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Extractant Synthesis Essay

Introduction

Palladium is a good catalyst and is widely used in hydrogenation and dehydrogenation reactions. Owing to its corrosion resistance properties and easy alloying, palladium and its alloys are also used in chemical industry, medical devices and jewelry manufacture [1,2]. As Pd(II) can form a number of complexes that are soluble in organic solvents [3], solvent extraction has become an effective technique in the recovery and separation of palladium from aqueous solutions [4,5,6,7]. One coordination chemistry property of Pd(II) is that it prefers to coordinate most strongly with polarizable atoms, a fact that has pushed the development of extractants bearing donor atoms such as sulfur, phosphorus and nitrogen. These ligands are ‘soft’ bases according to the empirical Pearson classification [9]. Sulfoxides are known to be highly selective for extraction of Pd(II), and have been widely used in the extraction of this species [10,11,12]. So far, most sulfoxides reported for this purpose are petroleum or dialkyl sulfoxides. In this work, a new sulfoxide extractant bearing a heterocyclic substituent, iso-amyl benzothiazolyl sulfoxide (ABSO, 3), was prepared by the oxidation of the corresponding iso-amyl benzothiazolyl sulfide ether (2, Figure 1). Its extraction behavior towards Pd(II) was also investigated and a Pd(II)-ABSO adduct – [PdCl2(ABSO)2] – was obtained in crystal form. The crystal structure of PdCl2(ABSO)2 showed that ABSO acts as a neutral unidentate ligand coordinated with Pd(II) via the benzothiazolyl N atom; this is quite different from general Pd(II) dialkyl sulfoxide complexes in which sulfoxides are coordinated with palladium via the O or S atoms of the ligand [13,14,15,16].

Figure 1. The synthetic route of iso-amyl benzothiazolyl sulfoxide

Figure 1. The synthetic route of iso-amyl benzothiazolyl sulfoxide

Abstract

The decontamination of dilute industrial effluents is a critical challenge for decreasing the environmental impact of mining and metallurgical activities. As an alternative to conventional processes, new extractant impregnated resins (EIRs) have been synthesized by the immobilization of Cyanex 301 and Cyanex 302 in alginate capsules using two different procedures (matrix-type immobilization vs. mononuclear encapsulation). These materials have been tested for Pb(II) sorption from acidic solutions. The Langmuir equation fitted well the sorption isotherms and the maximum sorption capacities vary between 24 and 80 mg·g−1 at pH 1, depending on the type and loading of the extractant in the EIR. Uptake kinetics were controlled by the resistance to intraparticle diffusion; though both the Crank equation (intraparticle diffusion) and pseudo-second order rate equation equally fitted uptake profiles. The amount of extractant immobilized in mononuclear capsules is lower than in matrix-type beads; this leads to lower sorption capacities but slightly better mass transfer properties. The balance between the advantages and drawbacks of the different systems makes more promising matrix-type capsules. The desorption of Pb(II) is possible using 1 M HNO3 solutions: metal ions were completely desorbed. However, the probable oxidation of the extractants (conversion to oxidized forms more sensitive to pH) reduces the sorption efficiency when they are re-used. View Full-Text

Keywords: Cyanex 301; Cyanex 302; lead; uptake kinetics; sorption isotherms; desorption; matrix-encapsulation; mononuclear encapsulationCyanex 301; Cyanex 302; lead; uptake kinetics; sorption isotherms; desorption; matrix-encapsulation; mononuclear encapsulation

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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