Effect of pH on Total Volume Membrane Charge Density in the Nanofiltration of Aqueous Solutions of Nitrate Salts of Heavy Metals

Abstract

The separation efficiencies of aqueous solutions containing nitric salts of Zn, Cu, Fe or Pb at various pH in process of nanofiltration have been investigated experimentally. These results were used to obtain the total volume membrane charge densities, through mathematical modelling based on the Donnan–Steric partitioning Model. The experimentally obtained retention values of individual heavy metal ions varied between 36% (Zn2+ at pH = 2), 57% (Pb2+ at pH = 2), 80% (Fe3+ at pH = 9), and up to 97% (Cu2+ at pH = 9). The mathematical modelling allowed for fitting the total volume membrane charge density (Xd), which yielded values ranging from −451.90 to +900.16 mol/m3 for different non-symmetric ions. This study presents the application of nanofiltration (NF) modelling, including a consideration of each ion present in the NF system—even those originating from solutions used to adjust the pH values of the feed.

Adopting Sustainable Jatropha Oil Bio-Based Polymer Membranes as Alternatives for Environmental Remediation

“…The rejection of Cu(II) ions started to increase with the increase in feed concentration from 60 ppm to 100 ppm at constant pressure (1.5 bar) and pH value (pH 5), as shown in Figure 3a, and these conditions might be due to the changes in the membrane density, as reported by other researchers [52]. To date, it is believed that the membrane charge density is influenced by the bulk ion concentrations, in which membrane charge density increases with the electrolyte concentrations [53][54][55][56]. This phenomenon was caused by the selective and additional ions adsorption on the membrane surface or in the pore wall.…”

“…This phenomenon was caused by the selective and additional ions adsorption on the membrane surface or in the pore wall. Here, the first stage involved the complexation formation, followed by the adsorption of the additional ions, thus influencing the membrane charge [55,57,58]. Such behavior is schematically illustrated in Figure 4.…”

Description of the variation of retention versus pH in nanofiltration of organic acids

“…When the solution pH is higher than the membrane isoelectric point (IEP), the membrane surface charge increases with pH and reaches a plateau value at pH of about 7-8. This was demonstrated by the measurement of the membrane zeta potential [12,13], as well as by mathematical modeling [14]. Thus, an effective pK a value can be estimated for the membrane, that is, the average pK a value of all the functional groups.…”

Comparative Analysis of Conventional and Emerging Technologies for Seawater Desalination: Northern Chile as A Case Study

“…Conceptual diagram of the conventional membrane technologies applied to desalination (Mentioned references[53][54][55][56][57][58][59][60][61][62][63]). …”