Synergistic Adsorption Of Cadmium And Phosphate On Hydroxyl-Fe-Bentonite Complex

Hydroxy-cation-bentonite complex is an important product in geochemical process,which widely exists in natural environment, including soil, sediment and so on. The hydroxylgroups on the surface of complex have very strong surface/intersurface reactivity, which havehigh adsorption capacity towards heavy metal cations and oxyanions, so it significantlyinfluence the environmental transport. In addition, it is reported that hydroxy-cation-bentonitecomplex had prepared use hydroxyl cation, and then used as materials for controlling thepollution of metal cations and oxyanions. However, the major research was focused on theadsorption of single pollutant, but many kinds of pollutants coexist in the environment usually,so it is necessary to verify the adsorption characteristics of heavy metal cations and oxyanionscoexist on hydroxy-cation-bentonite complexes, that is significant for understanding ofenvironmental pollutants migration characteristics and improving control efficiency ofpollutions.In the first part of this dissertation, The previous investigations about the structuralcharacteristics and applications of hydroxy-cation-bentonite complex are reviewedsystematically. Then hydroxyl-ferric-bentonite complex （HyFe-Bent） as adsorbent wassynthesized by modifying bentonite wih FeCl₃and Na₂CO₃, Cadmium and Phosphate arechoosed as adsorbate. The differences between adsorption capacity of P, Cd on HyFe-Bent insingle and simultaneous system are examined, simultaneous adsorption characteristics of Pand Cd on HyFe-Bent are also investigated, and then the mechanism of simultaneousadsorption are proposed. The main original conclusions of this work as follows:（1）The structures of HyFe-Bent have been investigated through measures such as XRD,BET, FTIR and XPS analysis. The results showed that hydroxyl-ferric has been formed in thebentonite, and microstructure of the HyFe-Bent was affected by dosage of Na₂CO₃.（2）It is found that in the single adsorption of P and Cd, the adsorption capacity ofHyFe-Bent2was the best, and the pH of system increased after adsorption of P, but oppositeon Cd adsorption; the temperature was beneficial to both adsorption of P and Cd onHyFe-Bent. All the results indicated that in the single system, the adsorption of P, Cd onHyFe-Bent mainly through ligand exchange, that P, Cd can displace-OH,-H of HyFe-Bentrespectively. The kinetic studies showed that the pseudo second-order rate equation could fitthe experimental data well. （3）It is found that the adsorption capacity of P, Cd on HyFe-Bent were higher than insingle system when P and Cd coexist, showed that besides ligand exchange mechanism,surface precipitation made P and Cd showed a synergistic adsorption effect. Meanwhile, theeffect of adding order of P and Cd on adsorption capacity are investigated, it is found that thesystem of Cd adsorption after P and simultaneous adsorption system have the similar results,however, the adsorption capacity of P and Cd in system of P adsorption after Cd was lowerthan in the simultaneous adsorption; the XPS results revealed that the form of P and Cd onHyFe–Bent was different in single and simultaneous adsorption system, therefore the processof Synergistic adsorption are proposed and surface complex forms is HyFe-Bent–P–Cd.Desorption experimental results showed that the desorption quantity of P, Cd in simultaneousadsorption are less than the single, indicated that P, Cd adsorption on HyFe-Bentsimultaneously is more stable.