PURIFICATION OF PHOSPHORIC ACID BASED ON PHOSPHORITES OF LOW GRADE CENTRAL KYZYL KUM IN THE PROCESS OF EXTRACTION WITH LIMESTONE AND OBTAINING FROM A MONO PHOSPHORUS FERTILIZER

Аннотация

The work describes the processes of purification of phosphoric acid based on phosphorites of the Central Kyzylkum from impurities of fluorine and sulfates in the process of extraction with calcium carbonate and the production of single phosphorus fertilizer by neutralizing the purified acid with calcium carbonate. Key words: phosphoric acid, extraction phosphoric acid, fertilizers, mineral fertilizers, phosphorus fertilizers, calcium carbonate, monocalcium phosphate, dicalcium phosphate, double superphosphate. INTRODUCTION. Fluorine compounds have a great harmful effect on the surrounding environment. Studies show that fluorine not only has a negative effect on plants but also causes various serious diseases in humans and other living organisms [1, 2]. Many plants have the ability to absorb large amounts of fluoride. For example, 57 to 1370 mg of fluorine is absorbed in 1 kg of tea and up to 4500 mg in cotton [2, 55 p.]. In this case, fluorine accumulates in the cotton seed, and most of it passes into the cottonseed oil. Studies show that when fluorine falls on the soil, including mineral fertilizers, the amount of fluorine in the crop also increases [3, S. 10–18]. In the presence of nitrogen-phosphorus- potassium fertilizers, the amount of fluorine absorbed by plants increases [4, S. 131–136]. MAIN PART. Phosphorous fertilizers are the main source of fluorine entering the soil. For example, apatite and phosphorites contain an average of 3.0 and 2.7% fluorine, respectively. Extractable phosphoric acid (WPPA) produced on the basis of Central Kyzylkum phosphorites contains about 1.2% fluorine. The method of deposition from acid using alkali metals in the form of silicon fluorides is not very effective, because the amount of silicon compounds soluble in acid in EFK is practically very small [5, S. 34-40]. During the processing of natural phosphates, the fluorine contained in them is distributed between gas, liquid (WPPA) and solid (phosphogypsum) phases. 80-85% of the raw materials (apatite and phosphorite) are converted into hydrofluoric acid during the production of phosphoric acid according to the dihydric scheme, and during its further processing, it becomes part of fertilizers. In order to fully satisfy the demand for fertilizers in agriculture, the increase in the production of phosphorus, especially complex fertilizers, creates a risk of fluorine saturation of soil, plants and water bodies [6, P. 55]. The negative effects of fluorine compounds that fall into the atmosphere and open water bodies and accumulate in living organisms and flora have been sufficiently studied [3, S. 10; 4, S. 131-136; 7, S.42-47]. Sodium and potassium sulfates, chlorides, phosphates, carbonates, and hydroxides are used to precipitate fluorine from WPPA in the form of silicon fluoride compounds of poorly 28 YOSH OLIMLAR ILMIY-AMALIY KONFERENSIYASI in-academy.uz/index.php/yo soluble alkali metals [8, S.191-206]. These methods are based on the chemical interaction of the above salts with the fluorinated acid contained in WPPA. The level of fluoride removal reaches 90%. According to this method, the level of fluorine removal in WPPA obtained from Central Kyzylkum phosphorites does not exceed 38-40%. The process of purifying WPPA based on Central Kyzylkum phosphorites with alkali metal salts is sufficiently presented in literature sources. It is suggested to clean WPPA first from sulfates and then from fluorine [9, S.2-4]. The process of defluoridation of WPPA based on Central Kyzylkum phosphorites with sodium sulfate, dihydrophosphate, metasilicate was thoroughly studied by the authors and it was shown that the level of fluorination can be increased from 38-40% to 80-85%, and the technology of WPPA defluorination was created. Fluorinated WPPA can be made from unenriched raw materials of Central Kyzylkum, calcium carbonate and oxide, washed enriched phosphorites [5-10] with desulfation materials are also available. A patent was obtained for the method of obtaining a nutrient precipitate by purifying WPPA from fluorine compounds and sulfates [6]. However, there are no materials for simultaneous purification of the extraction slurry from fluorine and sulfates in obtaining WPPA from Central Kyzylkum phosphorites. Currently, the demand for phosphate raw materials in the world is 190 million tons or 43 million tons of Р О per year. The demand for phosphate raw materials is expected to grow 2 5 by 1.3 million tons by 2020 and by 2 million tons by 2030. By 2050, the demand for raw materials will reach 220 million t of phosphate raw materials or 70 million t of Р О [7]. 2 5 As a result of the increase in the demand for phosphorous fertilizers in agriculture and the decrease of their stock from year to year as a result of the processing of phosphate raw materials into phosphorous fertilizers, it is one of the urgent tasks of the present time to include other types of raw materials in the production of phosphorous fertilizers along with phos