Abstract
Palladium (Pd) and platinum (Pt) are extensively used as catalysts in the petrochemical and automotive industries, and due to high demand for them on the market, their recycling from spent supported catalysts is clearly needed. To assess the content of Pd and Pt in catalysts in order to establish their commercial value or to evaluate the recovery efficiency of technologies used for recycling, reliable analytical methods for determination of these elements are required. Spectrometric methods, such as inductively coupled plasma optical emission spectrometry (ICP-OES) and graphite furnace atomic absorption spectrometry (GFAAS) are powerful tools that can be employed for the determination of Pd and Pt in various sample matrices. However, these methods allow only the injection of liquid samples. In this regard, the digestion of solid sample by microwave-assisted acid extraction procedures at high pressures and temperatures is often used. In this study, a microwave acid digestion method was optimized for the extraction of Pd and Pt from spent catalysts, using a four-step program, at a maximum 200 °C. The resulting solutions were analyzed using ICP-OES, at two different wavelengths for each metal (Pd at 340.458 and 363.470 nm, and Pt at 265.945 and 214.423 nm, respectively) and using GFAAS (Pd at 247.64 nm, Pt at 265.94 nm). Five types of spent catalyst were analyzed and the standard deviations of repeatability for five parallel samples were less than predicted relative standard deviations (PRSD%) calculated using Horvitz’s equation for all the analyzed samples.
Highlights
The six platinum group metals (PGMs) offer specific physicochemical properties, having high stability, resistance to chemical agents, malleability, and being used in a variety of industries [1,2,3]
PGMs are resistant to single mineral acids, mixtures of HCl, HNO3, HClO4, and HF are usually applied for digestion
The inductively coupled plasma optical emission spectrometry (ICP-OES) and graphite furnace atomic absorption spectrometry (GFAAS) techniques were validated for the analysis of Pd and Pt in spent catalysts, demonstrating that both methods are suitable for the determination of these elements
Summary
The six platinum group metals (PGMs) (platinum, palladium, ruthenium, rhodium, osmium, and iridium) offer specific physicochemical properties, having high stability, resistance to chemical agents, malleability, and being used in a variety of industries [1,2,3]. Palladium (Pd), platinum (Pt) and rhodium (Rh) are extensively used in the automotive industry as catalysts to reduce concentration levels of harmful compounds (CO, NOx , hydrocarbons) in exhaust emissions [6]. In catalysts, these elements are dispersed on a substrate (carrier) with porous structure (ceramic or metallic), to ensure their catalytic performances [7,8,9]. Argon flow rates: Outer gas 12 L min−1 ; Intermediate gas 0.8 L min−1 ; Nebulizer gas 1 L min−1. Peristaltic pump flow rate: 1.8 mL min−1 Wavelengths.
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