283432 Adsorption of Lead From Aqueous Solutions by Cotton Fabrics Modified with Citric Acid
The objective of this research was to modify cotton (i.e. cellulose) fabrics for the removal and recovery of lead (Pb(II)) from aqueous solutions. Cotton fabrics were modified with 0.6 M citric acid solutions and characterized by infrared spectroscopy (ATR-FTIR) and potentiometric titrations. Also, adsorption, desorption, and kinetic experiments in batch systems were conducted.
When modifying cotton fabrics with citric acid, density of functional groups increased up to 2.47 mmol/g in comparison with the non-modified fabric that had 0.61 mmol/g. In addition, estimated equilibrium constants for the modified fabrics can be associated in part to carboxylic groups of the citric acid. The appearance of carboxylic groups on modified fabrics was also confirmed by ATR-FTIR analyses. Maximum adsorption capacity of Pb(II) on modified fabrics, estimated with Langmuir isotherm, was 73.3 y 42.3 mg/g at pH 4 y 3, respectively, whereas non-modified cotton fabrics did not adsorb Pb(II) from water. Decrement in adsorption capacity suggests that Pb(II) and H+ ions compete for the same adsorption sites. On the other hand, it was possible to desorb around 92% of Pb(II) previously adsorbed on the modified cotton with using 0.1 M HCl solutions since the chemical equilibrium is shifted. Finally, adsorption kinetics can be predicted with a pseudo-second order model.
In summary, cotton fabric treated with 0.6 M citric acid has an adsorption capacity of Pb(II) up to 3.5 times greater than the activated carbon, and the adsorbed metal can be recovered almost completely with 0.1 M HCl. These results suggest that modified cotton fabric is a highly competitive adsorbent for the treatment of metal-containing wastewater.