Role of Post-Exposure Time in Co(II) Sorption of Higher Concentrations on Electron Irradiated Sheep Wool

Abstract

Sorption of Co(II) was investigated on natural as well as accelerated electron beam modified sheep wool involving low and high concentrations up to 200 mmol·dm−3. The sorption experiments confirmed the dependence of the sorption capacity not only on sorbate concentration and absorbed dose of energy, but also on post-exposure time. Post-exposure heating to accelerate transformation of the wool structure was of no effect on the sorption comparing with a simple storage for a period of 100 days. Under all tested conditions, the sorption maximum was measured for Co(II) concentration of 125 mmol·dm−3 and that was assigned to form a Co(II) complex with keratin. This assumption was tested on visible spectra of mixed solutions of Arginine and Co(II) to be a simplified model of Co(II) interaction with keratin. The sorption decrease is associated with generation of cross links between macro-chains through ligands of the Co-complex. The nodal points are a hindrance to diffusion of next ions into the fibers. Also, pH variations of aqueous extracts from the wool samples depending on absorbed dose and post-exposure time indicate complexity of the structural transformation being specific for each dose applied.

Some Properties of Electron Beam-Irradiated Sheep Wool Linked to Cr(III) Sorption

“…All obtained dependencies were monotonically growing, without extremes, and mostly tended towards convex. They were dissimilar to the expected standard relations because the sorbent and sorbate concentrations were atypical, as was shown for Cu (II) [25] and Co(II) [26]. This may be due to the specific effect of EB modifying the fiber bulk, not just its surface.…”

“…The growth is the same for every dose, since representation of the S-oxidized products on the surface is similar. Concerning the time lapse effect [26], for other, especially shorter time periods, these values may change due to the transformation dynamics of S-oxidized species. However, in principle, the PZC and IEP will not be identical for the irradiated and non-irradiated samples.…”

“…For simplified modelling of the interaction of Cu(II) and Co(II) with irradiated wool, the reaction with arginine was used [25,26], since arginine is one of the most abundant amino acids in keratin [36]. In both cases, the formation of soluble complex salts has been spectrally demonstrated.…”

“…Recent works have also presented a new radiative procedure of the modification using irradiation of sheep wool by accelerated electron beam [21,22]. Such treatment improves sorption affinity towards some metal cations [23,24,25,26]. However, much information is still unknown.…”

“…In general, all authors dealing with adsorption processes, applied low adsorbate concentrations and obtained some standard adsorption isotherms. Since we found interesting anomalies using higher Cu(II) or Co(II) concentrations [25,26] under the sorption on the irradiated wool, this study is focused on further data gathering connected with Cr(III) sorption on natural and electron irradiated sheep wool when Cr(III) concentration was higher, too. Investigation in this field is worthwhile, because sheep wool is a renewable and cheap resource that is usable for environmental cleaning as well as valuable material recycling.…”