Calling all amateur soap chemists -- Disodium EDTA experiment

[DeeAnna]

Short version:
Would people who have Disodium EDTA (I really do mean Disodium, not Tetrasodium!) do me a favor -- would you please try to dissolve Di EDTA in the lye solution you use for your next soap batch and report back? Some questions I have for you --

Does the Di EDTA dissolve easily in your lye solution?
If you use a lye solution that is 35% NaOH (or KOH) or stronger, does the lye solution remain clear after adding Di EDTA?
Do you have any observations, comments, tips, or tricks about using Di EDTA?
​

***

Long version:
Suppliers of soap and cosmetic ingredients may sell two forms of the chelator EDTA -- there's Disodium EDTA and there's Tetrasodium EDTA.

Tetra EDTA is highly soluble in plain water, so it's easy to use for many hand crafted bath and beauty products such as soap, lotions, etc. Di EDTA, on the other hand, is not nearly as soluble in plain water.

For this reason, many of us who use EDTA prefer to buy the Tetra version. Unfortunately, it's easy to forget there are two versions and purchase Di EDTA by mistake. In a recent thread, we discussed if and how Di EDTA can be successfully used if that's the version a person happens to have. See https://www.soapmakingforum.com/threads/how-to-make-tetraedta-in-39-solution.72729/

The key to dissolving Di EDTA is to dissolve it in a high pH (alkaline) solution, not plain water. So that got me to thinking -- any lye solution that would be used to make soap will have a much higher pH than is strictly needed to easily dissolve Di EDTA. So why not add Di EDTA powder to the lye solution and then make soap as normal?

Problem is -- I don't have any Di EDTA to test this theory, which is the reason for this thread. Carolyn (@cmzaha) says it works for her to dissolve Di EDTA in the lye solution she plans to use for soap making. She reports it just dissolves without any trouble.

Would others who have Di EDTA do me a favor -- would you please give this a try and report back?

Does the Di EDTA dissolve easily in your lye solution?
If you use a lye solution that is 35% NaOH (or KOH) or stronger, does the lye solution remain clear after adding Di EDTA?
Do you have any observations, comments, tips, or tricks about using Di EDTA?​

More info:

What is a chelator: https://classicbells.com/soap/chelator.html
Using tetrasodium EDTA in soap: https://classicbells.com/soap/EDTA.html
Using disodium EDTA in soap: Use the same dosage by weight as Tetra EDTA. (See link in the line right above.) You can use KOH or NaOH solution for dissolving Di EDTA.​

 

[Misschief]

I'm at work right now so can't really concentrate. Will answer tonight. I did try it on the weekend.

 

[Misschief]

Ok, I'm home now. I went with what Salted Fig wrote in one of her posts in the How to Make TetraEDTA thread. Towards the end of her post, she finished with:

Conclusion:
It's probably worth adding the extra hydroxide if you are using Disodium EDTA, but not entirely necessary.

Original Tetrasodium EDTA: 1000g of oil, 5g of Tetrasodium EDTA
Disodium version with NaOH: 1000g of oil, 5g of Disodium EDTA and 1g additional NaOH
Disodium version with KOH: 1000g of oil, 5g of Disodium EDTA and 1.5g additional KOH
Disodium version with KOH: 1000g of oil, 5g of Disodium EDTA and 1.6g additional 90% KOH

The batch of soap I made used 1000 g of oil, which is what most of my batches are, so I added 5 g of Disodium EDTA and 1 g additional NaOH. The DiEDTA was added to my lye solution. It dissolved fairly readily but did cloud the lye solution enough that I felt I should strain it into my oil mixture. There was no residue left in the strainer, which was my finest strainer. It did take a little extra stirring to incorporate the DiEDTA; I even used my mini blender, being very careful to make sure nothing splattered. I wasn't sure whether I should add the powder directly to the dry lye or into the water before adding the lye. I ended up adding it after the lye was dissolved.

I used a 33% lye solution but did add 1g extra lye.

 

[DeeAnna]

I would add Di EDTA powder to the lye solution.

If you add Di EDTA to just the water before adding the NaOH (or KOH), the Di EDTA is not going to dissolve well. It's all but insoluble in plain water.

I was wondering if a more concentrated lye solution might cloud when Di EDTA is added. I know Tetra EDTA will precipitate out of NaOH solutions when the lye concentration is about 35% or higher. The lye solution will look like milk and may even thicken up. If the lye concentration is below about 35%, this problem doesn't happen. It stands to reason that Di EDTA would probably do likewise.

Thank you, @Misschief!

