New water treatment plants help secure a positive legacy (Barrick Beyond Borders – October 20, 2016)

Water treatment plants at the Pierina mine in Peru are an important part of the mine’s closure plan

As part of its mine closure obligations, Barrick’s Pierina mine has built two new water treatment plants to safeguard local water quality. The Peru-based mine, which is winding down operations after 18 years, also built a cyanide detoxification plant to treat cyanide contained in the site’s heap leach pad.

“Cyanide is often used to leach gold contained inside ore, and this was the case at Pierina,” says Jorge Lobato, Environmental and Closure Manager at Pierina. “Even when operations at Pierina come to an end, cyanide will be present in the solutions from the heap leach pad and must be treated. The cyanide detoxification plant will operate until all cyanide has been consumed or destroyed on site.”

Pierina is located about 185 miles north of Lima in a high precipitation region of Peru. Average annual rainfall is 1,200 millimeters which, combined with natural conditions of the area, make conditions ripe for acid rock drainage. Acid rock drainage refers to the acidification of water that occurs when sulfide-based ore is exposed to air and water. It occurs naturally in the area due to the sulfur-based rock in the region and can be exacerbated by large open pits and waste rock produced during the mining process, if left exposed.

The new treatment plants will replace existing treatment facilities on site and underscore Barrick’s commitment to proper mine closure. “We made a substantial investment to build these plants and we are committed to the responsible closure of this mine,” Lobato says. “This is one of the first experiences in Peru of a large mine closure, and we want to set the standard for responsible, safe and sustainable mine closure.”

All water that comes into contact with the mine site is funneled to the water treatment plants before being discharged off site. Discharged water must comply with new regulations that recently went into effect in Peru. “There are limits for content of various metals, salts and the acidity level of the water,” says Wesley Ubillus, Process and Water Treatment Manager at Pierina.

Most of the water treated at the plants is not used by local communities, but some of it is channeled into several communities in the nearby Pucaurán and Pacchac valleys for irrigation use. Both treatment plants at Pierina contain reverse osmosis technology—sophisticated water purification technology that removes sulfate, carbonate and other salts from water.

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