Elsevier

Hydrometallurgy

Volume 175, January 2018, Pages 359-366
Hydrometallurgy

Extraction and separation of palladium(II), platinum(IV), gold(III) and rhodium(III) using piperidine-based extractants

https://doi.org/10.1016/j.hydromet.2017.12.019Get rights and content

Highlights

  • Extraction of Pd(II) from acidic media with N-alkylpiperidines is fast and efficient.

  • The best Pd(II) separation was obtained in the presence of Rh(III) from 0.1 M HCl.

  • The order of extraction ability towards examined noble metals ion from 0.1 M HCl is: Au(III) > Pd(II) ~ Pt(IV) > > Rh(III).

  • The order of extraction abaility toward examined noble metals ions from 3 M HCl : Au(III) > Pt(IV) > Pd(II) > > Rh(II).

  • Pd(II), Pt(IV), Rh(III) and gold(III) can be successfully separated in extraction-stripping process.

Abstract

Extraction of palladium(II) from hydrochloric acid media with novel piperidine-based extractants N-decylpiperidine (P-C10), N-dodecylpiperidine (P-C12), N-tetradecylpiperidine (P-C14) and N-hexadecylpiperidine (P-C16) has been investigated. Over 90% of palladium(II) from 0.1 M HCl solution can be effectively extracted with P-C12, P-C14 and P-C16 in toluene and the extraction equilibrium is achieved after 10 min. Increase in HCl concentration has a negative effect on the effectiveness of palladium(II) extraction. From among the examined stripping solutions the most effective are 0.5 M aqueous solution of ammonia and 0.1 M thiourea in 1 M HCl. The percentage of palladium(II) stripped from loaded organic phase (P-C12) reached nearly 100%. Also the selectivity of palladium(II) extraction over rhodium(III), platinum(IV) and gold(III) with the synthesized N-dodecylpiperidine (P-C12) has been investigated. The selectivity of extraction of palladium(II) over rhodium(III) from 0.1 and 3 M HCl with P-C12 was the best. Separation of palladium(II) from platinum(IV) or gold(III) is not so effective and it depends upon the acidity of aqueous solution. N-dodecylpiperidine also shows the extraction ability towards examined noble metal ions in the following order Au(III) > Pd(II) ~ Pt(IV) > > Rh(III) from 0.1 M HCl and Au(III) > Pt(IV) > Pd(II) > > Rh(III) from 3 M HCl. Palladium(II), platinum(IV) and gold(III) can be successfully separated through stripping from the loaded organic phase.

Introduction

Technological processes all over the world show relentless demand for precious metals, in particular palladium (Pd), rhodium (Rh), platinum (Pt) and gold (Au). The demand is still increasing, as these metals have been for many years used as catalysts in the organic technology processes, as boosters in motor vehicle catalytic converter systems and recently as afterburners in modern, environmentally friendly domestic furnaces installations. Besides the application in vehicle catalytic converter systems, palladium is used mainly in dentistry, jewelry and electrical engineering. Palladium has been widely used in electronic applications on account of its electrical conductivity and durability. Palladium-containing components are used in virtually every type of electronic device, from basic consumer products to complex military hardware. In addition, platinum is also used in jewelry products, in inorganic chemical, petrochemical, electrical, glass industry, dentistry, it also is a good capital investment. The world supply and demand of palladium is presented in Fig. 1. (Hagelüken, 2006, Hagelüken and Corti, 2010, Matthey, n.d, Matthey, 2016). Recovery of precious metals from spent materials is very important to replenish a gap between the demand and the limited supply from natural resources. Recycling of waste materials, like electronic scraps or spent vehicle catalytic converter systems is perfectly legitimate, not only due to the impact that the ill-managed waste may have on the environment, but also because of its profitability in view of the possibility of recovery of valuable components, including precious metals.

