Safe Cleaning of State of Maine Filters Using EDTA-Type (Ethylene-Diamine-Tetraacetic-Acid Type) Chelating Agents

摘要

An increasing number of gold and silver mining operations are employing cyanide solutions to effectively dissolve silver and gold from finely disseminated ores. Many 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.