PROJECT: Collahuasi Copper Mine
CITY: Rural, Northern Chile — 60 km South of Iquique
SOLUTION TYPE: Water Treatment
TECHNOLOGY USED: Complete, multi-stage on-site water treatment with zero liquid discharge.
The Compañía Minera Doña Inés de Collahuasi SCM — colloquially known as the Collahuasi Copper Mine — is an extensive mining operation located in rural Northern Chile, about 60 km south of the city of Iquique and about 4,440 meters above sea level. Two types of ores are extracted from three open-cut mines: copper and molybdenum. The facility also produces copper cathodes.
Mining activity in the Tarapacá Region of the Andean plateau began in the 1880s, according to the company. During this period, silver and copper deposits were mined. Activity halted during the Great Depression and resumed in the late 1970s after extensive research and exploration.
Modern operations at Collahuasi commenced in the 1990s with new construction. Actual operations began in 1999. The mine, which now produces about 3% of the world’s copper according to Bloomberg, has been in the news in 2012 because of production slowdowns. Production was disrupted by snowstorms, but operations have recently also been affected by labor stoppages and the discovery of lower grade ores on site. Output at the mine was reportedly already down by 10% in 2011 to 453,409 metric tons, which was attributed to adverse weather, according to Mining Technology.
The facility processes the mined ore on site, which creates a huge volume of contaminated and saline water. Before this water treatment project was completed, the water was discharged to the environment with only a minimal amount of treatment.
The surrounding area is arid, harsh and ecologically fragile. To eliminate any ecological problems that might result from the release of water — even treated water — into the environment, no water is released. The facility is a zero-discharge operation, with its water recycled for reuse.
To effectively treat these effluents and maximize water reuse while reducing discharge to the environment, a multistage treatment plant was required. The facility was designed, built, and commissioned in 2008 by Nirosoft Industries Ltd. of Israel.
To work in a remote location at such a high altitude made the project uniquely challenging in and of itself, but there were other interesting issues that needed to be addressed by Nirosoft engineers.
The mine operators wanted a treatment system that would enable them to reuse the wastewater. Some of the recycled water would be reused for ore processing, while other treated water needed to be sufficiently viable to irrigate the trees and other vegetation in a nearby reforestation project.
The treatment of mine wastewater poses a particular challenge to water professionals. The effluents created by mining activities typically contain high levels of organic compounds. Ore processing in particular creates large volumes of contaminated and saline water. The salinity and composition of these compounds varies significantly.
More specifically, the wastewater from the copper mine contains high levels of both total dissolved solids (TDS) and total suspended solids (TSS), high chemical oxygen demand (COD), and the water is also extremely hard. The feed water also contains high concentrations of SO4, silica, iron, and other metals. The amounts of these compounds and the water quality fluctuates based on the tailings’ composition and ore residue that may be present, which makes the treatment process even more challenging.
Additionally, mining operators must typically meet strict environmental regulations governing effluent discharge, some of which may be national in scope while there may also be specific local oversight.
To address this wide range of needs effectively, a multistage water treatment plant was designed, built, and commissioned in 2008 for Collahuasi by Nirosoft Industries Ltd of Israel. The turnkey project involved a complete study as well as the system installation. Additionally commissioning and onsite training were included in the scope of the project.
The raw wastewater — which is acid and extremely saline — is that which remains from rinsing during the ore separation process. The wastewater treatment plant was sized to accommodate a flow of 216 cubic meters/hour or about 5 ML/day, producing approximately 170 cubic meters/hour of product water.
The plant treats water in multiple stages, but some of these stages are accomplishing two or more key tasks simultaneously, according to Nirosoft executives. Such extensive treatment is important because the feed water quality is particularly challenging from the outset and the desired result is a zero-liquid discharge. All of the effluent must be suitable for reuse.
The system’s treatment stages include: sedimentation, dissolved air flotation, media filtration, activated carbon filtration, ultrafiltration, and reverse osmosis. In the sedimentation process, the suspended solids in the water are gravity settled. Then, through dissolved air flotation, various colloidal materials and dispersed particles are removed.
The water is then filtered to remove residual solids that may remain after the flotation stage. The removal of any dissolved organic material is completed with activated carbon filtration, followed by ultrafiltration. The latter step ensures that any residual suspended solids, colloidal and organic matter — including bacteria and viruses — are removed before the water is treated using reverse osmosis.
Removing as much sediment as possible is particularly important. It protects the infrastructure investment by making certain the membranes and other equipment used for reverse osmosis are neither fouled nor harmed by the water quality. Although this is important in any treatment process, water from mining in particular is full of sediment. The final polishing step in the water treatment process, reverse osmosis desalination, ensures that any dissolved salts and heavy metals are removed from the water before it is reused.