Modeling Cesium Ion Exchange on Fixed-Bed Columns of Crystalline Silicotitanate Granules

Abstract

A mathematical model is presented to simulate Cs exchange in fixed-bed columns of a novel crystalline silicotitanate (CST) material, UOP IONSIV IE-911. A local equilibrium is assumed between the macropores and the solid crystals for the particle material balance. Axial dispersed flow and film mass-transfer resistance are incorporated into the column model. Cs equilibrium isotherms and diffusion coefficients were measured experimentally, and dispersion and film masstransfer coefficients were estimated from correlations. Cs exchange column experiments were conducted in 5-5.7 M Na solutions and simulated using the proposed model. Best-fit diffusion coefficients from column simulations were compared with previously reported batch values of Gu et al. and Huckman. Cs diffusion coefficients for the column were between 2.5 and 5.0 × 10 -11 m 2 /s for 5-5.7 M Na solutions. The effect of the isotherm shape on the Cs diffusion coefficient was investigated. The proposed model provides good fits to experimental data and may be utilized in designing commercial-scale units.

Modeling of the adsorption breakthrough behaviors of Pb2+ in a fixed bed of ETS-10 adsorbent

“…Each of such factors must be appropriately accounted for to accurately simulate the overall column performance. Compared with the various mass-transfer rates, the adsorption rate is often observed to be faster [5]. Therefore, the overall uptake kinetics may be eventually determined by such steps as the mass transfer across the liquid film, diffusion across the * Corresponding author.…”

“…For adsorption on solids with a bimodal pore system like zeolite pellets, a heterogeneous model (also known as a macro-micro model) [5,12], which considers both macropore and micropore diffusion resistances, should be used. However, because of the complexity of the model, only one diffusion resistance (either the micropore or macropore resistance) is considered, thus simplifying the modeling [5].…”

“…For adsorption on solids with a bimodal pore system like zeolite pellets, a heterogeneous model (also known as a macro-micro model) [5,12], which considers both macropore and micropore diffusion resistances, should be used. However, because of the complexity of the model, only one diffusion resistance (either the micropore or macropore resistance) is considered, thus simplifying the modeling [5]. For example, it has been demonstrated that a two-phase homogeneous model (TPHDM) is sufficient for predicting the adsorption behaviors of zeolites toward various metal ions [5,12,13], assuming that (i) the metal ion concentration in the pore liquid is in instantaneous equilibrium with that on the solid surface, and (ii) the diffusion resistance in the micropores is negligible.…”

“…However, because of the complexity of the model, only one diffusion resistance (either the micropore or macropore resistance) is considered, thus simplifying the modeling [5]. For example, it has been demonstrated that a two-phase homogeneous model (TPHDM) is sufficient for predicting the adsorption behaviors of zeolites toward various metal ions [5,12,13], assuming that (i) the metal ion concentration in the pore liquid is in instantaneous equilibrium with that on the solid surface, and (ii) the diffusion resistance in the micropores is negligible. ETS-10, a zeolitic material [14] constituted from SiO 4 tetrahedra and TiO 6 octahedra, possesses a high cation-exchange capacity [15,16] because of the presence of tetravalent Ti in an octacoordinated state, which generates two negative charges balanced by alkali cations [17], namely Na + and K + .…”

“…In this work, the breakthrough behaviors of Pb 2+ ions on ETS-10 pellets in a fix-bed column were experimentally measured and theoretically simulated. Since the ETS-10 particles used for the fixed-bed adsorption possess a bimodal pore system with both intracrystal micropores and intercrystal macropores, the TPHDM [5] was employed to predict and optimize the breakthrough curves. The values of the model parameters, including liquid film mass-transfer coefficient (k f ), axial dispersion coefficient (D L ), and effective macropore diffusivity (D e ), were optimized and validated by comparing the model predictions with the experimental data.…”