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Practical Chemistry Question

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  • Practical Chemistry Question

    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.


  • #2
    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



    • #3
      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.
      Free software for calculating bolt circles and similar: Click Here


      • #4
        I Don't think it's so much chemistry going on....

        I think it's more a case of wetness & physics going on in your 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.


        • #5
          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.............


          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


          • #6
            B&D shop vac they are the only product made by B&D that don't suck.............
            Thats a BLOW to B&Ds reputation


            • #7
              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 twoAlistair
              Please excuse my typing as I have a form of parkinsons disease


              • #8
                Physical Chemistry

                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


                • #9
                  Not enough water. Throw the whole mess in the lake and stir it up. The aluminum will sink and the wood will float. JRouche
                  My old yahoo group. Bridgeport Mill Group



                  • #10
                    All you need to do is oxidize the carbons in the wood fibre and the aluminum is all that will be left.
                    Jim, By the river enjoying life...


                    • #11
                      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.


                      • #12
                        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.


                        • #13
                          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?
                          Murphy was an optimist


                          • #14
                            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.


                            • #15
                              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...
                              You never learn anything by doing it right.