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Issue 8, 2018
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Development of a general acid method for the digestion of gold ore samples together with a comparison of extraction solvents for gold and determination by microwave-induced plasma-atomic emission spectrometry (MIP-AES)

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Abstract

In this paper, we explore a variety of aqueous digestion techniques for the determination of gold, in a wide variety of mineral matrices. Acid digestion methods, based upon modified aqua regia in which a larger proportion of nitric acid (5 : 1 HNO3 : HCl) is involved, competes effectively with fire assay to deliver accurate and precise values for gold in a fraction of the time. Using this ratio of acids, simple sand-bath digestions deliver recoveries of 95 to 98% of gold certified reference values, after a digestion time of approximately 35 minutes. Focused infrared digestions, however, take only 15 minutes, and deliver higher recoveries, in the range of 95 to 104% of gold reference values. An ultrasonic digestion with 1,3-dibromo-5,5-dimethylhydantoin acting as a source of bromine, delivered mediocre recoveries of gold. Gold determinations were conducted using inductively coupled plasma-mass spectrometry (ICP-MS). Solvent extraction of gold from digestion solutions effectively preconcentrate gold and significantly reduces interference from major elements, except for those samples containing high concentrations of iron. The use of 2-octanone as extraction solvent exhibited greater sensitivity than the use of the conventional solvent, methyl isobutyl ketone (MIBK). Although 2-ethylhexanol was also effective at extracting gold, its lengthy time for phase separation and memory effects, which increased wash-in and wash-out times, made it a less attractive extraction medium. For solvent extraction methods, microwave induced plasma-atomic emission spectrometry (MP-AES) was used for the determination of gold.

Graphical abstract: Development of a general acid method for the digestion of gold ore samples together with a comparison of extraction solvents for gold and determination by microwave-induced plasma-atomic emission spectrometry (MIP-AES)

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Publication details

The article was received on 01 May 2018, accepted on 29 Jun 2018 and first published on 29 Jun 2018


Article type: Paper
DOI: 10.1039/C8JA00136G
Citation: J. Anal. At. Spectrom., 2018,33, 1336-1344
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    Development of a general acid method for the digestion of gold ore samples together with a comparison of extraction solvents for gold and determination by microwave-induced plasma-atomic emission spectrometry (MIP-AES)

    W. Helmeczi, E. Helmeczi, L. A. Baker, Y. Wang and I. D. Brindle, J. Anal. At. Spectrom., 2018, 33, 1336
    DOI: 10.1039/C8JA00136G

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