Quartz crystal microbalance analysis for cyanide and cyanide-degrading bacteria in gold process solutions

Guilfoyle, Laurence Michael (1998) Quartz crystal microbalance analysis for cyanide and cyanide-degrading bacteria in gold process solutions. PhD thesis, Murdoch University.

Abstract

Cyanide is used by the gold mining industry to extract gold from ore. The accurate measurement of cyanide in process solutions and the removal of cyanide from wastes are two areas of significant concern for the gold mining industry.

Biological cyanide destruction has been used successfully to remove cyanide from process solutions and leachate from heap leach pads. The aim of this work was to investigate cyanide degrading bacteria from gold mines in Western Australia.

In order to measure the activity of cyanide degrading bacteria, a method was developed to determine cyanide in small sample sizes. An apparatus and method for measuring cyanide ion in gold process solutions is described. The potential of a solution to leach gold was measured by quartz crystal microbalance, flow injection analysis. Cyanide levels from 0.5 to 500 mg L-1 were determined every two minutes on sample sizes from 0.1 to 2.5 mL. Also described is an apparatus and method for rapid measurement of weak acid dissociable (WAD) cyanide. A gas permeable membrane cell was combined with quartz crystal microbalance, flow injection analysis to measure WAD cyanide. WAD cyanide levels from 0.5 to 500 mg L-1 were determined every two minutes on sample sizes from 1.0 to 2.5 mL.

These methods were developed to measure the activity of cyanide degrading bacteria in gold process solutions. A sub species of the bacterium, Bacillus pumilus, was isolated from a gold mine in Western Australia. It degraded cyanide to ammonia and formate. The bacterium was found to exhibit high levels of cyanide degrading activity (800 units L*1) which was maintained after storage at 4°C as the bacteria did not sporulate under these conditions. This bacterium could not degrade WAD cyanide and could not grow in the presence of cyanide above 10 mg L-1.

A mixed culture of bacteria was isolated from a second gold mine that could grow in the presence of cyanide and could degrade 150 mg L-1 of WAD cyanide to below 0.5 mg L-1 in leachate from dump leached ore. Column tests showed that the addition of nutrients alone could stimulate bacteria already present in the ore to degrade cyanide. The rate of cyanide destruction in the nutrient only column was approximately half the rate of the column to which bacteria had been added. The nutrient only treatment method could reduce treatment costs for the decommissioning of heap leach pads as no bioreactor would be required.

Item Type:	Thesis (PhD)
Murdoch Affiliation(s):	Division of Science
Notes:	Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s):	Ralph, David and Dekker, Robert
URI:	http://researchrepository.murdoch.edu.au/id/eprint/52707

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