In the Arrowhead Region of Minnesota, many of the lakes one can see on an aerial map are mine pit lakes, formed in abandoned taconite pits and from their tailings ponds. Once taconite mining ends, rain water runs over the rock walls of the old dig sites to collect at the bottom and form lakes. That rock contains sulfide ores (such as pyrite) that react with water and oxygen, so dissolved sulfate accumulates in the water. Over time this concentration increases, reaching 1000 mg/L and more. This water seeps into the surrounding lands and eventually reaches creeks that flow into the watersheds of the region—both the Lake Superior and the Hudson Bay Watersheds.
Minnesota has prided itself on the wild rice that grows in the state. However, research shows that wild rice does not grow well in waters with high concentrations of sulfate. Minnesota standards since 1973, intending to protect wild rice, limit sulfate concentrations to 10 mg/L. High levels of sulfate can negatively impact other forms of life, including humans. It is important to the people of Minnesota that a cost-effective solution be implemented to remove sulfate from mining-impacted waters.
We at Clearwater BioLogic have developed a system that uses natural means to take sulfate out of water. We are able to remove sulfate even from concentrations of more than 1000 mg/L. Because our system operates under water, it works effectively in all seasons, including when air temperatures are 40 below zero. We can handle any rate of water flow. Even more important, we can reduce sulfate to 10 mg/L or to zero, depending on the goal. Because we use a modular system and inexpensive recycled materials with a huge surface area, our process has an excellent cost benefit relationship. Using natural, cost-effective methods, we can help ensure that water discharged from mining lands does not harm wild rice, while also providing a more economical method for mining companies to meet the sulfate standards of Minnesota.