Sorption characteristics and performance of an acid dye on a gel-type weak anion exchanger in a finite bath

The sorption behaviour of carminic acid on a gel-type weak anion exchanger was evaluated in a finite bath. Equilibrium and kinetic studies were employed to characterise the system. Adsorption isotherms were found to follow the Langmuir expression. Concentration-time profiles were obtained in a stirred vessel. The sorption kinetics was unaltered provided that the particle suspension criterion was met. Analytical equations were found for quantitative description of the system and to assist in scale-up. Fluid-side effects and intraparticle resistance mechanisms were revealed. The fluid-side mass transfer coefficient (k(f)) took an almost constant value of 2.6 x 10⁻⁵ m s⁻¹ under these experimental conditions. Amberlite IRA-67, owing to its gel structure, was treated so as to present a homogeneous diffusion type, and a solid diffusivity (D(s)) value of 3.16 x 10⁻¹⁰ m2 s⁻¹ was determined experimentally. This value was insensitive to stirrer speed and could be considered constant for further design purposes. Overall mass transfer in the system showed a mixed nature with a balanced contribution of both resistances (delta approximately equal to 1).