[Moopower]

Hi,

How do I separate a mixture of aluminum powder and sawdust? Help please!

Thank you

[Xenonman]

Those two are solids. So you'll need a method that separates solids. You can choose the best method by looking for the one that employs the biggest difference in properties between the things you want to separate.

Now, what's the biggest difference between aluminium and sawdust?

[Moopower]

Those two are solids. So you'll need a method that separates solids. You can choose the best method by looking for the one that employs the biggest difference in properties between the things you want to separate.

Now, what's the biggest difference between aluminium and sawdust?

Could I burn the mixture? The sawdust will burn off, leaving the aluminum right?

[Archer]

Aluminium powder is quite flammable too.

Think of another property which discriminates between the two.

[Moopower]

Aluminium powder is quite flammable too.

Think of another property which discriminates between the two.

Aluminum is a good conductor of electricity and sawdust isn't...

[Archer]

That's true but won't help you separate them.

What about physical properties?

[Moopower]

That's true but won't help you separate them.

What about physical properties?

I had initially thought of the densities but aluminum powder also floats in water.

[Archer]

Why does aluminium powder float on water? If it's more dense it should sink.

[Borek]

I had initially thought of the densities but aluminum powder also floats in water.

In general - it doesn't.

But I assume you have seen it floating - and there is no contradiction here. When there is not much aluminum dust, and it is very fine, some of it will stay on the water surface. This effect is only temporary and caused by the fact dust is difficult to wet and keeps on the surface because of the high surface tension of water. Adding any detergent (surfactant) will help it sink, but even stirring without a detergent will have the same effect.

[Moopower]

So what if there was also sand in the mixture then? Aluminum and sand will sink. Sawdust will float. Skim the sawdust off the top. How to separate the sand and aluminum? Melt aluminum and sand mixture? Or add hcl to the mixture since aluminum reacts with hcl? Sand was actually also in the original mixture but I didnt mention it since I know it sinks in water.

[Borek]

Chemical approach is always an option.

I believe you should be able to separate them with some clever use of the fact aluminum dust can float on the water if the conditions are right.

Such things are even done on industrial scale: http://en.wikipedia.org/wiki/Froth_flotation

[Moopower]

Ok thank you all for the help.

[Corribus]

Electrochemistry is also an option. Form a soluble salt with the aluminum using an oxidant, filter to remove other solids, then reduce back to aluminum. You probably won't have the same type of powder then, of course, so it depends on your needs.