Mass transfer limiting step determination and a new modified empirical model for Th(ІV) biosorption in a fixed-bed column

Abstract

In this paper, a new empirical model for predicting breakthrough curves of Th(ІV) biosorption using Ca-pretreated Cystoseria indica alga in a fixed bed column was presented. Also, the comparison of the proposed model with the Thomas, Yoon-Nelson, and Clark models showed that the new model had better agreement with the experimental data. Furthermore, the optimum flow rate of 2.5 mL/min with a maximum biosorption capacity of 213.20 mg/g was obtained using the proposed new model. Also, four mass transfer models, including internal mass transfer, external mass transfer, biosorption on active sites, and triple resistance, were used to determine the rate-limiting step and mass transfer mechanism. The internal mass transfer was considered the mass transfer controlling step. In addition, the sensitivity analysis of the mass transfer coefficients (kf, ks, kad) again showed that the internal resistance is the governing mass transfer resistance to the Th(ІV) biosorption process. The biosorption of Th(IV) from a real effluent by Ca-pretreated Cystoseria indica alga in a fixed-bed column was investigated to validate the new empirical model. The results demonstrated that the new empirical model could describe biosorption behavior more accurately than the Thomas model.