4 replies to this topic

[peaston]

hey, i am currently trying to design an experiment whereby i extract carbonates from concentrated seawater (retentate).

i know that i can use carbon dioxide to capture the ions in the water which can then be precipitated out.

since it would be a gas-liquid reaction i am guessing a tubular reactor (?) would be best, but I'm not sure on the conditions the reaction should take place at.

any one got any ideas on what i could do?

thanks!

[kkala]

1. Notes on the subject.
- Retentate seems to be the part of sea water not passing through the membrane in a reverse osmosis plant, http://wiki.answers....at_is_Retentate.
- Carbonates in sea water are described in http://www.livingree...ystem-t358.html. HCO3^- + CO3^2- form a buffer solution of pH ~8.2. HCO3^- concentration is much higher in sea water (evidenced by pH value too), see http://www.engtips.....cfm?qid=158905. Evidently Ca²⁺ is not in concentration high enough to precipitate.
- CO2 behaves as weak acid (dissociation constant K1=4.5*E-7). Addition of CO2 gas into the retentate will lower pH, HCO3^- will remain so, removal of carbonates by precipitation will not be promoted.
2. Carbonate precipitation in water can be realized by addition of hydrated lime, which will increase pH.
Ca(HCO3)2 + Ca(OH)2 --> 2CaCO3 + 2H2O (Betz, Handbook of Industrial Water Conditioning, 7th ed, 1976).
This is a rather inexpensive solution that could be the basis of the experiment.
3. If this scheme is tried, an agitated pot is required in the lab, to keep hydrated lime (Ca(OH)2) and precipitated CaCO3 in suspension. Also heating to some constant temperature will be probably needed, to increase reaction rate.
An industrial extension would require continuous stirred tank reactor (s), probably heated. Filtration would be the next step.
4. I do not know if the query is covered, "extract carbonates" may not mean "precipitate carbinates". Hopefully above is helpful. Purpose of experiment is not clear to me, probably you cannot dispose retentate as is? More explanations / data would help answering the query. Other opinions would be welcomed for this topic

Note: I believe negative feedback on their first questions of newbies had better be avoided. It does not help. Words could be more constructive.

Edited by kkala, 09 December 2011 - 03:16 PM.

[breizh]

Kostas has described the way I get use to operate the purification of Brine and eliminate Ca2+ . If the chemistry is fine in multiple vessels in serie it requires residence time for settling and pond to dispose the waste solid.
Hope this helps
Breizh

[kkala]

So readers should be aware that discussion is continued in the thread http://www.cheresour...hemical-rector/, titled "Designing a chemical reactor", started by peaston on Dec 16th 2011.

[peaston]

i want to delete this thread how would i go about doing so?