Separation and recovery of palladium from spent automobile catalyst dissolver solution using dithiodiglycolamide encapsulated polymeric beads Krishan Kant Singh a , Ritesh Ruhela b, *, Amrita Das b , Manmohan Kumar a, **, Ajoy K. Singh b , Rajendra C. Hubli b , Parma N. Bajaj a a Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India b Materials Processing Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India ARTICLE INFO Article history: Received 20 August 2014 Accepted 3 November 2014 Available online 29 November 2014 Keywords: Palladium Spent automobile catalyst DTDGA Sorption ABSTRACT Palladium selective ligand, N,N,N 0 ,N 0 -tetra-(2-ethylhexyl)-dithiodiglycolamide (DTDGA), was encapsu- lated in polymeric composite beads under simple laboratory conditions. The composite beads were evaluated for separation and recovery of palladium from simulated spent automobile catalyst dissolver (SSACD) solution. Batch extraction studies were carried out to understand the influence of various parameters on the sorption behavior of palladium. The beads showed maximum uptake of Pd at 3.0 M HCl. Pd sorption kinetics is found to be fast, and the kinetics data fit well in to the pseudo second-order equation model for the sorption of palladium ions onto the composite beads. Different sorption isotherm models were applied to the experimental data. Equilibrium data are represented well by the Langmuir isotherm equation, with a monolayer sorption capacity of 1.37mg/g for the swollen beads. The process mechanism is found to be complex, consisting of both intraparticle diffusion and film diffusion. More than 99% of palladium was back extracted in single contact using 0.01 M thiourea in 0.1 M HCl. Batch extraction studies with SSACD solution showed negligible uptake of Fe, Cr, Ni and Pt thus showing very high selectivity and extractability of the composite beads for palladium. ã 2014 Elsevier Ltd. All rights reserved. Introduction Palladium is currently finding widespread usage in several advanced technological applications such as electronics, fuel cells, hydrogen storage materials, catalysts (in automotive catalytic converters, oil refining and synthetic organic chemistry), etc. [1]. The natural abundance of palladium in the earth crust is very low and the present deposits will not be enough to meet its growing demand in near future, thereby making it one of the critical raw materials [2] . This has necessitated exploring the options of the separation and recovery of palladium from secondary resources, such as spent catalyst (e.g., originating from automobile and chemical processing industries), high level waste (HLW) solutions (generating from reprocessing of spent nuclear fuel), etc. While the use of Pd recovered from HLW solution will have some reservations in public domain, those recovered from spent catalyst will have no such issues. In this regard separation and recovery of palladium from the spent catalysts is attempted worldwide [3] . Liquid–liquid extraction have been considered as a promis- ing process for separating palladium from leach aqueous solutions (e.g., chloride leach liquors) of the spent catalyst, with high efficiency and selectivity [4,5]. Several extractants, namely, dialkylsulfoxides [6], 8-hydroxyquinoline [7] , dioctyl- sulfides [8], pyridine carboxamides [9], Cyphos 1 IL-101 [10] , and bis-(2,4,4-trimethylpentyl)-phosphinodithioic acid [11] ,N,N, N 0 ,N 0 -tetraoctyl-thiodiglycolamide (TOTDGA) [12] have been explored for the separation of Pd from HCl medium. Recently, we have also reported a novel ‘S’ donor ligand, namely, N,N,N 0 ,N 0 - tetra-(2-ethylhexyl)dithiodiglycolamide (DTDGA) [13], which has shown its remarkable extractability and selectivity for palladium over other metal ions present in nitric acid medium. The chelation through more than one donor sites of thio-etheric sulfur and amidic moiety, placed appropriately in the ligand, attributes to its high selectivity and extractability for palladium [14]. Since DTDGA molecule possess two thio-etheric ‘S’ atoms * Corresponding author. Tel.: +91 22 25592605. ** Corresponding author. Tel.: +9122 25593994; fax: +91 22 25505151. E-mail addresses: riteshr@barc.gov.in (R. Ruhela), manmoku@barc.gov.in (M. Kumar). http://dx.doi.org/10.1016/j.jece.2014.11.002 2213-3437/ ã 2014 Elsevier Ltd. All rights reserved. Journal of Environmental Chemical Engineering 3 (2015) 95–103 Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece