Sorptive Removal Of Lead, Propranolol And Dissolved Organic Matter From Water Using Modified Attapulgites

It is noteworthy that there are large high-quality reserves of attapulgite clay in China. Attapulgite is commonly used as sorbents for removing heavy metal ions and organic cationic contaminants, owing to its large specific surface area, cation exchange capacity, and the permanent negative charges on its surface resulted from the isomorphic substitutions in the tetrahedral layer. Nevertheless, Attapulgite has low affinity to negatively charged or neutral contaminants, and the non-selective sorption of metal ions on attapulgite is usually affected by the coexisting cations to a large extent. Moreover, there are some impurities in the natural attapulgite. In this study, the natural attapulgite was modified by different ways to improve the sorption capacity of different contaminants, and the structure and surface of the materials were characterized. The sorption behaviour and possible mechanisms of the modified attapulgites for the four contaminants were also studied. The main results obtained are as follows:(1) The natural attapulgite was activated by dilute hydrochloric acid and further functionalized by the amino group of ethylenediamine. The sorption of aqueous Pb(Ⅱ) on the as-prepared sorbent was evaluated by batch experiments. Results indicated that solution pH and sorbent dosage had significant effect on Pb(Ⅱ) sorption, but the ionic strength and humic acid has no obvious effect. The sorption kinetics were adequately described by the pseudo-second order kinetic equation while the sorption isotherms followed Dubinin-Radushkevich equation. Furthermore, the sorption ability of the modified attapulgite for Pb(Ⅱ) was higher than that of ATP due to the stable coordination bond between lead and the amino groups of the modified attapulgite through van der Waals force. Besides, EMATP has a good selectivity for Pb(Ⅱ), and the lead loaded EMATP can be regenerated easily by acid treatment. (2) Different attapulgite modification methods had been used and the acid-activated attapulgite was the most efficient sorbent of all to remove β-blocker propranolol from aqueous solutions. Results indicated that solution pH, ionic strength, adsorbent dosage, and humic acid had significant effects on propranolol adsorption. The adsorption process followed the pseudo-second order equation well and the adsorption data fitted well with the Langmuir isotherm equations. The adsorption of propranolol on acid-activated attapulgite may be mainly attributed to non-electrostatic surface complexation, electrostatic interactions, and ion exchange, and the sorbed propranolol molecules are on the external surface. The results indicate acid-activated attapulgite has potential value in the removal of propranolol from sewage and natural waters in engineering application.(3) Chitosan-coated attapulgite (CCATP) was prepared and selected for removing the organic pollutant tannic acid (TA) and humic acid (HA) from aqueous solution. Batch sorption tests indicated that CCATP exhibited higher sorption affinity towards aqueous TA and HA with a higher sorption capacity than ATP. The sorption isotherms of TA and HA onto CCATP both fitted the Freundlich model well, implying that sorption process was heterogeneous. The sorption process of TA and HA onto CCATP could be well described by the pseudo-second-order kinetic equation. The sorption of TA and HA onto CCATP was found to be strongly dependent on pH and ionic strength. The sorption of TA onto CCATP was a spontaneous and endothermic process. The sorption of TA can not be merely attributed to electrostatic interaction, and the hydrogen bonding as well as van der Waals interactions are also formed between TA and CCATP. The sorption of HA can be mainly attributed to electrostatic interaction between HA and CCATP. The TA loaded CCATP can be regenerated easily by acid treatment. The HA loaded CCATP can be regenerated in alkaline solution. The results indicate that the regenerated CCATP can effectively remove TA and HA from water.In summary, the modified attapulgites can effectively remove lead, propranolol, tannic acid and humic acid. The results of this study can be a reference for related academic research and can also be used to develop related sorbents for water treatment industry.