Preparation And Adsorption Study Of Fly Ash Magnetic Bead Composites

In recent years,with the continuous development of industry,the combustion waste fly ash generated by the coal-fired power plants and the heavy metal ions released by all kinds of nonferrous metallurgy/electroplating factory,caused seriousenvironment pollution.Therefore,the raw materialsfly ash can be modifacated via high polymer material,surface modification and surface grafting,which make it possible to selectively recycle heavy/precious metal ions.On the one hand the precious/heavy metals can be recycled,and on the other hand this methodcan achieve the goal of "using waste treat waste" and relieve pressure on the environmental pollution.In this study,the waste of thermal power plant fly ash magnetic beads(MFA)was used as raw material and the carbon layer was deposited on the surface of MFA by chemical vapor deposition method.After that,the preliminary modification of CMFA was completed by coating polydopamine layer(PDA)on the surface of carbon layer(PCMFA).Then,chitosan/fly ash magnetic bead composite absorbent(CPCMFA),thiourea grafted fly ash magnetic bead absorbent(TPCMFA)and amidine thiourea grafted fly ash magnetic bead absorbent(GPCMFA)were prepared using modified fly ash magnetic bead as the base material.They were applied to the adsorption of different kinds of heavy metal ions.CPCMFA adsorbent was prepared by sol-gel method and treated by freeze-drying with the fly ash magnetic beads coated by polydopamine and deposited on the carbon layer as the base material.Then,mixed with chitosan at a ratio of 3:1(chitosan:PCMFA)and dispersed by ultrasound.In order to evaluate the adsorption behaviors,the equilibrium state,kinetics and selectivity were studied by batch experiments.The effect of p H value on adsorption was also studied.The properties,composition,morphology and magnetism of the adsorbent beads were characterized by FT-IR,XRD,TG-DSC,SEM and VSM.The freeze-dried form adsorbent also showed higher adsorption capacity and selectivity of Ag(?),the reason for this may be the Ag(?)complexes form for linear which are more likely to form in the complicated space structure.In the p H of 4,the temperature of 30 °C under the condition that the maximum adsorption capacity of 56.82 mg/g.The experimental data can be well described by Langmuir isotherm and pseudo-second-order dynamic model.Thermodynamic data indicates that the adsorption process is spontaneous and endothermic.The results showed that the adsorption capacity of the adsorbent had no significant loss after five adsorption-desorption cycles.TPCMFA adsorbent was prepared by the base material PCMFA and thiourea(TU)was grafted on the surface of PDA which is rich in hydroxyl and amino groups TPCMFA adsorbent exhibited high adsorption capacity and high selectivity for Ag(?).By comparing the adsorption behaviors of CMFA,PCMFA and TPCMFA,it was proved that the adsorption effect after grafting thiourea was about 40% higher than that before grafting.EDS analysis proved the existence of S element in TPCMFA adsorbent,and XRD results proved the existence of substances similar to 2-thioacetoacylurea in TPCMFA adsorbent.The maximum adsorption capacity of this adsorbent can reach96.15 mg/g at 30°C on p H 5.By fitting the experimental data,the adsorption process conforms to Langmuir isotherm and pseudo-second-order kinetic model.Its thermodynamic data express that the adsorption process is a spontaneous endothermic and the higher temperature increases the adsorption efficiency significantly.The results showed that the adsorption capacity was about 70% of the new material after five adsorption-desorption cycles.The adsorption mechanism probablydominated the strong coordination by the S atoms in thiourea and Ag(?).GPCMFA adsorbent was prepared by grafted guanylthiourea(GTU)on the surface of polydopamine layer on PCMFA,which has the ability for simultaneous adsorption for Cu(?)and Pb(?).Then,the effect of p H for Cu(?)and Pb(?)of CMFA,PCMFA and GPCMFA were evaluated.CMFA and PCMFA for Cu(?)and Pb(?)has no obvious absorption effect.The maximum adsorption capacity for Cu(?)and Pb(?)of GPCMFA are 38.02 mg/g and 29.58 mg/g at 30°C on p H 3,respectively.By fitting the experimental data,the adsorption process conforms to Langmuir isotherm and pseudo-second-order kinetic model.The thermodynamic data of Cu(?)and Pb(?)show that the adsorption is a spontaneous endothermic process.