Sciencemadness Discussion Board - NaOH / Al separation (drain cleaner)

NaOH / Al separation (drain cleaner)

Diachrynic - 27-2-2018 at 11:32

I plan to extract chromium from stainless steel I dissolved via electrolysis of NaCl with sodium hydroxide. Found a promising thread on here.

So, as I don't know yet how much NaOH I'm going to need, I better source some more in advance. In any case it's a useful chemical.

I found a really cheap drain cleaner, half a kilo, pellets.
Now, the thing is there are some small bits of aluminum in there. If I wanted to make hydrogen, I couldn't care less, but in this case maybe purification isn't such a bad idea.

Unfortunately, the Al has a pretty similar size to the NaOH pellets, so a sieve probably wouldn't work.
Since the damn stuff is hygroscopic as hell, prolonged exposure to air will cake it together, so unless I work fast, picking out the Al manually could get difficult.
The densitys are similar as well (2.1and 2.6), so solvent / floating seems not possible.

Is there some "trick" to separate those two?

happyfooddance - 27-2-2018 at 11:38

This is a difficult problem, as you probably already know. I would try to dissolve the NaOH in a less-polar solvent like ethanol, and hopefully filter off the Al. Try at a few different temps, they will likely produce different results.

DraconicAcid - 27-2-2018 at 11:50

How big are the pellets? You might be able to put the sealed container on some sort of shaker, and let the aluminum settle to the bottom.

RawWork - 27-2-2018 at 11:58

Are you joking? That product came like that? Is it dry? Never seen it before...
To separate is impossible for amateurs/normal people. It reacts with each other, glass, carbon dioxide from air. My advice: give up.

happyfooddance - 27-2-2018 at 12:03

That is a good suggestion, DraconicAcid. The difference in densities isn't great, but time should do it.

Sodium hydroxide solution can be made, with calcium oxide or hydroxide, and sodium carbonate. CaO can be made from chalk.

There are easier ways to NaOH than this difficult separation.

That being said, the mix you have might work as is for your purposes, though it isn't ideal.

MrHomeScientist - 27-2-2018 at 12:03

It's very common for drain cleaners to do this; the gas produced helps loosen clogs while the NaOH does most of the work.
Biodiesel or soapmaking suppliers are good sources for clean hydroxide (NaOH and KOH), which I'd recommend over trying to purify something yourself.

Diachrynic - 27-2-2018 at 12:07

Quote: Originally posted by happyfooddance

This is a difficult problem, as you probably already know. I would try to dissolve the NaOH in a less-polar solvent like ethanol, and hopefully filter off the Al. Try at a few different temps, they will likely produce different results.

Hmm, so would I regain the NaOH by letting the solvent evaporate? I guess the hygroscopic nature could be a problem.

Quote: Originally posted by DraconicAcid

How big are the pellets? You might be able to put the sealed container on some sort of shaker, and let the aluminum settle to the bottom.

Fairly small, about 1-2 mm in diameter. I also thought they'd be bigger.
I'll get my hands on a sealable container and try that out.

Quote: Originally posted by RawWork

Are you joking? That product came like that? Is it dry? Never seen it before...
To separate is impossible for amateurs/normal people. It reacts with each other, glass, carbon dioxide from air. My advice: give up.

No, I'm not joking. Those drain cleaner companies add small bits of Al to it to increase heat and evolve hydrogen to get rid of clogs.
It's sealed in HDPE.

Welp, if my tries fail, I guess it should still work to dry stuff (desiccant).

RawWork - 27-2-2018 at 12:11

It's easy to separate Al from Na, of course, but if you wanna your Na to end up like chloride or carrbonate. But to keep Na hydroxide, have no idea, except doing something extreme or expensive. Not worth it.

happyfooddance - 27-2-2018 at 12:18

Quote: Originally posted by Diachrynic

Quote: Originally posted by happyfooddance

Hmm, so would I regain the NaOH by letting the solvent evaporate? I guess the hygroscopic nature could be a problem.

Moreso than the hygroscopic nature (pure etOH has no water) the problem would be the reaction with atmospheric CO2.

I have made NaOH many times, by salt metathesis and electrolysis, and CO2 is always the biggest problem. All of these processes are inefficient, you can make a pure solution easily by metathesis, for your purposes this might be something to look into.

Diachrynic - 27-2-2018 at 12:26

Damn, I wished I picked some up a few years ago in Denmark. They sell it pure in kilo quantities over the counter (also stuff like phosphoric acid, what for though).

happyfooddance - 27-2-2018 at 12:30

Useful chemical is right. I get anxiety anytime my NaOH (or KOH) supply gets below 1 kilo.

RawWork - 27-2-2018 at 12:33

Relax, Al won't interfere in most reactions, and will separate during reactions.

[Edited on 27-2-2018 by RawWork]

happyfooddance - 27-2-2018 at 13:28

Quote: Originally posted by Diachrynic

Damn, I wished I picked some up a few years ago in Denmark. They sell it pure in kilo quantities over the counter (also stuff like phosphoric acid, what for though).

