Sorption Statics of Cr(VI), Mo(VI), W(VI), Se(IV) Oxygen Anions by Nanostructured Al₂O₃||C Composite

By the methods of thermodynamic modeling, sorption diagnostics, analysis of particle zeta-potential, and UV-Vis spectrometry the equilibrium conditions of sorption interaction of CrO₄^2–, MoO₄^2–, WO₄^2–, SeO₃^2– oxygen anions in the region of chemical stability of Al₂O₃||C composite have been analyzed. The anion sorption isotherms are shown to follow the Langmuir model for a monoenergetic sorbent. The Henry region is observed at concentrations less than 1 μM. According to the established mechanism of surface complexation, the value of anions protonation constant (K₁) in the investigated pH range determines the sorption activity of the composite to these anions. This explains the correlation found between the ratio of parameters of acid–base sites {Al–O^–}, {Al–HO⁰}, and {Al–OH₂⁺} of composite K_M(1,2) and the protonation constant of anion K₁. It is shown that the Al₂O₃||C composite concentrates from dilute solutions both cations of d-, f-elements and oxygen anions of d-elements with the value of log K_d [mL/g] > 4, thereby exhibiting the properties of collective action sorbent.