Crystals precipitating from lyewater solution

[littlet602]

I'm occasionally having issues with the recipe I've been using for the last year or so. I've made this same recipe (with different FOs, sometimes no FO) about a dozen times, but I've had issues with it 3 of those 12 times.

My process with the lyewater is:

1. Dissolve non-iodized salt and citric acid in distilled water
2. Slowly add NaOH to salt/citric acid solution
3. Stir until clear
4. Let cool to 120 - 130 F

Sometimes I'll have small crystals form in the solution. It normally happens after the solution has gone clear and begun to cool, but one time they formed while I was still stirring my NaOH into the water.

Anyone know what these crystals are or why they're forming? I don't believe the solution is supersaturated upon cooling, but I could be incorrect here.

I love how easily available citric acid is, and love that it's easy enough to create sodium citrate from it. I have a feeling there is the possibility I am using it incorrectly.

I have used tetrasodium EDTA in the past, so I'm open to going back to that if need be, but I'd prefer to stick with citric acid/sodium citrate as my chelant.

I've attached a screenshot of the recipe I'm using. The 60 grams of water being reserved end up being mixed with table sugar at a 1:1 ratio and that solution is then added at emulsion/very thin trace.

 

[AliOop]

One guess is that after you have reserved 60g of the water to dissolve the sugar, and then dissolved your salt and CA in remaining water, there isn’t enough available water to dissolve the lye. But you’d need someone more science-y than I to tell you if that is truly the problem.

Are you also calculating the extra lye needed to account for the CA? I wouldn’t think that would cause crystallization but you mentioned not being sure you were using the CA correctly.

Hopefully one of our science folks can clear this up for you (no pun intended).

 

[littlet602]

One guess is that after you have reserved 60g of the water to dissolve the sugar, and then dissolved your salt and CA in remaining water, there isn’t enough available water to dissolve the lye. But you’d need someone more science-y than I to tell you if that is truly the problem.

Are you also calculating the extra lye needed to account for the CA? I wouldn’t think that would cause crystallization but you mentioned not being sure you were using the CA correctly.

Hopefully one of our science folks can clear this up for you (no pun intended).

Thank you for your input! It's killing me because I don't have the chemistry background, but I do have some common sense lol. I wouldn't think there is too little water to dissolve the solutes, but it is a possibility.

My lye calc does factor in extra NaOH for what is neutralized by the Citric Acid.

So far what I'm thinking as far as going forward:

• Try using the heat transfer method going forward so there is no time for these mystery crystals to form
• Dissolve the citric acid in water and add that solution at trace instead of adding citric acid to the water and allowing that to react with the NaOH
• Switch back to using EDTA
• Stop using a chelant altogether

But I was hoping to understand and prevent this issue if possible.

As a sidenote: All the batches that have given me this problem do not behave strangely, do not zap, do not have visible crystals.

 

[AliOop]

I like your idea of dissolving the CA in the separated water. It will still react with the lye when added at trace, but it won’t use up the available water that is needed to dissolve the lye initially. Worth a try!

 

[DeeAnna]

The milky precipitate is table salt (sodium chloride).

You're making a 7% solution of salt in plain water (30 g salt + 388 g water), which is fine.

Once you add the NaOH, the solubility of the salt changes because now you've got a salt-NaOH-water mixture, not just a salt-water mixture. The salt is the limiting ingredient -- only about 3-4% salt can remain dissolved when NaOH enters the picture. The NaOH, citrate, and sugar will remain fully dissolved -- they are all MUCH more soluble than the table salt.

The rest of the salt that was originally dissolved in the plain water will precipitate out in the lye solution. As the lye solution cools, less salt can remain in solution, which is why the hot mixture is clear and the cooled mixture is milky.

If it sits long enough, the salt will settle out leaving a clear solution that's saturated with salt and the excess salt as the sediment. There's no reason you can't use the mixture -- that's what most people do when they make brine (solsiefe sp?) soap -- just stir the precipitated salt into the liquid and make the soap.

 

[littlet602]

The milky precipitate is table salt (sodium chloride).

You're making a 7% solution of salt in plain water (30 g salt + 388 g water), which is fine.

Once you add the NaOH, the solubility of the salt changes because now you've got a salt-NaOH-water mixture, not just a salt-water mixture. The salt is the limiting ingredient -- only about 3-4% salt can remain dissolved when NaOH enters the picture. The NaOH, citrate, and sugar will remain fully dissolved -- they are all MUCH more soluble than the table salt.

The rest of the salt that was originally dissolved in the plain water will precipitate out in the lye solution. As the lye solution cools, less salt can remain in solution, which is why the hot mixture is clear and the cooled mixture is milky.

If it sits long enough, the salt will settle out leaving a clear solution that's saturated with salt and the excess salt as the sediment. There's no reason you can't use the mixture -- that's what most people do when they make brine (solsiefe sp?) soap -- just stir the precipitated salt into the liquid and make the soap.

Wow, thank you! That makes perfect sense. Especially because the one batch in which they formed almost instantly had a low (1.25:1) water:lye ratio, as I had planned to add goat's milk at trace.

It seems like the simplest solution would be to exclude the salt from my recipe, I could live with that.

Is there a risk of having anything fall out of solution if I choose to do a low (~1:1) water:lye ratio while still including the citric acid but excluding the salt in the future? Is there a way I could calculate the point at which it is a possibility?

 

[DeeAnna]

If you are wanting to use 7% salt based on the water, you're basically making a solseife (sp?) soap very similar to what many people do. So whether some precipitates as super-tiny crystals or not, does it really matter? If you're just adding salt for hardness, most people use a whole lot less than this.

As far as increasing the lye concentration and wondering if the sodium citrate will precipitate out -- I dunno. I'd say precipitation of the citrate would be less likely to happen if you didn't add table salt to complicate the situation. But that's just a guess. I don't have the references that would definitively answer that question. You'd need to experiment -- try it and see.