Computational Simulation of Filters Used in the Removal of Heavy Metals Using Rice Husks

The biofiltration technique is of great importance for the removal of heavy metals. In the present work, a laboratory-scale biofilter was modeled using rice husk as a filter material. The Wolborska model was used to know the dimensions necessary for the biofilter to function. The Langmuir and Freundlich isotherms were performed to quantify the filter adsorption process, showing that the Langmuir isotherms are the ones that present the highest correlation coefficient and best represent the removal process of Cd (II), Cu (II) and Cr (VI). According to the Langmuir isotherms, the maximum operating temperature allowed for this model was chosen, which was 303.15 K, because it presents the maximum removal of heavy metals. Regarding the pH variations for Cd (II) and Cu (II), the maximum removal was presented with a pH = 9.0 and for Cr (VI) with a pH = 3.0 the maximum removal was presented. According to the rupture curves, the blocking times were obtained for each height: for Cd (II) the highest tb for h = 0.55, Cu (II) the highest tb for h = 0.40 and for Cr (VI) the highest tb for h = 0.40.

Efficient Simulation of Chromatographic Processes Using the Conservation Element/Solution Element Method

Chromatographic separation processes need efficient simulation methods, especially for nonlinear adsorption isotherms such as the Langmuir isotherms which imply the formation of concentration shocks. The focus of this paper is on the space–time conservation element/solution element (CE/SE) method. This is an explicit method for the solution of systems of partial differential equations. Numerical stability of this method is guaranteed when the Courant–Friedrichs–Lewy condition is satisfied. To investigate the accuracy and efficiency of this method, it is compared with the classical cell model, which corresponds to a first-order finite volume discretization using a method of lines approach (MOL). The evaluation is done for different models, including the ideal equilibrium model and a mass transfer model for different adsorption isotherms—including linear and nonlinear Langmuir isotherms—and for different chromatographic processes from single-column operation to more sophisticated simulated moving bed (SMB) processes for the separation of binary and ternary mixtures. The results clearly show that CE/SE outperforms MOL in terms of computational times for all considered cases, ranging from 11-fold for the case with linear isotherm to 350-fold for the most complicated case with ternary center-cut eight-zone SMB with Langmuir isotherms, and it could be successfully applied for the optimization and control studies of such processes.

The Adsorption of Cadmium and Zinc Ions from Waste Waters in Agricultural Argilaceous Soils

The adsorption of cadmium and zinc ions from waste waters in agricultural argilaceaus soils have been studied, using a thermodynamic method in order to put in evidence the influence of adsorption conditions on adsorption degree. The adsorption isotherms, Langmuir and Freundlich, have been used to describe the adsorption equilibrium. The experimental data put in evidence that Cd2+ ions are more adsorbable (about 300 mmol/g) than Zn2+ ones (about 200 mmol/g). The Langmuir isotherms reflect more exactly the adsorption process of both Cd2+and Zn2+ ions, being recommended for thermodynamic parameters determination.