Portable XRF Analyzers for Measuring Gold in Activated Carbon

Activated carbon is routinely used as part of the gold recovery process at many mines around the world. Activated carbon is used in both carbon in leach (CIL) and carbon in pulp (CIP) techniques. These CIL and CIP techniques recover gold (Au) from pulp or solutions derived from the cyanidation process. According to the World Gold Council, more gold is recovered from cyanidation than any other process.

Gold cyanidation is a hydrometallurgical process that extracts gold from ore by converting the gold to a water-soluble coordination complex. Activated carbon adsorbs the gold from the resulting solution. The carbon is then stripped of the gold before being passed through an electrowinning circuit and smelted to produce gold bars.

Monitoring the content of gold and other elements within the activated carbon enables process optimization and maximum gold recovery. The Vanta™ portable XRF analyzer is used as a replacement for traditional laboratory techniques within the mine-site laboratory due to its speed, ease of use, and significantly improved accuracy and precision.

The Vanta analyzer provides accurate chemistry for more than 30 elements in solids and liquids, from trace level to percent level, from samples across the entire minerals cycle. The Vanta analyzer can be used to measure the gold loading of activated carbon from each of the tanks used as part of the process either in unprepared coarse form or after undergoing a fine grind.

Gold concentrations within activated carbon cover a wide range, often measuring as high as 10,000 grams/ton (g/t), or 1%. The Vanta analyzer is used to monitor silver (Ag), copper (Cu), and calcium (Ca) within carbon from various mine sites.

Monitoring calcium within activated carbon is useful. Lime is used as part of the cyanidation process, and repeated exposure to lime dosages blocks the pore spaces in activated carbon, reducing the carbon’s ability to extract gold. When too much calcium is detected, it is an indicator that new carbon is necessary or that the existing carbon should be regenerated. On a Vanta analyzer, calcium can also be analyzed at the same time as measuring gold, silver, and copper.

Portable XRF vs. Lab Results

The following graphs compare Vanta analyzer versus laboratory results for Au in activated carbon from various minesites and from certified reference materials. The results demonstrate excellent correlation and accuracy between lab and pXRF results. The results also demonstrate the pXRFs ability to monitor trends in Au adsorption within carbon at any minesite and provide support for mineral processing decisions and laboratory operations.

Portable XRF has been demonstrated to be an effective tool to monitor loading trends for gold in activated carbon. The Vanta analyzer’s results are very close to the laboratory results. Real-time monitoring made possible by pXRF can help maintain optimal carbon efficiency and reduce the costs and delays associated with lab analysis.