Adsorption Of Heavy Metal Ions By Modified PVA Material With Thiourea Compounds

Currently,with the development of society,it is one of the acknowledged industrial pollution that heavy metal waste is harmful from mine,smelt,plating and chemical industry.So recycling has become one of the focus.Sorption technique is attracting more attentions to the recovery of precious metals due to its advantages of high efficiency in detoxifying effluents,low operating cost and no secondary pollution causing.In this paper,three kinds of modified polymer adsorbents,TU-PVA,TU-PVA/PAA and Cu(II)-IIGPM were prepared by chemical grafting method using polyvinyl alcohol as base material and researched to offer an approach to the recovery of metals and to the removal of heavy metal pollutants from industrial waste water containing Ag(?)and Cu(?)ions.This thesis consists of the following parts:TU-PVA adsorbent is prepared by using polyvinyl alcohol(PVA)as substrate,using thiourea(TU)containing S,N atom,adding crosslinking agent to obtain TU-PVA.After confirming optimal conditions of preparing the TU-PVA with optimum selectivity properties through the orthogonal experiment,the research showed that the adsorption rate can reach up to 98.8% when ?(PVA)=10.0%,C(TU)=1.8 mol·L-1,C(GA)=2.56 mol·L-1 and crosslinking time=12 h.the preliminary study of binding mechanism between active groups of TU-PVA was carried out by implementing the infrared characterisation.Additionally,loose and transparent porous structure shown on the material surface was observed by using the electron microscopy(SEM)to characterise the surface morphology of the adsorbent.After adsorption of Ag(?)ions,the surface was more compact and the pores became smaller,and the EDS spectrum show that the silver content was as high as 13.61%.X-ray diffraction(XRD)results indicate that Ag(?)is in the form of silver sulfide crystal after adsorption.TGA thermogravimetric analysis demonstate that the stability of the material is better.The adsorption capacity of Ag(?)ions before and after modification was studied.The results illustrate that the maximum adsorption capacity of Ag(?)ions was 66.93 mg·g-1,and the whole process of Ag(?)ions was in accordance with the second order kinetic equation,and The equation of adsorption at room temperature conforms to the Langumir isotherm,which belongs to the monolayer adsorption.The results of adsorption and reusabilitystate clearly that TU-PVA has good selectivity for Ag(?)ions and reusability,and its selective adsorption mechanism is mainly determined by the coordination between TU-PVA and Ag,and a few of them are adsorbed by electrostatic action.The main characteristic of TU-PVA/PAA adsorbent material is the blends of Polyvinyl alcohol(PVA)and Polyacrylic acid(PAA),i.e.PVA/PAA,and treated as the substrate.The method of producing TU-PVA/PAA material is called chemical modification method.The technical condition can be made sure by considering the Ag(?)adsorption capability as standards,the results show the optimal conditions were m(PVA):m(PAA)=5.5:9,CGA=2.0mol·L-1,?(PVA)=10%,and CTU=1.8 mol·L-1.The results of FT-IR,SEM,XRD and XPS indicated that the primary hydroxyl(-OH)on PVA and(-NH2)on thiourea were bonded,it indicated that thiourea was successfully on the PVA,and its material surface has a loose and transparent porous structure;The results of XRD analysis show that it appears characteristic diffraction peak of Ag2 S when adsorbed Ag(?),which can explain its adsorption mechanism;TGA analysis shows the stability of the material.The adsorption performances are investigated on Ag(?)by the adsorbent,the results showed that the adsorption capacity of TU-PVA/PAA increased with the increase of temperature,and the adsorption capacity of Ag(?)was 31.28 mg·g-1 better than that of PVA(4.98 mg·g-1).the model of adsorption is fitted to Freundlich equation that 1/n<1 indicated TU-PVA/PAA adsorbed Ag(?)ions easily,and the whole adsorption processes for Ag(?)ions are according with second-order kinetic equation.The study of selective adsorption indicates that TU-PVA/PAA have good selectivity for Ag(?)ions and its adsorption mechanism is mainly coordination.It can be seen that the process is an endothermic process and the adsorption process is controlled by chemical adsorption.Cu(?)-IIGPM was prepared with Cu(?)as template and glutaraldehyde(GA)as crosslinker and PVA/GTU blend as film forming substrate.The technical condition can bemade sure by considering the Cu(?)adsorption capability as standards,the results show the optimal conditions were the mass concentration of PVA for 10%,the concentation of GTU for 1.0 mmol,GA for 0.056 mol·L-1 and the concentation of Cu(?)for 1.25 g·L-1.The results of FTIR show that the reactive groups of-NH2,C=N and C=S react with metal copper ions in guanylthiourea,and then the deformation vibration peaks of-SH appear at 2358 cm-1.SEM spectrogram analysis results indicate that the imprinted material produced obvious gully and the specific surface area increased after metal ion elution;XRD spectra analysis indicates that the exist of copper.The adsorptive performances are investigated on Cu(?)by the adsorbent material,the results show that the maximum of adsorption capacity for Cu(?)ions are 666.7mg·g-1.Adsorption at room temperature is in accordance with Freundlich isothermal curve,and 1/n<1,indicating that the membrane is easy to adsorb Cu(?)ions,the whole adsorption process of Cu(?)ions conforms to the second order kinetic equation.Selective adsorption studies show that Cu(?)-IIGPM has a good selectivity for Cu(?)ions.