prommis.uky.uky_flowsheet

University of Kentucky REE Processing Plant

Author: Marcus Holly

The University of Kentucky (UKy) rare earth element (REE) processing plant is designed to extract salable rare earth oxides from domestic U.S. coal and coal byproducts. While this implementation of the plant does not take into account all of the complexities and unit processes detailed in the 2019 report, it depicts the major phenomena by utilizing a series of conventional REE extraction techniques, including acid tank leaching, solvent extraction, precipitation, and product roasting.

Implementation

Figure 1 shows the process flow diagram for the simplified, steady-state UKy plant where the solid and liquid feeds are sent to a leaching tank for initial processing; then the solids (with some retained liquid) are separated out as a filter cake while the remaining liquid is sent to the solvent extraction process which is comprised of 2 distinct circuits. In the rougher circuit, solutes in the aqueous phase are transferred to the organic phase, and a portion of the depleted aqueous solution is recycled back to the leaching process while the remainder is sent to the cleaner circuit. The degree to which components are transferred from one phase to the other is dependent upon the unit’s partition coefficient for that particular component. In the cleaner circuit, solutes in the organic phase are transferred to the aqueous phase, and a portion of the loaded aqueous solution is recycled back to the rougher circuit while the remainder is sent to the precipitator. The precipitate (with some retained liquid) is sent to the roaster where the product rare earth oxides are generated, and the liquid from the precipitator is recycled back to the cleaner circuit.

Fig. 1 University of Kentucky flowsheet

Degrees of Freedom

The following variables must be specified by the user to run the UKy flowsheet:

• liquid feed volumetric flow rate and component concentrations

• solid feed mass flow and component mass fractions

• volume of leach tank(s)

• partition coefficients for each solvent extraction unit

• flow rate and component concentrations for organic make-up streams and HCl feeds

• liquid recovery fraction for solid-liquid separators

• precipitator inlet temperature

• roaster inlet temperature and pressure, outlet temperature, and pressure drop

• roaster gas and moisture molar flows, vapor component mole fractions, and oxide recovery fraction

• split fractions for each recycle loop

Default Flowsheet Specifications

Description	Value	Units
Leaching
Tank volume	100	\(\text{m}^3\)
Liquid feed volumetric flow	224.3	\(\text{L/hr}\)
Liquid feed H concentration	100	\(\text{mg/L}\)
Liquid feed HSO4 concentration	1e-8	\(\text{mg/L}\)
Liquid feed SO4 concentration	4800	\(\text{mg/L}\)
Liquid feed REE and contaminant concentrations	1e-10	\(\text{mg/L}\)
Solid feed mass flow	22.68	\(\text{kg/hr}\)
Solid feed inerts mass fraction	0.6952	\(\text{dimensionless}\)
Solid feed Al2O3 mass fraction	0.237	\(\text{dimensionless}\)
Solid feed Fe2O3 mass fraction	0.0642	\(\text{dimensionless}\)
Solid feed CaO mass fraction	0.00331	\(\text{dimensionless}\)
Solid feed Sc2O3 mass fraction	2.8e-5	\(\text{dimensionless}\)
Solid feed Y2O3 mass fraction	3.3e-5	\(\text{dimensionless}\)
Solid feed La2O3 mass fraction	6.8e-5	\(\text{dimensionless}\)
Solid feed Ce2O3 mass fraction	1.6e-4	\(\text{dimensionless}\)
Solid feed Pr2O3 mass fraction	1.7e-5	\(\text{dimensionless}\)
Solid feed Nd2O3 mass fraction	6.8e-5	\(\text{dimensionless}\)
Solid feed Sm2O3 mass fraction	1.5e-5	\(\text{dimensionless}\)
Solid feed Gd2O3 mass fraction	1.0e-5	\(\text{dimensionless}\)
Solid feed Dy2O3 mass fraction	7.5e-6	\(\text{dimensionless}\)
Solvent Extraction Rougher
Loading section organic feed volumetric flow	62.01	\(\text{L/hr}\)
Organic make-up REE and contaminant concentrations	1e-7	\(\text{mg/L}\)
Scrubbing section acid feed volumetric flow	0.09	\(\text{L/hr}\)
Scrubbing section acid feed H concentration	10.36	\(\text{mg/L}\)
Scrubbing section acid feed Cl concentration	359.64	\(\text{mg/L}\)
Scrubbing section acid feed REE and contaminant concentrations	1e-7	\(\text{mg/L}\)
Stripping section acid feed volumetric flow	0.09	\(\text{L/hr}\)
Stripping section acid feed H concentration	41.44	\(\text{mg/L}\)
Stripping section acid feed Cl concentration	1438.56	\(\text{mg/L}\)
Stripping section acid feed REE and contaminant concentrations	1e-7	\(\text{mg/L}\)
Solvent Extraction Cleaner
Loading section organic feed volumetric flow	62.01	\(\text{L/hr}\)
Organic make-up REE and contaminant concentrations	1e-7	\(\text{mg/L}\)
Stripping section acid feed volumetric flow	0.09	\(\text{L/hr}\)
Stripping section acid feed H concentration	41.44	\(\text{mg/L}\)
Stripping section acid feed Cl concentration	1438.56	\(\text{mg/L}\)
Stripping section acid feed REE and contaminant concentrations	1e-7	\(\text{mg/L}\)
Precipitator
Inlet temperature	348.15	\(\text{K}\)
Roaster
Pressure drop	0	\(\text{Pa}\)
Gas inlet temperature	348.15	\(\text{K}\)
Gas outlet temperature	873.15	\(\text{K}\)
Gas inlet pressure	101325	\(\text{Pa}\)
Gas inlet molar flow	0.00781	\(\text{mol/s}\)
Gas inlet O2 mole fraction	0.1118	\(\text{dimensionless}\)
Gas inlet H2O mole fraction	0.1005	\(\text{dimensionless}\)
Gas inlet CO2 mole fraction	0.0431	\(\text{dimensionless}\)
Gas inlet N2 mole fraction	0.7446	\(\text{dimensionless}\)
Moisture inlet molar flow	6.75e-4	\(\text{mol/s}\)
Oxide recovery fraction	0.95	\(\text{dimensionless}\)
Separators
Leaching solid-liquid separator liquid recovery fraction	0.7	\(\text{dimensionless}\)
Solvent extraction rougher load recycle split fraction	0.9	\(\text{dimensionless}\)
Solvent extraction rougher scrub recycle split fraction	0.9	\(\text{dimensionless}\)
Solvent extraction rougher organic recycle split fraction	0.9	\(\text{dimensionless}\)
Solvent extraction cleaner organic recycle split fraction	0.9	\(\text{dimensionless}\)
Precipitator solid-liquid separator liquid recovery fraction	0.7	\(\text{dimensionless}\)
Precipitator solid-liquid separator liquid recycle split fraction	0.9	\(\text{dimensionless}\)

