Experimental Study On Adsorption And Desorption Characteristics Of Heavy Metal Ions On Red Mud

Based on the background of the treatment of heavy metal pollution and the resource utilization of solid waste of red mud,this paper systematically analyzed the influence of single factor on the adsorption characteristics and mechanism of heavy metal ions on red mud through indoor static adsorption test,and studied the competitive adsorption characteristics and mechanism of mixed heavy metal ions on red mud.The desorption tests of three heavy metal ions on red mud were also carried out,and two adsorption-desorption models were used for fitting.Finally,the effects of red mud interlayer on the heavy metal migration process and the difference of the pollution interdicting capacity of different heavy metals were studied by the seepage test in one-dimensional soil column.The conclusions are as follows:(1)Factors such as initial pH and concentration of solution,reaction time,dosage and temperature of red mud have different degrees of influence on the adsorption of heavy metal ions on red mud.Other conditions are the same,the removal rate of heavy metal ions increases with the increase of dosage,temperature and pH of red mud.For Pb(?),Cd(?)and Cu(?)heavy metal ion solution with a concentration of 100mg/L,the optimal dose of red mud required is 1.0,1.5 and 2.0 g/L,respectively.Red mud can adsorb Pb(?),Cd(?)and Cu(?)in the solution well.When the initial pH values of Pb(?),Cd(?)and Cu(?)heavy metal ions were 4.2,5.0 and 4.0,respectively,the removal rate of heavy metal ions reached the best.(2)For the adsorption of single ions,the order of adsorption strength is Pb(?)>Cd(?)>Cu(?);Judging from the competitive adsorption of the three ions,the adsorption amount of heavy metal ions in the competitive system all decreased.According to the partition coefficient,the adsorption priorities of the three heavy metal ions are as follows:Pb(?)>Cd(?)>Cu(?).The adsorption priority degree of heavy metal ions on red mud is not only related to the properties of heavy metals themselves,but also related to the content of mineral components in red mud(such as hematite,goethite,fibronite,calcite,diaspore,quartz,diaspore,hydrosiloxalite).(3)The higher the concentration of heavy metal ions,the more significant the competitive adsorption effect between heavy metal ions,and the greater the reduction coefficient of removal rate k_r.The reduction coefficient k_r of heavy metal ion removal rate decreased with the increase of red mud dose,which indicated that increasing the red mud dose was helpful to improve the removal rate of heavy metal ions in the competitive system.(4)The adsorption-desorption of heavy metal ions has hysteresis phenomenon,and the adsorption-desorption curve has obvious nonlinear characteristics.Even after five successive dilution cycles are applied on the system,a small part of heavy metals are still desorbed.(5)The nonlinear adsorption-desorption model can better fit the adsorption-desorption test,and can reflect the influence of temperature and different heavy metal ions.The adsorption and desorption equilibrium constant of the nonlinear adsorption-desorption model also increases with the increase of temperature,indicating that the adsorption performance can be improved better with the increase of temperature.The order of nonlinearity of the adsorption-desorption curves of the three heavy metals is Cu(?)>Cd(Np)>Pb(Ang),which is opposite to the order of the adsorption strength of the three heavy metals on red mud.The weaker the adsorption capacity of heavy metals is,the closer the corresponding adsorption-desorption curves are to the non-linearity.(6)The red mud barrier layer has a great difference in the pollution intercepting capacity of the three heavy metal ions.The red mud barrier layer has a better pollution intercepting capacity of Pb(?)than Cd(?),and a better pollution intercepting capacity of Cd(?)than Cu(?).This order is consistent with the red mud adsorption order of the three heavy metal ions.It shows that the interception capacity of red mud barrier layer for three kinds of heavy metal ions is affected by its adsorption capacity for heavy metal ions.Red mud is an ideal impermeable material,which can not only play the role of impermeable,but also greatly reduce the content of heavy metal ions in soil pollutants.