Chemical degradation of trioctylamine and 1-tridecanol phase modifier in acidic sulfate media in the presence of vanadium (V)

The chemical degradation of the mixture of trioctylamine (extractant) and 1-tridecanol (phase modifier) in n-dodecane in contact with acidic aqueous sulfate solutions containing vanadium(V) has been investigated. The degradation of trioctylamine and 1-tridecanol is slow at room temperature but is significant on a scale of years. GC–MS analyses show evidence of the formation of 1-tridecanal, dioctylamine, N,N,N-octen-1-yl-dioctylamine and an unidentified degradation compound which may contain a double bond and a carboxylic acid function. The global degradation rate of trioctylamine and 1-tridecanol increases sharply when sulfuric acid concentration decreases (0.1–1 mol kg− 1 H2SO4) or when aqueous vanadium(V) concentration increases (0.02–0.1 mol kg− 1 V(V)). On the contrary, only a weak influence of trioctylamine concentration (0.2–0.5 mol kg− 1) and no significant influence of 1-tridecanol concentration (0.20–0.35 mol kg− 1) are observed. The formation of dioctylamine and N,N,N-octen-1-yl-dioctylamine arises from the presence of radicals generated by the oxidation of 1-tridecanol by vanadium(V). Several mechanisms of degradation are discussed on the basis of the identified degradation compounds.

Research Highlights
► V(V) in H2SO4 degradates trioctylamine (TOA) and tridecanol in dioctylamine and tridecanal.
► The degradation is responsible for a drop of the extraction efficiency of U(VI).
► Kinetics of degradation depends on V(V) and H2SO4 concentrations in aqueous phase.