Promotion of the Cupellation Method for Accurate Determination of Gold Alloy’s Karat Containing Platinum-Group Metals

Document Type : Research Article

Authors

1 Department of Chemistry, Isfahan University of Technology, Isfahan, I.R. IRAN

2 +\Institute of Standards and Industrial Research of Iran- Isfahan, I.R. IRAN

Abstract

The main standard method for gold karat determination is the cupellation method. However, this method is not sufficiently accurate to determine gold karat in the presence of insoluble Platinum–Group Metals (PGMs), such as Ir, Ru, and Rh. In this study, for the first time, a complementary method that can be used coupled with the reference cupellation method is presented for the highly accurate determination of gold karat containing PGMs. According to this method, gold metal was separated from the PGMs by dissolving parted cornets in aqua regia and then, its selective precipitation using an aqueous solution of SO2 gas as a reducing agent. The gold amount in alloys containing PGMs was determined using the suggested strategy with an excellent recovery, high accuracy (average relative error=0.12%) and precision (SD=0.6 for n=3). The optimized volume of aqueous SO2 solution was 35 mL that provides a gold recovery as high as 99.7% with enough big grain size and high purity (999.0‰). The proposed strategy was successfully used to determine the gold amount in secondary gold jewelry containing Ir, Rh, and Ru (a gold recovery of 99.9% with a relative error of 0.07 was obtained). The obtained karat was comparable with the other methods. Accordingly, the proposed method will be a promising simple and available assay for gold alloys containing PGMs, which could be used routinely in most cupellation labs all over the world.

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References

[1] Kloos D., Analysis of Gold Karat Alloys Using Proportional Counter Based Micro-EDXRF, [in] Proceedings of the Proceedings of the 24 th International Precious Metal Conference, (2000).
[2] ISO 11426:2014, Jewellery-Determination of Gold in Gold Jewellery Alloys-Cupellation Method (Fire Assay), ISO (2019).
[3] Haffty J., Riley L. B., Goss W. D., "Manual on Fire Assaying And Determination of the Noble Metals
in Geological Materials", Edited, United States Government Printing Office, Washington (1977).
[4] Raykhtsaum G., "Platinum Alloys", [in] Proceedings of the The Santa Fe Symposium on Jewelry Manufacturing Technology, 489-503 (2012).
[5] Maerz J., Platinum alloys: "Features and Benefits", [in] Proceedings of the The Santa Fe Symposium
on Jewelry Manufacturing Technology, 303-312 (2005).
[6] Raw P., "The Assaying and Refining of Gold, a Guide for the Gold Jewellery Producer", Edited, (1997).
[7] Corti B., "Assaying of Gold Jewelry-Ancient and Modern", [in] Proceedings of the The Santa Fe Symposium on Jewelry Manufacturing Technology, 49-70, (2001).
[8] Stankiewicz W., Bolibrzuch B. Marczak M., Gold and Gold Alloy Reference Materials tor XRF Analysis, Gold Bull., 31(4):119-125 (1998).
[9] ISO11596, Jewellery - Sampling of Precious Metal Alloys for and in Jewellery and Associated Products, (2008).
[10] Beamish F. E., "The Analytical Chemistry of the Noble Metals", Edited, Elsevier, (2013).
[11] Ott D., Raub C.J., Grain Sze of Gold and Gold Alloys, Gold Bull., 14(2): 69-74 (1981).
[12] McIntosh K.S., "The Systems Engineering of Automated Fire Assay Laboratories for the Analysis of the Precious Metals", University of Stellenbosch, South Africa, (2004).
[13] Rao C. Reddi G., Platinum Group Metals (PGM); Occurrence, Use and Recent Trends in their Determination, TrAC, Trends Anal. Chem., 19(9): 565-586 (2000).
[14] Syed S., Recovery of Gold from Secondary Sources—A Review, Hydrometallurgy, 115 (2012).
[15] Corti C.W., "Recovery and Refining of Gold Jewellery Scraps and Wastes", [in] Proceedings of the The Santa Fe Symposium on Jewelry Manufacturing Technology, 1-20 (2002).
[16] Beamish F., Russell J. Seath J., The Determination of Gold, Industrial & Engineering Chemistry Analytical Edition, 9(4) (1937).
Iranian Journal of Chemistry and Chemical Engineering
Volume 39, Issue 2 - Serial Number 100
March and April 2020
Pages 133-143

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