Determination of Gold, Palladium, and Platinum in Noble Metal Ores Prepared by Fire Assay

Importance of the topic

Analysis of gold, palladium, and platinum in geological samples is critical for resource evaluation, quality control, and environmental monitoring. Fire assay remains the preferred sample preparation technique for noble metal ores due to its ability to concentrate trace elements into a metallic prill. Traditional analysis by Flame Atomic Absorption Spectrometry (FAAS) requires costly consumables, flammable gases, and single‐element measurement, limiting efficiency in high‐throughput and remote laboratories. Microwave Plasma Atomic Emission Spectrometry (MP‐AES) offers a multi‐element approach, reduced operating costs, and safer operation, making it an attractive alternative for noble metal quantification.

Study Objectives and Overview

The primary goal of this study was to develop and validate a rapid, robust MP‐AES method for simultaneous determination of Au, Pd, and Pt in fire‐assayed ores. Using the Agilent 4210 MP‐AES with an integrated sampling valve, the work aimed to demonstrate linear dynamic range, sensitivity, precision, and comparability with established techniques such as FAAS and ICP‐OES.

Methodology and Instrumentation

A pulverized ore sample (30 g) was fused at 1100 °C with a specific flux to form a metallic prill. The prill was dissolved in aqua regia and diluted to a final volume for analysis. Six calibration standards (0.500–50.0 mg/L) and certified reference materials (CRMs GPP‐02 through GPP‐12) were prepared in similar matrices.

• Instrumentation

An Agilent 4210 MP‐AES fitted with a OneNeb Series 2 nebulizer, double‐pass cyclonic spray chamber, and easy‐fit torch was used. Sample introduction employed an AVS 4 four‐port switching valve and an SPS 4 autosampler. Nitrogen plasma gas was generated on‐site, eliminating external gas supplies. MP Expert software controlled nebulizer flow, viewing position, background correction, and wavelength selection. The MultiCal feature combined two emission lines per element to extend the linear range.

Results and Discussion

• Calibration and Linearity: Each element displayed a linear range from 0.500 to 50.0 mg/L with correlation coefficients >0.9999.
• Detection Limits: Method detection limits of 0.01 mg/kg for Au and Pd, and 0.02 mg/kg for Pt were achieved; limits of quantification were 0.03 mg/kg (Au, Pd) and 0.07 mg/kg (Pt).
• Precision and Stability: Repeatability was better than 1.5% RSD, and over 7 hours of continuous measurement, stability remained within 2.7% RSD.
• CRM Recoveries: Analysis of six CRMs by MP‐AES yielded recoveries within ±11% of certified values and matched results from ICP‐OES assessments.
• Real Sample Analysis: Ten ore samples were measured without further dilution, demonstrating robust performance in high‐matrix conditions and a throughput of approximately 80 seconds per sample.

Benefits and Practical Applications

This MP‐AES method delivers multi‐element capability, reduced consumable costs, and enhanced safety by using nitrogen plasma. Its integrated valve system minimizes matrix exposure and extends consumable life. Laboratories in mining, geochemical exploration, quality assurance, and field operations benefit from faster turnaround, lower operating expenses, and minimal infrastructure requirements.

Future Trends and Potential Applications

Emerging directions include expansion of MP‐AES to other trace and rare elements, integration with automated sample preparation, portable MP‐AES units for in situ analysis, and coupling with digital data management platforms. Continued improvements in plasma performance and software intelligence will further streamline high‐throughput and remote analyses.

Conclusion

The Agilent 4210 MP‐AES method provides a rapid, accurate, and cost‐effective alternative to FAAS and ICP‐OES for Au, Pd, and Pt determination in fire‐assayed ores. With excellent linearity, low detection limits, and robust long‐term stability, this approach enhances lab productivity and expands analytical capacity in diverse environments.

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