J. Roddy, C. F. Coleman, Sumio Arai
Apr 1, 1971
Citations
0
Influential Citations
59
Citations
Journal
Journal of Inorganic and Nuclear Chemistry
Abstract
Abstract The rate of iron(III) extraction by di(2-ethylhexyl)phosphoric acid (HDEHP, HA) in n-octane from acid perchlorate solutions, as FeA3. 3HA, is controlled by series and parallel reactions in the introduction of the first and second anion ligands, all occurring at the interface. (In the following subscripts, 1 and 2 refer to first and second anion ligands, m to extractant monomer, d and df to extractant dimer, s to interface saturation.) The measured rate [Fe] , r −d[ Fe ] [ Fe ] dt , is well fitted by the step rates (25°C) r 1m = 5·5 × 10 −4 [∑HA] 0·5 /[H + ] r 1d = 1·8 × 10 −3 [∑HA]/[H + ] for parallel reactions introducing the first anion ligand, in series with r 2 ≈ 4 × 10 −4 /[H + ] 2 r 2s = 1·5 × 10 −7 /[H + ] [Fe] r 2d = 9·0 × 10 −6 [∑HA] 1·5 /[H + ] 2 r 2df = 1·2 × 10 −5 [∑HA] 2 /[H + ] 2 for parallel reactions introducting the second anion ligand. Step 2s is zero order, while all the other steps are first order, with respect to the aqueous iron concentration. In extractions through a quiescent interface these step rates combine so that r = (r 1m + r 1d ) (r 2s + r 2d + r 2df )/∑r i and in extractions with dispersion mixing so that r = (r 1m + r 1d ) r 2 / (r 1m + r 1d + r 2 ) . The rate decreases slightly with increasing ionic strength, increases with increasing temperature (heat of activation ≈ 10–15 kcal/mole) and with conditions that increase the ionization of HA, and increases sometimes markedly with addition of proton-accepting complexers that can bypass the interface steps 1m and 1d with analogous reactions homogeneous in the aqueous phase.