Selective removal of Cu versus Ni, Zn and Mn by using a new carrier in a supported liquid membrane

A study on transport, kinetic selectivity and stability in SLM operations using a new carrier, the molecule 2-hydroxy-5-dodecylbenzaldehyde (2H5DBA) in kerosene, is described. A simple transport model is derived to evaluate the mass transfer coefficient in the membrane. Finally a comparison with the di-(2-ethylhexyl) phosphoric acid (D2EHPA) carrier in kerosene is made. The SLM system was employed and tested in the removal of Cu²⁺ from wastewater by using the operating conditions obtained from L–L extraction tests. Studies on the kinetics of copper extraction by using the 2H5DBA showed that complexation reaction is very fast. Transport tests were performed at different carrier concentrations (10%, 30%, 50% (v/v)) showing the improvement of SLM performance with increasing its concentration. Operating the SLM at optimum conditions (50% (v/v) 2H5DBA concentration in kerosene, feed pH 5, strip pH 2.2) final copper concentrations in the feed and strip phases were, respectively, 2.0 and 47.0 mg L⁻¹, starting from 50 mg L⁻¹ in the feed, meaning a significant up-hill transport. The fluxes (J) were calculated by fitting the experimental data of copper concentration in the feed by an exponential equation. They were used to calculate the transport (kinetic) selectivities of Cu²⁺ SLM separation over Ni²⁺, Zn²⁺ and Mn²⁺, given by the ratio J₀(Cu)/J₀(M), where M = Ni, Zn and Mn. The values were 37.4, 48.2 and 42.1, respectively. Transport and stability tests at the optimal carrier concentration by using the 2H5DBA and the D2EHPA in kerosene were carried out to compare them in terms of flux, lifetime and mass transfer coefficients. Experimental data evidenced for 2H5DBA a lower copper flux (8.67 mmol h⁻¹ m⁻² versus 36.71 mmol h⁻¹ m⁻²), a lower lifetime (20 h versus 57 h) and lower mass transfer coefficient in the membrane (3.00 × 10⁻⁷ m s⁻¹ versus 2.00 × 10⁻⁶ m s⁻¹) but the selectivity of the separation process can overcome the disadvantages.