Jarosite disposal

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... 

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

After dissolving the metal oxides, the iron is precipitated and removed as jarosite (for problems, see Section 9.6.2), followed successively by copper and zinc (liquid extraction with various complexing agents, stripping with sulfuric acid and subsequent precipitation crystallization), chromium (oxidation and precipitation as lead chromate) and nickel (crystallization as sulfate). The estimated costs are around 200 ton which is only slightly above the costs for disposal. 

All of the iron sulfate and a major portion of the alkali sulfates can be removed from the add extract water by a sequence of heating and lime treatment to form insolnble minerals such as gypsum. This water ean then be recycled to the water wash train. Under some (very earefiilly controlled) conditions, the predpitate formed ean be a Jarosite-like double salt, which can be easily disposed of or land-filled. 

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. 

A MINERALOGICAL STUDY OF JAROFIX PRODUCTS FOR THE STABILIZATION OF JAROSITE RESIDUES FOR DISPOSAL... 

---