Making carbon powder using fireplace and weak acid 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:

I have put some sawdust in an iron can.
I covered the opening of the can with clay, leaving only a small opening.
I put the can in a fireplace and let it heat to about $\pu{800 ^\circ C}$.
After removing, I ended up with about 1/3 volume of black powder.
I washed the powder with water and filtered the water out.
I placed the wet powder in a beaker and added more water.
I added about 12% hydrochloric acid to dissolve calcium and metal oxides and hydroxides.
The solution started bubbling slightly, so I left it for several hours with occasional mixing.
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?
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 : $40 - 70$ % $\ce{CaCO3}$, $5 - 10$ % $\ce{Na2CO3}$,  $5 - 10$ % $\ce{K2CO3}$, $2 - 3$ % $\ce{K2SO4}$, $2 - 5$ % $\ce{Ca3(PO4)2}$, $5 - 10$ % $\ce{MgCO3}$, $2 - 10$ % $\ce{SiO2}$, &lt; $1$ % $\ce{FePO4}$. Washing your charcoal with water and hydrochloric acid must remove all these substances, except $\ce{SiO2}$. This impurity cannot be removed.