New On-line Cyanide Analyser to Help Gold Milling Operations Achieve Significant Cost Savings

Xylem’s OI Analytical (USA) brand is pleased to announce the launch of a new on-line cyanide analyser for gold milling applications. The new CNSolution 9310, when incorporated into the gold milling process, can facilitate significant cost savings for mill operators.

Most gold occurs at very low concentrations in ores; less than 10grams/ton (0.001%). Hydrometallurgical extraction using cyanide is the only economically viable method of recovering gold from such low-grade ore. Leaching solutions typically contain cyanide in concentrations from 50 to 2,000ppm, and purchasing, transporting, handling and detoxifying cyanide is a major operating expense for gold mills.   

Accurately measuring cyanide available for leaching gold from ores containing copper and metallic sulphides is problematic, since copper complexes with cyanide and reduces the amount of cyanide available for leaching. To complicate the process further, titration methods commonly used for process control do a poor job of measuring available cyanide when copper is present. An excessive amount of cyanide must be added to the leaching solution to compensate for this measurement inaccuracy and to ensure a sufficient concentration is present for efficient extraction of gold.   

Adding excessive cyanide in the leaching process decreases the efficiency and increases operating costs associated with the detoxification stage. Gold mills performing cyanidation need to adhere to the International Cyanide Management Code which defines good practices and guidelines for use, treatment and disposal of cyanide. The code sets a limit of 50mg/L in tailings solution discharges, and to comply with this limit the spent cyanide solutions must be detoxified. Detoxification requires the use of strong oxidising agents to destroy cyanide and reduce its concentration, adding yet another layer of expense to the milling of gold. 

OI Analytical’s CNSolution 9310 On-line Cyanide Analyser measures available cyanide in precious metal leaching solutions per U.S. EPA Method OIA-1677 and ASTM D 6888-09. The gas-diffusion amperometry technique in these methods is proven to be free of interferences from copper and metallic sulphides, providing more accurate measurement of the available cyanide concentration. The CNSolution 9310 responds quantitatively to cyanide, as well as zinc, copper, cadmium and silver cyanide complexes over the entire instrument calibration/measurement range (0.2 to 2,000ppm).

The superior accuracy of the CNSolution 9310 facilitates tighter control of the cyanide concentration in the leaching process and oxidising agent usage in the cyanide detoxification process, thus significantly reducing the amount of cyanide needed. A ten percent decrease in cyanide usage can easily translate into a savings of hundreds of thousands of dollars per year in the leaching and detoxification costs for a milling operation.