(436c) Rare Earth Elements Extraction from Geothermal Brine Using Nanofluids

Rare earth elements (REE) are critical materials in a wide variety of applications such as generating and storing renewable energy. Extracting rare earth metals from geothermal brines is a very challenging problem due to the low concentrations of these elements and engineering challenges with traditional chemical separations methods involving packed sorbent beds or membranes that would impede large volumetric flow rates of geothermal fluids transitioning through the plant. We are demonstrating a simple and highly cost-effective nanofluid-based method for extracting rare earth metals from geothermal brines. Core-shell composite nanoparticles are produced that contain a magnetic iron oxide core surrounded by a shell made of metal-organic framework (MOF) sorbent functionalized with chelating ligands selective for the rare earth elements. By introducing the nanoparticles at low concentration (≈0.05 wt%) into the geothermal brine after it passes through the plant heat exchanger, the brine is exposed to a very high concentration of chelating sites on the nanoparticles without the need to pass through a large and costly traditional packed bed. Instead, after a short residence time flowing with the brine, the particles are effectively separated out with an electromagnet and standard extraction methods are then applied to strip the rare earth metals from the nanoparticles, which are then recycled back to the geothermal plant. This process was investigated in a magnetic separation loop system and parameters such as magnetic power, flow rate, particle dispersion and recycling lifetime were studied. We have shown that it is possible to retain the magnetic particles and recover the REE adsorption capacity of the magnetic particles after over 500 h continuous cycling. A detailed preliminary techno-economic performance analysis of extraction systems showed potential to generate a promising internal rate of return (IRR) up to 16%.