Isothermal Adsorption Characteristics and Kinetics of Cr Ions onto Ettringite
The isothermal absorption properties and kinetic model of Cr (VI) and Cr (III) onto ettringite were investigated using the batch adsorption method. IR analysis was used to study the difference and mechanism of the adsorption of chromium ions with different valence states. The results show that the adsorption of Cr(III) onto ettringite at 20 °C agrees with Langmuir’s isothermal model. The ion binding stability was significantly greater than that of Cr (VI). While the adsorption of Cr(VI) onto ettringite agrees with Freundlich’s isothermal model, the D-R model fits the adsorption isotherms of two types of valence Cr (R2> O.994). It can be concluded that the adsorption of Cr (III) onto ettringite is mainly by chemical adsorption and that the adsorption of Cr (VI) onto ettringite is mainly by physical adsorption. Dynamic model fitting and model parameter analyses show that the adsorption of Cr (III) onto ettringite agrees with the pseudo second order kinetics model given by Lagergren. The formation of chemical bonds is the main factor causing the fast adsorption. Cr (VI) adsorption is mainly dominated by liquid film diffusion, and the adsorption rate is much slower than that of Cr (III) adsorption.
Key wordsettringite Cr adsorption kinetics mechanism
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