RESEARCH OF THE PROCESS OF TWO-STAGE DECOMPOSITION OF DIFFERENT TYPES OF KYZYLKUM PHOSPHORITES WITH SULFURIC ACID IN ANHYDRITE MODE

ABSTRACT

The article studied the process of two-stage decomposition of PF, WDC and WCC with 93-94% sulfuric acid under anhydride conditions with the formation of concentrated H₃PO₄, CaSO₄ (1st stage) and monocalciumphosphate, superphosphate (2nd stage). Both processes are combined and carried out in one apparatus. For the decomposition process to occur in anhydride mode, a temperature above 120°C is required, and the sulfuric acid rate is not lower than 100-105%. To achieve the highest C_dec. of the phosphate component of sulfuric acid, 70-80% of the phosphate component must be supplied to the 1st stage of decomposition, and 20-30% to the 2nd, so-called neutralization stage. At the same time, C_dec. the result reaches above 90-92%, due to which the processes of ammonization, spring and storage ripening and drying are observed.

АННОТАЦИЯ

В статье изучен процесс двухстадийного разложения ФМ, МСК и МОК 93-94%-ной серной кислотой в условиях ангидридного режима с образованием концентрированной Н₃РО₄, CaSO₄ (1-ая стадия) и монокальцийфосфата, суперфосфата (2-стадия). Оба процесса совмещены и осуществляются в одном аппарате. Для протекания процесса разложения в ангидридном режиме необходима температура выше 120°С, а норма серной кислоты - не ниже 100-105%. Для достижения максимальной К_разл. фосфатного сырья серной кислотой на 1-ую стадию разложения необходимо подавать 70-80% фосфатного сырья, а на 2-ую, так называемую стадию нейтрализации- оставшиеся 20-30%. При этом К_разл. сырья достигает выше 90-92%, благодаря чему исключаются процессы аммонизации, созревания и складского дозревания, сушки.

Keywords: superphosphate, monocalciumphosphate, anhydride mode, two-stage decomposition.

Ключевые слова: суперфосфат, монокальцийфосфат, ангидридный режим, двухстадийный разложения.

Introduction

According to forecasts, the world population will increase from 7.2 billion in 2013 to 9.6 billion people by 2050, i.e. will increase by 40%, while food consumption will increase at a rate of 3.1% per year. Successfully addressing food security and supporting productivity growth, income generation and meeting this demand requires sustainable intensification of agricultural production. Agricultural productivity is expectedtoin crease by 60%[1; p.139-146].

According to the Program of Uzkimyosanoat JSC for deep processing of mineral resources for 2016-2030, drawn up in pursuance of the order of the President of the Republic of Uzbekistan, in 2023 it is planned to increase phosphorite production by 178%, and in 2030 - by 264%. That is, the volume of phosphate ore production will be 2.2 and 3.7 million tons, respectively.It also provides for the organization of the production of extraction phosphoric acid with a capacity of 160 thousand tons of 100% P₂O₅ and the production of sulfuric acid with a capacity of 650 thousand tons. Extraction phosphoric acid will be supplied to the Samarkand Chemical Plant for the production of ammophos in a volume of 330 thousand tons (150 thousand tons Р₂О₅), which will be one of the components in the production of complex NPK fertilizers at this plant. The production capacity of complex NPK fertilizers at the Samarkand chemical plant will reach 960 thousand tons in 2028.[2; 252p.]

Scientific research is being carried out around the world to obtain simple, double and triple superphosphates, based on the use of higher quality phosphate ores, but their reserves are being depleted. In this regard, special attention is paid to the development of intensive and economical methods that justify scientific and technical solutions in the following areas: development of a two-stage method for processing low-grade phosphorites with concentrated sulfuric acid in an anhydrite mode to produce granulated simple superphosphate for use under plowing and for main use[3; p.100-102, 4; №5395, 5; p.32-38].

Based on this, in this work the basics of a two-stage method for producing granulated superphosphate have been developed, thereby eliminating the stages of chamber ripening and warehouse ripening, ammoniation and drying of the finished product.

In this work, phosphate flour (PF), washed dried concentrate (WDC) and washed calcined concentrate (WCC), produced at the Kyzylkum phosphate complex in accordance with GSt 2825:2014, were used as phosphate raw materials. Their compositions are given in Table 1.

Materials and methods

For the purpose of their decomposition, concentrated sulfuric acid produced by Ammophos-Maxam JSC was used with concentrations of 70; 80; 90; 93 and 94.5% H₂SO₄.

Table 1

Composition of various grades of phosphorites of the Central Kyzylkum

When studying the process of decomposition of phosphate raw materials using a two-stage method, the kinetics of decomposition of phosphate raw materials with 93% sulfuric acid was first studied at a rate of 100% of stoichiometry.