Costing

Unit model costing in this flowsheet is preliminary and is based on the commercial scale unit model parameters provided in Table 4-28 \(^1\). However, this flowsheet is at the pilot scale, so while some of the unit model costing parameters have been scaled down accordingly, a more robust scale-down procedure of the costing parameters is necessary to accurately approximate the cost of this pilot scale system.

References:

[1] Steven Keim, “Production of salable rare earths products from coal and coal byproducts in the U.S. using advanced separation processes”, 2019

prommis.uky.uky_flowsheet.add_costing(m)

Set the costing parameters for each unit model.

Parameters:

m – pyomo model

prommis.uky.uky_flowsheet.build()

Build and connect the unit model blocks present in the University of Kentucky REE processing plant.

prommis.uky.uky_flowsheet.display_costing(m)

Print the key costing results.

Parameters:

m – pyomo model

prommis.uky.uky_flowsheet.display_results(m)

Print key flowsheet outputs.

Parameters:

m – pyomo model

prommis.uky.uky_flowsheet.fix_organic_recycle(m)

Fix the volumetric flow rate of the organic recycle streams and unfix the flow of make-up streams.

Parameters:

m – pyomo model

prommis.uky.uky_flowsheet.initialize_system(m)

Provide initialized values for all streams in the system.

Parameters:

m – pyomo model

prommis.uky.uky_flowsheet.main()

Run the flowsheet by calling the appropriate functions in series.

prommis.uky.uky_flowsheet.set_operating_conditions(m)

Set the operating conditions of the flowsheet such that the degrees of freedom are zero.

Parameters:

m – pyomo model

prommis.uky.uky_flowsheet.set_partition_coefficients(m)

Sets the partition coefficients for each finite element in the solvent extraction blocks.

Parameters:

m – pyomo model

prommis.uky.uky_flowsheet.set_scaling(m)

Set the scaling factors to improve solver performance.

Parameters:

m – pyomo model

prommis.uky.uky_flowsheet.solve_system(m, solver=None, tee=False)

Solve the model.

Parameters:

• m – pyomo model

• solver – optimization solver

• tee – boolean indicator to stream IPOPT solution