Photochemical Changes in Cyanide Speciation in Drainage from a Precious Metal Ore Heap

In drainage from an inactive ore heap at a former gold mine, the speciation of cyanide and the concentrations of several metals were found to follow diurnal cycles. Concentrations of the hexacyanoferrate complex, iron, manganese, and ammonium were higher at night than during the day, whereas weak-ac...

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Bibliographic Details
Published in:Environmental science & technology 2002-03, Vol.36 (5), p.840-845
Main Authors: Johnson, Craig A, Leinz, Reinhard W, Grimes, David J, Rye, Robert O
Format: Article
Language:English
Subjects:
Applied sciences
Chemical reactions
Cyanides - analysis
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Environment
Environmental Monitoring
Exact sciences and technology
Hydrogen-Ion Concentration
Metals
Metals, Heavy - analysis
Mining
Natural water pollution
Poisons
Pollution
Pollution, environment geology
Rainwaters, run off water and others
Risk Assessment
Waste Disposal, Fluid
Water Pollutants - analysis
Water treatment and pollution
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Summary:In drainage from an inactive ore heap at a former gold mine, the speciation of cyanide and the concentrations of several metals were found to follow diurnal cycles. Concentrations of the hexacyanoferrate complex, iron, manganese, and ammonium were higher at night than during the day, whereas weak-acid-dissociable cyanide, silver, gold, copper, nitrite, and pH displayed the reverse behavior. The changes in cyanide speciation, iron, and trace metals can be explained by photodissociation of iron and cobalt cyanocomplexes as the solutions emerged from the heap into sunlight-exposed channels. At midday, environmentally significant concentrations of free cyanide were produced in a matter of minutes, causing trace copper, silver, and gold to be mobilized as cyanocomplexes from solids. Whether rapid photodissociation is a general phenomenon common to other sites will be important to determine in reaching a general understanding of the environmental risks posed by routine or accidental water discharges from precious metal mining facilities.
ISSN:0013-936X
1520-5851
DOI:10.1021/es011064s