Lead (II) extraction by polymer inclusion membranes using Aliquat 336 as a mobile carrier
Polymeric membranes used for the selective transport and separation of metal species have emerged in recent years. In this work, the extraction and transport of Pb(II) in polymeric membranes (PM) using Tricapryl-methylammonium chloride (Aliquat 336) as a mobile carrier has been investigated. The optimum conditions of liquid - liquid extraction were determined. The liquid - liquid extraction tests showed a maximum extraction when the agitation time was greater than eight minutes. A good elimination of lead (extraction efficiency 80% to 94%) was observed. A membrane was prepared consisting of cellulose triacetate (CTA) modified by Aliquat 336 incorporated into the polymer as carrier; tris(2-ethylhexyl) phosphate (TEHP) was included as a hydrophobic plasticizer. The membrane polymer + plasticizer + carrier was characterized using chemical techniques as well as Fourier Transform Infrared spectroscopy (FTIR). The metal concentrations were determined by collecting aliquots at different time intervals from both the feed and strip solutions; these samples were analyzed with an atomic absorption spectrophotometer. Thickness (10 to 20 μm) and water content values showed that carrier inclusion in the CTA polymer resulted in a homogeneous and hydrophobic polymer inclusion membrane. The CTA polymerization process in the presence of carrier and plasticizer should cause changes in the intermolecular interaction of CTA chains. However, no signs for new chemical bonds between CTA, Aliquat 336 and TEHP using FTIR spectroscopy were observed. In transport experiments, the trans-membrane flux increased with increasing carrier concentration, reaching a limiting value at concentrations greater than 10‐3 M. The optimum values for the other fundamental parameters (metal concentration and pH) were determined; pH values in the range 1 ≤ pH ≤ 2 were shown to be the best conditions for maximum efficiency in the studied systems. Our results indicate that facilitated transport through plasticized membranes is an attractive and effective way to solve the long-standing problem of membrane stability, while improving the permeability to metal ions.