Improvement of methods for obtaining phosphorus fertilizers by mechanical activation

. The article deals with the process of mechanical activation and determination of the influence of activating additives on the degree of solubility of low-grade phosphoresces of the Central Kyzylkum. As well as mechanical activation of samples of various types of low-grade phosphoresces with the addition of acid salts NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , at a ratio of 5:5 in a mortar mill RM 200, with a mode of increasing the activation time to 60 minutes, by heating the resulting mixture to 200°C in various component ratios. Development of a waste-free and environmentally friendly technology for the production of NPK fertilizers.


Introduction
Today in the Republic of Uzbekistan one of the main directions of development of the chemical industry is the development of the most effective technologies for the complex processing of phosphoresces of the Central Kyzylkum, which are the main raw material base of enterprises producing mineral fertilizers.
In recent years, activation methods seem to be fundamentally promising in the processing of phosphorites, which allow solving the issues of saving decomposing reagents and improving the quality of the products obtained.These include mechanical, chemical, thermal methods and their combinations -mechanochemical and thermochemical methods of activation [1].
Activation by grinding, or mechanoactivation, is a new way of intensifying physical and chemical processes.It is based on a change in the reactivity of solids under the action of mechanical forces.Even now it is possible to determine the prospects for the use of mechanoactivation in a number of areas of science and production [2.].Activation by grinding makes it possible to improve the existing methods of processing minerals and outline ways to create completely new technological schemes for the chemical beneficiation of ores, the opening of refractory mineral raw materials and the integrated use of mineral resources.With the help of intensification of physical and chemical processes by mechanical action, it is possible to improve the quality of the charge, reduce the technological parameters of sintering and autoclave processing, accelerate and increase the extraction of metals by the hydrometallurgical method.Mineral substances activated by grinding are characterized by a high sorption capacity, which allows them to be used as catalysts or for industrial water purification, to capture valuable components.Activation by grinding has long been used in the production of phosphate rock used to improve soil fertility, but the possibilities of mechanical activation in the production of fertilizers are much wider.The mechanical activation of raw materials has already found application in the production of silica cite, a new building material, and the possibilities for improving the preparation of building materials have not been exhausted by this [3].
A new stage in the development of the mechanochemistry of inorganic substances is associated with the design of grinding equipment and the growing needs of industry for fine materials.
Studies of the mechanical activation of apatite's and phosphoresces led to the acquisition of a number of methods for the preparation of phosphorus fertilizers, proposed for implementation in order to increase the yield of fields [4].However, the application of one or another method of mechanical activation depends on the composition, structure and type of phosphoresce, and especially on the soil characteristics.Taking into account the fact that soils in the Republic of Uzbekistan are alkaline, mechanical activation of phosphoresces in the Central Kyzylkum is ineffective [5].
The need for chemical activation of phosphoresces is due to the electronic nature and structural features of phosphate, carbonate and silicate ions in their composition.The crystal structure formed from PO4 -3 , CO3 -2 ions is sensitive both to the actions of hydrogen ions and ions of the acid residue.In other words, under the action of acidic reagents in the phosphate and carbonate structural units of phosphoresces, enough defects are formed in calcium positions, leading to a deficiency of the latter.Because of this, in order to maintain electrical neutrality in the defect positions of Ca +2 ions, an isomorphic entry of a water molecule occurs, and most likely, hydronium ions [H3O + ] from the acidic medium.With an increase in the content of [H3O] + in the reaction medium, the decomposition of phosphoresces increases.In the case of high-carbonate phosphoresces, this process is accompanied by irreversible decomposition of carbonates with the release of CO2 (decarburization) and an improvement in quality indicators by an increase in the digestibility of P2O5 and CaO components.
Activation of minerals during their grinding is a complex multi-stage physical and chemical process, at each stage of which it is possible to single out the main phenomena that characterize this stage of activation, but not the whole process as a whole.On the basis of the conducted studies, with a certain measure of reliability, the prospects for the use of activation by grinding in various industries were determined.Activation of mineral substances by grinding can be successfully used in coal technology, for the intensification of hydrometallurgical processes, in the production of fertilizers, building materials, composite mixtures, etc., opens up the prospect of recycling mineral raw materials stored in dumps, increasing the integrated and rational use of mineral resources, and reducing the harmful effects of industry on the environment.First of all, the most promising is the use of activation by grinding in the processes of leaching, extraction, selective and gross dissolution of substances.The removal of the limiting stages of the process makes it possible to accelerate the transfer of solid components into a dissolved state many times over.Energy costs for activation pay off by saving time and more complete extraction of dissolved components.It should be noted that a promising direction of using activation by grinding is the preparation of composite mixtures.Composite mixtures are widely used in various industries.They are prepared as a charge before pyro processes, used in the preparation of press powders, used in the preparation of solid solutions for catalysts or other purposes.Activation by grinding should find application as a way to reduce the parameters of the main technological process: lowering the melting or sintering temperature, reducing the concentration (or pressure) of liquid and gaseous reagents.This will simplify the hardware design, improve the culture of production and improve working conditions.The prospects for combining technological operations are opening up.For example, coal bergenization requires two preparatory operations (coal grinding and hydrogen production) before the main operation, coal hydrogenation.All three operations can be combined in one apparatus -a mechanical activator, which will finely grind coal, produce hydrogen, and provide conditions for coal hydrogenation.Similarly, the operations of grinding a multicomponent ore are combined with the reduction of some metal oxide with hydrogen and its leaching in a state of lower valence.Activation by grinding should find application in solving the problems of the integrated use of mineral resources and reducing the harmful effects of industrial processing products on the environment.Its promising application is as follows -it is the disposal of production waste and the elimination of dumps, wastewater treatment with the trapping of valuable (and harmful) components on the activated surface, the upgrading of peat, coal and oil shale before burning with the simultaneous extraction of metals, sulfur and other valuable components, replacement of the roasting of sulfide and arsenic-containing concentrates without a roasting process based on mechanical activation.
Activation by milling is likely to be further developed as a new method for the chemical synthesis of inorganic substances.Finally, activation by grinding can be the basis of fundamentally new technological processes, when an auxiliary operation becomes the main and main one.The change in the physical state and chemical properties of mineral substances during their dispersion is of great scientific interest.The use of mechanoactivation in research work has its own prospects.In fact, the only way to speed up the studied physicochemical processes was to heat the reagents.However, heating inevitably brings the process to completely different conditions in terms of temperature and pressure.The study of processes occurring at room (and below) temperature presents certain difficulties because there is no way to accelerate these processes to such a level at which changes in the substance are observed.Activation by grinding, in our opinion, opens up the possibility of laboratory study of low-temperature physicochemical processes.In particular, it allows deploying physical modeling of natural processes occurring on the day surface at a speed that is noticeable only in geological time periods.Activation by grinding as a new way to intensify physical and chemical processes requires appropriate technical equipment.