 

[kayak1987]

Disodium EDTA is just an intermediate form between EDTA and Tetrasodium EDTA
the switch between the varoius form of EDTA is an equilibrium driven by the concentrations of sodium and hydronium ions (pH) and regulated by the constants of acidity and solubility.

Considering this, is "easy" to predict that in a solution with NaOH (where NaOH is in excess respect to "EDTA") so at High pH:
-EDTA will be very soluble beacuse the H+ are pulled out by the OH- and in solution you have EDTA(4-) now with his equilibrium with the various 1,2,3,4Na forms
-DiNaEDTA will be still soluble but more influenced by the common Na Ion
-Tetra Na EDTA didn't get any advantage of the pH and to dissolve needs to loose at least 1 Na+ that is in competition with the Na+ released by the NaOH

Other things to consider are that if there are other Ions in the solution you have new equilibriums to consider, dissociations and chelations equilibria
so if you don't use good deionized water is very hard to predict what is that gives to solution the milky look.

Antother thing to consider is that Saponification is a stechometric reaction where you need all the lye Sodium to turn the acid to soap, as well as EDTA is competing for sodium when can't no more stay in solution (because of water get consumed by saponification and after, evaporating during cure time), so if you are using EDTA or Di EDTA is better to consider not to discount too much the Lye or to add some Table salt to prevent side reactions that can lead to release fatty acids (and maybe rancidity problems)

 

[DeeAnna]

In this thread, I'm specifically asking soapers to share how-to-do-it (or how not do it) tips for using disodium EDTA in everyday soap making.

Science has its place, but empirical, practical knowledge is what I'm after here. Thanks....

 

[glendam]

I could try in my next batch, however, I am a bit concerned since I do not know much about how they actually work, only that tetrasodium EDTA is for soap and disodium EDTA is for lotions because of the ph (I have both and make both soaps and lotions). By adding disodium to the the lye water, is it becoming tetrasodium?

 

[DeeAnna]

...By adding disodium to the the lye water, is it becoming tetrasodium?

Yes, that's correct. Tetrasodium EDTA is very soluble and disodium EDTA is only slightly soluble in plain water. As you increase the pH by adding NaOH or other alkali, the disodium form gradually converts to the tetrasodium form. (I'm simplifying a bit here, but that's the essence of what happens.) We discussed this in this thread: https://www.soapmakingforum.com/threads/how-to-make-tetraedta-in-39-solution.72729/

I don't want anyone to do this experiment unless you are really curious about the outcome and want to try it for yourself. If you are fairly new to making soap or are uncomfortable with the idea of a failed batch of soap or of making a mess, I recommend that you do not participate in this experiment. Let the crazy folks like me give it a go and figure out what works first.

 

[glendam]

Thanks for explaining. I love experiments, just got Kevin Dunn’s book. I usually take videos of my soapmaking too, so I will report back once I get to make soap again, hopefully this week. I’ve been making for over a year.

Short version:
Would people who have Disodium EDTA (I really do mean Disodium, not Tetrasodium!) do me a favor -- would you please try to dissolve Di EDTA in the lye solution you use for your next soap batch and report back? Some questions I have for you --

Does the Di EDTA dissolve easily in your lye solution?
If you use a lye solution that is 35% NaOH (or KOH) or stronger, does the lye solution remain clear after adding Di EDTA?
Do you have any observations, comments, tips, or tricks about using Di EDTA?
​

***

Long version:
Suppliers of soap and cosmetic ingredients may sell two forms of the chelator EDTA -- there's Disodium EDTA and there's Tetrasodium EDTA.

Tetra EDTA is highly soluble in plain water, so it's easy to use for many hand crafted bath and beauty products such as soap, lotions, etc. Di EDTA, on the other hand, is not nearly as soluble in plain water.

For this reason, many of us who use EDTA prefer to buy the Tetra version. Unfortunately, it's easy to forget there are two versions and purchase Di EDTA by mistake. In a recent thread, we discussed if and how Di EDTA can be successfully used if that's the version a person happens to have. See https://www.soapmakingforum.com/threads/how-to-make-tetraedta-in-39-solution.72729/

The key to dissolving Di EDTA is to dissolve it in a high pH (alkaline) solution, not plain water. So that got me to thinking -- any lye solution that would be used to make soap will have a much higher pH than is strictly needed to easily dissolve Di EDTA. So why not add Di EDTA powder to the lye solution and then make soap as normal?

Problem is -- I don't have any Di EDTA to test this theory, which is the reason for this thread. Carolyn (@cmzaha) says it works for her to dissolve Di EDTA in the lye solution she plans to use for soap making. She reports it just dissolves without any trouble.

