METHOD OF OBTAINING LIQUID COMPLEX FERTILIZERS FROM INDUSTRIAL WASTE

ABSTRACT

The article studies the technology of obtaining a new type of liquid mineral fertilizer based on local raw materials and calcium-containing industrial waste. The processes of decomposition of calcium and magnesium carbonates with nitric acid and neutralization of excess acid with gaseous ammonia were studied. Based on laboratory experiments, it was found that it is possible to obtain liquid ammonia-type fertilizers containing calcium nitrate, ammonium nitrate and magnesium nitrate. The resulting product contains ammonium and nitrate forms of nitrogen, which are important nutritional elements for agricultural crops. The results of the study indicate the possibility of producing effective and economically viable liquid mineral fertilizers using local raw materials and industrial waste.

АННOТАЦИЯ

В статье исследуется технология получения нового типа жидкого минерального удобрения на основе местного сырья и кальцийсодержащих промышленных отходов. Изучены процессы разложения карбонатов кальция и магния азотной кислотой и нейтрализации избытка кислоты газообразным аммиаком. На основе лабораторных экспериментов установлено, что возможно получение жидких аммиачных удобрений, содержащих нитрат кальция, нитрат аммония и нитрат магния. Полученный продукт содержит аммонийную и нитратную формы азота, являющиеся важными питательными элементами для сельскохозяйственных культур. Результаты исследования указывают на возможность производства эффективных и экономически целесообразных жидких минеральных удобрений с использованием местного сырья и промышленных отходов.

Keywords: Liquid mineral fertilizer, ammonia, liquid ammonia, wastewater treatment, local raw material resource, calcium-containing waste, chalk, limestone, dolomite, nitrate compound, ammonia, calcium nitrate, urea.

Ключевые слoва: Жидкое минеральное удобрение, aммиакат, жидкий аммиак, отходы водоочистки, местный сырьевой ресурс, кальцийсодержащий отход, мель, известняк, доломит, нитратное соединение, аммиак, кальциевая селитра, мочевина

Introduction. The agrochemical complex is a key component of the Republic's economic development, on whose development the well-being of the population depends. Therefore, providing the agro-industrial complex with the necessary crop protection products, plant growth and development stimulants, and a wide range of mineral and organomineral fertilizers with various ratios of the main macronutrients-nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur-is an important way to increase crop yields. Increasing the application rate of mineral fertilizers no longer contributes to increased yields. In addition to nitrogen, phosphorus, and potassium, plants require calcium, magnesium, sulfur, and microelements. The Republic's strong industrial base for the production of mineral fertilizers, including single phosphorus fertilizers effective for application under autumn plowing, is directly related to the implementation of scientific advances in phosphate processing, expanding their range and content of macro- and microelements [1,2,3,4].

The purpose of this work is to study the technology of producing effective liquid mineral fertilizers containing, along with nitrogen and phosphorus, calcium, magnesium, sulfur, and microelements based on local raw materials, and to analyze their agrochemical effectiveness in order to increase the yield of agricultural crops and improve soil fertility.

In Uzbekistan, ammophos, obtained from phosphorites in the Central Kyzylkum Desert, is currently used primarily as a concentrated phosphorus fertilizer. As a result of its use, the amount of soluble and plant-available calcium, magnesium, and sulfur compounds added to the soil decreases annually, which in turn leads to a deficiency of these elements in the bodies of animals and plants. In the Republic, as a result of the implementation of specific large-scale measures, high results have been achieved in scientific research in the field of obtaining new types of liquid mineral fertilizers based on local raw materials and providing agriculture with high-quality mineral fertilizers[5,6,7,8].

In recent years, there has been an increase in the production and use of liquid fertilizers globally. Among developed countries, the largest volumes of liquid fertilizer production are found in the United States, the United Kingdom, and France[9-10].

The problems of producing liquid fertilizers have long been studied abroad, and this problem has now been virtually solved. Nevertheless, we present several studies on this topic. Fertilizers are prepared from an aqueous ammonia solution with the addition of ammonium nitrate, calcium nitrate, or urea [10-11]. These additives increase the effectiveness of fertilizers and reduce the gas pressure of ammonia. Continuous production of ammonia has been patented. Ammonia used as fertilizers is produced in two stages. In the first stage, solutions of NH₄NO₃, Ca(NO₃)₂, or a mixture of them are saturated with ammonia supplied from the second stage, while the mixture is simultaneously indirectly and directly cooled with water. The solution is then sent to the second stage, where it is saturated and cooled with liquid ammonia.

Methods. Research into the production of liquid mineral fertilizers was conducted under laboratory conditions. Nitric acid, natural carbonate-containing minerals (chalk, limestone, dolomite), and calcium-containing sludge from the water treatment plant of JSC Farg'onaazot were used as feedstock.

The calcium-containing feedstock was decomposed using nitric acid at a concentration of 50–60%, with an acid rate of 200% of the stoichiometry for CaO and MgO. Laboratory experiments were conducted in a cylindrical glass reactor equipped with a mechanical stirrer. The stirring speed was 150-200 rpm. The process was carried out at a temperature of 45-50°C for 30 minutes. The temperature was maintained using a water thermostat and a contact thermometer.

After the decomposition process was complete, the reaction mixture was held for 30 minutes, resulting in a calcium nitrate suspension with a small amount of insoluble residue. Liquid and solid phases were separated using a laboratory centrifuge.

