| Thallium pollution in water is an important environmental issue, which poses a serious threat to human health and the environment. Recently, thallium pollution incidents frequently occurred. Stringent regulations have been proposed on the content of thallium in receiving water by governments and organizations. Unfortunately, efficient thallium removal from contaminated waters to meet such stringent regulations is still a challenging task. In view of this, it is crucial to develop efficient techniques for thallium removal from contaminated water bodies.Hydrous manganese dioxide (HMO) is an environment-friendly, readily available, chemically-stable, and thermally-stable inorganic adsorbent, which usually exhibits amphoteric sorption behaviors. HMO particles possess large accessible surface areas and strong adsoption capacities toward most heavy metals. An amorphous HMO was synthesized by NaClO oxidation and characterized by X-ray diffraction (XRD). Uptake of thallium onto HMO was evaluated in terms of effects of solution pH, competing ions, temperature, and kinetics. The experiment results indicated that the amorphous HMO exhibited strongly preferable sorption towards T1(Ⅰ) at a high speed. Unfortunately, HMO particles cannot be directly employed for practical application in fixed-bed columns or any other flow-through systems due to the excessive pressure drop resulting from its submicrometer particle sizes and the difficulties in separation.To overcome the above problems, a novel hybrid sorbent, HMO-001, was prepared by impregnating nano-HMO particles within D-001, a kind of strongly acidic cation exchanger with sulfonic groups. D-001was selected as a host material mainly because of the Donnan membrane effect which brought by fixed strongly acidic cation exchanger with sulfonic groups. The X-ray diffraction pattern and TEM image of HMO-001demonstrated that the HMO particles loaded in the pores of D-001were mainly amorphous (partlyδ-MnO2) and in nano size. The HMO amount loaded within D-001was determined as9.5(w/w)%. The adsorption behavior of T1(Ⅰ) on HMO-001was affected by the solution pH. In the absence of Ca(Ⅱ), higher pH values were more favourable for T1(Ⅰ) removal, while the T1(Ⅰ) removal efficiency was higher at lower pH values in the presence of20mM Ca(Ⅱ). XPS analysis for T1(Ⅰ)-adsorbed HMO-001samples at pH2.2and5.8explained the underlying mechanisms for T1(Ⅰ) uptake by HMO-001. In the presence of Ca(Ⅱ), the HMO-001exhibited more preferable adsorption behavior toward T1(Ⅰ) than D-001(a macroporous polystyrene cation exchanger) and Amberlite IRC748(an iminodiacetic acid chelating exchanger). The adsorption of T1(Ⅰ) onto HMO-001can be fitted with pseudo-first-order kinetic equation. The sorption of T1(Ⅰ) onto HMO-001was very quick and the time for attaining absorption equilibrium was about150min. The adsorption isotherm can be well described with the Freundlich model. The adsorption processes were spontaneous and endothermic. Moreover, the exhausted HMO-001could be regenerated by NaClO solution with an alkalinity of7.8%and an active chlorine content of5.0%. HMO-001can be repeatedly used for at least10cycles without any significant efficiency loss. The effluent history of fixed-bed columns for a synthetic T1(Ⅰ)-contained solution, a T1(Ⅰ)-contaminated industrial effluent, and a natural water as the feeding solutions proved that HMO-001is a promising sorbent for highly efficient removal of thallium from waters, in terms of both sorption capacity and sorption selectivity. |
PDF Full Text Request