Bulk liquid membrane extraction of silver(I) with 2-mercaptobenzothiazole as a carrier: Kinetic approach

Abstract

The transport and separation of silver(I) ions across a bulk liquid membrane by 2-mercaptobenzothiazole (MBT) as carrier were investigated. The efficiency of Ag(I) transport was studied as a function of different parameters. The maximum of Ag(I) recovery was 85% in the presence of thiourea 0.1 M at pH 1, as complexing agent in the receiving phase, for a short extraction time of 4 h. A selective separation between Ag(I) and Mn(II) ions from equimolar mixture Ag–Cu–Mn solutions was performed. Besides, we have applied the kinetic model involving two consecutive irreversible first-order reactions to calculate the pseudo-first-order apparent membrane entrance and exit rate constants k_e and k_s, respectively. Under optimal conditions, the kinetic model curves of time dependence of silver concentrations (R) in the feed, membrane and receiving phases showed a good agreement with the experimental results. The apparent rate constants values were 6.93 × 10⁻³ min⁻¹ for k_e and 6.81 × 10⁻² min⁻¹ for k_s. The transport of silver(I) is mainly controlled by the slow reaction of the formation of Ag–MBT complex at the membrane entrance.

Keywords:

• Bulk liquid membrane
• Silver extraction
• Apparent rate constants
• 2-mercaptobenzothiazole
• Thiourea stripping agent
• Separation factor