Kinetics of Stripping Ni(II) from the Ni‐BTMPPA Complex/BTMPPA/Kerosene System by Sulfate‐Acetato Solution. Issue 9 (14th June 2016)

• Record Type: Journal Article
• Authors: Biswas, Ranjit Kumar; Karmakar, Aneek Krishna; Rahman, Md. Saidur
• Is Part Of: International journal of chemical kinetics. Volume 48:Issue 9(2016)
• Page Start: 504
• Page End: 512
• Publication Date: 2016-06-14
• Subjects: Chemical kinetics -- Periodicals; 541.394
• DOI: 10.1002/kin.21009
• Languages: English
• ISSNs: 0538-8066

Abstract

ABSTRACT: The kinetics of stripping of Ni 2+ from a Ni‐BTMPPA complex, dissolved in a kerosene solution of BTMPPA (H2 A2, Cyanex 272), by acidic sulfate‐acetato solution, was studied using the single (falling) drop technique and flux (F) method of data treatment. The empirical flux equation at 303 K is F b (kmol/m 2 s) = 10 −4.35 [Ni 2+ ] (1+10 −3.42 [H + ] −1 ) −1 ([H2 A2 ](o) 0.5 +2.50 [H2 A2 ](o) ) −1 (1+6[SO4 2− ]) (1+3.20 [Ac − ]). Activation energy ( Ea ), entropy change in activation (Δ S ± ), and enthalpy change in activation (Δ H ± ) were measured under different experimental conditions. Based on the empirical flux equation, Ea and Δ S ±, the mechanism of Ni 2+ stripping is provided. In a low [H + ] region, the stripping reaction steps appear as [NiA + ] → Ni 2+ + A − and [Ni(HA2 )2 ](int) → [NiHA2 ] + (int) + HA2(int) − in lower and higher concentration regions of free BTMPPA, respectively, provided [SO4 2− ] and [Ac − ] are kept low. However, at higher [H + ] concentrations, the stripping is under diffusion control. With increasing [SO4 2− ] and [Ac − ], the enhancement of the rate is attributed to the attack of the Ni(II) complex by SO4 2− or HSO4 − and Ac − to form NiSO4 or NiHSO4 + and NiAc + complexes. Negative Δ S ± values indicate that the rate‐determining stripping reaction steps occur via an substitution nucleophilic, bimolecular (SN 2) mechanism.