Reducing mercury pollution by training Peruvian artisanal gold miners

Abstract

In 2010, in the Piura region, north of Peru, 10,000 artisanal miners and more that 160 processing plants were dispersed in 158,000 ha applying extremely primitive techniques to extract gold using 5 to 10 t of mercury to amalgamate the whole ore. The US Department of State and the University of British Columbia established a project to train miners from 2010 to 2013 on mining and processing methods. A demonstration plant in Portovelo, Ecuador was used to train 46 Peruvian, 50 Colombian and 115 Ecuadorian small miners and processors on methods to reduce and eliminate mercury increasing gold recovery by gravity concentration, flotation and cyanidation. Miners had the opportunity to learn unit operations of mining engineering and they realized that their rudimentary processes were very inefficient to extract and recover gold from complex sulphide ores. Ore buyers in the Piura region provide a better deal for the miners who are currently selling their ores for 50% of the gold content analyzed by local chemical labs. By selling to ore buyers, miners have in their hands, at the end of one day, more money than if they had amalgamated the ores. Due to this fact and through education, mercury levels in the region were reduced at least by 50% from the 2010 levels. A pre-feasibility study of a small processing plant operating with gravity concentration, flotation and cyanidation of the concentrates revealed that with Au grade equal or above 10 g/t, even with 50% of gold recovery and at USD 1300/oz of Au, a 10 t/day plant is still profitable.