The kinetics of liquid-liquid extraction of metals in a rotating diffusion cell. A rotating diffusion cell is used to study the rates of extraction of divalent transition metals by di-(2-ethylhexyl)-phosphoric acid and a sulphur analogue. A chemical-diffusion model describes the rate curves.

摘要

A rotating diffusion cell (RDC) has been used to study the kineticsudof extraction of the transition metals cobalt (II), nickel (II), copperud(II) and zinc (II) from sulphate solutions into either of two extractantsudheld in n-heptane; di-(2-ethylhexyl) phosphoric acid (D2EHPA) or di-(2-udethylhexyl) dithiophosphoric acid (D2EHDTPA). The metal concentration wasud10 mM and the aqueous pH was held at 4.5. The extractant concentration wasudvaried between 0.015 to 0.4 M. In the case of cobalt extraction by D2EHPA,udthe metal concentration and the pH were varied Different diluents andudmodifiers were also studied.The rate of extraction by D2EHDTPA was found to be faster than D2EHPA.udA comprehensive mathematical model, based upon established two filmudtheory, was developed and used to describe the above experimental results.udThe model was also used to predict values of the important parameters. ... These values compared well with those found by other authors but usingudquite different experimental techniques.udOS4 In the case of cobalt extraction by D2EHPA, the more polar diluentsudlowered the initial rate. The overall model predicts such behaviour whereudthe rate is also dependent on the partition coefficients of the extractant.udFinally, the theory of the RDC allows the prediction of the diffusionudlayer thicknesses, this information together with the reaction zone thicknessudis used to explore the influences of diffusion and chemical reaction on theudoverall transfer process. The diffusion processes are calculated to be theudmost important of the two. This is especially so for the D2EHDTPA systems.