption equilibrium of As?III?in the FMCTO system could be achieved more quickly than in the Fe-Mn binary oxide?FMBO?system,whereas the aeration of O₂could promote the removal of As by FMCTO.Most of the As???was adsorbed within 2 h,and the kinetics data were described well by the pseudo-second-order model.The Freundlich model fitted the isotherm data better than the Langmuir model,indicating chemical reactions occurred during the adsorption process.?2?The optimal As???removal was achieved at a p H range of 6.0–7.0.The coexisting anions would decrease the efficiency of As???removal by the following order:CO₃^2-<Si O₃^2-<PO₄^3-.In contrast,Ca²⁺and Mg²⁺had a certain role in promoting the reaction.A regeneration method was developed by using sodium hydroxide solution for As elution from saturated adsorbents,which permitted FMCTO to keep over 75%of its As adsorption capacity even after five adsorption regeneration cycles.When dealing with real As-contaminated water,the concentration of As???is less than 10?g/L?the maximum concentration level for arsenic in drinking water?.Overall,FMCTO is a promising adsorbent for effectively removing As from As-contaminated groundwater in engineering application.?3?The analysis results of SEM and BET indicated that FMCTO was a macroporous material with a large specific surface area of 176.00 m²/g.EDS-mapping and FTIR results showed the uniform distribution of Fe/Mn/Cu elements and numerous hydroxyl groups on the adsorbent surface,respectively.During the process of As???removal,Mn oxide in sorbent is mainly responsible for As???oxidation,while both Fe and Cu oxides are dominant for adsorbing As???and newly-formed As???.During the removal of As???by FMCTO,Mn???and·O₂^-will be produced to promote the conversion from As?III?to As?V?,and the enhanced oxidation of As?III?in a FMCTO+O₂system can be split into three pathways,including:?1?As?III?molecules are adsorbed onto the FMCTO surface firstly and then oxidized to As?V?via the electron transfer from As?III?to Mn⁴⁺and Mn³⁺.?2?The released Mn?II?ions after the consumption of Mn O₂are adsorbed on FMCTO and oxidized to form reactive intermediate Mn?III?species via catalytic oxidation.The rapid formation and turnover of Mn?III?species in a Mn?III?/Mn?II?cycle can promote the oxidation of soluble As?III?and adsorbed As?III?on the FMCTO surface.?3?Oxygen are adsorbed on the FMCTO surface and act as an electron acceptor in the“O?Cu”or“O?Mn”electron-transfer processes,thereby forming the reactive oxygen species of·O₂^-,which can efficiently oxidize soluble As?III?and adsorbed As?III?.Compared to the oxidation active sites on Mn O₂,Mn?III?intermediate products and superoxide ROS are less affected by the adsorption of As?V?.Therefore,it can be concluded that the outstanding capacity of FMCTO for the removal of As?III?can be mainly attributed to the multi-path oxidation mechanisms,which not only accelerate the oxidation rate of As?III?but also alleviate the interactive interference between As?III?oxidation and As?V?adsorption.