MEASUREMENT OF CONCENTRATION PROFILES AND DETERMINATION OF INTERFACIAL REACTION-MECHANISM IN FERRIC ION EXTRACTION SYSTEM BY D2EHPA

In extraction of ferric ion with D 2 EHPA, concentrations of ferric io n near the interface were measured by a position-scanning spectrophoto meter, and the dependencies of reaction rate on ferric ion, extractant dimer, and hydrogen ion concentrations were elucidated. Based on the experimental results, with the aid of concentration dependencies of in terfacial tension, it was clarified that 1) in the extraction region, emulsions are formed in the organic phase, 2) the extractant reacts wi th ferric ion to form a 1 : 2 intermediate complex, 3) the rate of rea ction is proportional to ferric ion concentration and is inversely pro portional to hydrogen ion concentration, showing a first-order depende ncy on dimer extractant concentration in lower extractant concentratio ns, but zero-order in higher extractant concentrations, and 4) the rat e of reaction can be explained by assuming that the kinetic model in w hich the primary 1 : 2 intermediate complex formation reaction between ferric ion and adsorbed dimer extractant is rate-determining.