The intensive Leaching of Gold Concentrates Containing Cyanicides

Campbell, Sarah (2002). The intensive Leaching of Gold Concentrates Containing Cyanicides Honours Thesis, School of Engineering, The University of Queensland.

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Author Campbell, Sarah
Thesis Title The intensive Leaching of Gold Concentrates Containing Cyanicides
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 2002
Thesis type Honours Thesis
Supervisor Nursen Guresin
Grant Steward
Total pages 113
Language eng
Subjects 091405 Mining Engineering
Formatted abstract
The recovery of gold via a gravity circuit is a beneficial and economical process to all operating plants. However the efficiency in this circuit is an important factor to consider. The intensive cyanidation process for treating gravity concentrates is becoming more favourable in the gold processing industry today. The cyanidation process is an efficient means of obtaining high gold recoveries from the gravity circuit. The process requires high concentrations of cyanide to leach high grade gold ores.

However when high concentrations of cyanide consuming minerals exist in the concentrate this method becomes uneconomical as they inhibit gold dissolution, resulting in poor gold recovery and high operating costs. This is particularly true for copper minerals.

The ammonia-cyanide leaching system is an alternative approach to leaching these ore types, it is believed to be able to significantly improve the selectivity of gold leaching by reducing the copper extraction. It is proposed that the ammonia stabilises a copper(II)–ammonia-cyanide complex such as Cu(NH3)4(CN)2 which is responsible for gold dissolution.

The aim of this project is to study the leaching characteristics of a gravity gold concentrate and a final flotation concentrate and to improve the recovery rate of gold via the use and control of leaching parameters. Two test work phases were conducted and include: a study of the kinetics of gold leaching and a study of the selective leaching process. The hypotheses for these test work phases are:

The intensive cyanidation leaching process is an effective method of the recovery of gravity gold concentrates.

The ammonia-cyanide leaching process increases the selectivity of gold extraction over copper extraction in gold concentrates containing cyanicides.

Two different concentrates were used in this thesis. The first concentrate used was the gravity concentrate gained from the Knelson Concentrators at Placer Dome’s Osborne Mine. The second concentrate used in this thesis was the final flotation concentrate from the Cadia Hill Gold Mine. This is a copper-gold concentrate, which typically contains in excess of 20% copper.

The results from the experimental work conducted showed that very high gold recoveries are attainable in the gravity gold concentrate via the use of intensive cyanidation, the recoveries in these tests reached in excess of 98%. In the same tests the copper recoveries were very low at only 4%. The ammonia-cyanidation leaching process proved to have no significant effect on the suppression of copper in the gravity gold concentrate and obtained gold recoveries less than those obtained in intensive cyanidation.

The kinetic study on the intensive cyanidation of the gravity concentrate showed that at lower levels of cyanide and higher levels of oxidant the rate of reaction was more favourable. This was also favourable in the cyanide consumption analysis that was performed which gave a consumption of 13kg/t of cyanide.

The results obtained in ammonia-cyanidation of the final flotation concentrate showed that with increasing ammonia concentration the recovery of gold decreased and the recovery of copper increased. Suggesting that the copper was being selectively leached as opposed to the gold. The gold recoveries obtained in these tests reached a maximum of 47%. A mineralogical analysis of the concentrate showed that the gold was encapsulated with pyrite and chalcopyrite therefore the rate of dissolution is subject to the diffusion of cyanide solution to the gold surfaces.

The intensive leaching process proved to be an efficient means of recovering gold from the gravity circuit as the majority of gold dissolution occurred in the first four hours of leaching. However the ammonia cyanidation showed no advantages in the processing of the gravity gold concentrate.

The mineralogy of the flotation concentrate proved to be in appropriate for ammonia-cyanidation as it consumed large amounts of cyanide and resulted in low gold recoveries.
Keyword Gold Leaching

Document type: Thesis
Collection: UQ Theses (non-RHD) - UQ staff and students only
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Created: Fri, 28 Nov 2014, 12:38:48 EST by Asma Asrar Qureshi on behalf of Scholarly Communication and Digitisation Service