(212g) Greener Extraction of Rare Earth Elements from Coal Fly Ash

Rare earth elements (REE) are metallic elements that include 15 of the lanthanides, scandium, and yttrium. The global for REE increases every year as these REE’s are used in many modern technological innovations from microchips, electric cars, and solar panels, to fighter jets and satellites. China controls 90-100% of the REE available on the commercial market. In recent years the U.S. has increased its efforts to secure more stable domestic sources of REE. Coal fly ash (CFA) is a very fine powdery material from the combustion of finely-ground coal in heat and power plants. CFA is one of the largest types of industrial waste generated within the U.S., producing nearly 130 million tons in 2014, and some CFA contains as much or more of the desired REE than REE ores.

Typical REE extraction processes require strong acids with the associated hazards. Researchers at Sandia National Laboratories have developed a lab-scale process to extract REE from coal fly ash under relatively mild conditions, using water, supercritical CO₂, and small organic acid chelators. The goal of this project is to determine the engineering parameters and, where possible, process simplifications to enable scale-up. Experiments have been conducted with increasing levels of complexity on two types of a locally-sourced CFA to quantify the return on investment for each increase in temperature, pressure, reaction time, and reaction components. The first experiments were conducted in batch at atmospheric pressure on a stirring hot plate with and without chelator, followed by extractions in a 1.8-L batch reactor under nitrogen then CO₂. REE were quantified using inductively coupled plasma spectroscopy and compared to the quantities extracted under full-complexity processing and under traditional strong-acid conditions. Extraction efficiencies will ultimately be combined with processing cost models to identify the most feasible REE extraction process.