Jarosite process residues

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 ... 

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. 

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. 

In a modification the conversion process, the jarosite residue is hydrothermaHy decomposed to hematite by autoclaving at 220—250°C. This solubilizes zinc and other metal values and the hematite has a potential for iron recovery. Hematite stockpiles are less of a problem than jarosite because hematite is denser and holds up less of the soluble metals. 

Iron in the feed concentrate is rejected either as unreacted pyrite mixed with elemental sulfur or as jarosites in the leach residue. The pyrite/sulfur mixtures said to be suitable for indefinite storage, but the well known environment effects caused by pyrite weathering are likely to make storage of this material a less than straightforward problem. Besides this, there are problems associated with the disposal of the leach residues from the pressure leach process. 

In the ultimate analysis it may be pointed that the aforesaid hydrolysis processes are no doubt technically very satisfactory and tolerable, but environmentally this is not the case. The different processes yield jarosite, goethite and hematite, all of which retain considerable amounts of other elements, especially, zinc and sulfur. The zinc originates mainly from undissolved zinc roast in the iron residues, and sulfur from sulfate, which is either embodied into the crystal lattice or adsorbed in the precipitate. As a consequence of the association of the impurities, none of these materials is suitable for iron making and therefore they must be disposed of by dumping. The extent of soluble impurities present in the iron residues means that environmentally safe disposal not an easy task, and increasing concern is being voiced about these problems. An alternative way of removing iron from... 

Goethite A process for removing iron from leach liquors from hydrometallurgical leaching operations. Used in recovering zinc from the residues of the electrolytic zinc process. See also Jarosite, Haematite. 

Jarosite [Named after the mineral, first recognized at Jarosa, Spain] A process for removing iron from the leach liquors from hydrometallurgical operations. First used in 1964 in processing zinc sulfate liquors at Asturiana de Zinc, Spain. Also used for recovering zinc from the residues from the electrolytic zinc process. See also Goethite, Haematite. 

The residue from any hydrometallurgical process would be similar. Clearly, if iron was not a part of the starting material some would usually be added to remove the sulphate either as sodium or potassium jarosite and there would be less ferric hydroxide and a greater proportion of sulphur. 

With exception of leach residue (jarosite, goethite, etc.) disposal, the process is environmentally sound. 

The Sherritt-Cominco process was developed as an alternative to smelting of sulfide concentrates. The key feature of the Sherritt-Cominco process is the removal of iron before the leaching of copper. The concentrate is thermally activated and leached with sulfuric acid to dissolve iron. Iron is precipitated as jarosite. The leach residue is pressure leached with oxygen in acid solution to convert copper sulfides to copper sulfates. The solution is purified by the coprecipitation of Te, As, Bi, Sb, Pb, and Se with Fe2C>3. The electrolyte contains 30 g L 1 Cu and 140 g L 1 sulfuric... 

The ZPL process consists of an autoclave, in which zinc concentrate reacts with pure oxygen under pressure, and a sulphur separation area. This plant produces a zinc sulphate/jarosite residue sliury which is piunped to the sulphide leaching plant for further processing, and the production of elemental sulphur. 

The sulphide leaching plant (SUP) receives feed from all of the fiont-end zinc plants roasters, ZPL, and OLP. This plant treats calcine, ZPL slurry, and OLP electrolyte using a weak acid and neutral leaching process to produce impure SLP electrolyte and residue. The residue consists mainly of zinc foiites, paragoethite, jarosites, lead sulphate, as well as coprecipitated impurities. The residue slurry is fed to the lead smelter. 

Most of the world s zinc production is obtained via the roast/leach/electrowinning (RLE) process. Starting from sulphidic concentrates, this hydrometallurgical process allows the production of special high-grade zinc. During this process, an iron rich residue (goethite or jarosite) is produced. This residue has to be stockpiled, and this is clearly an environmental issue for the future. 

T.T. Chen and J.E. Dutrizac, Mineralogical Study of Jarofix Products for the Stabilization of Zinc Industry Jarosite Residues , Second International Symposium on Extraction and Processing for the Treatment and Minimization of Wastes . V. Ramachandran and C.C. Nesbitt, Eds., The Minerals, Metals and Materials Society, Warrendale, PA, U.S.A., 1996,659-672. 

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