View Full Version : Practical Chemistry Question

05-14-2006, 03:14 AM
I'll have to direct this question to those who have a much higher expertise in chemistry than I have (probably most of you!)

Here is the situation; I recycle, and so I collect all of my aluminum chips from my machining aluminum into my wet vac.

One machining job I did was on pine boards, and I cleaned it up with the same vacuum. Now I have a vacuum with probably 10 pounds of aluminum and a few pounds of sawdust.

My thinking was that I could simply add water. The metal would sink, and the wood would float.

This isn't what happened.
The aluminum and wood were perfectly miscible.
It became like a paste.

So, it doesn't seem to be a simple density question. I know that Aluminum has a great affinity to carbon. I know that wood has a lot of carbon. I am thinking that the aluminum and the wood are attracted by the valence electron structures. I've got some more ideas but It has been years since I've studied chemistry.

Why doesn't the aluminum sink, and the sawdust float?

Thank you for your input.


05-14-2006, 04:05 AM
Sawdust will soon absorb enough water to sink; if your wet vac was already wet, maybe with coolant, perhaps by the time you got to it the sawdust was already waterlogged. Either that or coolant /cutting fluid on the swarf was binding the two together. If it's an oily pine, the oil in the timber might be enough to do that.
Or if it's all bone dry there must be another explanation ;)


05-14-2006, 08:00 AM
Aluminum has practically zero affinity for carbon. The simple explanation is that wet ground/chopped wood contains partially dissolved lignin, which is sticky. It sticks to the aluminum. When wood is ground up it releases the lignin in the cell walls which is a bio-polymer resin. This is the basis behind mechanical wood pulping processes for making short grain pulp.

You can try throwing in some potassium metabisulfite tablets used to preserve wine as this is what is used in the chemical pulping process to separate the lignin by dissolving it from the cellulose wood fiber. It may need to be heated. Be aware that some people are very sensitive to bisulphites and it can cause a severe allergic reaction from breathing the vapors.

05-14-2006, 08:05 AM
I think it's more a case of wetness & physics going on in your vacume...as has already been said. The Aluminum chips were probably wet with coolant, then you added a bunch of sawdust. (How dry was the wood?)
Surface area of the media involved often has a lot to do with how much water it will retain (think sand). Sawdust and Al chips both will "absorb" or "adsorb" (sorry, I can't remember which term is srtictly technically correct in this instance, too many years & too much beer...) water because of this.
I think your shop vac just has a big wet lump of Al & sawdust....maybe pour out the chips & try washing the sawdust off with a hose, or sloshing them around in a container of water. Use a "bag" made of large-mesh plastic screen, maybe.

John Stevenson
05-14-2006, 08:09 AM
Just use a Black and Decker shop vac.
This way when you are done sucking the crap up, it catches fire and all you are left with is the alloy, the rest burning off.

For anyone who has never used a B&D shop vac they are the only product made by B&D that don't suck.............


05-14-2006, 08:25 AM
B&D shop vac they are the only product made by B&D that don't suck.............
Thats a BLOW to B&Ds reputation

Alistair Hosie
05-14-2006, 11:45 AM
get a large box of cotton buds and thern spend a day seperating the aluminium and wiping each peice with the buds till you gat a nice shine, then store them in a seperate pile seems obvious really shouldn't take morenayear or two:DAlistair

05-14-2006, 12:59 PM
Surface tensions on either the al or the wood dust need to be altered/enhanced. For the same reason you make soapy suds in the washing machine: to float the dirt and lint to the top to be drained to sump. Try a little foaming soap i.e. dish detergent in conjunction with a double handfull of chips in a five gallon pail. Slosh around, check to see the al chips go to the bottom and the wood dust in suspension with the suds.

College chemistry prof showed us how to alter the non-wetting characteristics of natural oils found on duck feathers. In nature, the feathers float, but to wash away the oil, the feathers would wet/sink. Of course the prof knew what we would do to the waters in the duck pond

05-14-2006, 01:36 PM
Not enough water. Throw the whole mess in the lake and stir it up. The aluminum will sink and the wood will float. JRouche

05-14-2006, 01:44 PM
All you need to do is oxidize the carbons in the wood fibre and the aluminum is all that will be left.

05-14-2006, 06:41 PM
Here's a lowtech approach to resolve your problem: Lay the material out and let it dry (in the sun). Thereafter, break up the composite. MIx in water and the sawdust will float and the aluminum will sink. Alternately, take the dried material and mix in permanent antifreeze (ethlyene glycol) which has a specific gravity of 1.13. The higher specific gravity (than water) will further aid the separation.

