Abstract
The separation of inorganic ions by membrane filtration of aqueous solutions through NF-membranes was investigated. The single and binary salt solutions of NaCl, MgCl 2 , Na 2 SO 4 and MgSO 4 were used in this study. These salts are the most commonly found in natural water resources. From the research literature it was stated that NaCl has a very low rejection range with NF membranes while MgCl 2 is moderately rejected, Na 2 SO 4 and MgSO 4 are very highly rejected salts. Thus, these four salts provide a full range of rejection behavior for the NF system and hence constitute an ideal system. In addition, these salts have a very high solubility in water so there would not be any cake layer formed due to precipitation of salts at the surface of the membrane where a significantly higher concentration of salt can be developed due to concentration polarization.
Highlights
The aim of our research is to investigate the effect of an accompanying anion on the NF separation of cations by the aid of a DL membrane which is commercially available
5.1 Investigation of NaCl solution First we conducted the nanofiltration of UPW water containing 0.1 mol/dm3NaCl through the DL nanofiltrating membrane
In case of NaCl separation the curves of the single ion transmission of the sodium and chloride ions overlap, indicating that the sodium and chloride ions are passing the membrane together. It is clear from the experiment, that the transmission of the Na+as well as the Cl− ions through the nanofiltration membrane are high
Summary
The aim of our research is to investigate the effect of an accompanying anion on the NF separation of cations by the aid of a DL membrane which is commercially available. For this reason we investigated simple bivalent and monovalent ions (Na+, Mg2+, Cl−, SO24− ). For a given set of operating conditions, the salt rejections (R) follows the order: RMgCl2 < RMgSO4 < RNa2SO4. These two facts, typical of electrically charged membranes, are qualitatively in agreement with the ion exclusion principle [5–7]. Similar effects have been reported when acidic salt solutions were filtered: nitric acid and sodium nitrate permeation was enhanced by the addition of magnesium nitrate and in a separate study, sulphuric acid permeation was enhanced by the addition of copper sulphate [10, 11]
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