Methodology and results of the study
Various types of phosphoresces of the Central Kyzylkum were used as phosphate rock for research.Kyzylkum phosphoresces belong to the widespread granular carbonate type and, in terms of their rational composition, are analogous to the largest phosphoresce deposits of the African-Arabian phosphoresce province, but differ from them in a relatively low content of useful components.
Phosphorus-containing ores are a complex system, both in terms of the composition of minerals and the structure of apatite, a plastic matrix that is prone to various isomorphic substitutions.
The main ore mineral is Franco lite or carbonate Fluor apatite, which contains phosphorus pentoxide.Associated elements are fluorine and uranium.Fluorine is included in the crystal lattice of Franco lite; its average content in the ore is 2.12%.Uranium is present as an isomorphic impurity; its content in ores is insignificant (0.002-0.006%).
Table 1 show the composition of low-grade phosphoresces of the Central Kyzylkum used for research.Acid salts NH4H2PO4, (NH4)2HPO4, NH4HSO4 и, and KHSO4 were used as acid additives.In order to find out their activation ability during mechanical activation of lowgrade phosphoresces with these additives.
To determine detailed information about the composition and structure of low-grade phosphoresces in the solid phase, we carried out an electron microscopic analysis using the SEM method (Figure 1).As can be seen from the results of the scanning electron microscope, the predominant phase in the structure of the sample is calcium phosphate -fluorocarbon ate apatite, calcium is present, also in the form of dolomite.Silicon is present predominantly in the form of quartz.Phosphoresce is characterized by a well-pronounced eolith-grained structure with a predominance of phosphate cement, intensive development of carbonate cement (dolomite), sometimes turning into quartz cement.Thus, according to the results of complex studies, it has been established that fluorocarbon ate apatite is the main mineral of phosphoresce fines and is presented in the form of iolites (multilayer rounded grains).Calcite and dolomite form fine-grained inclusions of various shapes.Quartz in the structure of phosphoresce is in the form of fragmental grains.Ferrous minerals in properties close to hydro goethite in phosphoresce are in the form of separate small inclusions.
To study the mineral, chemical and granulometric composition of low-grade phosphoresces of the Central Kyzylkum and the main rock-forming minerals contained in it, standard methods for their averaging and sampling for research were used in the work.For chemical analysis, photometric, gravitational, titrimetric and other methods were used.
The chemical analysis of the studied materials was performed according to the accepted method.Extraction of assailable phosphorus from phosphoresce samples was carried out with a 2% solution of citric acid.The content of the lemon-soluble form of phosphates was determined by the method of differential colorimetric of the phosphorus-vanadiummolybdenum complex on a UV-1280 spectrophotometer (Shimadzu, Japan) measuring in the visible spectral range from 190 to 1100 nm.
The contents of Ca +2 , Mg +2 were determined by the complex metric method and CO2 -by chromatographic and titrimetric methods.The ion metric method was used to determine the amount of fluorine in the raw material from the obtained samples.This method is based on measuring the concentration of fluorine in a solution using a fluorine-selective electrode without the initial release of fluorine.To determine the nitrogen content in the composition of mineral fertilizers, the formalin method and the Devard method were used.
The content of potassium in the composition of the obtained samples was determined by photometry in a flame photometer.Thermograviometric studies were performed using a modern thermo analytical system, including differential thermal analysis, thermogravimetry, and determination of the rate of mass change using a LabSys Evo synchronous thermo gravimetric analyzer (Seta ram Instrumentation, France).Differential thermal analysis is designed to measure thermodynamic characteristics (heat and temperature of phase transitions and physic-chemical reactions), as well as to register changes in the mass of solid and powder materials in the temperature range from 25 to 1600 0 C. Research conditions: temperature range from room temperature to 900 0 C. Temperature change rate -from 0.01 to 100 0 C/min; sensitivity of the 3D sensor 0.5mV/mW and a high heating/cooling rate of the oven 100 0 C/min, the speed of the chart tape advance is 2 mm/min.
The method of infrared spectroscopy was used in the work, with the help of which information about the structure and positions of molecules relative to each other was obtained.
IR spectroscopy (IR) studies were performed using an IRTracer-100 IR-Fourier spectrometer (Shimadzu, Japan).The IR study was carried out by pressing samples weighing 1-1.5 mg per 500 mg of KBr powder obtained by grinding KBr single crystals, followed by pressing into one monolithic tablet.
The study was carried out on powder X-ray diffract meters Empyrean (PANalytical B.V., Netherlands) and XRD-6100 (Shimadzu, Japan).The sample powders were thoroughly mixed to obtain a sample with an average content.Semi-quantitative X-ray phase analysis by the Rietveld method was carried out using the software "Profex -Open source XRD and Reitveld Refinement".
To confirm the violation of the structure of activated phosphoresces, electron microscopic analyzes were carried out.Microscopic examination of the surface of the obtained samples using an NLSD-307B screen microscope.
The compositional and structural characteristics of the feedstock were studied using an EVO MA-10 scanning electron microscope (Carl Zeiss, Germany) with an energy-dispersive elemental analyzer (Oxford Instruments, Great Britain).
Mechanical activation was carried out on a laboratory machine -a mill-mortar Retsch RM 200 with a rotation speed of 100 rpm at 50 Hz.Fractional analyses was performed on a laboratory analytical sieving machine Retsch AS 200, which has an electronic setting of the amplitude and time of sieving of loose particles.
The granulometric composition after grinding the sample using sieve analysis was distributed over the following fractions (Table 2).To determine the granular composition of phosphoresce raw materials; we used an analytical vibration machine Retsch AS 200.It was found that all samples contained particles with average diameters ranging from 45 to 4000 microns (Figure 2).

