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.

Functionalized fibers, especially polyacrylonitrile fibers (PANF), have attracted wide interest as an effective and economical material for environment and water protection. In this study, polyacrylonitrile fibers modified with hydroxylamine hydrochloride were used as an adsorbent to remove hexavalent chromium ions from aqueous solutions. The novelty of the present study compared to the literature is the functionalization of polyacrylonitrile fibers surface by optimizing cost and energy while achieving a yield fast removal rate and high adsorption capacity of hexavalent chromium from aqueous solutions. The amidoximated polyacrylonitrile fibers were characterized using Fourier Transform InfraRed spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The results confirmed the success of polyacrylonitrile fibers modification. The adsorption capacity was evaluated by investigating the effect of initial pH solution ranging from 2.0 to 7.0, the adsorbent dose varied from 0.05 to 0.25 g, the initial Cr (VI) concentration range was (5–70 mg g−1), the temperature varied from 5 to 60°C, and the contact time ranged from 0 to 180 min. We have used the Langmuir and Freundlich adsorption models to describe the equilibrium sorption data. The maximum adsorption capacity estimated using the Langmuir model reached 32. 57 mg g−1 under optimal conditions. The thermodynamic parameters (ΔG, ΔH, and ΔS) were also determined. In addition, the adsorbent showed a desorption rate of Cr (VI) up to 92% with 0.5 mol of NaOH, which can be reused for three adsorption–desorption cycles. The overall data showed the efficiency of amidoximated polyacrylonitrile fibers in removing Cr (VI) from aqueous solutions. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13146, 2019

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Amidoximated polyacrylonitrile fibers (AO-PANF) was synthesized using hydroxylamine chelating agent to prepare an effective adsorbent for heavy metal and dyes removal. This study is the continuation of an earlier study and focuses on the characterization of the adsorbent. The thermal properties of adsorbent were evaluated using TGA and DSC analysis. The mechanical properties of the adsorbent were also been investigated. Characterization results reveal an improvement of thermal stabilities due to the modification process using hydroxylamine chelating agent. However, a reduction in mechanical properties was showed.