Kinetics of Solvent Extraction of Copper(II) by Bis‐(2,4,4‐Trimethylpentyl)Phosphonic Acid using a Single Drop Technique

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.