The experiments were carried out in a thermostated reactor equipped with a paddle stirrer at 122°C. The duration of contact of the components was 2, 5, 10, 20, 40 and 60 minutes[6; p.32-41, 7;doi:10.1088/1755-1315/939/1/012055].

Results and discussion

As can be seen from table.2., with an increase in the duration of decomposition of  PF with sulfuric acid (2-60 min.), the decomposition coefficient (C_dec.) of phosphate raw materials increases (up to 90.02-92.32%). At the same time, there is an increase in the ratio of the soluble form of P₂O₅ to its total content and a decrease in total acidity (the sum of sulfuric and phosphoric acids) from 16.68 to 15.39%. It can be seen that during the decomposition of WDC, the temperature of the reaction mass increases to an average of 130°C, and for WCC – to 175°C.

The content of total and free forms of  P₂O₅ in the decomposition products of  WDC and WCC  turned out to be significantly higher than in the decomposition of PF. In addition, an increase in the relative content of the aqueous form of P₂O₅ to its general form was noted in the decomposition products (Fig. 1).

*The free acid content was determined as the sum of free sulfuric and phosphoric acids.

Figure 1. Free acidity of products during the decomposition of various phosphorites.

As can be seen, the free acidity of the products during the decomposition of PF is 15.39-16.68% and 19.77-21.42% during the decomposition of WDC, and for WCC this figure varies between 18.51-19.98%. By increasing the duration of the decomposition process from 2 to 60 minutes. the content of the general form remains practically unchanged and amounts to 13.55-14.11% when using WDC and 13.52-13.91% when using WCC. The content of the aqueous form of P2O5 is 12.39-13.08% for WDC and 12.57-13.24% for WCC. The relative content of the water-soluble form varies respectively within the range of 91.44-92.70% and 92.97-95.18%.

It was found that 20 minutes are sufficient for the decomposition of PF, WDC and WCC,  while P₂O_5aq. : Р₂О_5sol.=92.10% for PF and 92.24% WDC, and for WCC 93.37%. This is much faster than when producing superphosphate using a chamber scheme (1.5 hours), and C_dec. raw materials are sufficient to neutralize acidity.

Table 2.

Decomposition coefficient of various phosphorites with 93% sulfuric acid depending on the duration of interaction

Conclusion

We can conclude that the optimal option is to take the decomposition process of phosphate raw materials within 20-30 minutes, because with a further increase in duration, no increase in the decomposition coefficient (C_dec.) is observed, and with less time the required mass is not formed in the required quantity. It should be noted that the relative high acidity of the product can have a beneficial effect on carbonate gray soils of  Uzbekistan. The main phases of products from PF, WDC and WCC are monocalcium phosphate and its monohydrate, dicalcium phosphate and its monohydrate, anhydrite and calcium sulfate hemihydrates.

References:

1. R.T. Burns; L.B. Moody; I. Celen; J.R. BuchananOptimization of phosphorus precipitation from swine manure slurries to enhance recovery / Water SciTechnol (2003) 48 (1): рр. 139–146. https://doi.org/10.2166/wst.2003.0037.
2. Beglov B.M., Namazov Sh.S., Reymov A.M., Seytnazarov A.R. Aktivasiya prirodnogo fosfatnogo sir'ya. – Tashkent, 2020. – 252s.
3. Tadjiev S.M., Samadov M.S., Namazov Sh.S., Urmanov S. Tovarnie svoystva superfosfata, poluchennogo iz fosforitov Sentral'nix Kizilkum// Nauchno-texnicheskiy jurnal'. Vestnik FPI. – 1998, № 2, s. 100-102.
4. Predvaritel'niy patent №5395. Sposob polucheniya prostogo superfosfata / Yusupbekov N.R., Tadjiev S.M., Xolikberdiev Yu., Beglov B.M., Namazov Sh.S i. dr. Axborotnoma. 1998 g. №4 po zayavke №IHDR 9800205 ot 25.03.1998 g.
5. Tadjiev S.M., Namazov Sh.S., Beglov B.M. Razrabotka texnologii prostogo superfosfata iz fosforitov Tashkura potochnim metodom // Jurn.xim. prom-st' segodnya. (Moskva) –2004. -№4. -S.32-38.
6. Otaboev X.A., Badalova O.A., Namazov Sh.S., Radjabov R., Seytnazarov A.R., Beglov B.M. Dvuxstadiynaya obrabotka fosforitovoy muki sernoy kislotoy - osnova potochnoy texnologii polucheniya prostogo superfosfata // Ximicheskaya promishlennost' segodnya. – 2020. – №3. – S. 32-41.
7. Kh Otaboev et al 2021 IOP Conf. Ser.: Earth Environ. Sci. 939 012055.