Zinc-Dust Process:
Some important producers still use the zinc-dust process, which was
developed by BASF.
The basic reactions are:
Zn + 2SO2 = ZnS2O4
ZnS2O4 + 2NaOH = Na2S2O4 + Zn(OH)2
An aqueous slurry of zinc dust is treated in a stirred reactor with cooling at 40 degree C with liquid or gaseous sulfur dioxide to give zinc dithionite. After completion of the reaction the solution is passed through a filter press to remove unreacted zinc dust and impurities from the zinc. The zinc is then precipitated from the zinc dithionite by adding sodium carbonate or sodium hydroxide in stirred vessels. The zinc carbonate or hydroxide is removed in filter presses. Anhydrous sodium dithionite is precipitated from the clarified sodium dithionite solution by concentration under vacuum and addition of sodium chloride at > 60 degree C. It is filtered, washed with methanol, and dried at 90 – 100 degree C.
Reference: "Sulfites, Thiosulfates, and Dithionites". Ullmann's Encyclopedia of Industrial Chemistry. Wiley Online Library. doi:10.1002/14356007.a25_477. ISBN 978-3527306732.
- Badges
- Science topic
- Similar topics
- Biological Science
- Biota
- Eukaryota
- Fungi