Cost Effective Technology of Alunite Ore Processing

Soda-alkaline method of alunite ore processing includes crushing, grinding and enrichment (flotation) of the alunite ore. Enriched alunite ore, containing 50 - 60% of alunite, is roasted at temperatures between 520о – 620о С for 1 – 3 hours. Roasted alunite is further leached with sodium carbonate solution (5–20 %). Proportion of sodium carbonate for binding of SO3 aluminum sulfate in alunite accounts for 100 – 110 % of stoichiometric quantities. Leaching takes place at temperatures around 70 – 100о С for 0.5 – 2.0 hours. Solution of the resulting pulp contains all the potassium sulfate from alunite and sodium sulfate from soda. Solution of sulfates is separated from the insoluble residue and is fed for conversion with potassium chloride. As result of this conversion we obtain quantities of potassium sulfate (fertilizer) and table (common) salt. The remaining insoluble residue contains all the aluminum oxide from alunite and waste rock. Further processing of the insoluble residue based on the Bayer out-of-autoclave process produces alumina and quartz sand. Besides alumina, this method makes it possible to get four times more the amount of potassium sulfate and certain volumes of table salt. Taking into account the processing capacity of Ganja Alumina Plant (150,000 tons of alumina per year), this method allows the production of fertilizer, potassium sulfate (370,000 tons per year), coagulant for purification of water from mechanical impurities (49,000 tons per year), table salt (NaCl) (126,000 tons per year), and quartz sand for non-ferrous casting and production of construction materials (300,000 tons per year). Approximate yearly financial efficiency of the soda-alkaline technology for processing of 150,000 tons of alumina per year will be around 171,46 million USD.