Iron(II) sulfate (FeSO4) is an example of an ionic compound. It is found in various states of hydration (FeSO4·H2O, FeSO4·4H2O, FeSO4·5H2O, FeSO4·7H2O); the heptahydrate is also called green vitriol, copperas, or melanterite (a mineral that commonly occurs with pyrite). Iron(II) sulfate has a blue-green color, monocliniccrystal structure, and is water-soluble. Its molecular weight is 151.9026 g/mol. Its melting point is 64°C, and at 90°C it loses water of hydration to form the monohydrate, a white powder known as the mineral szomolnokite when it occurs naturally. Iron sulfate pentahydrate forms the mineral siderotil.
In each case the object is to re-oxidise the ferroussulphate back to the ferric sulphate state in accordance with reaction (e) in order to reutilise the ferric ion for the copper leaching duty (reactions (a) and (b)) without the need for excessive supply of ferric sulphate into the leach slurry.
Because the ferroussulphate is continuously re-oxidised to the ferric state, which is simultaneously or sequentially employed in the copper leaching process, there is no need for the addition of excessive quantities of ferrous or ferric sulphate into the leach slurry or solution.
During the leaching process, ferroussulphate was oxidised to ferric state which in turn reacted with chalcocite and covellite to form copper sulphate and elemental sulphur.
The ammonium sulphate solution is separated from the hematite or magnetite, and a portion of the separated ammonium sulphate solution is recycled to the ammonium jarosite precipitation step, the remaining portion of the separated ammonium sulphate solution being recovered.
The feed solution containing dissolved ferroussulphate can be treated with ammonium sulphate and oxygen in such a manner as to precipitate ammonium jarosite, with the precipitated ammonium jarosite then being separated from the treated solution to produce an ammonium jarosite slurry and a separated solution containing sulphate ions.
The ammonium sulphate solution can then be separated from the insoluble iron oxide, and at least a portion of the separated ammonium sulphate solution recycled to the ammonium jarosite precipitation step, with the remaining portion of the separated ammonium sulphate solution being recovered.
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