At PolyMet Mining, we value wild rice as an important Minnesota natural resource – it’s a sacred plant for the Anishinaabe (Ojibwe) people, an economic crop, and it provides habitat and food for waterfowl. Some of us who work for PolyMet Mining obtain permits to harvest wild rice each year for our own personal use.

The PolyMet project will meet Minnesota’s sulfate standard for wild rice, using reverse osmosis (RO) technology. Established in 1973, the protective standard limits sulfate to 10 milligrams per liter in waters used for the production of wild rice.

What is Reverse Osmosis?

  • Advanced water-purification method that removes impurities from water using a semipermeable membrane (a very tight, sheet-like, spiral-wound filter).
  • Developed more than 40 years ago by the U.S. Navy to create drinking water from seawater for submarine crews.
  • Proven technology used in the food and beverage industry; pharmaceuticals; manufacturing; and boiler-feed-water, ballast-water and drinking-water treatment.
  • Successfully treated more than 26 billion gallons of water in Ashkelon, Israel, at one of the largest desalination plants in the world.

How does RO work?

  • Water containing elevated concentrations of minerals is forced through a very tight membrane using high pressure.
  • The dissolved  contaminants are retained on the pressurized side of the membrane, and the pure water is allowed to pass to the other side.

PolyMet’s successful pilot plant

To demonstrate that our project will effectively treat water containing sulfates, we worked with GE Water & Process Technologies and Minnesota-based Barr Engineering to design and build an RO pilot plant. The pilot plant successfully removed sulfate from nearly 3 million gallons of water, proving the PolyMet project can meet Minnesota’s wild rice standard, along with all other applicable federal and state water-quality standards.

Next steps

RO technology is proven, sustainable and scalable, meaning we can easily add more units to meet the needs of our operations. After the PolyMet project receives all necessary permits, we’ll build a full-scale wastewater treatment plant at the plant site.

Sign up for updates to stay current on the RO process and PolyMet Mining news.