Rare-earth element extraction from geothermal brine using magnetic core-shell nanoparticles-techno-economic analysis

[Display omitted] •Provided knowledge on a novel separation method for rare earth element extraction from geothermal brines using magnetic nanoparticles.•Demonstrated a continuous magnetic nanofluid extraction process and estimated the lifetime of the nanoparticle using a loop cycling test.•Provided a techno-economic analysis and calculated the internal return rate for Eu extraction from a geothermal brine sample from Slaton Sea.•Revealed key parameters that impact the IRR of the magnetic nanofluid extraction technology. Rare earth elements (REEs) are critical materials having 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 passing through a geothermal power plant. We demonstrate a simple and highly cost-effective nanofluid-based method for extracting rare earth metals from geothermal brines. Core-shell composite nanoparticles that contain a magnetic iron oxide core surrounded by a shell made of metal-organic framework (MOF) sorbent functionalized with chelating ligands were produced to selectively extract rare earth elements. A flowsheet model is used to estimate the capital and operating cost of a potential process to extract Eu from geothermal brines in the Salton Sea area using the magnetic nanofluid technology. The techno-economic analysis (TEA) results show that the annual productivity of Eu from the outlet brine stream of a typical 20 MW geothermal power plant is about 2151 kg. The capital cost to apply the PNNL magnetic nanofluid technology is about $6.8 M and the internal return rate (IRR) for this investment is about 18.1% based on the information collected for the year 2018. Sensitivity analysis has been carried out for some key parameters such as the REE concentration and price and adsorbent cost to reveal their impacts on the IRR.