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 CO
2 will precipitate anything from Cl
-, SO
42- nor HCO
3+.
From K
+, Na
+ and even Ca
2+, CO
2 would precipitate only a part.
But you should precipitate most magnesium as a bicarbonate (here under) or maybe a carbonate (needs only 1CO
2, 44g)
Mg
2+ (24.3g) + 2H
2O + 2CO
2 (88g the pair)
Mg(HCO
3)
2 + 2H
+The accumulation of H
+ may well hinder the complete precipitation of Mg - I'm very unsure here. NaHCO
3 instead of CO
2 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 CO
2 is that the residual brine isn't very polluting, and you can recycle all the CO
2 to emit none, including from Mg(HCO
3)
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.