Calcium nitrate anhydrous and ammonium sulfate crystalline obtaining from phosphate fertilizers wastes
A.V. Shilyaev, I.D. Troshkina
Section: Ecologization of industry
Extractive phosphoric acid and phosphoric mineral fertilizers processing forms wastes, phosphogypsum is the main. Phosphogypsum is not widely used due to its low radioactivity. Most of it is accumulated in dumps for long-term storage. Phosphogypsum can be considered as a potential source of calcium, sulfur, phosphorus and rare earths (REs) of the cerium group. The aim of the work is to develop a technology for obtaining calcium nitrate Ca(NO3)2 anhydrous, ammonium sulfate (NH4)2SO4 crystalline and REs’ concentrate from phosphogypsum. We develop a basic process flow diagram that allows separating REs’ concentrate from calcium and sulfur compounds. (NH4)2SO4 is a product of the reaction between phosphogypsum and an excess of ammonium carbonate solution. The resulting phosphochalk is separated from the (NH4)2SO4 solution by filtration. The (NH4)2SO4 solution is neutralized with sulfuric acid to pH 4–6, evaporated, and (NH4)2SO4 crystallized. Phosphochalk is dissolved in excess nitric acid. The resulting acidic Ca(NO3)2 solution is cooled to -10 °C to separate the Ca(NO3)2·4H2O crystals. After the above separating the REs’ concentrate is precipitated with ammonia. After washing with nitric acid at -10 °C, the crystals are dissolved and neutralized with CaCO3
to pH 4. The resulting chalk pulp is filtered, separating Ca(NO3)2 solution from insoluble impurities of calcium phosphate and fluoride. The purified Ca(NO3)2 solution is evaporated and granulated to obtain Ca(NO3)2 anhydrous.
ISSN 1995-4301
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