Ultrasound-assisted leaching of rare earths from the weathered crust elution-deposited ore using magnesium sulfate without ammonia-nitrogen pollution

The in situ leaching process of China's unique ion-adsorption rare earth ores has caused severe environmental damages due to the use of (NH₄)₂SO₄ solution. This study reports that magnesium sulfate (MgSO₄) as a leaching agent would replace (NH₄)₂SO₄ by ultrasonically assisted leaching to deal with the ammonia-nitrogen pollution problem and enhance leaching process. At leaching conditions of 3 wt% MgSO₄ concentration, 3:1 L/S ratio and 30 min, the total rare earth leaching efficiency reaches 75.5%. Ultrasound-assisted leaching experiments show that the leaching efficiency of rare earths is substantially increased by introducing ultrasound, and nearly completely leached out after two stage leaching process. Thus, ultrasonic-assisted leaching process with MgSO₄ is not only effective but also environmentally friendly, and beneficial to leach rare earths at laboratory scale.