Hi all,
I'm going to separate MgCl2 from a electrolyte solution containing MgCl2 (182 g/L), CaCl2 (458 g/l), NaCl (4 g/L), KCl (4g/L). Given that both concentration of MgCl2 and CaCl2 is very high, Is there any suitable method for separation and extraction of both MgCl2 and CaCl2 ?
I. You may consider to alkalinise the solution, possibly by adding sodium hydroxide, what would quantitatively precipitate the alkaline earth hydroxides. The precipitate could then be separated by vacuum filtering or centrifugation, and redissolved, with diluted hydrochloric acid, as MgCl2 and CaCl2.
Thank you for your answer,
Is it possible to separate MgCl2 and CaCl2 from each other by solvent addition or fractional crystallization?
II. By adding milk of lime to the MgCl2 / CaCl2 mixed aqueous solution, magnesium hydroxide precipitates quantitavely, while CaCl2 can be recovered in the mother solution after separation of the precipitate: MgCl2 (aq) + Ca(OH)2 (aq) → Mg(OH)2 (s)↓+ CaCl2 (aq). By heating the mother solution it is possible to decrease the solubility of Ca(OH)2, which would further precipitate, thus improving the separation selectivity. The obtained precipitate would contain both magnesium and (excess) calcium hydroxide. Both could be redissolved as chlorides with diluted hydrochloric acid. By repeating the process, the selectivity could be improved.
IIl. Alternatively, one might take advantage of the considerably higher solubility of CaCl2 in ethanol, as compared with MgCl2, to recrystallize a purified salt from a previous MgCl2 / CaCl2 mixed salt. The selectivity could be further improved by repeating the process.
IV. Still another separation method could be considered. After alkalinisation of the initial solution by adding sodium (or potassium) hydroxide, the alkaline earth hydroxides can be quantitatively precipitated and separated (by vacuum filtering or centrifugation). The solubility in cold water is much smaller for Mg(OH)2, compared with Ca(OH)2. Consequently, it is possible to selectively dissolve the Ca(OH)2, by washing the powder mixture of calcium and magnesium hydroxides with icy water. The washed precipitate would be essentially composed of Mg(OH)2. The washed precipitate could be redissolved with diluted hydrochloric acid, as MgCl2. The spent icy water, containing Ca(OH)2, can be neutralised with diluted hydrochloric acid, thus yielding diluted CaCl2 solution.
Your answers are quite good.
I am familiar almost with precipitation method and know about it. In method (II), is it means that I am beginning to evaporate brine, then dissolved the obtained salt in ethanol? Is there another solvents instead of ethanol for separation of MgCl2 from MgCl2 / CaCl2 mixed salt?
How do you see the schematic in attached file?
V. I think that methanol could possibly substitute for ethanol as a viable solvent to separate the MgCl2 / CaCl2 mixed salt by crystallization (Cf. III).
VI. About crystallization from aqueous solution ― Water lacks selectivity to efficiently separate the mixed salt, by either evaporative or cooling crystallization, in a single stage. Depending on brine composition, it might be possible to selectively crystallize either calcium or magnesium chloride at a first stage. Due to the lack of selectivity of the solvent, the resulting mother brine would still contain both salts dissolved in significant amounts. It may be possible to crystallize the other salt at a second stage. The composition of the brine may have to be adjusted before each stage, so that the crystallization of double salt can be avoided. The remaining mother brine may, in principle, be recycled, to some extent.
Dear Dr. C. A. Queiroz,
Thank you for your help and useful information.
However, as a conclusion, what do you propose an approach to separate magnesium chloride from brines with the following composition?
MgCl2: 182 g/L
CaCl2: 458 g/l
NaCl: 4 g/L
KCl: 4g/L
What is the most efficient and economical method? Of course, as is obvious, the extraction of calcium chloride with magnesium chloride seems reasonable. In fact, I do not want to lose any of these beneficial compounds.
Sincerely, very Sincerely
S. yousefi
VII. As a first guess opinion, not based in quantitative process analysis, I would say that from the economical perspective, producing magnesium hydroxide may actually be more attractive than to produce magnesium chloride. Consequently, I think that lime addition to the brine (Cf. II) could provide a rather reasonable starting point for further process development and analysis.
Dear Mr Yousefi, Just to ask if this brine is found in Khoor Biabanak?
Dear Mr Seyedbagheri,
Yes, of course. This is exactly Khoor Biabanak's brine.
Thank you
Dear collegue, you could try with cation-exchange resins. I recently published a method of off-line separation of solutions from charge matrix: https://doi.org/10.1111/ggr.12376. There are some references on on-line separation methods. Good luck, calcium is hard to remove; at least I used a Meditarenian see of bidistilled HCl.
- Badges
- Science topic
- Similar topics
- Biological Science
- Anatomy
- Tissue