Sorption studies of strontium on carbon nanotubes using the Box–Behnken design

摘要

Adsorption of Sr on multi-walled carbon nanotubes (MWCNTs) was investigated to explore their possible use as an efficient adsorbent for nuclear waste streams. MWCNTs were purified and oxidized with HNO_3 prior to testing adsorption. Oxidized MWCNTs were then employed in batch experiments as sorbent of Sr from aqueous solutions. The Box–Behnken experimental design was used to suitably vary the parameters of interest, i.e., temperature, initial Sr~(2+) concentration, and shaking time. Langmuir, Freundlich and Dubinin–Radushkevich models were applied to fit the adsorption isotherms. The Dubinin–Radushkevich model exhibited the best agreement. Adsorption kinetics was also studied; it was well described by a pseudo-second-order rate model. Adsorption thermodynamics was investigated in the temperature range 293–333 K; the variations of the standard free energy (ΔG°), standard enthalpy (ΔH°) and standard entropy (ΔS°) were obtained. Oxidized MWCNTs show the potential to be a promising candidate for the preconcentration and solidification of Sr from large volumes of aqueous solution.