Crustal Imaging and Characterization Team

Stable isotopes and cyanide geochemistry

Task Objectives

Cyanide (the CN- anion) is the key metallurgical reagent that has allowed for profitable mining of numerous large-tonnage, low-grade gold deposits over the past three decades in the United States and elsewhere. In addition to being highly effective in leaching gold from crushed ores, cyanide can also be toxic to wildlife and humans. Its use in ore processing inevitably leads to releases to the environment, either permitted or accidental. Because the quantities of cyanide released to the environment are large (total of 700 metric tonnes for the U.S. in 2000 according to an EPA estimate), and because cyanide concentrations in some accidental releases have been well above toxicity limits (Summitville, CO in 1995; Baia Mare, Romania in 2000), cyanide use at metal mines is being very closely scrutinized for its environmental risks at the local, national, and international levels.

A major stumbling block in assessing the environmental risks of cyanide use is the fact that it can be present in many different chemical forms and complexes. These different cyanide forms (1) vary in their inherent toxicity, (2) change in relative abundance as physicochemical conditions change, (3) vary in their tendancy to attenuate naturally, and (4) are difficult to analyze accurately. Despite a considerable amount of research that has been conducted on cyanide chemistry over the past two decades and considerable debate between promoters and opponents of mining development, large gaps remain in the understanding of cyanide behavior in the environment. There is an urgent need for additional information on the environmental behavior of cyanide to provide for improved regulatory oversight and improved remediation strategies.

The primary objectives of this task are to arrive at an understanding of

1. the complete inventory of cyanide species and complexes that occur in liquid and solid wastes at cyanide leach operations, and
2. the factors controlling their stability.

Achieving these objectives will require us to address some intermediate objectives, including the development of optimal sampling and sample preservation protocols, and the implementation in our laboratories of recent developments in ion chromatography, Fourier transform infrared spectroscopy, and stable isotope geochemistry. Through a collaboration with USGS fish toxicologists at the Columbia Environmental Research Center, we also plan to test the toxicity of cyanide species that are important in mineral processing wastes and for which the toxicity is unknown.

Statement of Work

1. Perform a study of cyanide speciation at a heap leach operation. The objective will be to evaluate our new ion chromatography method for individual cyanometallic complexes. By cross-referencing with our standard cyanide analytical methods, we will validate the new method and also collect valuable information of long-term environmental risks associated with cyanide.
2. We will facilitate and capitalize on any projects where cyanide analysis is of interest. In recent years we have provided analyses of Katrina sediment from New Orleans, as well as analyses of water, soil, and ash from locations where cyanide-containing forest fire retardants had been applied. Because cyanides are widespread environmental toxins, and because cyanide use in mineral processing is increasing as global gold production skyrockets, we anticipate that our expertise will be in demand this year, as it has been in past years.

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