Conceptual Process to Produce ThO 2 from Monazite Bradley Bennett 1 & Robert M. Counce 1 & Patrick Zhang 2 & Rasika Nimkar 3 & Jack S. Watson 1 Received: 21 August 2019 /Accepted: 7 March 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020 Abstract This study level process design represents an economically viable method for extracting thorium dioxide and other rare earth elements from monazite ore. This paper incorporates results from the 2019 capstone project from the honors Design Internship in Green Engineering in Chemical and Biomolecular Engineering. In this activity, senior students in Chemical Engineering at the University of Tennessee (UT) focused on the development and study of a process for the recovery of thorium dioxide and P 2 O 5 from monazite. While not mandated, the process offers rare earth oxides as attractive byproducts. The project focused on recovery of byproducts rather than the creation or addition to waste streams. Additionally, (1) the process economics relied heavily on recovery of rare earth byproducts, (2) thorium handling portions of the process could be effectively segregated from rare earth and phosphate handling portions of the process, and (3) thorium and uranium content of waste streams should be carefully managed and eliminated where possible. Keywords Chemical engineering . Process design . Simulation . Thorium . Rare earth elements 1 Introduction The purpose of this paper is to develop a conceptual recovery process for thorium dioxide from its primary source, monazite. Monazite contains phosphate compounds of rare earth elements, uranium, and thorium. The thorium content of monazite (as ThO 2 ) varies up to 20% with 5 to 10% being typical [8]. Monazite from Florida beach deposits reportedly contains 50 to 60% rare earth elements (as oxides) and 4 to 5% thorium (as ThO 2 )[1]. Thorium is more abundant than uranium and appears to be an important source of nuclear energy for the future. Thorium is a fertile material with importance being derived from its ability to accept a neutron and decay to uranium-233 which is a fissile material. This paper incorporates results from the 2019 capstone pro- ject from the honors Design Internship in Green Engineering in Chemical and Biomolecular Engineering. In this activity, senior students in Chemical Engineering at the University of Tennessee (UT) focused on the development and study of a process for the recovery of thorium dioxide and P 2 O 5 from monazite, motivated by the interest from the nuclear power industry in thorium as a fissile material. In the design, radiolog- ical aspects of the process are neglected to focus on chemical behavior. One of the authors, Bradley Bennett, was part of that class [2] and is the lead author of the current study. While not mandated, the process offers rare earth oxides as attractive byproducts. The project focused on recovery of byproducts rather than creation or addition to process streams as a method to provide economic viability for the plant design and incorpo- rate environmentally conscientious design decisions. Recent review on recovery of thorium and rare earth ele- ments of monazite have been completed by Kumari et al. [7], Ault et al. [1], and Chelgani et al. [3]. Primary approaches to thorium processing involve (1) dissolution of the feed min- erals to produce an aqueous solution, (2) a series of selective precipitation and solid-liquid separations, (3) advanced puri- fication, typically with solvent extraction, and (4) calcination/ drying. Dissolution may proceed with either strong acids or strong bases. The process presented here proceeds through steps 1, 2, and 4 from above and utilizes sulfuric acid as the dissolution agent. Additionally, this work incorporated results from the reaction scheme described by Rodliyah et al. [10] with the determination of new reaction pathways through it- eration within the software simulation. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s42461-020-00203-y) contains supplementary material, which is available to authorized users. * Bradley Bennett bbenne13@vols.utk.edu 1 The University of Tennessee, Knoxville, TN, USA 2 Florida Industrial and Phosphate Research Institute, Barton, FL, USA 3 OLI Systems, Inc, Cedar Knolls, NJ, USA Mining, Metallurgy & Exploration https://doi.org/10.1007/s42461-020-00203-y