Rare Earths in Phosphate: Characterization & Extraction

Abstract

Much of this chapter is based on results from a multi-year research project supported by the Critical Materials Institute (CMI), an Energy Innovation Hub funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office. It also draws substantial materials from two projects funded by the Florida Industrial and Phosphate Research (FIPR) Institute, Florida Polytechnic University. Under the CMI project, FIPR Institute was engaged in three major activities: 1) chemical and mineralogical characterization of rare earth elements (REEs) in different phosphate processing streams, 2) concentration of uranium and REE (rare earth element)-containing materials from the various processing streams, and 3) extraction of REEs and uranium from the concentrated materials. This chapter covers the main findings of those three efforts, and is divided into four parts. Part I covers chemical analysis and basic properties of different samples. Part II is a detailed process mineralogy study of the amine flotation tails. Part III focuses on isolation and characterization of rare earth (RE) mineral particles in three samples using two advanced techniques, dual energy (DE) rapid scan radiography and high resolution X-ray microtomography (HRXMT). Part IV presents process development work on the concentration of REE-containing materials and extraction of REEs.In Part I, six samples were collected from a central Florida phosphate operation, including 2000 pounds of amine flotation tails, 5 full 5-gallon buckets of waste clay, 100 pounds of ground phosphate rock, 2 full 5-gallon buckets of phosphoric acid, 50 pounds of wet phosphogypsum, and several barrels of phosphoric acid sludge. These samples were analyzed for rare earth elements, uranium, thorium, routine chemical compositions, and radioactivity. Results show total REEs of 70-2600 ppm in the samples, with uranium ranging from 25-120 ppm. Radium-226 analyzed about 20 pCi/g in phosphogypsum, 28 in phosphate rock, and 0.2 in phosphoric acid, and the corresponding uranium-238 numbers are 2.8, 20 and 36 pCi/g. Simple sizing and chemical analysis of phosphogypsum (PG) revealed an extremely encouraging piece of information on REEs in PG. About 65% of the REEs in PG is concentrated in the minus 500 mesh (approximately 30 microns) fraction that represents less than 10% of the total PG mass. Another fact is that the finest fraction also contains most of the thorium but little uranium.In Part II, a detailed process mineralogy study was conducted on the amine flotation tails sample using a Mineral Liberation Analyzer, the most advanced instrument for this type of study. Two rare earth minerals were detected in the amine tails including monazite and xenotime. The monazite monomers average 1.27%