I am doing a little home experiment trying to make as pure carbon powder as I can. I plan to then used it to eat up oxygen from a container where I want to try to melt aluminum.

My process was following:

  1. I have put some sawdust in an iron can.
  2. I covered the opening of the can with clay, leaving only a small opening.
  3. I put the can in a fireplace and let it heat to about $\pu{800 ^\circ C}$.
  4. After removing, I ended up with about 1/3 volume of black powder.
  5. I washed the powder with water and filtered the water out.
  6. I placed the wet powder in a beaker and added more water.
  7. I added about 12% hydrochloric acid to dissolve calcium and metal oxides and hydroxides.
  8. The solution started bubbling slightly, so I left it for several hours with occasional mixing.
  9. I washed the resultant powder with water twice and left it to dry.

Did I manage to purify the carbon in the powder somewhat? Did the use of acid bring any benefit?

  • $\begingroup$ 2x yes, obviously. I don't understand what you're asking for here. Your sequence sounds like you know what you're doing. $\endgroup$
    – Karl
    Mar 18, 2021 at 21:38
  • $\begingroup$ Only that wood ash also contains carbonates. Hence the bubbling. Hydroxides don't survive at 800°C. $\endgroup$
    – Karl
    Mar 18, 2021 at 21:41
  • $\begingroup$ @Karl I don't know if I know what I'm doing. I followed what I thought would work, and wanted to check if this is the right approach to remove impurities and leave relatively pure carbon. $\endgroup$ Mar 18, 2021 at 22:02

1 Answer 1


The result of your first pyrolysis must be charcoal plus the mineral constituants that are present in wood ashes. Now the wood ashes are usually a mixture of : $40 - 70$ % $\ce{CaCO3}$, $5 - 10$ % $\ce{Na2CO3}$, $5 - 10$ % $\ce{K2CO3}$, $2 - 3$ % $\ce{K2SO4}$, $2 - 5$ % $\ce{Ca3(PO4)2}$, $5 - 10$ % $\ce{MgCO3}$, $2 - 10$ % $\ce{SiO2}$, < $1$ % $\ce{FePO4}$. Washing your charcoal with water and hydrochloric acid must remove all these substances, except $\ce{SiO2}$. This impurity cannot be removed.


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