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Modelling and simulation of molybdenum extraction by HDEHP ion-exchanger and DMDOHEMA solvating extractant

Abstract : Molybdenum is an element which is co-extracted with other lanthanides or actinides by many organic solvents in liquid-liquid separation processes. Thus, it is often necessary to manage this element to prevent any pollution of the process output. This paper describes the studies carried out by CEA - DRCP to model and better understand the behavior of molybdenum in the EXAm process. The originality of this liquid-liquid extraction process is the simultaneous presence of two extractants in the organic phase, following two types of mechanisms: extraction by solvation thanks to DMDOHEMA or HDEHP, extraction by ion exchange with HDEHP. Although these two extractants play a specific role for the extraction of lanthanides in each step of the process, with this organic phase only the HDEHP extracts molybdenum, whatever the acidity of the aqueous phase. Unlike lanthanides or americium, speciation of molybdenum in the aqueous phase varies depending on the experimental conditions (pH, concentration of molybdenum). Extraction mechanisms are in principle different for each species. At high acidity, Mo is well simulated by using a Mo(DEHP)2 organic complex. On the other hand, low acidity leads to a more complicated chemistry of molybdenum involving various species in aqueous and organic phases. For this study, over a range of pH greater than 1, it was decided to limit to three species (one cation, one anion and one neutral species): MoO42-, MoO3 and MoO22+. Therefore, the intermediate species, dimers and polymers are initially represented by with one of those three species. Molybdenum is extracted by one of three types of mechanisms, depending on pH value: cation exchange, extraction by solvation or anion exchange. It should be noted that experimentally only the MoO2DEHP2HDEHP2 complex was identified in the organic phase. Experiments were used to determine the values of the constants associated with equilibrium. The model was implemented in the PAREX simulation code to design flowsheets. The calculation results were compared with experimental data from tests carried out in mixer-settlers. The comparison showed the good accuracy of the model. It can be used to predict behavior of the chemical system, including changes in pH associated with the extraction and back-extraction of Mo at low acidity. This modeling can be easily adapted to other separation processes, such as rare earth extraction processes, for which it is necessary to manage molybdenum as an impurity.
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Submitted on : Tuesday, November 10, 2020 - 11:36:37 AM
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  • HAL Id : cea-02997814, version 1




V Vanel, C Marie, M Duchesne, X Hérès, V Pacary, et al.. Modelling and simulation of molybdenum extraction by HDEHP ion-exchanger and DMDOHEMA solvating extractant. ISEC 2014 - 20th International Solvent Extraction Conference, Sep 2014, Würzburg, Germany. ⟨cea-02997814⟩



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