Conversion jarosite

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. 

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 residue in the distillation reactor is then reconstituted with water, refiltered and sent on for iron removal. The iron is removed by conversion to jarosite (NaPe3 (SO4) 2 (CH) 6). The jarosite is filtered away and converted back to ferrous sulfate (FeS04) far sale to the fertilizer and water treatment industries. Approximately 1000 lbs of FeS04 7H20 are generated from each 20 ton batch. 

The first evidence for the conversion of silicate minerals of stony meteorites in Antarctica was reported by Gooding (1986a) who detected the presence of clay mineraloids, gypsum, K-Fe sulfates (jarosite ), and rust on the surfaces and in cracks of achondrites and chondrites from Elephant Moraine (EET) and the Allan Hills. These weathering products had formed primarily from glass and plagioclase in the fusion crust and in cracks in the interiors of the meteorite specimens. 

G.A. Reynolds, The Jarosite Group of Compounds - Stability, Decomposition and Conversion, MSc Thesis, University of Newcastle, NSW, Australia, 2007, 173pp. 

The concentration and/or activity of dissolved Fe(III) is thus controlled by different mineral phases depending on the pH. This is illustrated in Fig. 3, which plots the pH-dependent variation in the concentration and speciation of dissolved iron in different mine pit lakes of the IPB. Among the 15 pit lakes studied, jarosite was only observed to precipitate in Corta Atalaya, so that this mineral controls the apparent equilibrium which seems to exist between dissolved and particulate Fe(ni) in this lake. Conversely, ferrihydrite is the mineral form under which Fe(III) precipitates in Los Frailes pit lake. Most lakes, however, seem to be at or near equilibrium with respect to schwertmannite, which not only controls the solubility of Fe(III), but also buffers the systems at pH 2.5-3.5 (through reaction (5)), and sorbs toxic trace elements like As [5-14, 24—28]. 

Conversion process. In this process, introduced by Outokumpu Zinc, the leaching of zinc ferrite and the precipitation of iron as jarosite are combined in a single step with the concentration of the sulfuric acid kept at 30 g/L by adding spent acid according to the following chemical reaction ... 

There are some technical processes where one solid is dissolved by a chemical reaction, while a precipitate is formed by the same reaction. Well known examples are the conversion of ilmenite (iron II titanate) to titanium hydroxide in the sulfuric acid process, or the conversion of zinc oxide to jarosite (iron II zinc sulfate). Such reactions can be sununarized by... 

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