Modelling Solvent Extraction of Uranium with Molybdenum Control in SysCAD

Summary

In this technical presentation, Kevin Hefner explores how thermodynamic modeling can be applied to simulate and optimize uranium solvent extraction circuits while controlling molybdenum contamination. Using SysCAD and literature-based isotherm data, he demonstrates how equilibrium constants are fitted to extraction chemistry for uranium, molybdenum, and acid systems. The presentation walks through the design and simulation of extraction, stripping, washing, and regeneration circuits, highlighting operational sensitivities such as feed grade, strip flow, and molybdenum concentration. Hefner shows how combining first-principles thermodynamics with empirical data enables accurate process predictions, improved uranium recovery analysis, and more effective circuit optimization across a wide range of operating conditions.

Takeaways

• 😀 Thermodynamic modeling is a powerful approach for simulating solvent extraction circuits, offering predictive capability across a wide range of operating conditions.
• 😀 SysCAD software supports multiple thermodynamic engines, parallel processing, and Python integration for efficient process modeling and optimization.
• 😀 Solvent extraction cells consist of a mixer for intimate phase contact and a settler for phase separation, forming the building blocks of extraction circuits.
• 😀 Uranium extraction relies on acidified tertiary amines reacting with uranyl sulfate to form organic uranyl sulfate complexes, with log K values determined from literature data.
• 😀 Molybdenum competes with uranium for extraction, and its presence in the feed requires careful consideration to minimize negative effects on uranium recovery.
• 😀 Data fitting using literature isotherms and Python optimization enables accurate calculation of equilibrium constants for both uranium and molybdenum extraction.
• 😀 The solvent extraction circuit design includes extraction, scrubbing, stripping, washing, and regeneration stages, each affecting overall uranium recovery and reagent usage.
• 😀 Wash cells can inadvertently re-extract uranium from organic phases, while regeneration cells neutralize organic and remove residual acids, impacting uranium losses.
• 😀 Sensitivity analysis shows that operational parameters such as head grade, number of strip cells, O/A ratio, and molybdenum concentration significantly affect process efficiency.
• 😀 Elevated molybdenum in the feed increases regeneration requirements and uranium losses, highlighting the need for careful feed management.
• 😀 Combining first-principles thermodynamic models with empirical data provides a flexible and accurate modeling approach suitable for different stages of project development.

Q & A

What is the main focus of Kevin Hefner's presentation?

The presentation focuses on modeling a uranium solvent extraction circuit using a thermodynamic approach, including the control of molybdenum.

What are the different approaches to solvent extraction modeling mentioned in the presentation?

Three approaches are mentioned: defining reaction extents, using plant isotherms, and applying a thermodynamic modeling approach.

Why is the thermodynamic approach advantageous compared to other modeling methods?

It allows for detailed modeling of pure system isotherms, accurate prediction of competitive extraction over a wide operating range, and relies only on the free energy of organic species, providing better applicability under varying conditions.

How was uranium extraction chemistry modeled in this study?

Uranium extraction chemistry was modeled using acidified tertiary amines to extract uranyl sulfate complexes. Log K values for four reactions were calculated by fitting literature isotherm data.

What role does molybdenum play in the solvent extraction circuit modeling?

Molybdenum is an anion that competes with uranium for extraction by acidified amines. Its concentration affects uranium recovery and organic regeneration requirements.

How were the isotherm data fitted to the thermodynamic model?

Isotherm data were fitted using a single-stage shakeout simulation in SysCAD, controlled via Python and optimized iteratively using the SciPy package to minimize the difference between predicted and experimental values.

What are the key components of a solvent extraction cell?

A solvent extraction cell has a mixing chamber for intimate mixing of organic and aqueous phases, and a settling chamber with weirs and coalescer plates to separate the organic phase from the aqueous phase.

What was observed about uranium extraction and stripping in the baseline simulation?

Most uranium extraction occurred within the first one or two stages, while stripping work was distributed across multiple strip cells. Some residual uranium remained due to wash cell re-extraction and incomplete stripping.

How do wash cells affect uranium loss?

Wash cells recover acid but also promote re-extraction of uranium into the organic phase, increasing uranium loss, particularly during regeneration.

What operational parameters were analyzed for sensitivity, and what were the effects?

Parameters analyzed included head grade, number of strip cells, O:A ratio, and molybdenum concentration. Changes affected loaded strip concentration, reagent usage, and uranium losses, highlighting the importance of balancing process conditions.

What is the primary source of uranium loss in the modeled circuit?

Organic regeneration was identified as the major source of uranium loss, more so than raffinate, due to the need to neutralize acid and remove contaminants.

What are the key advantages of using first-principles thermodynamic models in SysCAD?

They provide wide applicability over varying operating conditions, allow seamless embedding of thermodynamic calculations in a flowsheet, require no user-defined reactions, and can incorporate metallurgical test data for process optimization and design.