Bottle roll testing for cyanidation of gold ores: Problems related to standardized procedures on difficult-to-process ores

Abstract

This paper evaluates the influence of some of the critical parameters of bottle roll testing procedure on gold extraction results and leaching behaviour. The conventional testing procedure with special emphasis to the testing duration, feed particle size, and NaCN concentration in the starting leach-solution, was assessed critically and compared with alternative approaches regarding these parameters. In conventional testing, test duration is typically 96-144 hours; test is conducted on finely ground feeds of usually-150 μm; and test is started with a lixiviant that involves a NaCN concentration of usually 1 kg/tonne of ore, without identifying NaCN consumption tendency of the ore. Using results from three case studies, it was shown in this work that, applicability of these parameters without questioning/considering the specific features of a given Au ore is highly questionable: Test duration and feed particle size may have significant impacts on the measured Au extraction value, particularly with Au-ores that include preg-robbing matter and/or cyanicides. Au extraction and NaCN consumption profiles proposed that standardized application of bottle roll testing to challenging Au-ore types would yield misleading/overrated results. It was seen that extended testing periods on feeds that had equivalent particle size to field applications would yield more reliable estimation of field scale leaching behaviour. It was also shown that using a standard NaCN dosage in the starting lixiviant may be misleading, particularly for ores with cyanicides. A preliminary testing step to solely identify the NaCN consumption tendency of an Au-ore with cyanicides is suggested to accurately adjust the NaCN concentration of the initial leach-solution.