Developing Fluorescence-Based Sensors to Support Rare Earth Element Separation

Rare earth elements (REEs) are essential to most renewable energy technologies. Unfortunately, as we transition to sustainable energy production, the demand for REEs rapidly grows well beyond the current rates of production. As a result, novel means of efficient, scalable, and easily adaptable methods for processing primary and recycled feedstocks are needed. Development and integration of sensors for highly selective in-line monitoring can support more efficient design and testing of such novel separation processes as well as more cost-effective deployment of those separation flowsheets. Work here will explore the application of fluorescence spectroscopy, a highly sensitive and selective technique, to quantify multiple lanthanides in complex mixtures, including known interferents or quenching agents. Results include identification of the optimal excitation wavelength and the limit of detection of various rare earth elements, as well as the performance of data-science-based quantification approaches in streams where "unknowns" are present. Overall, the data science tools in conjunction with optical sensor data were able to quantify analytes in the presence of other lanthanides anticipated to be in the actual industrial stream. Here, we include the characterization of lanthanides in a microfluidic device similar to those used in new process development. This study demonstrates the capability of utilizing fluorescence spectroscopy to quantify analytes in a complicated solution matrix, suggesting this as a successful approach for in-line monitoring to optimize the separation efficiency in an industrial stream.