Abstract
The present investigation deals with the adsorption of chromium(III) from alkaline media, as representative of highly-caustic component solutions of nuclear tank wastes, using multiwalled carbon nanotubes. The adsorption of Cr(III) has been studied under various experimental conditions, i.e., stirring speed of the aqueous solution, initial metal and adsorbent concentrations, NaOH concentration in the aqueous solution, and temperature. The rate law indicated that chromium adsorption is well represented by the particle diffusion model, whereas the adsorption process fits with the pseudo-second order kinetic model within an exothermic setting. Equilibrium data fit to the Langmuir type-2 equilibrium isotherm in a spontaneous process. Chromium(III) can be eluted from metal-loaded nanotubes using acidic solutions, from which fine chromium(III) oxide pigment can ultimately be yielded.
Highlights
The results derived from this investigation revealed that the stirring speed had no influence on the time required for the system to reach equilibrium (Figure 1), since for every stirring speed investigated here, at 30 min of contact time between the aqueous solution and the adsorbent, 85% of the chromium(III) from the solution had been adsorbed onto the carbon nanotubes, whereas equilibrium was reached after 120 min at all stirring speeds
The stirring speed had an influence on the maximum metal uptake onto the nanotubes (Table 2). As shown from these results, a maximum chromium(III) uptake was achieved at 1000–1500 min−1, with this being attributable to the fact that at these stirring speeds, the minimum of the aqueous layer was reached and adsorption was maximized
The developed investigation was useful for the recovery of chromium(III) from alkaline conditions, the adsorption was dependent upon the NaOH concentration in the aqueous solution
Summary
Nanotechnologies are among the most important topics in today’s investigations; among them, adsorptive nanomaterials have shown their tremendous potential, and different compositions and configurations of these nanomaterials are being investigated for different applications [1,2,3,4,5,6]. These techniques have been extensively used in separation science, i.e., metal recovery from pregnant and waste solutions, the obtaining of precious and strategic metals, and the treatment of effluents which include, e.g., toxic metals. Cr(III) desorption is accomplished by the use of acidic solutions
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