Lead Adsorption On Goethite, Hematite And Its CD-MUSIC Model Fit

The heavy metal lead is a common pollutant in the environment..Once Lead or its component enters the body, human organs will have a negative role. In the soil, iron oxides have a strong adsorption capacity for Pb+, so the iron oxide has an important role for the control of migration and the inhibition of biological activity and toxicity of lead conversion.In this paper, to synthetic goethite, hematite as an adsorbent, we use experimental methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area for characterization. We were respectively determined the amount of charge by an Automatic potentiometric titrator and the Ca2+and Pb2+concentration of goethite and hematite adsorption by Atomic Absorption Spectrometric. Consequently, we studied Pb adsorption of goethite and hematite in different condition of pH, ion strength and the presence of Ca2+.Through CD-MUSIC model fit the experiment data.we could obtain adsorption form information and the adsorption mechanism about Pb adsorption on goethite and hematite. Through research, we could obtain the following results:Firstly,the pH of Pb adsorption on goethite and hematite is very obvious. The adsorption capacity is lower due to the adsorption rate is small when the pH of four and five. The adsorption rate increases more obvious when the pH rises. Pb2+adsorption capacity that pH is six was significantly higher than adsorption capacity that pH is four or five.Secondly,ionic strength is also a very important factor. The higher the ionic strength is, the greater the amount of Pb adsorption on goethite and hematite. That is0.1mol/L KNO3>0.05mol/L KNO3>0.01mol/L KNO3.But ionic strength is not very significant when the pH is very low. For Pb2+adsorption on goethite and hematite,Ca2+is significantly inhibited when pH is six in the presence of Ca+.It is able to occupy some adsorption sites of goethite and hematite. Compared with hematite, the amount of Pb2+adsorption on goethite is much higher.This also shows that the active surface and surfactant of goethite are numerous and large.Finally, the adsorption mechanism was studied through simulation of the experimental data about goethite and hematite from CD-MUSIC model. For goethite, the curve that is obtained by acid-base titration was fitted. The PZC is9.2and the site density of FeOH-0.5is3.45site/nm2while Fe3O-0.5is2.7site/nm2. Bidentate mononuclear structure is formed and the structure is≡(FeOH)2PbOH while the complexation constants is15.31.But for hematite, the curve that is obtained by acid-base titration was fitted. The PZC is8.5and the site density of FeOH-0.5is2.66site/nm2while Fe3O-0.5is2.36site/nm2. Bidentate mononuclear structure is also formed and the structure is≡(FeOH)2Pb+while the the complexation constants is9.3.