Complete digestion of refractory platinum group metals using single reaction chamber technology

Why is complete digestion of refractory PGMs a critical analytical challenge?

Platinum group metals (PGMs) such as iridium (Ir), ruthenium (Ru), and rhodium (Rh) are essential materials in high-value industrial sectors including catalysis, electronics, advanced coatings, and electrochemical technologies. Their exceptional chemical stability, particularly in oxide form, makes complete dissolution a critical and persistent challenge in analytical workflows.

In this guest article, Milestone explores how single reaction chamber (SRC) microwave digestion technology can achieve quantitative digestion (>99%) of refractory PGMs under highly aggressive conditions, while maintaining safety, robustness, and reproducibility. The discussion is based on experimental evidence obtained using the ultraWAVE 3 platform, with emphasis on practical implications for analytical laboratories.

What makes iridium, ruthenium, and rhodium so difficult to digest?

Ir, Ru, and Rh exhibit extreme resistance to chemical attack due to their noble character and strong metal-oxygen bonding in oxide phases. Conventional microwave digestion systems often struggle to reach the combination of temperature, pressure, and chemical aggressiveness required for complete dissolution, especially when using highly corrosive reagents such as hydrochloric and perchloric acids. Incomplete digestion can lead to poor recoveries, biased analytical results, and increased uncertainty, which is unacceptable for trace and ultra-trace elemental analysis.

An additional challenge is the variability in reactivity among PGMs originating from different production routes or aging histories. As a result, digestion protocols must be sufficiently robust and flexible to accommodate different material forms while minimizing procedural blanks and safety risks.

How does single reaction chamber microwave digestion address these challenges?

Single reaction chamber technology addresses these challenges by processing all samples within a single, pressurized chamber rather than in individually sealed vessels. This technology enables precise and uniform control of temperature, pressure, and atmosphere across all samples. The system is designed using chemically resistant materials that tolerate prolonged exposure to aggressive acid mixtures, ensuring consistent performance even under extreme operating conditions.

By combining high temperature and pressure with active stirring and controlled atmosphere, SRC technology enables rapid and complete dissolution of refractory PGMs, including metallic and oxide forms, while supporting higher sample masses than typically achievable with conventional systems.

Experimental overview

Representative Ir, Ru, and Rh samples, including metallic and oxide forms from different sources, were subjected to microwave-assisted acid digestion using SRC technology. For oxide materials, a preliminary reduction step was applied to convert the oxides into their metallic state prior to digestion.

Digestion efficiency was assessed using a gravimetric approach, based on the determination of residual solids following mineralization. Multiple reagent systems were evaluated to assess both primary and alternative digestion strategies, with the goal of achieving quantitative dissolution while addressing laboratory-specific constraints related to reagent handling.

What do the digestion results reveal about SRC performance?

The optimized SRC-based digestion protocol achieved complete dissolution (>99%) for Ir, Ru, and Rh in their metallic forms.

The results also highlighted that not all PGMs respond identically to the same chemical conditions. Differences in dissolution behavior were observed depending on sample origin and history, reinforcing the need for adaptable digestion strategies. In this context, alternative oxidizing systems were shown to be effective for specific sample types, providing flexibility for laboratories with restrictions on perchloric acid use or specific analytical requirements.

Importantly, the SRC platform demonstrated the ability to safely handle highly corrosive chemistries while maintaining low blanks, reproducibility, and operational durability.

What are the practical implications for analytical laboratories?

The findings presented in this experiment demonstrate that SRC microwave digestion technology provides a reliable and scalable solution for the preparation of refractory PGM samples.

Key benefits include:

• Quantitative digestion of highly inert metallic PGMs
• Effective processing of oxide materials with appropriate pre-treatment
• Support for higher sample masses, improving detection limits
• Enhanced safety when working under extreme chemical conditions
• Flexibility in reagent selection to match laboratory constraints

These capabilities make SRC technology particularly well suited for laboratories involved in high-accuracy elemental analysis of precious and strategic metals.

What conclusions can be drawn for advanced PGM sample preparation?

Achieving complete and reproducible digestion of refractory PGMs remains a critical requirement for accurate chemical analysis. Single Reaction Chamber microwave digestion technology enables quantitative dissolution of Ir, Ru, and Rh by combining extreme operating conditions with robust system design.

When paired with appropriate pre-treatment strategies for oxide materials, this approach delivers reliable performance across a wide range of PGM sample types. As a result, SRC technology represents a powerful and future-proof solution for advanced analytical laboratories dealing with the most challenging inorganic materials.

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