Surface mining for rare earth elements used in smartphones and wind turbines is difficult and rarely done in the United States. Scientists wanted to know if they could pull the metals, present at trace levels, from geothermal brines using magnetic particles. The particles, wrapped in a molecular framework shell known as a metal-organic framework, or MOF, should easily trap the metals and let the rest flow past. However, the team led by Pete McGrail at Pacific Northwest National Laboratory found the magnetic strength dropped by 70 percent after the MOF shell was formed.