Application of Polymer Inclusion Membranes Doped with Alkylimidazole to Separation of Silver and Zinc Ions from Model Solutions and after Battery Leaching

Abstract

New materials, such as polymer inclusion membranes, can be used for water and wastewater treatment. In this paper, the selective transport of silver(I) and zinc(II) ions from nitrate solutions through the polymer inclusion membranes (PIMs), which consist of cellulose triacetate as a polymeric support, o-nitrophenyl pentyl ether as a plasticizer, and either 1-hexylimidazole (1) or 1-hexyl-2-methylimidazole (2) as an ion carrier, is studied. Both Zn(II) and Ag(I) model solutions (CM = 0.001 M, pH = 6.5), as well as the solutions after the leaching of a spent battery with a silver–zinc cell (silver-oxide battery), are tested. The results show that Zn(II) ions are effectively transported through PIMs containing either carrier, whereas Ag(I) is more easily transported through PIMs doped with (1). In the case of the leaching solution after 24 h transport, the recovery coefficients of Ag(I) and Zn(II) for PIMs doped with (1) are 86% and 90%, respectively, and for PIMs doped with (2), 47% and 94%, respectively. The influence of basicity and structure of carrier molecules on transport kinetics is discussed as well. PIMs are characterized by using an atomic force microscopy (AFM) technique.

Some Critical Remarks about Mathematical Model Used for the Description of Transport Kinetics in Polymer Inclusion Membrane Systems

“…Therefore, it should be concluded that this equation (Equation 3) is inapplicable i.e., the assumption of linearity is incorrect and the model is inadequate. It should be noted that incorrect distribution of residuals was also observed in the results presented by other authors for the transport of various substances in PIM and SLM systems [3,10,[13][14][15][16]. In order to avoid this problem, a number of researchers select initial points for which the linearity of Equation 3and normality of distribution is maintained.…”

“…In the above equation, V f denotes the volume of the feed solution (m 3 ), A-an area of membrane (cm 2 ), c f -the concentration of a substance at the given time t in the feed solution [mol/cm 3 This model is primarily applied for quick calculation of the initial flux (J i , mol/cm 2 s)-a parameter which describes the transport efficiency and corresponds to the maximum flux observed in the membrane system:…”

“…which describes the change of transported substance concentration in the stripping solution (c s ), vs. denotes the volume of the stripping solution [cm 3 ]. It should be noted that Equation 3is frequently applied for the description of membrane transport in systems in which some of the above mentioned assumption are not fulfilled.…”

“…In such systems, it cannot be assumed that the distribution constant at the feed/membrane interface is much larger than that at the membrane/stripping interface. Accordingly, the lack of model fit is particularly apparent in the ln(c f /c f,t = 0 ) vs. time plots on which the experimental points deviate from the linear model [3,10,[13][14][15][16].…”

“…A simple kinetic model equation proposed by Danesi [ 1 , 2 ] is one of the most frequently applied in description of various substance transports through supported liquid membranes (SLMs) and polymer inclusion membranes (PIMs). This equation was used for the transport description of metal cations [ 3 , 4 , 5 , 6 , 7 ], inorganic anions [ 8 ], as well as a variety of organic substances such as phenol [ 9 ], carboxylic acids [ 10 ], and herbicide [ 11 ]. This useful model can be easily derived from Fick’s first law after assuming linear concentration gradients, steady-state diffusion with fast interfacial reaction, low concentration of substance in the feed (donor) solution, and much larger distribution constant at the feed/membrane interface than that at the opposite side [ 1 ].…”