This work deals with the removal of sulfate ions from aqueous solutions onto modified wool fibers (WFs) used as adsorbent. The esterified wool fibers (EWFs) were prepared from the esterification of the pristine raw wool fibers (RWFs) by using methanol in the presence of HCl as a catalyst. Thereafter, we characterized the modified wool fibers by using various methods, such as titration for functionalization degree calculation, Fourier transform infrared spectroscopy and thermogravimetric analysis. Further, we studied parameters affecting sulfate removal from water onto both the EWFs and the RWFs, such as solution initial pH, initial concentrations, contact time, a mass of the adsorbent and the temperature. To assess the adsorption theoretical trends of sulfate ions from water onto the EWFs adsorbent, we compared the experimental adsorption results to Langmuir, Freundlich, and Dubinin-Radushkevich models. A good agreement was found between the experimental data and those predicted by the Langmuir model, which yielded a maximum monolayer adsorption capacity of 123.08 mg g -1 . Also, the adsorption kinetic results of the sulfate ions removal from water onto the EWFs adsorbent were found to follow a pseudo-second-order model. Finally, adsorption thermodynamic parameters including Gibbs free energy ΔG°, enthalpy ΔH°, and entropy ΔS°, have been estimated and showed that the sulfate ions adsorption onto the EWFs adsorbent is spontaneous, endothermic and favorable. The overall data indicate that the EWFs have economic and environmental advantages, since their uses are not limited only to adsorption but they can also be regenerated.

The reaction of raw wool fibers (RWFs) with methanol, ethanol and n-propanol catalyzed by HCl has been found to modify carboxyl side chains. The effect of esterification of wool on its behavior toward acid dye has been studied. Esterified wool fibers (EWFs) showed an increase in acid dye affinity, and dyed esterified wool shows an increase in dye fastness to washing. The process of esterification with alcohols/hydrogen chloride caused some modification of carboxyl and other groups. The surface modification of wool fibers was determined by FTIR, modification rate of carboxyl groups and the acid dye distribution of RWFs and EWFs with various alcohols was evaluated by Datacolor.

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