Sodium jarosite

Sodium jarosite and gypsum are the major species in the commercial Noranda Inc., CEZinc jarofix product. The finer gypsum particles are formed by the reaction of Na-jarosite and cement, whereas the large crystals are from the original gypsum filter cake. Trace amounts of zinc ferrite, hematite and quartz are present in the jarofix product they originate fiom the jarosite residue. Trace amounts of calcium hydroxide which is a cement reaction product, of calcite which forms from the air-carbonation of of Ca(OH)2, and of Ca-Al-Fe oxide ( Ca4Al2Fe08.5 or Ca2(Al,Fe)205) which is a common cement decomposition species are also detected in the jarofix product. 

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. 

Abundant yellow or white salt crusts are present on waste rock and at the surface of the soil. The crusts comprise alum-like sulfate minerals containing variable amounts of sodium, potassium, iron and aluminium, such as the mineral jarosite. They are often very soluble in water, releasing acid and precipitating ferric hydroxides. 

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. 

Results of batch leach tests performed on tailings from the Grants Mineral Belt, New Mexico are summarized in Tables IV and V. These results represent the average of two analyses on the acid leach tailings samples. Table IV contains the elemental concentrations of the sand and silt and clay-sized fractions, as well as the soluble concentration of each element found when 100 g of material is leached with 250 mL of sodium hexametaphosphate solution. The right-most column presents the ratio of the elemental concentration associated with the silt and clay-sized fraction to that of the sand-sized fraction, and it is presented as an enrichment factor. The high enrichment factors for As, Mo, Cr, Se, and V may be due to the fact that these elements are adsorbed onto jarosite, montmorillonite, and ferric oxyhydroxides (9-141. Speciation... 

Table HI reports the compositions of the partly reacted jarosite particles in laboratory jarofix products which were stored for various periods. All the jarofix products were prepared with Na-jarosite residue and cement, plus an appropriate amount of water no gypsum filter cake nor lime were added to the mixtures. The analytical data of Table III represent the average compositions of the bulk particles. It is evident that the reacted jarosite particles in the freshly cured products have undergone a major reduction in their SO4 content however, there are significant increases in the Fe, Ca and Si contents relative to the original jarosite composition. The sodium content remains essentially the same. By contrast, the reacted jarosite particles in the aged products contain lesser amounts of Fe, Ca and SO4 than those of the freshly cured products, and this likely reflects the elimination of the Ca5Fe2(SO4)3(0H)i2.nH20 phase.

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]. 

In addition to the hematite precipitation - acid regeneration chemistry, sodium and potassium in seawater react with aluminum in solution to form alunite, resulting in low net extraction. Alunite precipitation also regenerates acid, helping to minimize acid consumption, analogous to jarosite precipitation in atmospheric leaching. Sodium alunite precipitation, as shown in equation 9, is an analogue of jarosite precipitation in equation 3. 

Aluminum to sulfiir ratios in residues point to iron co-precipitation, such that an alunite-jarosite compound is formed, typically about two-thirds alunite and one-third jarosite. The sodium plus potassium to sulfur ratios indicate that 10 to 20% of the alunite-jarosite is in the hydronium form. Kyle [27] gives a useful summary of these phenomena while Johnson and co-workers [15, 16] have carried out detailed studies into the effects of alkali addition and leach liquor salinity on PAL. Some typical assays are shown in Table 2 and Table 3. 

The stability of jarosite containing residues from atmospheric leaching has been studied in depth by Reynolds [34]. It was found that residues are chemically stable if kept in contact with alkali (sodium) containing liquors. Jarosite breakdown in the absence of such liquors is retarded in the... 

The potassium in jarosite may be replaced by sodium, producing natrojarosite (. v.) from which it is indistinguishable optically. Jarosite is also closely related in chemistry to hydronium-jarosite (q.v.), also known as carphosiderite, which has the chemical formula (H20)Fe3(S04)2 (0H5)H20 (Moss, 1957). The particle morphology of hydronium-jarosite and jarosite are so similar that they may be confused if optical mineralogy is used alone for identification. 

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