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Safe Cleaning of State of Maine Filters Using Edta-type Chelating Agents.
MISSING :12 pages
An increasing number of gold and silver mining operations are employing cyanide solutions to effectively dissolve silver and gold from finely disseminated ores. Many of these operations use small, packaged processing systems like the state of Maine filter system, which employs zinc precipitation of gold and silver. Solution- clarifying filters in these systems become blinded with calcium carbonate (caco3) scale and require frequent (every 2 to 10 days) dismantling of the filter units for acid cleaning. This is a hazardous operation as it is not compatible with the alkaline cyanide leach solutions and may result in the evolution of toxic hydrogen cyanide (hcn) gas during cleaning and during any accidental acid spill. The Bureau of Mines has investigated an alternative, nonacidic method of cleaning blinded state of Maine filters that employs ethylene-diamine-tetraacetic-acid (edta) type chelating agents to dissolve the scale. In situ cleaning of a 150-st/d state of Maine filter with edta-type chelating agents was successfully demonstrated. Greater than 90 pct of the caco3 scale was removed in about 10 min with circulation of 31 l of 2.5-Pct-edta solution through the filter unit. The edta cleaning method not only eliminates the cyanide hazard in filter cleaning but is advantageous from the standpoint of operating costs and productivity.
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Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division