EDXRF Analysis of Gold (Au) in Leaching Solution

Trace gold (Au) content can be recovered by processing different ores, slags, and tailings. The process involves grinding of the ore into a fine powder, followed by processing the resultant material through different steps in order to create slurry. Precise estimation of the gold content during leaching utilizing gold cyanidation or other liquid processing is essential to obtain optimal control over the extraction process.

Figure 1.

The availability of a fast and user-friendly technique to perform measurements enables both skilled and unskilled workers to make more frequent measurements. The NEX QC+ EDXRF analyzer from Rigaku is the ideal solution to fulfill this requirement. With proprietary filters, the NEX QC+ analyzer delivers unprecedented sensitivity and lower detection limits through direct excitation. This article demonstrates the analysis of gold in leaching solution using the NEX QC+ EDXRF analyzer.

The Rigaku NEX QC+ EDXRF Analyzer

Figure 2. The Rigaku NEX QC+ EDXRF Analyzer

Instrumentation

Model: Rigaku NEX QC+
X-ray tube: 4 W Ag-anode
Detector: SDD
Sample Type: Leaching solutions
Film: Kapton (7.5um)
Analysis Time: 100 sec
Environment: Air
Options: 6-position autosampler tray

Sample Preparation

Each sample was made by feeding 6 g of solution into a standard 32 mm XRF measurement cell and then explored directly on the NEX QC+ EDXRF analyzer.

Calibration

A set of four calibration standards assayed by AA was used to build a simple linear empirical calibration. The results are listed in Table 1. Correlation plot of gold is shown in Figure 3.

Element: Au SEE: 0.16 ppm
Units: ppm Correlation: 0.9999
Sample I.D. Assay Value Calculated Value
2 2.0 2.2
6 6.0 5.8
23 23.0 23.0
41 41.0 41.0

Figure 3.

Repeatability

Instrument repeatability or precision is detected by measuring each sample in static position for 10 repeat analyses using a measurement time of 100 seconds per analysis. The results of the analyses are listed in Table 2.

Element: Au Units: ppm
Sample Standard Value Average Value Std Dev
2 2.0 2.4 0.4
6 6.0 5.8 0.6
23 23.0 22.8 0.7
41 41.0 40.5 0.7

Detection Limit

Ten repeat analyses of a DI water sample carrying no gold were performed with the sample in static position in order to determine the standard deviation. The lower limit of detection (LLD) is set as three folds the standard deviation. The LLDs reported in Table 3 is for a measurement time of 100 seconds. The LLD is also determined for longer analysis times of 200 to 400 seconds.

Element Empirical LLD Measurement Time
Au 1.3 ppm 100 sec
Element Estimated LLD Measurement Time
Au 0.9 ppm 200 sec
0.8 ppm 300 sec
0.7 ppm 400 sec

Results

It is not required to use a purge gas like helium in this analysis. The analysis of all samples was performed in an air environment using a single measurement condition for a total measurement time of 100 seconds per sample. The samples are caustic in nature in the leaching process. The XRF measurement cells and optics are protected from the caustic environment by Kapton film thanks to its superior resistance to caustic materials. The calculated empirical detection limit was 1.3 ppm at a count time of 100 seconds. Lower detection limits can be obtained at longer count times.

Conclusion

The results demonstrate the ability of the Rigaku NEX QC+ EDXRF analyzer to measure gold content in aqueous solutions while processing gold from ores, slags or tailings. The NEX QC+ has a compact and rugged design and utilizes a touch screen interface that facilitates faster and simpler measurement when compared to conventional wet chemistry techniques, thus enabling better control of the extraction process.

This information has been sourced, reviewed and adapted from materials provided by Rigaku.

For more information on this source, please visit Rigaku.

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