The development of accurate predictive models is critical to the develop­ment of novel separations and to the design and refinement of existing processes. The flowsheets for each UREX+ process module were developed using the AMUSE code (Regalbuto et al., 2004). AMUSE is an updated version of the Generic TRUEX Model (GTM). The GTM was developed during the 1980s to design multistage countercurrent flowsheets for the TRUEX solvent extraction process (Vandegrift et al., 1993, 1995).

AMUSE predicts how components distribute among the aqueous and organic phases based on the compositions and characteristics of the aqueous and organic phases at given process conditions. It accomplishes this by calculating the distribution ratios, or D values, of the stream components. The predicted distribution ratios are highly accurate over a wide range of aqueous phase compositions due to the use of chemically correct models that are based on the thermodynamic activities. A countercurrent mass balance algorithm yields the final predicted elemental composition in the extraction system for both organic and aqueous phases.

The AMUSE code is composed of two major sections, SASSE and SASPE. The material balance calculations are performed in the SASSE section, which calculates multistage countercurrent flowsheets using calcu­lated distribution ratios. The SASPE section performs the distribution ratio calculations, for all of the components, based on elemental compositions and characteristics of the aqueous and organic phases. When AMUSE is used to calculate flowsheets based on the user defined input such as (1) equipment type, (2) feed compositions and locations, and (3) general flowsheet specifications (e. g., number of stages, temperature, flow rates) an iterative process among the SASSE and SASPE sections is performed as follows:

1. The SASPE section of the model will calculate distribution ratio (D) values from stage compositions generated by SASSE.

2. The SASSE section will then refine the calculated D-values based on the compositions calculated with SASPE.

3. The iterative process continues until convergence among the two modules is achieved.

4. The output report is generated that includes the compositions of all of the components in the organic and aqueous phases for each stage of the process.

AMUSE readily calculates flowsheets for PUREX, UREX, SREX, CCD-PEG and TRUEX as it can estimate the distribution coefficients for these processes internally. Flowsheets for other solvent extraction pro­cesses, including CSSX, FPEX, and TALSPEAK can be generated using appropriate user specified D-values. AMUSE is then used to perform sen­sitivity analysis on the designed process flowsheets in order to determine the effects of flow rate variation, compositional variability, other-phase car­ryover, temperature excursions, etc. The results of the sensitivity analysis establish the process operating envelope.