Fig. 2. Change in the mass ratio of low-grade phosphoresces after sieve analysis
From the diagrams, it was revealed that the largest number of fine fractions of grains in the phosphoresce ore of the first layer is greater than the rest.There are more particles with a size of 125 µm in the ore of the second layer.This means that the ore of the second layer has an average grain size of 20% of the total mass.
In order to determine the effect of activating additives on the degree of solubility of lowgrade phosphoresces, samples of various types of low-grade phosphoresces were mechanically activated with the addition of acid salts NH4H2PO4 and (NH4)2HPO4 at a ratio of 5:5 in an RM 200 mortar mill with modes of increasing the activation time to 60 min.The resulting mixture was heated to 200°C at various ratios of components.
To confirm the violation of the structure of activated phosphoresces, electron microscopic analyzes were carried out.The results of an electron microscopic study of samples of mechanically activated phosphoresces are shown in Figure 3.
According to the results of an electron microscopic image, one can see about a decrease in the size of crystals, a change in the crystal lattice, and the origin of amorphization.Figures 3a, 4a, 5a show the original low-grade phosphoresce with a characteristic finegrained structure and polydispersity of particles.When comparing high-resolution electron microscopy images (Fig. 3b, 4b, 5b), it can be seen that the separation of the phosphate part occurs and the release of quartz and aluminosilicate glass grains into a fine-grained space and the absence of large grains, since during the activation process their average size decreased by more than 2 times compared with non-activated phosphoresce.
On electron microscopy images (Fig. 3.c, 4.c, 5.c) the activated sample has a multilayer structure, consisting of a shock-absorbed surface layer, a heavily deformed layer containing many micro cracks, a weak deformation layer and a core.
According to the results of electron microscopic studies (Fig. 3, 4, and 5), one can indirectly judge the degree of defectiveness of the crystal structure depending on the activation time, the introduction of additives and the effect of temperatures.
In order to determine the effect of activating additives on the degree of solubility of lowgrade phosphoresces, samples of various types of low-grade phosphoresce were mechanically activated with the addition of acid salts NH4H2PO4 and (NH4)2HPO4 at a ratio of 5:5 in a mortar mill of the RM 200 type with an increase in activation time to 60 min, the resulting mixture was heated to 200 0 C.In the course of laboratory studies, samples were taken and their chemical composition was determined.
The results of the experiments showed that when mixing a mixture of a ratio of 50:50 of the addition of NH4H2PO4

