The safety of storing mining waste in a tailings basin has been a critical part of the debate over copper-nickel mining in northern Minnesota, with some environmental advocates warning that failures and spills could unleash toxic slurry into nearby waters.
Now, in a major shift, one of two companies hoping to build a copper-nickel mine says it plans to store much of its waste using a “dry stack” method, an emerging technology that many of the same environmental nonprofits — and some mining experts — argue will better prevent water pollution.
Twin Metals Minnesota, which plans to mine just outside the Boundary Waters Canoe Area Wilderness, said Thursday it would abandon its plan to use a tailings basin, which entails waste rock being covered in a pond held back by a dam.
The company instead plans to use dry stacking, a process by which miners remove water from waste and work it into a sandy mixture which is then covered with soil and vegetation and put on a liner.
The state Department of Natural Resources has previously questioned whether the method can work in Minnesota’s cold and wet climate. But Julie Padilla, Twin Metals’ chief regulatory officer, called dry stack tailings “best available technology.”
For the rest of this article: https://www.minnpost.com/environment/2019/07/twin-metals-changes-its-plan-to-deal-with-mine-waste-to-a-strategy-lauded-by-some-environmentalists/