Making ferrous sulfate (FeSO4), also called copperas or iron sulfate.
Copperas is green in solution or in crystal form.
Ferrous sulfate is good to use to precipitate gold from acidic solutions.
2AuCl3 + 6FeSO4 à 2Au (s) + 2Fe2(SO4)3 +Fe2Cl4
Iron sulfate will also precipitate platinum from boiling hot solution if pH 7.
FeSo4 crystal can be used to detect dissolved gold in solutions in the spot plate,
This is useful also if the gold is in solution with another precious metal, we can use the copperas crystal to test for gold in one dish of spot plate (brown ring) this precipitates the gold and remaining solution moved to another dish in spot plate and tested for other precious metal.
Copperas crystals (green) these crystals will oxidize easily if not stored properly, dry (acid low) and exposed to air (turning brown) the brown crystals will not precipitate gold, most all copperas I have found in garden centers has oxidized and is useless for our needs here.
The green copperas crystals, when made should be kept fresh in storing, I will keep them wet, few drops of sulfuric acid to keep them acidic, store in air tight plastic container (screw on plastic lid with seal an old stump remover bottle is what I use), they have a very long shelf life this way.
It is as easy to make a large batch of ferrous sulfate, as it is to make a small batch of copperas.
You need as pure iron as you can get (not steel), soft Iron laminates from old transformers, or electric motors, is what I use.
An old transformer cut iron laminate welds (hacksaw or angle grinder Etcetera), remove copper winding an save (to rewind another transformer, old motor, use as wire, or throw in your copper scrap metal pile), separate the iron laminates, cut into small pieces (with tin snip’s), use torch to burn off shellac and oils, add this Iron to dilute sulfuric acid (10% H2SO4), (the dilute acid is best as iron can passivate (not dissolve) in strong sulfuric acid), you can dilute battery acid (one part 32% battery acid to two parts water), or dilute the drain cleaner in water.
:shock: Always add the concentrated sulfuric acid to water slowly watching the temperature rise from reaction).
Never add water to concentrated sulfuric acid it will boil out and splash all over you burning you severely or blinding you}
The iron will dissolve slowly in cold solution, heating will speed the reaction, you can boil this solution of iron metal and dilute sulfuric acid because the sulfuric acid has such a high boiling point so gases evolved are mainly just water in fumes.
I use a Pyrex Mr. coffee pot, or white corning ware casserole dish on solid iron metal burner electric hot plate.
After as much iron as will dissolve (dissolves into the concentrating acid) lower temperature and pour this green solution into another jar, letting un-dissolved iron metal and carbon settle well.
Filter solution back into evaporating dish and boil down to crystals, when you get a few inches of crystals cool solution somewhat then pour into a clean jar let cool more and crystals settle, decant liquid back into boiling vessel and make more crystals, this concentrated solution can be used also.
