Scale-Up of Self-Regenerating Semi-Batch Adsorption Cycles through Concurrent Adsorption and Reduction of Cr(VI) on Sheep Wool

Abstract

A previous publication by our group reported that adsorption of Cr(VI) on sheep wool reached 99% when allowed a long residence time, with concurrent reduction to Cr(III). In this study, the process was scaled up by optimizing a pilot plant based on semi-batch adsorption cycles. This yielded Cr(III), which is about 300 times less toxic than Cr(VI), and can be precipitated using lime at high pH. Since the reduction step is slower than the adsorption one, an adsorption column was designed to perform semi-batch operation cycles, whereby the extended “off cycle” allows reduction to take place. Since reduction of Cr(VI) frees active sites on wool, the plant acts in lieu of in situ regeneration, accompanied by additional adsorption of Cr(VI). The results show that 97% of the column efficiency can be recovered within 24 h of “off cycle”. Wastewater from a local electroplating industry was treated by this method with high removal of Cr(VI), reaching the limit permitted by environmental standards. This study also reveals that typical concentrations of heavy metals, present in wastewater produced from electroplating, had no substantial antagonistic interference with Cr(VI) adsorption.

The Application of Sheep Wool in the Building Industry and in the Removal of Pollutants from the Environment

“…Also, following the findings from work [43], Badrelzaman et al [45] performed the optimization of the same process at a pilot plant based on semi-batch adsorption cycles. This process, including regeneration, was verified on real wastewater from an electroplating company.…”

“…Ray et al [44] The optimization of wool regeneration; designing a pilot plant. Badrelzaman et al [45] The removal of Alizarin red S (ARS) dye adsorbing on wool from wastewater; the simultaneous regeneration of ARS and removal of Cr(VI).…”

Polyaniline nanofibers, a nanostructured conducting polymer for the remediation of Methyl orange dye from aqueous solutions in fixed-bed column studies

“…These include polypyrrole nanofibers [ 28 ], activated carbon [ 30 ], modified coffee waste [ 31 ], chitosan hydrogel beads [ 32 ], magnetic iron oxide/carbon nanocomposite [ 33 ], amino-crosslinked hypromellose [ 34 ], bentonite and coffee grounds activated [ 34 , 35 ], waste ash [ 36 ], populous tree leaves [ 37 ], manganese-rich synthetic mica [ 35 ], etc . However, all of these adsorbents were explored in batch adsorption mode, which is well acknowledged to provide insufficient information for scaling up [ 38 , 39 , 40 ]. Therefore, it is imperative to develop a new, highly efficient adsorbent, and investigate its behavior in continuous flow fixed-bed column adsorption studies.…”