adding potassium to the spent, silver nitrate laden solution, and precipitating everything out (presumably this renews the original ferric nitrate)
G’day. Sorry; I think you would need to replace the spent ferric
nitrate with fresh material. I am afraid I am going to be what many
people will feel to be “academic”. However I believe I have to
mention that when talking about ‘inorganic’ salts which are
composed of a metal part and an acid part, such as ferric nitrate or
ferric chloride that one should really mention the whole name. I
am specifically referring to the suggestion of ‘adding potassium’
to ferric nitrate containing silver nitrate.
Now the metal potassium is a silvery white metal so soft it can be
easily cut with a blunt knife like butter. It is violently reactive
in contact with water, will rush about on the surface of the water,
catch fire and probably explode. Yet salts of potassium are often
pretty harmless. Example; potassium chloride, potassium sulphate,
etc.
I believe the idea in the quotation given above was really to add
potassium CHLORIDE to the solution, and so the chloride part would
combine with the silver in the spent solution producing silver
chloride which is quite insoluble. If the liquid is then well shaken
the silver chloride precipitate will clump and thus become easy to
filter out. If this is washed, then dissolved in sodium or
potassium cyanide solution, it can be recovered by electroplating
out as pure silver on a stainless steel electrode. I would also point
out that when sodium or potassium chloride is added, the potassium
or sodium part will replace the silver part of the ferric nitrate
and silver nitrate, but render the solution far less active.
Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