Conclusion
The data of physicochemical methods and thermal analysis show that during mechanoactivation and mechanochemical activation, a deep violation of the crystal structure occurs, the introduction of carbonate and hydroxyl groups to compensate for the defectiveness of the structure and the formation of new compounds that also have a defective structure.The result of the appearance of this imperfection is an increase in the reactivity and solubility of activated samples.
With mechanical and chemical activation, a high softening of phosphate raw materials is carried out in the presence of acid salts.In this method, due to the destruction of the structural rings of phosphates under the action of strong shocks and friction, its crystallinity decreases, the specific surface area increases, and it becomes amorphous.As a result of mechanical and chemical activation, a plant-assailable form of P2O5 is formed in phosphoresces, and their granulation or tableting is necessary.To maintain the required strength of a product with a particle size of not more than 250 mm, it is necessary to ensure its good grinding in wet soil conditions.
The completed complex of studies on the mechanical activation of various types of lowgrade phosphoresces with the addition of NH4H2PO4 and NH4H2PO4 allows us to draw the following important conclusion that, under optimal conditions, the assailable form of P2O5 digestible, P2O5water, CaOdigestible increases.and SaOwater.This is a good prerequisite for the development of a waste-free and environmentally friendly technology for the production of NPK fertilizers, and the involvement of low-grade phosphoresce raw materials in the production of complex mineral fertilizers will significantly expand the phosphate raw material base and produce a wide range of fertilizers.

Fig. 3 .Fig. 4 .Fig. 5 .
Fig. 3. Microscopic images of a mixture of potassium hydrogen sulfate and phosphoresce at 1 hour activation a) -initial phosphoresce; b) -activated mixture of potassium sulfate and phosphoresce when activated for 1 hour; c) -an activated mixture of potassium sulfate and phosphoresce, activated for 1 hour, heated at a temperature of 400°C.

Table 1 .
Chemical composition of low-grade phosphoresces of the Central Kyzylkum