05-14-2006, 08:49 PM
Why not burn the saw dust to get the aluminum. If you blow air on it very lightly as it burns you should have only fly ash left with the aluminum. I have not tried it but I have burned a lot of wood. It needs a hot fire.

05-14-2006, 11:24 PM
No chemistry. Surface tension of the water or some other sticky as others mentioned is likely the problem. Adding soap has been mentioned and will help unstick. Vigorous stiring will help.

If both floating add detegent and stir. Trapped air and or wetting is sticking it together.

If both sinking add salt or antifreeze this will raise the density to where the wood will float.

If both sort of mixed up in the water. Add more water should be like milk not a paste and should feel like water not maple syrup when stirrred. Stir and leave for a while should separate eventually.

I'm curious why are you separating them?

05-15-2006, 01:34 AM
You are probably right. I might just as well throw the whole lot into the pot and just let it burn off. Still I thought it was very interesting how it took together. The sawdust was very clean and dry and some of it was pretty fine. I just assumed it would float and the aluminum would sink. It took right to the aluminum and made soup. It all eventually settled to the bottom wood and metal together. The metal was pretty clean too and the coolant that I was using was a water based coolant that was something like a 20/1 water/coolant ratio. After filling up my wet-vac with water it's pretty well diluted whatever coolant was left on the chips. There seems to be an affinity between the two (wood & aluminum.) I'll try not to mix the two ever again. Thanks for the replys.

05-15-2006, 03:15 AM
Dump it all out on the driveway and blow the wood away with a leaf blower (or wind) and scoop up the aluminum chips (that is assuming you want to keep the Al for some reason.) Then again, aluminum does come from the ground anyway... :)

05-15-2006, 03:35 AM
This might be too simple, but why don't you just suck up one or the other? You want salvaged aluminum, clean and suck it up. Dump and suck anything else you want.

I think, I am not sure, that aluminum scrap is worth more, today, than cedar chips..

If you want to save the cedar chips, good luck.



05-15-2006, 10:56 AM
Take it from someone who harvested his firewood from a lake for fifteen years, waterlogged wood sinks.

If you dry out and try to burn the combination, you might have a bigger fire than you've bargained for. It depends upon how fine the aluminum particles are. If fine enough you'll have either an explosion or a really nasty fire.

Take my advice. Write this one off to experience. The salvage value of the aluminum isn't going to pay for your time and effort.

My 2ยข


05-15-2006, 11:21 AM
HEY, speaking of fire...you could always throw a little magnesium in there and start your own business!

05-15-2006, 12:56 PM
There seems to be an affinity between the two (wood & aluminum.)

Didn't anybody read my post? I serviced equipment in two pulp mills for over 20 years and learned a fair amount about wood pulping from the guys there. The lignin is like glue. When you saw up the cells in the wood it comes out. It's sticky and sticks to the aluminum.

To be technical, the reason that it sticks to the aluminum is that lignans contain hydroxyl groups that are electropositive because of the hydrogen atoms in the OH groups. Aluminum is electronegative so the lignans tend to stick to it. This is how many adhesives work including the lignans which are members of the phenolic family.

05-15-2006, 12:59 PM
And....there he goes again! Evan, I have a childhood friend just like you..we argue all the time about his Theories and My common sense. I tell him, some things man will never know, no matter how many words and theories he can come up with. He never believes me nor do I believe him. He used to be a preacher also, so it goes to show. I grew up in a household of 3 high school teachers, so nowdays I try to stay from the theoritical (electropositive because of the hydrogen atoms in the OH groups. ) You don't think anybody gives a rat's Ass about that , do you? Evan, just chill out and speak the facts. I know the so-called science you speak of. Most will NEVER be proven in our lifetimes, if ever. Sometimes you have problems just answering a question. This is machining, not science class.

05-15-2006, 01:01 PM
Ask a question and I will give the answer, if I know it. You may note that there are many questions asked on many topics that I do not reply to. That is because I do not know the answer.

05-15-2006, 01:14 PM
Very good, same here.

Weston Bye
05-15-2006, 01:25 PM
... though he hardly needs it:

Quote from Dilbert- "Do you want the simple but misleading explanation or the one you won't understand?"

Keep up the good work, Evan

05-15-2006, 01:28 PM

What part of this did you not understand?

The lignin is like glue. When you saw up the cells in the wood it comes out. It's sticky and sticks to the aluminum.

05-15-2006, 01:34 PM
Evan, what part do you not understand..the problem was wood sticking to aluminum. Here's a rough example..throw your dirty socks and shorts into a vat with aluminum--add some water, now what do you think will happen? See the relationship between cloth, wood and any alloy..then add water.? Don't forget, H2O has oxygen, what's in oxygen--water.

