Abstract
The selective recovery of chromium remaining in tannery effluents after the leather tanning process is highly desirable to potentiate its reuse, simultaneously minimizing the ecotoxicity of these effluents. To the best of our knowledge, this work evaluates for the first time the ability of a chitosan-based membrane for selective recovery of chromium from a tannery wastewater by subsequent diafiltration and selective chromium desorption, envisaging their integration after tannery wastewater treatment by reverse osmosis (RO). A polyethersulfone (PES) microfiltration membrane top-coated with a chitosan layer (cs-PES MF022) was used for selective recovery of Cr(III), from concentrate streams obtained by treatment of synthetic and real tannery effluents through reverse osmosis (RO), through a diafiltration process. The diafiltration of the RO concentrates was conducted by an intermittent addition of water acidified to pH 3.6. The prepared cs-PES MF022 membranes were able to retain 97% of the total mass of Cr(III) present in the RO concentrates, from a real tannery effluent, with a selectivity of 4.2 and 5 in reference to NH4+ and Cl−, respectively, 12.9 and 14.6 in reference to K and Na, and >45 in reference to Mg, Ca, and S. Such a high selectivity is explained by the preferential adsorption of Cr(III) onto chitosan, and by the relatively high permeability of cs-PES MF022 membranes to the other ionic species. Proof of concept studies were performed to investigate the desorption of Cr(III) at pH 2 and 5.8. A higher Cr(III) desorption degree was obtained at pH 2, leading to a final solution enriched in Cr(III), which may be re-used in tannery operations, thus improving the process economy and reducing the hazardous impact of the effluents discharged by this industry.
Highlights
Leather tanning requires the use of a large variety of chemicals, such as tannins, sulphates, phenolics, surfactants, and ion salts
The concentrates of real tannery effluent was obtained by reverse osmosis (RO) treatment of a real tannery effluent supplied by TAMEG-Rouiba-SPA—a Leather Industry located in Rouiba, close to Algiers (Algeria), whereas the concentrate of a synthetic tannery effluent was obtained by RO treatment of a synthetic solution, prepared in the lab, mimicking the composition of the real effluent in terms of the inorganic content
The concentrate of a tannery synthetic effluent obtained by reverse osmosis (RO) was processed by diafiltration using the chitosan modified membranes, aiming at a selective recovery of chromium
Summary
Leather tanning requires the use of a large variety of chemicals, such as tannins, sulphates, phenolics, surfactants, and ion salts. Cr(III) is used in the form of chromium sulphate Cr2 (OH) (SO4 ) for the conversion of collagen from skin into commercial leather. This process results in the production of high wastewater volumes with appreciable chromium content [1] that increases the ecotoxicological impact of the tannery effluents [2]. Several physicochemical and biological approaches have been used to reduce the organic and inorganic content of tannery wastewaters, including coagulation/flocculation induced by specific chemical agents [3], electrocoagulation [4], solvent extraction [5], adsorption [6], aerobic or anaerobic biological treatment [7], incineration [8], chemical oxidation [9], membrane filtration [10,11,12], and via process integration, such as by combining coagulation with microfiltration [13] or electrodialysis [14,15]. Different adsorbents, such as clays [16,17], activated carbon derived from different biological [18] and non-biological materials [19] with distinct morphologies [20], and chitosan-based compounds [6,21,22,23,24,25,26] have proved to allow for an efficient capture of metals from target effluents
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
