It's incredibly effective with ewaste. You can have a completely black solution that's almost like warm treacle because it's so full of multiple metals and yet it drops the gold like a metaphorical stone.
In this circumstance it makes absolutely no difference whatsoever if the Ferrous Sulphate isn't 100% perfectly green. Picking out the bits that arent is fine. Incidentally I find sealing it in a 20 litre plastic white container keeps it perfect for ages.
I'll probably cause a few sharp intakes of breath here but for dirty drops in a 3 or 5 litre glass I crumble it up by hand and put it in as crystals. Stir vigorously, test and add more if required. That way there's no additional volume of waste. If you have a solution with a lot of gold in it (30g plus) then you're going to be adding an awful lot of volume to it in order to add the required amount of liquid Ferrous Sulphate to drop out all the gold.
If there are excess crystals in your dropped gold- then wash it with hot water and they remove themselves from the equation.
