SULFATE ADDITIVES FOR INTENSIFICATION OF THE FILTRATION OF LOW GRADE PHOSPHORITE-NITRIC ACID SUSPENSION

Abstract

In the process of opening phosphate rocks and extracting the main component by acid extraction, a stage of isolation of the insoluble residue from the obtained suspensions by filtration is necessary. This will ensure an increase in the concentration of nutrients in the products of processing natural phosphorites used as model minerals. The insoluble residue on the filter baffle is a filter layer, the dense structure of which prevents the effective process of separating the liquid-solid system. In order to intensify the filtration process of nitric acid suspension based on low-quality high-siliceous phosphorite of the Polpinsky deposit, the effect of sulfate additives: sulfuric acid, ammonium sulfate and potassium sulfate on the structure of the sediment and, accordingly, the filtration time of the suspension and washing of the sediment was studied. The content of the administered additives varied in the range of 10 - 30 weight %. The results of the study of the microstructure of sediments – vertical cross–section and their surface obtained using the scanning electron microscopy method allowed us to establish that the introduction of the studied additives leads to an increase in the porosity of the layer due to the formation of large druses from single crystals of calcium sulfate dihydrate - gypsum. This improves the filtration properties of the sediment layer, reducing the filtration and washing time. It should be noted that, all other things being equal, the effectiveness of potassium sulfate additives is higher in comparison with sulfuric acid and ammonium sulfate additives. Its advantage lies not only in improving the rheological properties of suspensions, but also in the presence of potassium in the system as a nutrient component during the processing of nitric acid extract for complex fertilizers. The effective concentration of potassium sulfate in the system was experimentally established at 20 weight. %. At the same time, the maximum value of the filtration rate of the suspension is 0.537 m3/(m2∙h), which is 1.08 and 1.03 times higher compared to the filtration of suspensions containing ammonium sulfate and sulfuric acid, respectively. The revealed trend extends to the precipitation washing rate - the maximum value corresponds to 0.750 m3/(m2∙h), which exceeds the corresponding comparison samples by 1.1 and 1.15 times.