Project Synopsis

Perform a pre-feasibility study for a process to extract and refine rare earth elements.

Project Summary


Process Engineering Associates, LLC (PROCESS) was subcontracted by the client, a regional detail engineering firm, to provide process engineering support for a pre-feasibility study for a process to extract and refine rare earth elements (REE) for the ultimate client, a rare earth minerals processor.

Process Flow Diagrams (PFDs) including Heat and Mass Balances (HMBs) were produced for the physical upgrade and for the hydrometallurgical sections of the plant.  The HMBs were developed using a combination of METSIM for the metallurgical processing and CHEMCAD to optimize the design of the distillation unit.  PROCESS worked in collaboration with the client to develop bench scale and pilot plant test work and to analyze the data provided by the testing.  Both models were developed using test data.

The project also included a year-by-year operating cost and rare earth oxides (REO) production analysis based on the project mining plan.

The physical upgrade process units include crushing, screening, milling, gravity separation and magnetic separation while the hydrometallurgical process includes hydrochloric acid leaching, oxalate precipitation, metathesis, nitric acid leaching, thorium separation, REE precipitation, REE drying and dehydration, hydrochloric acid distillation, oxalate crystallization, and effluent treatment.

The leach unit uses a combination of fresh and recycled hydrochloric acid in a counter-current process to solubilize the REE from the ore and generate a pregnant leach solution (PLS).  The oxalate precipitation unit reacts oxalate ions from fresh and recycled sodium oxalate and oxalic acid with the PLS to selectively precipitate REE and thorium as oxalates.  The oxalate precipitate is further processed in the metathesis unit while the barren solution is sent to the distillation unit.  The metathesis unit reacts the oxalate precipitate with sodium carbonate to form solid REE and thorium carbonates and a recycled solution of sodium oxalate.  The REE and thorium carbonates are then leached with nitric acid and the thorium is selectively precipitated.  The pH of the resulting thorium free REE nitrate solution is then raised to precipitate REE as hydroxides.  The hydroxides are dewatered and dehydrated to form a pure thorium-free rare earth elements oxide concentrate.  The barren solution from the oxalate precipitation unit is processed in the hydrochloric acid distillation oxalate crystallization unit to recover hydrochloric acid and oxalic acid.  The resulting effluent is neutralized before disposal.


Industry Type

  • Mining and Minerals Recovery

Utilized Skills

  • Bench and pilot plant test support
  • Hydrometallurgical unit operations design

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