Abstract
The kinetics of the forward and backward extractions of copper(II) by the bis‐(2, 4, 4‐Trimethylpentyl)phosphonic acid process have been investigated using the single drop technique and flux (F)‐method of data treatment. The (F)‐equation for the forward extraction of Cu(II) from the sufate‐acetato medium by bis‐(2, 4, 4‐trimethylpentyl)phosphinic acid can be represented by: F~f~ (kmol m^–2^ s^–1^) = 10^–8.64^ [Cu^2+^]~(ini)~ $ [{\rm H}^+]^{-1}_{\rm (int)} $ $ [{\rm H}_2 {\rm A}_2]^{0.5}_{\rm (o)} $ [HSO~4~^–^]^1^. Analysis of this equation gives, F~f~ (kmol m^–2^ s^–1^) = 10^–4.88^ [CuHSO~4~^+^] [A^–^]. An activation energy of ca. 13.7 kJ mol^–1^ indicates that the diffusions of CuHSO~4~^+^ and A^–^ to the aqueous film of the interface (and not the chemical reaction between these two species to form CuHSO~4~.A) are rate controlling. The (F)‐equation for the backward extraction of Cu(II) from the [CuHSO~4~A.HA] complex in the organic phase by an aqueous sulfate‐acetato solution can be expressed as: F~b~ (kmol m^–2^ s^–1^) = 10^–5.68^ [CuHSO~4~A.HA]~(o)~ (1 + 10^–3.67^ [H^+^]^–1^)^–1^ $ [{\rm H}_2 {\rm A}_2]^{-0.5}_{\rm (o)} $ $ [{\rm SO}^{2-}_4]^{-1} $. Analysis of this equation results in two equations, F~b~ (kmol m^–2^ s^–1^) = 10^–9.797^ [CuHSO~4~A.HA]~(o)~ [A^–^]^–1^ [HSO~4~^–^]^–1^ and F~b~ (kmol m^–2^ s^–1^) = 10^–8.127^ [CuHSO~4~A.HA]~(o)~ [A^–^]^–1^ $ [{\rm SO}^{2-}_4]^{-1} $ at higher and lower aqueous acidities, respectively. Low activation energies (< 20 kJ mol^–1^) indicate that the stripping processes are diffusion controlling at both regions of H^+^ concentration. The value of K~ex (rate)~ (k~f~/k~b~ = 10^–2.967^) matches well with the K~ex (eq)~ (10^–3.19^) value within the experimental limitations.