Disposing lye

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TashaBird

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I’ve got a lye solution of unknown percentage that I’d like to dispose of. Can it be used to clean drains safely? Or how would you get rid of it?
 

AliOop

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As long as you aren't on a septic system, yes, pour it down the drains.

I actually prefer to flush with hot water so none of the grease in the pipes resolidifies and sticks around. :)
 

TashaBird

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Thank you! Maybe I’ll dispose of it a bit at a time too. I would like to use the container to master batch some lye, intentionally! This is left over from a miscalculation on a soap batch awhile ago, and I have no idea what concentration it is.
 

Kari Howie

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I’m on two septic systems and I pour lye down any clogged drains we have with no apparent adverse effects. We also have our systems pumped out every 4-ish years.
Update: I just did a quick online search and a couple sources said no lye in the septic system because it can kill the good bacteria. I started making Levain-based bread (similar to using sourdough starter) which involves throwing a lot of excess yeast-laden starter down the drain so I feel like it feeds the septic system. No data to back that up. However, more concerning than harming the biome in my septic system is that lye can hurt the septic tank according to what I gleaned from an internet search. So I guess you could dispose of your lye at a recycling center (dump) where they are set up to dispose of hazardous wastes.
 
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ResolvableOwl

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Or how would you get rid of it?
Depends why you want to dispose of it. If it's just because you don't know the concentration, you could reconstruct it from measuring its density (e. g. with a hydrometer intended for brewing/winemaking), or abusing lye purity check (aka titration). Once you know how much NaOH per kg is in there, you can use it for soaps via the lye masterbatch option of common soap calculators.

If the lye is somehow contaminated, or has pulled a lot of CO₂ from the air (soda skin/crust/crystals sedimenting out), then it's best to get rid of it.
 

TashaBird

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Depends why you want to dispose of it. If it's just because you don't know the concentration, you could reconstruct it from measuring its density (e. g. with a hydrometer intended for brewing/winemaking), or abusing lye purity check (aka titration). Once you know how much NaOH per kg is in there, you can use it for soaps via the lye masterbatch option of common soap calculators.

If the lye is somehow contaminated, or has pulled a lot of CO₂ from the air (soda skin/crust/crystals sedimenting out), then it's best to get rid of it.
Oh wow! That is cool to know for future reference! I may still have a hydrometer around somewhere. This one does indeed have some funk going on, as you described. Plus, my poor pipes could probably use a little degreasing. But, I love learning new stuff about how it all works! Thank you!
 

AliOop

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I’m on two septic systems and I pour lye down any clogged drains we have with no apparent adverse effects. We also have our systems pumped out every 4-ish years.
Update: I just did a quick online search and a couple sources said no lye in the septic system because it can kill the good bacteria. I started making Levain-based bread (similar to using sourdough starter) which involves throwing a lot of excess yeast-laden starter down the drain so I feel like it feeds the septic system. No data to back that up. However, more concerning than harming the biome in my septic system is that lye can hurt the septic tank according to what I gleaned from an internet search. So I guess you could dispose of your lye at a recycling center (dump) where they are set up to dispose of hazardous wastes.
I've heard of people adding vinegar to neutralize their lye solution, so it will not negatively affect their septic system to pour it down the drain. Perhaps @ResolvableOwl could give some tips on how to figure out the amount of vinegar needed to neutralize it?
 

ResolvableOwl

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Geez 😂 … when you're grown up, you all will (have to) know how to do it by yourselves.

NaOH: molar mass = 40 g/mol (get the value from Wikipedia, or compute by yourself from a periodic table)
Acetic acid: molar mass = 60 g/mol

So 60 g of acetic acid will neutralise 40 g of NaOH

60 g acetic acid are contained in 60 g × 100%/5% = 1.2 kg vinegar (5% strength).

So you'll need 1.2 kg/40 g = 30 times the amount of regular vinegar, i. e. 30 g for each g of NaOH.
 

TheGecko

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I’ve got a lye solution of unknown percentage that I’d like to dispose of. Can it be used to clean drains safely? Or how would you get rid of it?
Yes. Commercial drain cleaner is made with Sodium Hydroxide.

Without getting into my long, sorry tale of substandard plumbing woes and the big hoe under my lower driveway (which should be fixed this summer), I make up two gallons of 35% Lye Solution every three months and pour it down our drains (and toilet) while it's still warm (but not hot). I pour it in slowly and then let it sit for a couple of hours and then follow it up with a gallon of really hot water. Prior to getting into soap making, I was buying my 'drain cleaner' Home Depot and it wasn't cheap. It cost me around $40.00; now I spend about $8.00.
 
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