Extraction Kinetics of Phosphoric Acid from the Phosphoric Acid—Calcium Chloride Solution by Tri-n-butyl Phosphate

Abstract

The design and enlargement of extraction equipment require kinetic data on the extraction system. In this study, the extraction kinetics of phosphoric acid from the phosphoric acid—calcium chloride solution by tri-n-butyl phosphate (TBP) was investigated using a constant-interfacial-area cell with laminar flow. The extracted complexes were demonstrated to be H3PO4·TBP, H3PO4·2TBP, and H3PO4·3TBP by equilibrium studies. The effects of stirring speed, temperature, and interfacial area on the extraction rate were investigated. The results indicate that the extraction process is under mixed control by the extraction reaction at the interface and the diffusion of the reactant in the aqueous phase. The extraction rate is first-order with respect to H3PO4 and TBP with a rate constant of 10–5.34 L·mol–1·s–1. A mixed-control regime model is proposed. The forward extraction rate constant and the diffusion coefficient of the reactant in the aqueous phase were calculated to be 6.86 × 10–6 and 6.47 × 10–5 L·mol–1·s–1, respectively.