Experimental and theoretical study of nanofiltration of weak electrolytes: SO42–/HSO4–/H+ system

Abstract

Over recent years, nanofiltration (NF) has been considered as an effective way to improve processing steps in metallurgical and hydrometallurgy applications dealing with mixtures of metal ions in sulphuric-acid-dominated solutions. The principal advantage of NF membranes over reverse osmosis (RO) membranes is their ability to allow for a practically free passage of acid, while metallic species, especially multi-charged species, are efficiently rejected. In general, these sulphuric solutions cover a range from strongly acidic solutions with pH below 1 up to moderately acidic solutions of pH 3. Over this range, changes in the feed acidity influence both the aqueous electrolyte solution speciation (SO /HSO /H) and the membrane acidbase properties (protonation of carboxylic and amine groups). However, few studies have been published on the trans-membrane transport of inorganic species coupled to changes in their speciation as well as to the properties of the membrane phase.

Ion Selectivity in Brackish Water Desalination by Reverse Osmosis: Theory, Measurements, and Implications

“…Related work that also considers pH effects and acid-base reactions is refs. [20][21][22][23][24], with some differences being that advection is neglected, membrane charge is not considered, and the model formulation uses virtual concentrations. Other related work focusing on extending the classical models, and including membrane charge and reactive ions, is refs.…”

Treatment of Electroplating Wastewater Using NF pH-Stable Membranes: Characterization and Application

“…On the other hand, the rejection of chloride by both NF membranes barely changes with pH, while the retention of sulfates decreases at pH 2, as a consequence of sulfate speciation into bisulfate and the higher positive zeta potential of the membranes. Several authors have also reported that speciation into bisulfate is responsible for the lower sulfate rejection as the pH is decreased [30,52]. Lopez et al argued that the transport of single-charged ions (such as HSO − 4 ) is favored over that of multi-charged ions by means of the dielectric exclusion phenomena [21].…”

“…A previous in-house study devoted to the effect of pH and membrane charge on the nanofiltration of acid mine drainage showed promising results in terms of simultaneous high heavy metals rejection and low rejection of sulfates, which can be utilized as a way of separating the metals from the accompanying sulfur-containing compounds [29]. The transport of inorganic species coupled to changes in their speciation has been studied by López et al [30], who also report a strong decrease in the rejection of total sulphate (SO 4 2− /HSO 4 − ) as the fraction of single-charged hydrogen sulphate (HSO 4 − ) in the feed increases.…”

“…Therefore, big room for improvement exists. Compared to other alternatives such as electrolytic deposition, electrodialysis and RO, NF offers a relatively lower energy consumption [30]. This is due to the fact that NF membranes show low rejection of hydronium ions, leading to their similar concentrations on the permeate and retentate sides.…”

Increasing sustainability on the metallurgical industry by integration of membrane nanofiltration processes: Acid recovery

“…In some cases, such as the weak electrolytes, ions can be presented as free ions and forming complexes between them, which have a noticeable impact on the separation performance. Some studies have coupled chemical equilibrium reactions with SD model [27,28].…”