Calibrating HCN Instruments at Low Concentrations

Gold mines worldwide use cyanide to extract gold from ore. As environmental standards have increased in most mining areas around the world, cyanidation plant tailings must be treated to remove the cyanide and various cyanide compounds, including hydrogen cyanide (HCN), before they are discharged into a tailing storage facility. Methods to remove the cyanide and destroy it have increased in cost to the point where processes to recover the cyanide for reuse have become more cost effective than purchasing new cyanide.  

Throughout the process, no matter which methods are being used, the potential for HCN to volatilize into the air exists. Inhaling HCN can result in chronic, acute, or even fatal effects.

Currently global regulatory bodies are reviewing HCN to determine whether to reduce the current Peak (ceiling) of 10ppm to a much-reduced level of 1 ppm. 

This will cause the gold mining industry to improve the technology for measuring HCN to such a low concentration. Tradition gas detection instruments with electrochemical sensors may not be capable of measuring down to this low concentration so more sensitive gas analysers may be required.

Furthermore, calibration gas in non-refillable cylinders (NRC’s) have a minimum concentration currently of 10ppm. Gas manufacturers will have to develop new capabilities if they are to produce 1 or 2ppm HCN in non-refillable cylinders.

CAC GAS recognises the need for alternative solutions for calibrating HCN instruments at low concentration and have a few different options currently available.

High Pressure/large volume cylinders:

Specialty gas mixtures in high pressure (large volume) cylinders provide a solution when calibrating HCN instruments down to 5ppm. The larger cylinder size provides a cost-effective solution for calibrating and testing HCN instruments. The cost per litre of the calibration gas reduces by more than 60% with the larger cylinder size over smaller NRC’s.  

Electronic calibration gas generators:

Electronic gas generators are an ideal solution when calibrating HCN instruments with concentrations as low as 0.05ppm. Electronic gas generators use an electrochemical source to generate the HCN which makes it safe, with no shelf life of the source and easily transportable from one location to another. Easy to use, different source sizes are available to meet the volume of gas required. Sources are interchangeable providing calibration gas for other gas detection devices.

Gas mixers/splitters:

For larger facilities where many HCN instruments are being calibrated a gas mixer or splitter could be used to reduce a higher HCN gas mixture of 10ppm down to low ppm or ppb concentrations. Devices such as the Zephyr can provide multiple calibration concentrations from one cylinder mixture. This permits testing instruments across their measurement range to a traceable standard. Completely programmable the gas mixer can replicate the gas concentration with a push of a button.  

CAC GAS provides calibration and specialty gas solutions throughout the entire gold mining process. Our gases are offered in a variety of cylinder sizes to meet the requirement at each step of the process. We also offer a full line of gas control products and gas distribution systems, providing a complete solution for all applications within the gold mining process.