Currently, the recovery of PGMs from natural and spent materials is carried out using traditional pyrometallurgical or hydrometallurgical methods. Hydrometallurgical processing of waste materials has been the area of the most intensive research in the field of wet techniques for the last two decades. The advantage of the wet methods is that they are more precise, predictable and easier to control. In addition, they do not require the use of complex and expensive equipment to ensure proper temperature and process conditions. A disadvantage of hydrometallurgy is formation of harmful to the environment solutions, which should be managed and if possible, reused. Hydrometallurgical processing can be broken down to three general steps: leaching, solution concentration, separation and purification (solvent extraction, adsorption and ion exchange) as well as metal recovery. Solvent extraction in hydrometallurgical processing is a suitable method for removal of PGMs from low concentrated sources and allows their separation and purification (Bernardis et al., 2005, Cui and Zhang, 2008, Iwakuma et al., 2008). Many different extractants have been investigated and proposed for palladium(II) extraction, including alkyl derivatives of 8-hydroxyquinoline (Cote and Demopoulos, 1994), hydroxyoximes and ketoximes (Cleare et al., 1981, Rane and Venugopal, 2006, Shen and Xue, 2007, Wisniewski and Szymanowski, 1996, Nguyen et al., 2016), dialkyl sulphides and sulphoxides (Pan and Zhang, 2009, Pan et al., 2008, Preston and du Preez, 2002, Zhu et al., 2006), organophosphorus extractants (Gupta and Singh, 2013, Men'shikov et al., 2009, Zhidkova et al., 2009), various kind of amide derivatives (Anpilogova et al., 2014, Huang et al., 2015, Ortet and Paiva, 2015, Paiva et al., 2014, Regel-Rosocka et al., 2007), and phosphonium ionic liquids (Cieszynska and Wisniewski, 2010, Cieszynska and Wisniewski, 2011, Cieszynska and Wisniewski, 2012). Also hydrophobic amines and quaternary ammonium salts have been used as extractants for recovery and separation of palladium ions. Extraction properties of amine depend on their structure and the type of substituent. The ability of simple amines to extract metal complexes with nitrates and halides increases in the order: primary < secondary < tertiary < quaternary (Belova et al., 2007, Lee et al., 2009, Najafi et al., 2015, Nguyen et al., 2015, Rovira et al., 1998, Swain et al., 2010). It is supposed that the heterocyclic amines, like N-alkylpiperidine, should exhibit comparable or better extraction properties of metal ions such as palladium(II), platinum(IV) and rhodium(III) than simple amines.

Looking for an extractant capable of fast extraction of palladium ions, we proposed to synthesize and test N-alkylpiperidines: N-decylpiperidine (P-C10), N-dodecylpiperidine (P-C12), N-tetradecylpiperidine (P-C14) and N-hexadecylpiperidine (P-C16). It is the aim of the work to establish the extraction abilities of the synthesized N-alkylpiperidines (P-C10, P-C12, P-C14 and P-C16) to extract palladium(II) from hydrochloric acid solutions of various concentrations. The selectivity of palladium(II) extraction over rhodium(III), platinum(IV) and gold(III) with the synthesized N-dodecylpiperidine (P-C12), in the presence of toluene, has been investigated.

Section snippets

Reagents

Commercial palladium chloride PdCl2 (99%, Avantor Performance Materials Poland S.A., Poland), platinum chloride PtCl4 (99%, Avantor Performance Materials Poland S.A., Poland), rhodium chloride RhCl3 (98%, Sigma-Aldrich, Poland), gold chloride AuCl3 (99%, Sigma-Aldrich, Poland) hydrochloric acid (analytically pure, 35–38%, Chempur, Poland), sulfuric acid (analytically pure, 95%, Chempur, Poland), nitric acid (analytically pure, 65%, Avantor Performance Materials Poland S.A., Poland), ammonium

Effect of contact time and HCl concentration

The effect of contact time on the palladium(II) extraction was studied by contacting the aqueous feed containing 1 mM Pd(II) in 0.1 M HCl with 2 mM P-C10, P-C12, P-C14 and P-C16 in the presence of toluene. The transfer of palladium(II) to N-alkylpiperidines examined as the organic phase was very fast. About 5 min was necessary to achieve the equilibrium of palladium(II) extraction, which is a great advantage of the examined reagents (Fig. 3). The efficiency of palladium(II) extraction with the

Conclusions

Four N-alkylpiperidines (P-C10, P-C12, P-C14 and P-C16) have been synthesized and their ability to extract palladium(II) from hydrochloric acid solutions was studied. The results presented in this paper prove that N-alkylpiperidines can be used as extractants for the removal of palladium ions from chloride media. The efficiency of palladium(II) extraction depends on HCl concentration, extractant concentration, type of extractant diluent, metal concentration and contact time of the phases. The

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