i can't find crafting of toxic dust

You should be able to create it in a Yuoki's form press machine from contaminated water after researching Yuoki's washing tech. I was able to find the recipe by searching in FNEI (box in the top left of the screen). If you don't see the recipe in FNEI, you can click the gear and check "Show disabled recipes" in the FNEI settings, which will show you locked recipes and the tech you need to unlock to get them.

Toxic dust isn't made its a byproduct from pressing mud from toxic dust Washing copper/iron gives you containment water an pure copper/iron and the contaminated water can then be pressed to make wet mud & toxic dust. Definitely there