Parameter estimation for trace element sorption on a new granular iron oxide

Abstract

In order to acquire information on sorptive systems suitable for predictive and design applications, it is necessary to gather and analyze data in bench or prototype reactors, the most common types being batch and packed column. In this paper, data from both types of reactor are presented and contrasted for the case of two trace elements, cadmium and chromate, sorbing to a granular form of iron oxide. The granular oxide was developed in conjunction with the ALCOA Laboratories specifically for use in column reactors. Data are analyzed using a surface coordination chemical approach and film transfer, surface and pore diffusion transport models. Governing coefficients are extracted using nonlinear optimization techniques which provide an objective interpretation of the data without the errors introduced by various linear transformations or analysis bias. Results indicate that both experimental techniques are capable of accurately measuring the equilibrium coordination constant for sorption reactions, however batch estimates for the total sorptive capacities are consistently lower than column estimates, which range from 1.1 mg/g for Cd to 3.3 mg/g for CrO4. In addition, when column adsorption and desorption data are taken together, it is possible to obtain reliable estimates of rate‐controlling parameters. This is not generally possible for batch systems under conditions representative of those encountered during environmental control.