SEPARATION OF METALS BY CONTINUOUS ANNULAR CHROMATOGRAPHY WITH STEP ELUTION

A continuous annular chromatograph (CAC) was used to separate dilute aqueous mixtures of iron and chromium salts using Dowex 50W-X8 as the sorbent. While an isocratic separation of the two species could be easily obtained, this mode of operation resulted in excessive dilution of the products. Introduction of a step in eluent concentration, however, permitted a much more efficient separation of the two metals. Separation of Fe 3+ and Cr 3+ remained nearly complete but elution of the more strongly retained species (Cr 3 +) occurred over a much narrower angle and dilution of the product streams was significantly reduced or even eliminated in some cases. A theoretical model was developed to describe the operation of the continuous annular chromatograph with step elution. With the inclusion of significant dispersive factors (axial dispersion and film mass transfer resistance), the solution of the model equations provided an excellent prediction of the experimental CAC data. Similar improvements to the CAC performance can also be obtained for other separations by manipulating the appropriate variables in a similar manner.