The resulting acidic solution, containing excess nitric acid, was sent to the neutralization stage in a high-speed ammoniator-evaporator, where free acidity was neutralized with gaseous ammonia at a temperature of  90-100°C to a pH of 6.5.

The chemical composition of the resulting liquid fertilizers was determined based on the content of the main nutrient components – nitrate and ammonium nitrogen, calcium, magnesium, and other compounds.

Results. Nitric acid, natural minerals containing calcium and magnesium carbonates and wastewater treatment plant waste were used as feedstock for the research.

Sludges with the following salt compositions (Table 1), in wt.%, were used for the research.

Table 1.

Chemical and salt composition of sludge

The acid rate chosen was 200% of the stoichiometry for the decomposition of calcium-containing waste. Laboratory experiments on the decomposition of calcium-containing waste were conducted in a cylindrical glass reactor equipped with a stirrer.

The required amount of calcium-containing sludge was loaded into the reactor, and nitric acid was gradually added while stirring (stirrer speed 150-200 rpm). Nitric acid rates were varied within the range of 55-60%, based on 200% of the stoichiometry for CaO and MgO in the carbonate feedstock. The calculated amount of carbonate feedstock (chalk, limestone, dolomite, calcium-containing waste) was dosed in nitric acid portions over 5-10 minutes. The reactor was located in a water thermostat. The optimum temperature of 45°C-50°C was maintained using a contact thermometer. After stopping the acid reagent dosing, the reaction mixture was held for 30 minutes. A calcium nitrate suspension containing a small amount of solid phase (insoluble residue) was obtained. A laboratory centrifuge was used to separate the solid and liquid phases.

The resulting acidic solution, containing excess nitric acid, is fed to a high-speed ammoniator/evaporator, and the free acidity is neutralized with gaseous ammonia at a temperature of 90-100°C due to the heat of reaction. After completion of the experiments, the resulting acidic solution was neutralized with gaseous ammonia to a pH of 6.5.

The standard nitric acid concentration is 200% of the stoichiometry for CaO and MgO in the carbonate feedstock (Tables 2 and 3).

Table 2.

Indicators of nitric acid decomposition of calcium-containing (100 g) industrial waste.

Table 3.

Indicators of neutralization of excess HNO₃ with gaseous ammonia (rapid ammoniaization)

When using calcium-containing sludge, a liquid ammonia fertilizer is obtained with the following composition (in mass%): Ca(NO₃)₂=27.4-32.5%, Mg(NO₃)₂=1.4-1.6%, NH₄NO₃=28.6-33.2%, H₂O=31-41%, N ammonia nitrogen =5.3-5.8%, N nitrate nitrogen =10-11.7%, Nototal nitrogen =15.3-17.5%, ∑sum of nutrient components = 57.6-67.2, etc.

The chemical composition of the resulting liquid fertilizers is shown in Table 4.

Table 4

Chemical and salt composition of the products

Note: by steaming ammonia obtained using the second option to a moisture content of about 25%, it is possible to increase the concentration of nutrients (nitrogen and other salts).

When liquid ammonia evaporates at a humidity level of 25%, the resulting liquid fertilizer has the following composition (in wt.%):

Ca(NO₃)₂=35.0-35.3%, Mg(NO₃)₂=1.6-2.0%, NH₄NO₃=36.1-36.3%; H₂O=25.0%, impurities 1.5-2.0; N_{ammonia nitrogen} = 5.8-6.7%, N_{nitrate nitrogen} = 12.7-12.8%, Total N _nitrogen = 18.6-19.4%, Sum of nutrient components = 73.0-73.3%.

At this moisture content, ammonia does not crystallize and flows well at room temperature.

Option 2 differs from option 1 in that the neutralized ammonia is saturated with urea to a total nitrogen content of over 27%.

Table 5.

Nitric acid decomposition rates of calcium-containing (100 g) industrial waste

Table 6.

Technological indicators of the process of neutralization of excess HNO₃ with gaseous ammonia (high-speed ammoniaization)

Ammonia composition in mass%. Ca(NO₃)₂=18.9, NH₄NO₃=19.0, Mg(NO₃)2=0.9, (NH₂)₂CO =38.2, H₂O=22.0, Total nitrogen =27.9, N_{ammonia nitrogen} =21.1, N_{nitrate nitrogen} =6.8, ∑_{sum of nutritional components} =77.0.

Table 7.

Chemical and salt composition after saturating the suspension with urea (N=46.3%)

Note: The process can use 50-60% HNO₃ and a calcium component containing 85-90% calcium carbonate, 3-4% magnesium carbonate, etc.

Conclusion. The conducted research demonstrated the feasibility of efficiently producing liquid mineral fertilizers using local raw materials and calcium-containing production waste. It was found that decomposition of carbonate raw materials with nitric acid followed by neutralization of the solution with gaseous ammonia allows for the production of liquid ammonia-type fertilizers containing calcium, magnesium, and various forms of nitrogen.

The resulting liquid fertilizers are characterized by a high nutrient content and good processing properties, such as fluidity, lack of caking, and ease of transportation and application to soil. The use of this technology enables the efficient use of local mineral resources and production waste, as well as a reduction in fertilizer production costs.

The practical significance of the conducted research lies in the feasibility of implementing the developed technology for the production of liquid mineral fertilizers containing nitrogen, calcium, and magnesium, which contributes to increased soil fertility and crop yields.

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