TWO-STAGE ACID PROCESSING OF WASHED DRY CONCENTRATEINTO GRANULATED SIMPLE SUPERPHOSPHATE

Background. Single-sided phosphate fertilizers include simple, enriched and double superphosphates. They are especially effective when applied under fall plowing. Simple superphosphate isproduced by decomposition of natural phosphates with sulfuric acid, enriched - with a mixture of sulfuricand phosphoric acids, and double - with phosphoric acidby chamber, flow or chamber-flow methods. Kyzylkum phosphorite complex produces washed and burned concentrate (WBC) for ammophos production. Washed and dried concentrate (WDC) is an intermediate phosphorite product used to obtain WBC. Of practical interest is the processing of WDC into simple superphosphate. Purpose. Study of the process of obtaining simple superphosphate by two-stage acid treatment of WDC under anhydrite conditions. Methodology.The decomposition of WDC is carried out in two stages: at the first stage, the main part of WDC (70-80%) decomposes at 130°C with concentrated H 2SO 4to form phosphoric acid (45-50% P 2O5 ) and calcium sulfate of the anhydrite form, and inthe second Stage acidic reaction mass containing concentrated Н 3РО 4is neutralized by the remaining amount of WDC (20-30%), resulting in the formation of monocalcium phosphate. In order to improve the conditions for granule formation of the superphosphate mass, the process of its rounding is carried out inthe presence of water. P2O5content free in the reaction mixtures and finished products was determined by titration with 0.1 n NaOH using indicators of methyl orange and phenolphthalein. In products, the total,assimilable and aqueous forms of P 2O5were determined by the photocolorimetric method. The strength of the granules was measured according to GOST 21560.2-82. Originality.The optimal conditions for two-stage sulfuric acidprocessing of WDC under anhydrite conditions have been found, where concentrated phosphoric acid and anhydrous calcium sulfate are formed at the first stage of processing, and monocalcium phosphate at the second stage. The second stage is actually the basis of the mechanism for the formation of monocalcisphosphate and granulation of the superphosphate mass, where a skeleton of calcium sulfate crystals saturated with phosphoric acid acts as a granulation center. Finding.It is shown that an increase in the time of sulfuric acid treatment of MSA from 2 to 60 minutes leads to an increase in the coefficient of its decomposition. It turned out that 20 minutes and a 100% H2SO 4norm are enough for the maximum decomposition of WDC. Neutralization of acidic phosphoric acid gypsum mass with 220% WDC rate is actually the beginning of the superphosphate granulation process. To improve the conditions of granulation, the process of rolling the superphosphate mass must be carried out in the presence of at least 15% water. In this case, superphosphate is obtained of a sufficiently high quality (0.17-0.96% P2O5free , 17.42-18.34% P2O5total , of which 70-80% is in a water-soluble form, the strength of its granules is ˂2MPa). Highlights: - sulfuric acid treatment of WDC carried out in twosuccessive stages: 1 st stage of sulfuric acid treatment of WDC: formationof concentrated Н 3РО 4and CaSO 4crystals; 2 nd stage of neutralization of phosphoric acid gypsum mass with WDC: formation of monocalcium phosphate and granulation of superphosphate mass.