Is it possible to get rid or at least reduce the concentration of sulphate in water in a simple, low cost way, that would be suitable for large amounts of water, without too much disturbing the ion composition or adding toxic substances?
The prefered aproach would be adding something that would cause it to precipitate. Yes, I know, sounds like I need a wizard :).
Dear Alja,
1. Precipitation of Sulfates: inorganic textbooks record that the earth alkaline metal ions Ca2+, Sr2+ and Ba2+ form insoluble solids. Unfortunately the most abundant and environmetally benign Ca2+ form the best soluble material: CaSO4 (gypsum), while the least soluble BaSO4 requires the least abundant and most expensive Ba2+.
Moreover, although the solubility of BaSO4 is quite low (K = 10E-10), there are still 10E-5 mol/l Ba2+ ions in solution.
2. Anion-exchanger materials: However when capturing SO42- these materials need to release other anions to the solution, such as OH-, Cl-, HCO32-.
3. Anaerobic bacteria might reduce SO42- to SO2 or SH2 which can degass from the solution. However, this means very special reaction conditions and maybe a long reaction time.
Good luck
The simplest most cost-effective way is addition of Ca2+ ions (of lime) to water thereby leading to the formation of gypsum . Any compound, that is water-soluble & contains free Ba2+ ions, is harmful to human health. This also applies to compounds containing free Sr2+ ions which act against human bones.
Removal of sulfate ions from water has been done using physical operations such as ion-exchange, nano filtration (NF), and reverse osmosis (RO). RO is more costly than NF.
The following article is useful to read:
https://www.wateronline.com/doc/sulfate-removal-technologies-a-review-0001
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