Obtaining potassium sulphate by conversion of potassium chloride and ammonium sulphate

09035


Introduction
Mineral fertilizers have a positive effect on the growth, development and productivity of agricultural crops.Among them, the most important are mineral fertilizers rich in phosphorus, nitrogen and potassium, the lack of which elements negatively affects the growth and development of plants.Each agricultural crop has a great need for potassium fertilizers.The practice has shown that when applying 1 ton of potassium fertilizers, grain yield can be increased by 2-3 t/ha, potatoes -by 20-33 tons, and sugar beets -by 35-40 tons.In industry, potash fertilizers are mainly produced in the form of KCl, K2SO4, and KNO3.
In the Republic of Uzbekistan, as well as in the Russian Federation, the need for potash fertilizers is very high [1].The main reason for this is the insufficient volumes of their production and their high cost of production.Previously, to meet the needs of the country's agriculture, this type of mineral fertilizer was imported from abroad.Thanks to the commissioning of the only enterprise in Central Asia for the production of potash fertilizers, Dekhkanabad Potash Plant JSC, specializing in the production of potash fertilizers, mainly potassium chloride, the import of these products into the country was stopped.Due to the high chlorine content in potassium chloride and its impacts on soil and plants in the republic, the need for potash fertilizers that do not contain chlorine is increasing.
As you know, potassium sulfate is the most promising product for the production of potash fertilizers.It is main feature is that it does not contain chlorine, it can be used on any soil and all types of crops [2].
By applying this fertilizer to potatoes, vegetables, flax, grapes, citrus fruits, and flowers, the yield can be increased several times.The need for potassium sulfate is especially high when growing vegetables and flowers in greenhouses.
There are 2 main methods for producing potassium sulfate:  conversion method. method of processing natural minerals.Currently, there are no large producers of this product in the CIS countries, which is due to the lack of a developed raw material base for the production of sulfate potassium fertilizers.To obtain potassium sulfate, conversion methods are mainly used based on the interaction of sulfate salts with potassium chloride according to the reaction [3]: here, Meions Ca 2+ , Mg 2+ , Fe 2+ , Na + , NH4 + and etc.According to the conversion method, potassium sulfate is mainly obtained by reacting potassium chloride with sulfuric acid, sodium sulfate and ammonium sulfate.Currently, the production of K2SO4 with a nutrient content of less than 48% has been launched in the Gallaaral district of the Jizzakh region of the Republic of Uzbekistan.H2SO4 and KCl are used as raw materials.The process is based on the following reaction: This reaction is endothermic and increasing temperature has a positive effect on it.The resulting K2SO4 product is cooled and crystallized.Special devices are required to store and transport the hydrochloric acid formed as a result of the process.The conversion process for producing potassium sulfate from sulfuric acid must be carried out from materials that are resistant to acidic environments, which leads to an increase in the cost of the final product.In addition, working with sulfuric acid can pose a danger to the life and health of workers.All of the above raises the need to develop simpler and safer production technology.

Experimental part
Obtaining potassium sulfate from the conversion of ammonium sulfate and potassium chloride has several advantages.The process is carried out at low temperatures in simple devices.The process is based on the following reaction: To carry out this reaction, 30% KCl solutions and 40% (NH4)2SO4 solutions are prepared and mixed.The process is carried out at a temperature of 30-40 ℃ for 20-30 minutes.Potassium sulfate crystals gradually form [4].The solution is then cooled and the crystals are separated.The yield of potassium sulfate crystals is 92-95%.The ammonium chloride produced by the flow can be used as fertilizer or to produce other products.
The studies were carried out as follows: (NH4)2SO4 was added to potassium chloride in a stoichiometric ratio according to reaction (3), and such an amount of distilled water was added that during the conversion the K2SO4 content in the solution did not reach saturation and was about 11%.After intensive stirring on a mechanical stirrer, the suspension was filtered, and then the compositions of the solid and liquid phases were examined for SO4 2-, CI -, NH4 + , and K + ions using known methods.The content of SO4 2 -ions was determined by the gravimetric method, and K+ -by the flame photometric method.CI -, and NH4 + -by complexometric titration.The compositions of the solid phase were controlled by X-ray phase analysis.

Results and discussion
The conversion process is influenced by several factors, namely: temperature, duration, speed of mixing of the reagents, particle size of ammonium sulfate, and KCl consumption rate depending on stoichiometry.To select optimal conditions for conducting this process, the influence of these technological parameters on obtaining high-quality products with a high degree of conversion was studied.An increase in temperature and an increase in the consumption rate of potassium chloride did not have a significant effect on the degree of use of the NH4 + ion, therefore all subsequent studies were carried out at 22 ℃ and a stoichiometric consumption rate.
In the first series of experiments, the effect of mixing duration on the decomposition of the studied salts was investigated.The experiments were carried out using ammonium sulfate fraction -0.25 mm, stirring mode -200 rev/min, temperature -22 ℃.It has been established that this process occurs at high speed and within 5 minutes.stirring, the degree of utilization of K + ions is 85.23% (Table 1).It was found that when mixing the components for 20-30 minutes.the reaction rate increases even more and during this period of time reaches a maximum value of 92.08%.With a further increase in the stirring duration, the reaction slows down and practically no increase in the degree of utilization of K + ions is observed.
The influence of stirring duration and stirrer rotation speed on the degree of utilization of NH4+ ions for various ammonium sulfate fractions was studied (Table 2).The production of K2SO4 is the second stage of the process.The suspension obtained in the first stage was subjected to filtration, resulting in a precipitate containing about 94.15% (NH4)2SO4 and a filtrate with 7-8% K2SO4.Potassium sulfate was isolated from the filtrate by removing water from it by evaporation.It was found that when 19.2% of the water from the initial mass is evaporated, the solution becomes cloudy, which is associated with the formation of sparingly soluble ammonium salts, which were then removed by hot filtration.The purified solution was subjected to repeated evaporation of water to 70.1% and cooling, as a result of which a product containing 99.8% K2SO4 crystallized into the solid phase.The obtained data are presented in Table 3.In the case of complete removal of water (experiment 2) without separation of sparingly soluble ammonium compounds, the resulting sediment contains only 95.9% or 53.5% K2O, which fully satisfies the requirements of agriculture.

Conclusions
A new simplified and waste-free technology for producing potassium sulfate has been proposed.The method consists of obtaining this salt by the conversion method of interaction of ammonium sulfate and potassium chloride in an aqueous medium.Optimal conditions for the process of obtaining potassium salt have been developed: the stoichiometric ratio of the starting components, temperature conditions and mixing duration.The final product (suspension) is filtered, resulting in the release of a precipitate containing 96-97% NH4CI and filtrate 3-6% K2SO4.When the resulting solution is evaporated, a sol containing 96-99% K2SO4 crystallizes.

Table 1 .
Qualitative and quantitative indicators of the conversion of ammonium sulfate and potassium chloride ammonium sulfate fraction -0.25 mm, stirring mode -300 rev/min, temperature -22 ℃.

Table 2 .
The influence of stirring duration and stirrer rotation speed on the degree of utilization of NH4 + ions for different fractions of ammonium sulfate

Table 3 .
Compositions of silks and sediments obtained by evaporation of filtrates after the conversion of ammonium sulfate and potassium chloride