DK made me a coal sifter out of a plastic milk crate and a piece of half inch metal fabric over ten years ago. He cut the metal fabric a little big so it would wedge into bottom of the crate. The crate has hand holds so I can shake it easily. That size metal fabric works well with pea, nut and stove coal.
The sifter works great! I shake it over a small garbage can. The four corners of the crate sort of fit on the can's rim so I can rest it there. I don't have to lift it hardly at all.
I, too, picked up some "free" basement coal last year and it was the dirtiest coal I'd ever seen. From the amount of soil in the bags I would guess they had it stored on the yard before bagging it. It also had a lot of fines from handling it so much. The soil and fines had settled to the bottom of the bags so we just shoveled from the top and only sifted when we got to the bottom of a bag. That way I didn't have to do a lot of shaking at any one time.
I also use the sifter when I've had to shut down the stove and there is a lot of unburned coal among the ash. It's not pretty but it was cheap and it works. Lisa