Simple Model for Characterizing a Donnan Dialysis Process

Abstract

The objective of this work is to characterize the kinetics of Donnan dialysis process by a simple model. The Nernst–Planck equation is simplified by neglecting the membrane swelling pressure and assuming an average diffusion coefficient for all ions. Experimental data are presented on the permeation of monovalent phosphate ions from a KH2PO4/NaH2PO4 feed solution to a NaCl receiver solution using two different anion exchange membranes: a low flux membrane (Fumasep FAB) and a high flux membrane (Selemion AMV). Measurements indicate a brief initial ion exchange process in which the membrane is loaded with phosphate ions. Phosphate transport data fit the predicted correlations and provide values of the overall kinetic coefficient. The kinetic coefficients derived from both membranes were found to increase linearly with the membrane phosphate concentration. The phosphate dialysis data of the low flux membrane were found to be controlled by a diffusive process, while the data of the high flux membrane were found to be mass transfer controlled. The increase of the kinetic coefficient with phosphate concentration is shown to be related to the increase in membrane ion diffusivity with its solution concentration.

Donnan Dialysis Desalination with a Thermally Recoverable Solute

“…Na + concentrations in the feed and receiver solutions are close to the Donnan equilibrium values of 9.1 and 90.9 mM, respectively (indicated by dashed violet lines), as determined by eq . A decreasing mass transfer rate of Na + is observed as DD progresses: 59% of the change in Na + concentration occurred in the first hour and only 3% from 4.0 to 8.0 h. This trend is consistent with the expected gradual diminishing of the driving force for Na + transport in batch experiments as the solution concentrations approach Donnan equilibrium. − Meanwhile, the negatively charged CEM effectively blocks Cl – permeation from the feed chamber to the receiver chamber. At the end of the experimental run (8.0 h), only 0.867 ± 0.178 mM of Cl – accumulated in the receiver chamber, with >99% of Cl – retained in the feed chamber.…”

Efficient Phosphate Sequestration in Waters by the Unique Hierarchical 3D Artemia Egg Shell Supported Nano-Mg(OH)2 Composite and Sequenced Potential Application in Slow Release Fertilizer

“…Thus, finding an effective approach to balance the increasing phosphate input into waters becomes an urgent goal. As yet, various efficient methods have been proposed, including chemical precipitation, biological treatment, , membrane extraction , and adsorption process, − to address the potential phosphate sequestration. Aiming at the enhanced trace phosphates removal, adsorption technology might be a favorable choice due to its efficient performances and economical views.…”

Electrodialysis in Aqueous-Organic Mixtures

“…This is referred to as concentration polarization. Under these circumstances, the overall mass transfer coefficient for each ion is determined by the sum of two resistances: a resistance related to the ion diffusion through the membrane, as given by Equation 2, and a resistance related to the mass transfer from the solution bulk to the membrane(82). Eventually, a limiting current density I lim.…”