Look into what I said, salt metathesis. For your purposes you should be able to get exactly what you need. To make CaO you only need chalk and a fire. Sodium bicarbonate, AFAIK is not restricted anywhere. With sodium carbonate and CaO, you have NaOH in solution and calcium carbonate as a precipitate.

The catch is, you almost always have either NaOH sol. with a little bit of carbonate contamination, or Ca contamination. Usually both. But I think it would be much preferable to Al contamination for your purposes.

Diachrynic - 28-2-2018 at 07:21

Yeah, I know that route. A bit too much effort for NaOH I feel - Well, I'm kind of lazy.

Anyway, I did some testing.

The size of the pellets is actually closer to 0.5 mm diameter. Al has also that size.

I tried the box-method, and it didn't really work. The Al was on the top, on the bottom, and everywhere in between. Maybe patience and a better technique could change that.

The good news I might have found a method which could work okay.

So in my lab it is bloody cold, freezing. (This morning -13 C outside, now -6 C)
When I measured my destilled water, it instantly turned into a icy slushy mass.
I dissolved my drain cleaner in there. (9 g in 100 g water, to make a approximatly 2M solution.)
Turns out I forgot a important thing: The Al does not give a shit about the lye when it is dilute and really really cold.
The heat was just enough to melt the ice. Solution was not hot at all.
Since there is a time delay between the mixing and the Al starting to really react which is even greater when it is cold, there was no visible reaction.

Now, I think I could just filter/sieve the Al off!

The reaction of the lye with the Al took about 2-3 minutes to kick in.

(Unfortunatly, a small scale test suggested that either the dissolution of chromium hydroxide is painfully slow or my lye was not concentrated enough. I hope the latter is the case. Filtrate was clear like water. Further testing required.)

Rhodanide - 28-2-2018 at 07:51

Quote: Originally posted by Diachrynic

I plan to extract chromium from stainless steel I dissolved via electrolysis of NaCl with sodium hydroxide. Found a promising thread on here.

So, as I don't know yet how much NaOH I'm going to need, I better source some more in advance. In any case it's a useful chemical.

I found a really cheap drain cleaner, half a kilo, pellets.
Now, the thing is there are some small bits of aluminum in there. If I wanted to make hydrogen, I couldn't care less, but in this case maybe purification isn't such a bad idea.

Unfortunately, the Al has a pretty similar size to the NaOH pellets, so a sieve probably wouldn't work.
Since the damn stuff is hygroscopic as hell, prolonged exposure to air will cake it together, so unless I work fast, picking out the Al manually could get difficult.
The densitys are similar as well (2.1and 2.6), so solvent / floating seems not possible.

Is there some "trick" to separate those two?

Now why the hell would any company KNOWINGLY sell those mixed?!
That makes no sense, were the designers high when they came up with the idea? Is there even any benefit to having Al present? What even....

Diachrynic - 28-2-2018 at 08:01

This was already asked and answered in this thread.

Hydrogen and heat loosens up clogged pipes.

(Although there is really not much in there...)

RawWork - 28-2-2018 at 09:18

They probably relied on fact that dry chemicals don't react. But that's close to dangerous. Somebody may drop a drop of water in container accidentally...boom! But hydrochloric acid is not far from that considering safety. Nor are other acids, peroxide... Temperature here is -20 tonight, worst night in a year. Tommorow and onwards it won't drop below zero even during night. So hopefully I'll live.

[Edited on 28-2-2018 by RawWork]

LearnedAmateur - 28-2-2018 at 13:01

Eh, hydroxide and aluminium + water isn’t really anything exciting, definitely no explosions or anything unless you’re in a poorly ventilated space, holding an ignition source particularly close, and dump in a whole load of water. Even sodium bicarbonate and vinegar is a more vigorous reaction than mixing concentrated NaOH solution with aluminium foil, IME, which would be more so than adding water to a mixture of solid pellets since those particular products are designed for controlled gas production and higher temperatures (exothermic dissolution as well as exothermic reaction).

AJKOER - 28-2-2018 at 18:12

A long shot, if the aluminum is an alloy containing a small amount of iron, try a magnet!

Another idea, try rapidly adding chilled distilled water and quickly drain off leaving behind the Al pieces. Results in a solution of NaOH with some NaAl(OH)4 impurity.

clearly_not_atara - 1-3-2018 at 07:36

The danger would be if evolved hydrogen were trapped under a ceiling and accumulated.

subskune - 3-3-2018 at 12:16

Quote:

Another idea, try rapidly adding chilled distilled water and quickly drain off leaving behind the Al pieces. Results in a solution of NaOH with some NaAl(OH)4 impurity.

Works! I've already done that. if you are fast < 30 sec. almost nothing will happen. Use a known volume of destilled water and you'll have a nice solution, which is more useful than anhydrous in some applications.