Selectivity of alginate gel for Cu over Zn when acidic conditions prevail

When cupric and zinc ions existed at relatively high concentrations (100 ppm each) in the aqueous media, a Na–alginate solution can be directly dispensed into the aqueous media (initial pH: 2.6–5.4) circulating in a loop fluidized-bed reactor to produce spherical alginate gels in situ that contain both Cu and Zn. An extended Langmuir model for two adsorbates competing for the same type of binding sites was tested against batch absorption data obtained with these gels. Conditional binding stability constants for Cu–alginate and Zn–alginate and binding capacity of the alginate were obtained from the proposed model for each initial pH. Selectivity calculated as the ratio of the stability constant of Cu–alginate to that of Zn–alginate was found to be about 10.