S.V. Pisupati, M. Rezaee
The Pennsylvania State University,
United States
Keywords: environmental remediation, acid mine drainage, extraction, critical minerals
Summary:
The Commonwealth of PA, through coal mining, has been a provider of energy and a driver of economic development of the US Due to these activities, there are 5,500 miles of streams producing billions of gallons of acidic water runoff from abandoned coal mines. The acidic water leaches rare earth elements and other critical minerals when flowing through coal and other associated materials. Presently this acidic water is treated by building and operating expensive treatment facilities by the State to meet the environmental regulations. PA DEP's Bureau of Abandoned Mine Reclamation (BAMR) operates eight facilities that use costly caustic chemicals and 50 systems that use limestone to alleviate this water pollution of major water bodies. Various non-governmental organizations such as watershed groups and conservation districts operate roughly 350 sites in the State. The United States and the world have seen exponential growth in the use of critical minerals for various applications, ranging from sustainable energy and national defense to modern electronic and medical applications. The United States is 100% import-reliant for 12 of 50 critical elements identified by the United States Department of Interior. Another 31 have net import reliance greater than 50% of consumption. Acid mine drainage (AMD) associated sludge is an excellent resource to extract REEs, particularly the high-value heavy REEs and other CMs (such as Al, Co, and Mn), which are essential components of advanced technologies. A recent study conducted by the Penn State researchers revealed that Pennsylvania AMD streams originated from abandoned mines, and coal refuse piles of lower Kittanning coal seam contain the most sought-after heavy rare earth elements. These waste sources contain varying concentrations of rare earth and critical mineral (CM) elements required for the nation's sustainable development. Significant challenges for the extraction of CM from these coal-based waste materials include: 1) low REEs content in the materials and low separation efficiency of the conventional extraction processes; 2) high costs to build and treat the acidic water with expensive chemicals, thereby, high acid consumption in downstream chemical processes and 3) strong acid requirement for leaching of the elements, adversely impacting the environment. To address these challenges, Penn State has recently developed a novel process to recover these critical minerals, tested the process for proof of concept, and patented the process by the investigators. Penn State's process has significant advantages over conventional recovery methods. The process utilizes 1) acid-less leaching for AMD instead of caustic chemicals, 2) selective recovery of iron, aluminum, and REEs from pregnant leaching solutions (including AMD) using environmentally friendly chemicals, and 3) chemical-free extraction of Cobalt and Manganese (battery materials) to obtain high purity products which will render the discharge water harmless to meet the environmental regulations. This paper discusses the three-stage process developed by PSU and efforts to design and demonstrate a nominal 10,000 gallons per day capacity pilot-plant to produce concentrates of Fe, Al, REEs, Co and Mn.