Evidence of an iron-gold corrosion cell during the Zadra pressure elution of loaded carbon

The file is a zipped PDF document.Extremely fine free gold was originally discovered on the surface of carbon fines within the carbon fines settling hopper at Omai Gold Mine Ltd. (OGML). This discovery prompted an intensive metallurgical investigation to determine the genesis of this gold and how to control it so as to prevent fine gold losses to carbon fines and tailings. The initial scope of work involved an extensive carbon handling circuit sampling campaign for the purpose of defining the extent of the fine gold occurrence within the carbon handling circuit. This campaign revealed that very fine free gold was present in the various carbon elution, screening, and reactivation products.Scanning electron microscopy studies demonstrated that the fine gold had a dendritic morphology similar to Merrill-Crowe gold precipitates. This observation gave rise to the thought that the fine gold was most likely the by-product of a cementation process as opposed to some native occurrence. Fugitive fine gold discharge from the electrowinning circuit was tested, but eliminated as a possible source of the fine gold. The initial sampling campaign also demonstrated that the fine gold was present in the eluted carbon before and after the carbon reactivation kiln, thereby ruling out the possibility that the fine gold genesis was the result of a high-temperature reduction process. It also revealed that the fine gold was not entering the carbon handling circuit via loaded carbon transfers from the carbon-in-pulp circuit to the carbon elution vessel.As implausible as it seemed at the time, attention then shifted to the carbon elution stage as a possible source of the fine free gold.At this juncture of the investigation, it was realized that, notwithstanding operating temperature, the Merrill-Crowe and carbon elution processes occur under similar physical and chemical conditions. The authors therefore hypothesized that higher temperatures such as those present during the carbon elution process, combined with the presence of a metal or substance of adequate electrochemical ‘nobility,’ might theoretically precipitate or cement gold from high-grade gold cyanide eluate during the loaded carbon elution cycle. Pursuing this possibility, the investigation subsequently identified significant quantities of grinding circuit fine iron and magnetic mineral grit entrained in the loaded carbon stream ahead of the carbon elution vessel.Laboratory and plant tests were designed and executed to explore the hypothesis that metallics and/or mineral magnetics were mediating the fine gold cementation phenomenon. The tests demonstrated that fine steel retrieved from grinding circuit pulps was capable of cementing fine gold from loaded carbon eluate under identical carbon elution conditions.Several remedial options were subsequently investigated to minimize or eliminate the phenomenon. These options included testing a magnetic separator to remove entrained steel and magnetic mineral grit from the loaded carbon prior to elution, optimizing loaded carbon screen washing effectiveness, barren solution oxidation, and carbon-in-pulp viscosity control. Each of the options were successful to varying degrees but none one of them was capable of halting the phenomenon completely.It has since been established that the gold cementation phenomenon described herein occurs at many other carbon-in-leach and carbon-in-pulp gold plants worldwide. Furthermore, it has since been proven that the phenomenon is also mediated by certain mineral sulphides such as those referred to during the coarse of this investigation as magnetic grit.Personal communication with those plants where the phenomenon is known to occur has established that fine gold production is variable in extent from site to site.In conclusion, the genesis of fine free gold within the carbon handling circuit at OGML was proven to result from a cementation process that is mediated by an iron-gold corrosion couple during the Zadra pressure elution of loaded carbon. The fundamental science and plant operating conditions of the phenomenon were investigated as were potential corrective methods.The authors recommend that those operations with a Zadra pressure elution circuit undertake audits to determine the extent of fine gold in their carbon handling circuit and quantify the extent of fine gold losses to carbon fines and tailings. It is further recommended that applied research into this phenomenon be undertaken for the purpose of characterizing its precise physico-chemical nature and, potentially, identifying effective remediations.
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Summary: The file is a zipped PDF document.Temporal and other factors contributing to the occurrence of occupational accidents at an underground coal mine in Turkey between the years 1992 to 2000 have been analyzed. Occupational accidents in mines result in both loss of time and money, and can cause debilitating injury or death and intense hardship imposed on family, friends, and dependents, for which no amount of compensation is sufficient. Thus, occupational accidents should be analyzed carefully in...
Publication: CIM Bulletin
Author(s): M.K. Ozfirat, P.M. Ozfirat, C.O. Aksoy, C. Pamukcu, C. Tatar
Issue: 1091
Volume: 1
Year: 2006
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Summary: The file is a zipped PDF document.Destress blasting or preconditioning, a rockburst control measure, has been tried to control strainbursts since the beginning of the 20th century. The concept of destress blasting evolved from the observation that the zone of highly fractured rock immediately surrounding some deep underground openings seems to offer some shielding to both the occurrence of and damage from rockbursts. It was argued that extending and maintaining this zone of the fractured rock...
Publication: CIM Bulletin
Author(s): H.S. Mitri, M.R. Saharan
Issue: 1091
Volume: 1
Year: 2006
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Summary: The file is a zipped PDF document.Real options valuation is an alternative net present value framework that is able to incorporate both management flexibility and dynamic project risks. In this paper, management is considering the development of a satellite low-grade zone while operations in a developed high-grade zone continue. If the low-grade zone is developed prior to high-grade zone exhaustion, mine capacity must be expanded before additional production from the low-grade zone can be...
Publication: CIM Bulletin
Author(s): M.R. Samis, D.G. Laughton, R. Poulin
Issue: 1091
Volume: 1
Year: 2006
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Summary: The file is a zipped PDF document.The environmental management of mining operations has evolved considerably over the last two decades. Factors such as changing values of modern societies, globalization of trade, climate change, and regulations oriented towards sustainability have led to the introduction of environmental management systems (EMSs).Cambior is a medium-size gold mining company, incorporated in 1986. A rapid growth in its northwestern Quebec-based operations and its geographical...
Publication: CIM Bulletin
Author(s): S. Vézina
Issue: 1091
Volume: 1
Year: 2006
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Summary: The file is a zipped PDF document.The importance of blasting to mill operations has been discussed in a series of publications, especially in the last decade. Literature suggests that there are two types of benefits from finer blast fragmentation: productivity increases and decreased energy requirements at the mill. Productivity increases have been linked to fragmentation improvements while energy requirements in the mill can be expected if the work index changes with blasting.In the present...
Publication: CIM Bulletin
Author(s): P.D. Katsabanis, S. Gregersen, G. Kunzel, M. Pollanen, C. Pelley, S. Kelebek
Issue: 1091
Volume: 1
Year: 2006
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Summary: The file is a zipped PDF document.IntroductionThis paper describes a novel software application that has the capability to autonomously capture images of blasted rock material and analyze them to generate the particle size distribution. The system can also process a batch of rock images captured during a fixed duration of time and produce the overall particle size distribution. The new method has different layers of segmentation modules, which allows the system to respond to a wide range of...
Publication: CIM Bulletin
Author(s): G.K. Mann
Issue: 1091
Volume: 1
Year: 2006
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