Ferric sulphate, leach process

The Regenerated Ferric Sulphate Leach Process (RFSL)... 

The object of this ptq>er is to describe a process developed to treat a Canadian zinc concentrate. The first part of the paper examines the ferric sulphate leaching of the concentrate. The second part examines the effects of ferrous oxidation by SO2/O2 this reoxidation can be effected in-situ, i.e., during the leach, or ex-situ in a separate vessel. The third part briefly discusses options to treat the resultant leach solution and recover the zinc from it. 

The process described in this paper combines the two reactions discussed,in the prior sections i.e., the ferric sulphate leach of sphalerite and the reoxidation of the ferrous sulphate generated during the leach, to be able to continue the leach. 

The In-Situ Regenerated Ferric Sulphate Leach (RFSL Process... 

Atmospheric processes have also been studied. As examples, the FCL process (Ferric Chloride Leach) extensively investigated and developed by CANMET (2), and a nitrate-based process (3) could be cited. The ability of ferric ions to oxidise various sulphide minerals, in particular sphalerite, has been known for years, and this was the basis for the FCL process. One of the perceived difficulties of the FCL process is the use of a chloride medium, and there are several incentives to operate in a sulphate system, not the least of which is the fact that the sulphate system is extremely well established. 

The regeneration of the ferric sulphate can, in practice, be effected in two ways. Firstly, it can be effected in the same vessel where the leach is operating this option is called the direct, or in-situ, process. The second option is to effect the regeneration of ferric sulphate in a vessel different than the leach vessel, on the solution only this option is named the indirect, or ex-situ, process. 

The novel process proposed here (RFSL) involves regeneration of the ferric ion using SO2/O2 mixtures. The regeneration can be effected directly during the leach (in-situ process), or in a separate vessel on a clear liquor (ex-situ process). In-situ regeneration tests indicated a 33% absolute increase in zinc extraction in 6 hours under otherwise similar conditions. Ex-situ regeneration of ferric sulphate was successful and proceeded according to a well establi ed mechanism. 

Gold. Because of the extreme toxicity of cyanide, a number of alternative leaching processes have been devised for gold ore. The only one of these to be commercialised involves thiourea, which uses ferric sulphate as an oxidant ... 

In the modern Hunt-Douglas process the ore is leached with dilute sulphuric acid, and the copper converted into cupric chloride by addition of ferrous chloride or calcium chloride. The use of the calcium salt entails removal of the calcium sulphate by filtration. The cupric salt is precipitated as cuprous chloride by reduction with sulphur dioxide, and the precipitate is converted into metallic copper by treatment with iron, or into cuprous oxide by the action of milk of lime. In this process the amount of iron needed is proportionately small, ferric hydroxide is not precipitated, and silver is not dissolved. 

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