Kinetics of thorium extraction with di-(2-ethylhexyl) 2-ethylhexyl phosphonate from nitric acid medium

• Extraction kinetics of thorium with DEHEHP from nitric acid medium was studied.
• A constant interfacial cell with laminar flow performed well in the kinetics study.
• Extraction has mixed controlled kinetics, and the slow step occurs in bulk phase.
• Rate equation was also obtained by slope analysis.

The extraction kinetics of thorium (IV) by di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP) in n-heptane from nitric acid medium was investigated by using a constant interfacial cell with laminar flow. Parameters affecting the mass transfer mechanism such as stirring rate, temperature, specific interfacial area, Th (IV) concentration, DEHEHP concentration, and interfacial tension were studied. The rate equation of extracting thorium determined by slope analysis was as follows: -d[Th]/dt = k0·[Th4 +]0.72·B0.80·[NO3−]0.82. The extraction regime was deduced to be mixed controlled by investigating the influence of stirring rate on extraction rate and by considering the activation energy (Ea; 27.46 kJ/mol). The extraction rate was independent of the specific interfacial area, which indicated that the bulk phase was the reaction zone. Furthermore, thorium extraction increased the specific gravity (d) of the organic phase and interfacial tension (γ).