Sustainable Development
WATER QUALITY AT THE MINE
PolyMet will mine ore that contains a very small amount of sulfur — only about 0.7%, which is far less than massive sulfide ores at other mines that may have sulfur concentrations of 30% or more. Mining can expose sulfur to oxygen and water, which can potentially generate acid rock drainage.
PolyMet has used a stringent protocol to separate waste rock into categories. The rock will be placed on separate stockpiles designed to address the acid-generating potential of each category of rock.
Waste rock stockpiles will have engineered foundations, drains, liners, and covers. A collection system will collect all water that contacts exposed mining rock in the stockpiles and mine pit. This water will be treated at a wastewater treatment facility before it’s sent to the tailings basin for reuse in the process.
PolyMet has designed a number of safeguards to protect water quality at the mine. These safeguards include perimeter dykes to keep water from leaving or entering the mine site, a wastewater treatment plant to treat process water and individualized plans to protect nearby rivers and water bodies.
Water treatment system is designed to collect, treat and reuse mine water that contacts and sulfide bearing rock.
WATER QUALITY AT THE PLANT
Water to concentrate the ore will be recycled from the tailings basin and reused. Process water will be maintained in a segregated, closed-loop system and recycled within the processing system.
WASTE MANAGEMENT
Tailings left after concentrating the ore will be pumped to and deposited on the existing tailings basin. In the processing plant, concentrating is designed to recover both metals and sulfur. PolyMet will sell the recovered metals, and the sulfur will be used to provide fuel for processing. The remaining washed sand and silt (tailings) are very low in sulfur. Testing has shown the tailings will not generate acid.
Residues from processing the concentrate will be managed in a segregated hydrometallurgical residue disposal facility, constructed similar to a landfill.
AIR QUALITY
PolyMet will install new, state-of-the-art air emission controls on existing crushing and grinding equipment.
Because sulfur in the ore provides the energy to fuel processing, air emissions will be minimal. PolyMet will emit less than 0.05% of the sulfur dioxide of conventional base metal refining and use about half the energy. PolyMet will not use coal.
Very small amounts of mercury are found in the ore; most will stick to waste rock and remain in the tailings basin. Actual amounts were so low in pilot tests that sophisticated equipment could not detect any mercury emissions.
PolyMet will be a minor source of hazardous air pollutants under federal regulations. Emissions of common air pollutants such as particulate matter, sulfur dioxide or nitrous oxides, are far less than at most other mining and industrial operations.
CLOSURE
A comprehensive, detailed closure plan prepared according to state regulations will ensure the site is closed in a safe and environmentally sound manner.
Financial assurance regulations require PolyMet to provide an adequate source of money to pay for closure and reclamation. This money is not available to the mine owner or creditors. It is available to the state in the event of bankruptcy or if the mine owner doesn't perform the required closure and reclamation.
Planned closure activities include:
- Capping waste rock stockpiles.
- Collecting water from stockpiles and sending it to a wastewater treatment plant.
- Sloping and vegetating pit walls.
- Backfilling the East Pit and constructing a passive wetland treatment system that will receive water from the wastewater treatment plant and overflow to the West Pit. About 40 years after mining ceases, the West Pit will overflow water that meets water quality discharge limits into the Partridge River.
- Reclaiming the tailings basin and creating wetlands.
- Covering hydrometallurgical residue cells and collecting and treating any drainage.
- Demolishing all mine and plant structures and revegetating the site.