Removal Of Heavy Metals By Nanocomposites Derived From Sepiolite

As a kind of significant environmental pollutants,heavy metals bring great potential risk to environment and human's health.Heavy metals can be spread into wastewater by human productive activity and food chains.Hence,the treatment and supervision of heavy metals have attracted wide concern.At present,the methods to remove heavy metals in wastewater can be grouped into biological method and nonbiological method.Adsorption is widely used for its easy to operate,efficient,low-cost and no secondary pollution.In particular,nanomaterials have been garnered global attention for pollution treatment because of its strong affinity,large specific surface area and excellent sorption capability.Nanomaterials and nanotechnology are widely applied to environmental science and engineering's area.Clays are popular in adsorbents of heavy metals for its high surface area,wide range and low cost.In this work,three kinds of materials?SiO₂-Mg?OH?₂nanocomposite,SiO₂-Mg?OH?₂-Fe₃O₄nanocomposite,Sepiolite-MgO-?-Fe₂O₃ nanocomposite?derived from sepiolite were prepared for the removal of heavy metals in wastewater,and the main conclusions were as follows:?1?Removal of Cr?III?by SiO₂-Mg?OH?₂ nanocomposite derived from sepioliteremove Cr?III?in waterSiO₂-Mg?OH?₂ nanocomposite was prepared by sequential acid-base treatment of sepiolite.The magnesium ions in the structure of sepiolite were leached out by acid-treatment and transformed into Mg?OH?₂ by the addition of ammonia,leading to the formation of SiO₂-Mg?OH?₂ nanocomposite.The removal capacity of SiO₂-Mg?OH?₂ nanocomposite to Cr?III?was enhanced greatly compared to sepiolite under different pH values.The maximum amount of Cr?III?removed is 411.1 mg/g,and the residue concentration of Cr?III?was far below EPA limit after the low level Cr?III?treatment.The adsorption isotherm of SiO₂-Mg?OH?₂ to Cr?III?could be described by the Freundlich model,and the adsorption kinetics followed the pseudo-first-order model.?2?Removal of Pb?II?by SiO₂-Mg?OH?₂-Fe₃O₄ nanocompositeSiO₂-Mg?OH?₂-Fe₃O₄ nanocomposite was obtained by a microwave refux method,and the SiO₂-Mg?OH?₂ naocomposite was selected as support material.The SiO₂-Mg?OH?₂-Fe₃O₄ nanocomposite shows an excellent removal ability to Pb?II?under a wide range of pH conditions.Its maximum removal capacity to Pb?II?is 244.5mg/g,and the Pb?II?residue concentration was far below EPA standard,when it was applied in the low level Pb?II?treatment.The adsorption isotherm of SiO₂-Mg?OH?₂-Fe₃O₄ could be described by the Freundlich model,and the adsorption kinetics followed the pseudo-first-order model.Taking into its facile preparation and easy separation by magnetic method,the prepared sample has great potential application in wastewater treatment.?3?Removal of Yb?III?and Eu?III?by sepiolite-MgO-?-Fe₂O₃ magnetic nanocompositeThe nanocomposite of sepiolite-MgO-?-Fe₂O₃ was fabricated by calcination of sepiolite-Mg?OH?₂-Fe₃O₄,and the precursor was synthesized by microwave-assisted reflux method.Sepiolite-MgO-?-Fe₂O₃ posses favourable removal capacity to heavy metals under acid pH value.The maximum removal capacity of Yb?III?and Eu?III?by nanocomposite are254.2 mg/g and 253.7 mg/g,respectively.The adsorption isotherm of Sepiolite-MgO-?-Fe₂O₃ could be described by the Freundlich model,and the adsorption kinetics followed the pseudo-second-order model.Well removal capacity in acidic condition and good magnetic separation indicate the application potential of sepiolite-MgO-?-Fe₂O₃ in acid mine drainage treatment.