Process optimization, kinetics, and thermodynamics for the selenium extraction from Cardamine violifolia

Abstract

Selenium supplementation is an effective means for its deficient population to maintain their health. The selenium extraction is one of the most important procedures for preparing its supplements. This work provided a systematic investigation on the selenium extraction process from Cardamine violifolia. Firstly, the selenium extraction process was optimized by using the single factor analysis and response surface optimization. Its optimal conditions were particle size 60 mesh, stirrer rotation speed 125 r min⁻¹, initial extraction pH 9, extraction temperature 70 ℃, ratio of water to material 100 ml g⁻¹ and extraction time 27 min. Under its optimal conditions, the selenium concentration in the extracted liquid reached 4.45 µg ml⁻¹. Then its kinetics were investigated, and its kinetic data was in good agreement with the pseudo-first order kinetic model. Its mass transfer coefficient k ranged from 0.0765 to 0.1411 min⁻¹ when its temperature changed from 40 to 70 ℃. And its apparent activation energy ΔE was 22.84 kJ mol⁻¹. Finally, its thermodynamic parameters were calculated, its enthalpy change ΔH was 30.07 KJ mol⁻¹, its entropy change ΔS was 99.3 J mol⁻¹ K⁻¹, and its Gibbs free energy ΔG was range from −1.00 to −3.96 KJ mol⁻¹ when its temperature changed from 40 to 70 ℃. These thermodynamic parameters indicated that the selenium extraction process from C. violifolia was a spontaneous, endothermic and entropy increasing process. This work provides useful information to industrialize the selenium extraction from C. violifolia for its supplement preparation.