Modeling Adsorption of Metal Ions from Aqueous Solutions

The second part of KINEQL, which calculates adsorption rates under the condition that adsorption is controlled by mass transfer, is described in this article. The adsorption process is analyzed again in terms of three separate but interacting phenomena: surface ionization, complex formation, and the presence of an electrostatic double layer adjacent to adsorbent surfaces. A general form of a rate expression, suitable for transport-controlled cases, is formulated; this rate expression represents an approximate form of the intraparticle equation that has been found by other investigators to be very accurate for batch processes. Sample calculations demonstrating the use of the algorithm to calculate adsorption histories of cadmium on aluminum oxide are presented. Matching of experimental results with model calculations is obtained only after a combined macropore and micropore diffusion model is employed. In this model, macrodiffusion and microdiffusion act in parallel and independently. Reasonable values of the transport parameters are obtained in the case where only the simple metal ion diffuses into the interior of the adsorbents.