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ABSTRACT
Owing to the recent increase in the global demand for Co, new cobalt–nickel refinery capacity is required. While solvent extraction is one of the most important separation and purification techniques in hydrometallurgy, pertraction, also called membrane-based solvent extraction, offers various advantages over conventional solvent extraction. In this study, pertraction was used to purify a pregnant leach solution obtained from spent hydrotreatment catalysts that had been produced by Minemet. A block flow diagram and mass balance for the cobalt–nickel refinery were developed and used in the experimental design. Extraction isotherms were determined as well as mass transfers optimised using a circulating batch pertraction setup for both synthetic and industrial cobalt–nickel mixed metal solutions. A comprehensive set of models was applied to translate the experimental data into a conceptual design of the industrial cobalt–nickel pertraction refinery to process pregnant leach solution from the Minemet plant.
Nomenclature
| A | = | area membrane contactor (m2) |
| Aq | = | feed flow rate (L/h; m3/s) |
| D | = | distribution coefficient (–) |
| DF | = | feed side distribution coefficient (–) |
| DR | = | raffinate side distribution coefficient (–) |
| Dgm | = | geometric mean of the distr. coeff. (–) |
| kaq | = | mass transfer coeff. at aq. interface (m/s) |
| kM | = | membrane mass transfer coefficient (m/s) |
| korg | = | mass transfer coeff. at solvent interface (m/s) |
| kov | = | overall mass transfer coefficient (m/s) |
| N | = | number of modules in series (–) |
| Org | = | solvent flow rate (L/h) |
| PLS | = | pregnant leach solution |
| Vaq | = | feed volume (L) |
| Vorg | = | solvent volume (L) |
| x | = | concentration in the feed (g/L) |
| xF | = | feed concentration (g/L) |
| xR | = | raffinate concentration (g/L) |
| y | = | concentration in the extract (g/L) |
| y* | = | solvent loading capacity (g/L) |
| yR | = | extract concentration (g/L) |
| = | mole fraction in solvent (mol/mol) | |
| ∆ptotal | = | total pressure drop over module (kPa) |
| ∆pbubble | = | membrane bubble point pressure (kPa) |
| η | = | viscosity at 20 °C (mPa.s) |
| L | = | dimensionless position in PX-column (-) |
Acknowledgments
The authors gratefully acknowledge Mr Deon van Rensburg of ChemQuest for supplying the Shellsol D70 diluent and Minemet for supplying the pregnant leach solutions.