Heavy metals removal/recovery from industrial wastewater has become a prime concern for both economic and environmental reasons. This paper describes a comparative kinetic study of the removal/recovery of copper(II) from aqueous solutions by bulk liquid membrane using two types of coupled facilitated transport mechanisms and three carriers of different chemical nature: benzoylacetone, 8-hydroxyquinoline, and tri-n-octylamine. The results are analyzed by means of a kinetic model involving two consecutive irreversible first-order reactions (extraction and stripping). Rate constants and efficiencies of the extraction (k 1 , EE) and the stripping (k 2 , SE) reactions, and maximum fluxes through the membrane, were determined for the three carriers to compare their efficiency in the Cu(II) removal/recovery process. Counter-facilitated transport mechanism using benzoylacetone as carrier and protons as counterions led to higher maximum flux and higher extraction and stripping efficiencies due to the higher values of both the extraction and the stripping rate constants. Acceptable linear relationships between EE and k 1 , and between SE and k 2 , were found.
Abstract:The presence of heavy metals in aqueous solutions above certain limits represents a serious threat to the environment due to their toxicity and non-degradability. Thus, the removal of these metals from contaminated waters has received increasing attention during recent decades. This paper describes the removal of Cu(II) from aqueous solutions by emulsion liquid membranes, through a carrier-facilitated counter-transport mechanism, using benzoylacetone as the carrier and HCl as the stripping agent (protons as counter-ions). To optimize the Cu(II) removal process, the effect of the following operating parameters on the on the stability of the emulsion liquid membrane and on the Cu(II) removal efficiency was studied: feed pH, HCl concentration in the permeate phase, carrier and emulsifier concentration in the membrane phase, feed phase/emulsion phase and permeate phase/membrane phase volume ratios, emulsification time and speed in the primary emulsion preparation and stirring speed in the whole feed phase/emulsion phase system. Typical membrane transport parameters, such as flux and permeability, were also determined. Optimal Cu(II) removal conditions were: 5.5 feed pH, 10 kg/m 3 benzoylacetone concentration in the membrane phase, 18.250 kg/m 3 HCl concentration in the permeate phase, 50 kg/m 3 Span 80 concentration in the membrane phase, 200 rpm stirring rate, 5 min emulsification time, 2700 rpm emulsification rate, 2:1 feed:emulsion volume ratio and 1:1 permeate:membrane volume ratio. In these optimal conditions, 80.3% of Cu(II) was removed in 15 min with an apparent initial flux and permeability of 0.3384 kg·m −3 ·min −1 and 0.3208 min −1 , respectively.
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