The Minnesota Court of Appeals remanded an air-emissions report that had been issued to PolyMet Mining Corp. back to the Minnesota Pollution Control Agency for additional explantion.

The court ruled that the Minnesota Pollution Control Agency hadn’t sufficiently justified granting the permit after opponents raised allegations that PolyMet was planning a much larger mine.

“While disappointed in the court’s decision, we stand firmly in our belief that the Minnesota Pollution Control Agency appropriately accounted for the potential effects of the NorthMet Project and will expeditiously provide the supporting explanation requested by the court,” PolyMet said in a statement. “The facts and science that prove the project can meet air quality standards are not in doubt. Copper, nickel, palladium and cobalt are high demand metals for infrastructure projects and the production of electric vehicles and renewable and clean energy technologies including solar panels, wind turbines and batteries. These mineral resources need to be mined to support future clean energy and electric mobility technologies consistent with the priorities of the Biden Administration and as outlined in a June 2021 White House report on vulnerabilities within essential supply chains. Critical minerals such as those PolyMet will produce and large capacity batteries were two of the vulnerabilities identified in the 250-page report.”

The Associated Press reported that environmental groups and a Native American tribe pointed to a report that PolyMet filed with Canadian regulators that suggested PolyMet was considering expanding the mine to four times the size that the air permit would allow.

The appeals court last year said the MPCA hadn’t adequately evaluated whether the air permit understated the company’s real plans, only to have that ruling overturned by the Minnesota Supreme Court. The high court ruled in February that the MPCA wasn’t required by federal law to investigate the allegations of “sham permitting.”

The Supreme Court sent the case back to the Court of Appeals to consider whether the agency correctly concluded that PolyMet would comply with all terms of the permit, and whether PolyMet had failed to fully disclose all relevant facts or submitted false or misleading information to the agency.

The openpit mine and processing plant near Babbitt and Hoyt Lakes would be Minnesota’s first copper-nickel mine and would produce minerals needed for the transition to a green economy.