Jarosite process

The jarosite process controls both alkaU metals and sulfate in the zinc-plant circuit and consumes Htde neutralizing agent. It is used in 16 plants worldwide, which account for ca 25% of the noncommunist world s primary zinc output. 

In the jarosite process, the precipitation of iron occurs from acidic sulfate solutions as one of a group of basic ferric sulfates known as jarosites. The conditions for the precipitation of iron in the specific form of jarosite require a solution pH of about 1.5 and a temperature of about 95 °C. The reaction may simplifiedly be represented as ... 

The conversion process (developed by Outokumpu) is a modification of the jarosite process and involves simultaneously zinc ferrite dissolution and jarosite precipitation in the same reaction vessel. The overall reaction may be represented in simplified form as ... 

The principal differences between the goethite and the jarosite processes take place following the hot acid leaching of the zinc ferrite residues. In the goethite process, the liquor from hot acid leaching, holding (in g l-1) 100 Zn, 25-30 Fe3+ and 50-60 H2S04, is initially subjected to a reduction step, where the ferric iron is reduced to the ferrous form by reaction with unroasted zinc sulfide concentrate at 90 °C ... 

Jarlite, 2 3641 meta-Jarlite, 2 364t Jar molding, 12 732-733 Jarosite process, 26 567-568 Jar test, 22 56... 

The filtrate from the jarosite process is now ready for copper electrowinning. In this step, copper is extracted from the sulfate electrolyte down to a concentration of 500 ppm. While leaving the nickel, tin, chrcme, cadmium and zinc in solution. Each batch produces 679 lb6 of cathode copper of 99% purity. 

The jarosite process separates icon(III) from zinc in acid solution by precipitation of MFe2(0H)g(S0 2 where M is an alkali metal (usuaUy sodium) or ammonium (see Fig. 2) (40,41). Other monovalent and hydronium ions also form jarosites which are found in the precipitate to some degree. Properly seeded, the relatively coarse jarosite can be separated from the zinc-bearing solution efficiently. The reaction is usuaUy carried out at 95 0 by adding ammonia or sodium hydroxide after the pH has been adjusted with calcine and the iron oxidized. The neutral leach residue is leached in hot acid (spent + makeup) with final acidity >20 g/L and essentiaUy aU the zinc, including ferrite, is solubilized. Ammonium jarosite is then precipitated in the presence of the residue or after separating it. If the residue contains appreciable lead or silver, they are first separated to avoid loss to the jarosite waste solids. Minimum use of calcine in jarosite neutralization is required for TnaxiTniiTn recovery of lead and silver as weU as zinc and other metals. 

V. Arregai, A. R. Gordon, and G. Sleintveit. The Jarosite Process—Past. Present and Future, in... 

The future leaching plant is based, as is the present installation, on the jarosite process. The project contemplates two separate circuits one to treat concentrates with high silver content and another one to treat the concentrates with low silver content. Both circuits are integrated after separation of the Pb/Ag residue. 

The main process for recovering zinc fiom sulphide concentrates is, of course, the hydrometallurgical roast-leach-electrowin or pressure leach-electrowin approach. This process is not readily ade )table to increasing amounts of non-zinc elements in the feed. In the 1980 s the Low Contaminant Jarosite Process (2) was developed at the Electrolytic Zinc Co. of Australasia in Tasmania and this might have been developed further to enable plants to be fed with less pme sulphide concentrates. Faced with the rising social pressure to improve the disposal of iron residues, however, the company had to pursue other routes to meet those pressing requirements. 

Alkali addition for iron precipitation, associated with sulfuric acid leaching of nickel laterites, has been considered periodically since the late 1960s, shortly after the development of the jarosite process for iron control in zinc refining. 

Development of the Jarosite process in the zinc industry in the 1960s led to an understanding that iron could be precipitated from nickel laterite atmospheric leach solutions, at moderate acid levels, by the addition of an alkali such as potassium, sodium, or ammonia, whilst maintaining a temperature in excess of 90°C [4]. 

Processes requiring sulphation require the use of aqueous or concentrated sulphuric acid. ..as the sulphating agent. In many cases the leach liquors produced are highly contaminated and recovery procedures play a vital part. Fortunately, it has recently become easier to remove dissolved iron using either the jarosite process or the goethite process. ... 

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