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Author Topic: CO2 and Brine precipitation Reactions  (Read 295 times)

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seza

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CO2 and Brine precipitation Reactions
« on: December 28, 2018, 02:20:47 AM »

Seasons greeting to all,

I hope you clever people can help me:

I am trying to "precipitate" ions/solids dissolved in natural salt lake brine with CO2 injection,

the dissolved solids/ions are:
====
:: Ca 2+ ------->   32.8  g/l
:: Mg 2+ ------->   72.7 g/l
:: Na+ ---------->  56    g/l
:: K+ ------------> 21.4 g/l
:: Cl -------------> 208    g/l
:: SO4 2- ------>   36.2  g/l
:: HCO3- ------>     0.4 g/l
====

My questions to you are:
1. What are the conditions needed to facilitate such as a reaction like pressure/temp?
2. How much CO2 do I need for a given amount of brine - say 1 ton?
3. what are the balanced equations to precipitate all the elements listed?

Many thanks for your help,
seza.
 
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Enthalpy

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Re: CO2 and Brine precipitation Reactions
« Reply #1 on: January 02, 2019, 07:54:19 AM »

Hi seza, I'm not easy at all with that, but I hope to trigger better answers from other people. So:

I don't believe CO2 will precipitate anything from Cl-, SO42- nor HCO3+.

From K+, Na+ and even Ca2+, CO2 would precipitate only a part.

But you should precipitate most magnesium as a bicarbonate (here under) or maybe a carbonate (needs only 1CO2, 44g)
Mg2+ (24.3g) + 2H2O + 2CO2 (88g the pair)  :rarrow:  Mg(HCO3)2 + 2H+
The accumulation of H+ may well hinder the complete precipitation of Mg - I'm very unsure here. NaHCO3 instead of CO2 could be a parry then.

The process seems a decent way to claim selectively magnesium from brine, which is meaningful since magnesium has the commercial value. The ion composition you cite is also richer in magnesium than usual. After all, to precipitate all ions, you could just evaporate the water.

An alternative process with the same useful result would pour Ca(OH)2 in the brine to precipitate Mg(OH)2. One nice aspect of CO2 is that the residual brine isn't very polluting, and you can recycle all the CO2 to emit none, including from Mg(HCO3)2 decomposed by heat.

Your brine looks almost saturated. I suppose it shall not be saturated if you want to separate some components by precipitation. To obtain purer Mg if this is your goal, less concentrated brine looks preferable.

Temperature has a limited effect that depends on each salt. Gas pressure helps dissolve more gas, so many bar should hasten the process but they make it more dangerous. Good mixing, for instance as a mist, matters too.
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