Reaction of urea with citric acid in aqueous solutions at molar ratios of 1 : 1, 1 : 2, and 2 : 1 and the solubility of urea citrate were studied. The data obtained can serve to optimize use of citric acid as a physiologically active substance or nitrification inhibitor and in production of liquid fertilizers containing urea.Urea is a frequent component of many liquid integrated fertilizers. Interaction of urea with citric acid can affect phase equilibria in the systems constituting liquid complex fertilizers.Urea is highly reactive. Many urea compounds obtained in reactions with mineral or organic acids are known [135]. Citric acid is a necessary component in the system of biochemical reactions of the cellular respiration. Along with other tricarboxylic acids, citric acid is contained in small amounts in mitochondria of all the cells. Another function of citric acid is to support the acid3base equilibrium and ionic composition in a living body. Citric acid is a typical chelate forming agent in reactions with metal ions. It can also inhibit nitrification [6] and hence is of interest as a component of liquid complex fertilizers.There is no reliable information on how urea reacts with citric acid. Fragmentary tentative results have been published previously [7].In this study, we examined the reaction of urea with citric acid in aqueous solutions and determined the main physicochemical properties of the reaction product.Urea CO(NH 2 ) 2 and citric acid C 6 H 8 O 7 . H 2 O were of chemically pure grade. The compositions of the substances were determined by chemical and physicochemical analyses. The nitrogen content was found in solutions and in the solid phase [8 310].A thermal analysis of solids was performed on a Du Pont Instruments 990 Thermal Analyzer at a heating rate of 10 deg min 31 .The IR spectra were recorded on a Spectrum GX (Perkin Elmer) FT-IR spectrometer in KBr pellets. An X-ray phase analysis was performed on a DRON-6 diffractometer with copper radiation and nickel filter within the 0o3166.5o range of diffraction angles with a relative error at no more than 0.5%.Mixtures of urea (Ur) and citric acid (HCit), taken in molar ratios of 1 : 1, 2 : 1, and 1 : 2, were dissolved in water taken in amounts corresponding to the weight ratio of the sum of the reactants to water of 1 : 0.25, 1 : 0.5, 1 : 0.75, and 1 : 1. The solutions were prepared at room temperature and, in a number of cases, were heated, if required, for complete dissolution of the initial substances. The results are listed in Table 1. As can be seen, a precipitate is formed at a 1 : 1 molar ratio; its chemical composition corresponds to urea citrate with a nitrogen content of 11.1 wt %. Practically no nitrogen remains in solution. At Ur : HCit = 2 : 1, a substance with~11 wt % nitrogen content precipitates, but nitrogen remains in solution in Table 1. Chemical composition of aqueous solutions containing urea and citric acid and of precipitate ÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Ur/HCit ³ Weight ratio ³ Nitrogen content, wt % ³ ÃÄÄÄÄÄÄÄÄÄÄ...
The ever-increasing intensity of agriculture is causing irreversible qualitative changes in the soil. Soil conservation and improvement is a priority of EU agro-environmental policy. However, this is also one of the most difficult challenges for agriculture. Various ways for sustainable agriculture have been proposed. One way to provide arable soil with humic substances is through the use of humic extracts. The aim of this work is to create a humic product for soil improvement from local raw materials, i.e., Lithuanian peat. Lithuanian peat samples from various peatlands with a different degree of humification were studied. The chemical composition of peat was determined using various methods (chemical analysis, AAS, XRD, SEM), and the optimal conditions for obtaining peat extracts were established. After examination of the chemical composition and properties of the peat extracts produced using 0.5 N KOH, it was determined that the sample with the highest degree of humification, (H8) Ezerelio JCS “Klasmann-Deilmann” (EKD), contained: 0.7% N; 0.1% P2O5; 25.87% humic acids and 0.76% fulvic acids. It had a density of 1015 kg·m−3, dynamic viscosity of 1.490 mPa·s, electrical conductivity of 33.3 mS·cm−1 and pH of 12.9.
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