Would others who have Di EDTA do me a favor -- would you please give this a try and report back?

Does the Di EDTA dissolve easily in your lye solution?
If you use a lye solution that is 35% NaOH (or KOH) or stronger, does the lye solution remain clear after adding Di EDTA?
Do you have any observations, comments, tips, or tricks about using Di EDTA?​

More info:

What is a chelator: https://classicbells.com/soap/chelator.html
Using tetrasodium EDTA in soap: https://classicbells.com/soap/EDTA.html
Using disodium EDTA in soap: Use the same dosage by weight as Tetra EDTA. (See link in the line right above.) You can use KOH or NaOH solution for dissolving Di EDTA.​

 

[glendam]

Ok, I was able to try this over the weekend.
It did not dissolve easily by just hand stirring with a spoon.
It seemed to dissolve better with a blender (I blended in low, but it is a powerful motor and it even the "Low" is pretty fast.
My lye concentration is 33% and it stayed cloudy. Finer particles settled at the bottom, so I blended before adding to the oils.
Here are links to the recipe and to the video:
https://www.lyecalc.com/recipe/master-with-lard-strawberry-superman

 

[Misschief]

I decided to try the Di EDTA once more and did it a little differently this time, just cuz I could. I did the same weight of oils, 1000 grams, and this time I added the Di EDTA to the water before adding the lye. It immediately went to the bottom and sat there in a blob. And I do mean a blob. It didn't flatten out like most powders would do. I tried to stir it into the water and the blob separated into smaller blobs. Once I added, and stirred in the lye, I stirred it until I couldn't see any more solid bits.

It remained cloudy enough that I couldn't really see whether there were any bits left but I decided to strain it before adding to my oils. There was quite a bit more in the strainer than the last time but not as much as I had expected.

Conclusion: add the Di EDTA after you've made your lye solution, not before adding the lye. It will dissolve much better.

 

[DeeAnna]

Thank you @glendam and @Misschief! I appreciate your help. I'll watch your video when I get a bit more time, Glendam.

I know Tetra EDTA will cause precipitation when added to the lye solution when the NaOH concentration is around 35% or more. The Tetra EDTA can even thicken the solution into a white pudding or gravy texture, which is rather alarming if you're not expecting it. When the NaOH concentration is lower, the solution will remain clear (or gradually return to clearness if it was cloudy). I suspect this is also happening with your Di EDTA turning the lye solution cloudy.

I see Glendam used 33% NaOH solution. Misschief -- did you also use 33% solution in the last batch you described in Post 11?

 

[Misschief]

Thank you @glendam and @Misschief! I appreciate your help. I'll watch your video when I get a bit more time, Glendam.

I know Tetra EDTA will cause precipitation when added to the lye solution when the NaOH concentration is around 35% or more. The Tetra EDTA can even thicken the solution into a white pudding or gravy texture, which is rather alarming if you're not expecting it. When the NaOH concentration is lower, the solution will remain clear (or gradually return to clearness if it was cloudy). I suspect this is also happening with your Di EDTA turning the lye solution cloudy.

I see Glendam used 33% NaOH solution. Misschief -- did you also use 33% solution in the last batch you described in Post 11?

Yes, 33%... that's my usual strength.

 

[DeeAnna]

Good to know. Thanks!

 

[glendam]

When I have used tetra, the solution did go clear, though I recall having a handful of particles floating. With disodium, it appeared to go somewhat clear but if stirred, it went back to being cloudy, the finer particles would just settle at the bottom.
In the making of this other soap last December, I used tetra at the same lye concentration of 33% in case you want to compare the lye solution clearness. It is at the 00: 26 seconds time frame:
Apple and cinnamon soap with Madder root

 

[DeeAnna]

@glendam -- My experience has been the same as yours -- Tetra EDTA is clear in lye solution under about 35% NaOH concentration. The floating particles you saw on the lye solution with the Tetra could very easily be sodium carbonate from NaOH reacting with CO2 in the air. When the concentration rises higher than about 35% is when the Tetra becomes a problem.

I watched your video in Post #10 -- thank you again for sharing that! I see it definitely takes some fiddling to get the Di EDTA to dissolve. Adding the powder all at once might be contributing to the clumping problem -- similar to what happens when a person adds dry flour to simmering gravy. It might be helpful to lightly shake the powder into the liquid while stirring to minimize the size of the clumps. Or maybe what you did in the video is as good as it gets -- patiently stir the mixture after adding the powder until the clumps largely dissolve.