| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 642783 | Separation and Purification Technology | 2011 | 7 Pages |
The adsorption of inorganic anions, namely, bromate, chloride, chlorate, iodate, nitrate, perchlorate, dihydrogen phosphate, and sulfate on activated carbon was studied. The free energy of adsorption was calculated by including chemical interaction, solvation, and electrostatic attraction. Results showed that specific chemical interaction between anions and the activated carbon surface played a major role on the adsorption process. Attempt was made to correlate solute properties such as hydration number, hydration enthalpy, and free energy of hydration to the degree of adsorption. Results showed good linear relationship between the free energy of adsorption and the properties of the solutes, specifically the hydration number, the free energy of hydration and the hydration enthalpy for all anions studied with a correlation coefficient (R2) of 0.97, 0.87, and 0.86, respectively, except sulfate and dihydrogen phosphate. The results suggested that the adsorption of sulfate and dihydrogenphosphate followed mechanisms different from that of other oxyanions, which mostly are the conjugate bases of strong BrÖnsted acids. The competition between perchlorate and other anions for the activated carbon was studied as well. Among all inorganic anions studied and in the concentration range of 0.1–1.0 mM, only nitrate competed with perchlorate for adsorption. A competition model based on the Langmuirian type was adequate to describe the adsorption of oxyanions in bisolute system on activated carbon.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ The adsorption of inorganic anions, namely bromate, chlorate, chloride, iodate, nitrate, perchlorate, sulfate, and (di-hydrogen) phosphate on activated carbon F400 followed the Langmuir adsorption isotherm. ▶ The removal of bromate and chlorate was both adsorption on and reduction by F400. ▶ Specific chemical interaction played the primary role in the adsorption of inorganic anions on activated carbon F400. ▶ Among all anions studied, only nitrate showed competition adsorption with perchlorate. ▶ The change of free energy of adsorption followed the following order: ClO4− > NO3− > SO42− > H2PO4− > ClO3− ≈ BrO3− > IO3−. ▶ The competition adsorption model derived based on the Langmuir adsorption equation adequately can describe the competition in adsorption between nitrate and perchlorate.