05-15-2006, 01:39 PM
I also gave a simple answer. Potassium metabisulfite is available any place that sells wine making supplies. Throw in a few tablets and it will dissolve the lignin. The sawdust will unstick.

05-15-2006, 01:44 PM
You're right to a certain extent, so, let's ask all members just how many pounds of Potassium they have stored on their shelves in their shops at any given moment ---and what do they do with it? You should know that Potassium is a very strong poison to stop the heart?

Weston Bye
05-15-2006, 01:54 PM
Potassium a poision? I found myself in the hospital once where they they discovered that my blood potassium was very low. Intravenous potassium while I was there. Banannas and some other fruits & vegetables are high in potassium. Death by banannas? All things in moderation.

05-15-2006, 02:00 PM
Potassium and sodium metabisulfite are food preservatives. They are used in everything from salads to dried apricots. You wouldn't eat elemental potassium any more than you would eat elemental sodium.

An imbalance of either element is harmful and can be deadly. They are essential electrolytes in the body and the proper balance is mandatory. So what does this have to do with the question at hand?

05-15-2006, 02:06 PM
You and Wes didn't get my point. Now, how many members have the potassium in stock..on their shelves..How much do they need?

05-15-2006, 02:25 PM
Wood chips are none metallic when the scrapper drags that little magnet over the box of aluminum none will slick. The wood will burn off in the remelt why stress over it. Or just bag up that batch separately and move on with more productive endeavors. ;)

05-15-2006, 02:30 PM
How much do they need? (potassium)
None. It's potassium metabisulfite that is needed. It has the same relationship to elemental potassium that salt has to sodium. I don't have any sodium on my shelf but the grocery store has salt. They also have potassium metabisulfite tablets, AKA campden tablets.

John Stevenson
05-15-2006, 02:38 PM
32 posts over a few pounds of scrap alloy ????????

I think more people want to get a life round here.


05-15-2006, 02:42 PM
John, have to agree with you on that idea. Evan, now can you just help people out with machining, instead of Science lessons that no one cares about?

05-15-2006, 02:46 PM
Science lessons that no one cares about?

Does this mean you are no one?

05-15-2006, 03:23 PM
Highly educated just like you..'ol Buddy. Also found out over the years that people, especially machinists, are not that involved in theory. Hell, any one of us can kick back and justify everything on theory. But then there are practical people like me that want to make parts and build a mechanism or two that can be utilised in a real world environment..such as their own shop.

05-15-2006, 03:27 PM
Well, if your sawdust sticks to your aluminum swarf you know what to do (and why). This was a chemistry question.

05-15-2006, 03:31 PM
Now you see the folly in the question. No need for a science lesson or project that no one would try anyway.

05-15-2006, 06:50 PM
I take my potassium every morning One a day. Mix aluminum and magnesium and weld railroad rails.

05-16-2006, 03:19 AM
Highly educated just like you..'ol Buddy.

I'd like Evan to reply as to whether he is highly educated or whether he is a Practical Machinist.

Every post of his shows some damned practical, and some damned beautiful, machining. Not, necessarily the result of 22 years of schooling, more the result of 22 or 40 years of machining.

I am not kissing ass, as I just read the naysay post, where there are 3 guys who are considered to be the Gospel, and everybody else is to be ignored.

Most here are looking for advice, not experts. 17 "Experts" can answer the questions of thousands of "newbies. Experts do not come to forums to ask questions. They might stick around to see if they can help. If they don't see anything they can help with, we are stuck with what we have, and I think what we have is pretty good.

HAs anybody not gotten a decent answer, here? Gotten their problems solved? At LEAST a hint as to which direction they should go?

Some are trying to kill a damned good forum.



05-16-2006, 11:00 AM
I'd like Evan to reply as to whether he is highly educated or whether he is a Practical Machinist.

I never stop learning, here and elsewhere. I don't have any fancy pieces of paper that attest to my education but learning is what I live for.

As for the practical side, I have been doing metal work and working on machines most of my life, both as employment and as a hobby. I was trained by the military in airframe repair and worked in the business for about 5 years. I also worked as a fitter building barges and other heavy steel fabrication. I always wanted a job where I didn't have to clean up after myself. Oh well, some dreams are never realized... :D

05-16-2006, 01:09 PM
Evan is a Home Shop Machinist here,On the other board HE is a Practical machinist.
Either way I consider him highly educated,weather its book learning or OJT.
Your opinion may vary.