Gold Processing

Application Note EDXRF1299

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The at-line analysis of gold in impregnated stripping solutions during the electrowinning process is demonstrated.


Gold ore processors commonly utilize the cyanide leaching technique to recover trace gold content. After the gold is leached out of the ore, it is typically absorbed onto activated carbon in processes such as Carbon-in-Pulp (CIP), Carbon-in-Leach (CIL), or Carbon Column (CC). Once absorbed, the gold is stripped from the Carbon and the impregnated stripping solution fed into the electrowinning process where the gold is recovered by electrolysis. By measuring the gold in the stripping solution at-line, operators can quickly and easily determine when the solution will be barren of gold, significantly improving the plant’s efficiency. The Rigaku NEX QC+ offers a simple and low cost at-line analytical technique for measuring such solutions. Non- technical operators obtain results in as little as 100 seconds without the need for special sample preparation, sample conditioning or technical knowledge.

NEX QC+ high-resolution EDXRF analyzerModel: NEX QC+

Unit conversion

The simple conversion shown here is made without conversion for relationship between volume of liquid solution to volume of ore material.

1 troy oz/ton = 34.3 ppm
1 ppm = 0.029 troy oz/ton


A simple linear empirical calibration was built using a suite of 4 calibration standards assayed by AA. Calibration can be made in units of ppm or troy oz/ton.

Element: Au
Units: troy oz/ton
Sample I.D. Assay value Calculated value
2 0.058 0.064
6 0.174 0.168
23 0.667 0.667
41 1.189 0.667

EDXRF1299 Correlation plot AuCorrelation plot Au troy oz/ton

Element: Au
Units: ppm
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

EDXRF1299 Correlation plot Au ppmCorrelation plot Au ppm


Instrument repeatability (precision) is determined by ten repeat analyses of a sample in static position. Precision results are summarized here.

Element: Au
Units: troy oz/ton
Sample Standard value Average value Std. dev
2 0.058 0.070 0.012
6 0.174 0.168 0.017
23 0.667 0.661 0.020
41 1.189 1.175 0.020

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

Comparison to AA technique

Several unknown samples were measured by AA (Atomic Absorption spectroscopy) and NEX QC+ in side-by-side testing. The results are shown here and indicate excellent correlation between AA and Rigaku XRF.

EXRF1299 Comparison to AA TechniqueConclusion

The NEX QC+ offers analysts and technicians a simple yet powerful and versatile system for quantifying elemental composition using the empirical approach. The results of this study indicate that given stable samples, proper sample handling and proper calibration technique, the Rigaku NEX QC+ EDXRF can achieve excellent results in monitoring the concentration of gold in strip solution during the processing of ores, tailings and slags.

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