Research On Adsorption Mechanism Of Attapulgite For Heavy Metals

Electroplating,mining,smelting,fuel,battery and chemical industries are often associated with heavy metal pollution.Studies have shown that heavy metals have potential harm to the ecosystem due to their biological accumulation,persistence and toxicity.Therefore,the research and development of heavy metal treatment methods and technologies are of great significance to the protection of the ecological system and the healthy development of human beings.Attapulgite,a natural mineral,is widely used as an adsorbent for heavy metals due to its wide range of sources,potential cost-effectiveness and environmental protection characteristics.At present,most studies on the adsorption of heavy metals by attapulgite only focus on the modification of attapulgite without giving play to the inherent adsorption advantages of attapulgite.In this paper,the mechanism of heavy metals adsorption by attapulgite was analyzed from the micro level through the calculation of the first principle,so as to provide theoretical guidance for better use of attapulgite's adsorption effect on heavy metals in practice.The full-magnesium attapulgite model Si₁₆Mg₈O₄0?OH?₄?OH₂?₈·32H₂O has been firstly builded for optimization.On this basis,other stable models of attapulgite with different aluminum contents have been obtained by atomic substitution.The stability of attapulgite with different aluminum contents was obtained by studying the scatter plot of aluminum content and cohesive energy.Secondly,bulk phase adsorption of Al-poor attapulgite?25 at %?,Al equal to Mg attapulgite?50 at %?and Al-rich attapulgite?75 at %?on Cr,Mn,Ni,Cu,Zn,As,Cd,Sb,Hg and Pb has been studied considering both displacement and clearance forms.According to the bulk-phase adsorption energy,the adsorption effect of different heavy metals was preliminarily determined,and the mechanism of action between heavy metals and attapulgite has been deeply explored by analyzing the stable configuration,electronic state density and charge density difference after adsorption.Bader charge analysis has been carried out for different aluminum content systems,and the influence of aluminum content on heavy metal adsorption has been analyzed on the basis of that whether the outer electron of O atom is the full state in the system.Finally,based on the results of bulk-phase adsorption study,the surface adsorption performance of the 10 heavy metals mentioned above has been studied by selecting the Al-poor?25 at %?attapulgite by finding the surface model with the minimum surface energy.The corresponding surface adsorption energy has been calculated,and the visualized surface stable spatial configuration has been exploited to investigate the chemical environment after the adsorption of heavy metals.The state density analysis has been used to determine the bonding situation of atoms,and the charge density difference and Bader charge analysis have been qualitatively and quantitatively used to analyze the charge transfer case of the adsorption system,respectively.This study has found that the content of magnesium is close to that of aluminumthe in the most stable attapulgite,and the low aluminum content of attapulgite is beneficial to heavy metal adsorption in interstitial doping.When the aluminum content of attapulgite is 25 at %,it is easy to adsorb Cr,Mn,Cu,Ni,Cd and Pb,while As is the most difficult to adsorb.The adsorption system mainly relies on the bonding of heavy metals with O atoms to stabilize.When the aluminum content of attapulgite increases,the interaction between heavy metal and O atom is weakened,which will reduce adsorption effect.The surface adsorption can indicate that 25 at % attapulgite is easy to adsorb heavy metals Cr,Cu,As,Sb,while hard to adsorb Cd,Mn.