Analysis of Silver and Gold in Lead and Zinc Ore Minerals Using XRF

Introduction to Lead and Zinc Processing

Based on the type of ore used as a charge, lead and zinc can be used can be produced pyrometallurgically or hydrometallurgically. Ore concentrate containing zinc, lead or both is fed in some cases after sintering into a primary smelter in the pyrometallurgical process. Lead concentrations can be 50-70%, and the sulfur content of sulfidic ores is in the range of 15-20%.

The concentration of zinc is in the range of 40 to 60%, with sulfur in the sulfidic ores in the range of 26 to 34%. A blast of oxygen or hot air is used to oxidize the sulfur present in the feed to sulfur dioxide (SO2). In traditional processes, blast furnaces are used for reduction and refining of lead compounds to produce lead bullion. This refining process removes any remaining non-lead materials such as gold, silver, bismuth, zinc, and metal oxides such as oxides of antimony, arsenic, tin, and copper.

While the gold and silver are considered to be pollutants in the refinement process, these elements can be more profitable than the primary ore elements. The accurate trace analysis for silver and gold is thus very important. Wavelength dispersive x-ray fluorescence is the quickest and best method for this analysis.

Instrument

Thermo Scientific ARL PERFORM’X series spectrometer used in this analysis was a 2500W system. This system is configured with 6 primary beam filters, 4 collimators, up to nine crystals, two detectors, helium purge and our 5GN+ Rh X-ray tube for best performance from ultra-light to heavier elements thanks to its 50 micron window. Analytical stability month after month is a new X-ray tube fitted with a low current filament.

The ARL PERFORM’X offers excellent performance and sample analysis safety. Its unique LoadSafe design includes a series of features that prevent any trouble during sample pumping and loading. Liquid cassette recognition prevents any liquid sample to be exposed to vacuum by mistake. The primary chamber is protected by vacuum collecting any loose powders in a specially designed container, easily removed and cleaned by any operator using the secutainer system.

For spectral chamber protection, the ARL PERFORM’X uses a helium shutter designed for absolute protection of your goniometer during liquid analysis under helium operation. A special X-ray tube shield provides total protection against sample breakage or liquid cell rupture in the “LoadSafe Ultra” optional configuration.

Samples and Methods

The samples were fine powders and were pressed into solid pellets without adding any binding agent. All calibration samples were synthetically created.

Results and Discussion

Table 1 shows the analytical conditions used, while Table 2 demonstrates the good sensitivity of the method and the limits of detection achieved.

Table 1. Analytical conditions.

Elements Line Crystal kV mA Counting time (s)
Ag LiF200 60 40 60
Au LiF200 50 50 200
Au LiF200 50 50 200
As LiF200 50 50 30
Cd LiF200 60 40 30
Cu LiF200 50 50 20
Fe LiF200 50 50 20
Pb LiF200 50 50 20
Zn LiF220 50 50 20

Table 2. Performance and limits of detection.

Elements SEE R2 LoD
Ag 0.01% 0.9989 NA
Au Lα 0.00% 0.99993 0.18
Au Lβ 0.00% 0.99971 0.09

Figures 1, 2 and 3 show the calibration lines obtained in the zinc and lead ore materials. With detection limits less than 0.1ppm for gold in a calibration ranging for 0.5ppm to 13ppm, the ARL PERFORM’X shows very high accuracy and sensitivity.

Figure 1. Calibration for silver in mineral.

Figure 2. Calibration for Gold in Kα in ore minerals.

Figure 3. Calibration for Gold Kβ in ore minerals ores.

Precision

Table 3 shows the repeatability of an ore sample. The same sample was studied 10 times and the results were obtained. The precision in the table illustrates the incredible stability of the ARL PERFORM’X.

Table 3. 10-run repeatability test on synthetic sample #3.

Line Unit Ag Kα g/ton Au Lβ g/ton Au Lα g/ton Cu Kα % Fe Kα % Pb Lβ % Zn Kα % As Kβ % Cd Kα %
Run 1 339.6 0.56 0.63 0.0231 5.2321 0.6174 0.967 0.0806 0.0081
Run 2 366.3 0.55 0.6 0.0231 5.1961 0.629 0.9694 0.0811 0.0079
Run 3 348.9 0.58 0.59 0.0233 5.2826 0.6047 0.9656 0.0803 0.008
Run 4 349.3 0.47 0.56 0.0233 5.2197 0.6373 0.9648 0.0811 0.0079
Run 5 363 0.47 0.62 0.0233 5.1905 0.621 0.9645 0.0807 0.0079
Run 6 353.7 0.45 0.61 0.0233 5.2367 0.6352 0.97 0.0808 0.0081
Run 7 342.4 0.49 0.58 0.0232 5.205 0.6166 0.9647 0.0805 0.008
Run 8 357.9 0.48 0.57 0.0233 5.2697 0.6283 0.9661 0.0807 0.0079
Run 9 357.8 0.64 0.63 0.023 5.1611 0.6279 0.9675 0.0806 0.008
Run 10 370.5 0.52 0.63 0.0232 5.2437 0.6288 0.9647 0.0807 0.008
Av. 354.9 0.52 0.6 0.0232 5.2237 0.6246 0.9664 0.0807 0.008
SD 10.08 0.06 0.026 0.0001 0.0371 0.0098 0.002 0.0003 0.0001
RSD% 2.84 11.51 4.37 0.46 0.71 1.57 0.21 0.31 0.99

Conclusion

The ARL PERFORM’X XRF spectrometer has an excellent sensitivity allowing the analysis of silver and gold in lead and zinc ore minerals with excellent precision and accuracy. This ability helps provide a more cost effective and profitable mining operation.

About Thermo Fisher Scientific - Elemental Analyzers

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This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers.

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