Purification of CaCl2 with Ca(OH)2?

[biom]

Do you think it is good idea to put some kalkwasser in CaCl2 solution and to remove the residue. The goal is to purify solution from heavy metals/phosphates that could be present in CaCl2.

 

[Randy Holmes-Farley Verified Community Expert]

That will certainly pull out some of those things, but it will leave a fair amount of hydroxide in the solution (but not as much as in limewater due to the very high calcium concentration forcing the equilibrium below to the left).

Ca(OH)2 <--> Ca++ + 2OH-

So whether to do it or not may depend on how problematic those metals and phosphate are, and what impact that hydroxide might have on how you dose the calcium (slow would be fine, all at once may not be if the dose is high).

You may have seen it, but I discuss that removal process here:

Chemistry And The Aquarium: Metals In Limewater ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/issues/may2003/chem.htm

 

[biom]

I'm using auto doser, dosing only 8 ml per hour so the high pH is not a problem. My CaCl2 is analytical grade, but last time I noticed black particles on the bottom of the canister after dissolution, so my analytical grade calcium is not that pure,that is why I want to be sure no unwanted heavy metals will enter my tank. And I dont have tests for heavy metals, just tested for ammonium - it was negative.

 

[Randy Holmes-Farley Verified Community Expert]

OK, that sounds like a reasonable plan. It's an interesting idea.

 

[biom]

Thank you Randy for all your help and education. I'll try and report back.

 

[Randy Holmes-Farley Verified Community Expert]

Sounds good.

You might measure the pH of the concoction if you have a meter available. We could calculate the hydroxide present at saturation (and Jim probably will ), but a measure would be nice too.

Happy Reefing.

 

[JimWelsh]

Recrystallize it. It is a very easy and efficient means of purification. Here's a fun little timelapse video I did of the sudden crystallization of a supersaturated solution of CaCl2 after a "seed crystal" is added.

 

[biom]

Sounds good.

You might measure the pH of the concoction if you have a meter available. We could calculate the hydroxide present at saturation (and Jim probably will ), but a measure would be nice too.

Happy Reefing.

Yes i'll do that, but what will happened if the solution contains MgCl2? I suppose Mg(OH)2 will precipitate and since is more insoluble than Ca(OH)2 will lower pH?

Thank you Jim very nice video, yes recrystallization is another very good option despite fact that certain amount of the calcium chloride will be lost.

 

[Randy Holmes-Farley Verified Community Expert]

Yes i'll do that, but what will happened if the solution contains MgCl2? I suppose Mg(OH)2 will precipitate and since is more insoluble than Ca(OH)2 will lower pH?

Thank you Jim very nice video, yes recrystallization is another very good option despite fact that certain amount of the calcium chloride will be lost.

Yes, Mg(OH)2 will precipitate, along with any excess solids of Ca(OH)2 and any CaCO3 that forms.

I think that those solids do a fair amount of the filtering, binding other things (phosphate and metals) onto their surfaces.