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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...

Principles of green engineering require that material inputs are renewable. To this regard, a partial or a full substitution of one of the feedstocks with the waste from other industries can minimize the environmental impacts. Potash rock is a source of a key potassium (K), but its environmental impacts, including land use and greenhouse gas emissions during the mining and beneficiations, are of concern. Carnallite rock is used to electrochemically produce elemental magnesium (Mg) and yields solid sludge waste with K2O content of ∼43% and Mg content of 2.0%.This carnallite-derived waste is characterized physically and chemically and utilized to manufacture compound NPK fertilizers. The mesoporous waste material structure was found which facilitated the wet granulation process in spite of low 6 m2/g measured surface area. Trace metal concentrations measured were low and did not pose significant limitations from the regulatory point of view. Several high-K2O-content fertilizer formulations were proposed and granulated using both laboratory and industrial wet granulation in a rotary drum. Large K2O amount from the carnallite processing waste, up to 10 times that from mined KCl, was utilized in these fertilizers. The sustainability impact of the overall process was assessed by evaluating the averted greenhouse gas (GHG) emissions when carnallite-derived waste was substituted for potash rock. It was found that up to 5000 t of CO2/year per 100 000 t/year NPK 10-20-20 fertilizer can be avoided if waste is used rather than the potash rock.

Seeking to obtain bulk (NPK -nitrogen, phosphorus, potassium), chlorine-free fertilizers, the infl uence of interaction between potassium chloride and ammonium dihydrogen phosphate in aqueous solutions at temperature of 20, 40, 60 and 80°C has been investigated. Components of the solid phase have been identifi ed by methods of chemical and instrumental analysis: radiography (X -ray), infra -red molecular absorption spectroscopy (IR) and scanning electron microscopy (SEM). It has been observed that the largest amount of solid state potassium dihydrogen phosphate was obtained at 60-80°C, when the potassium chloride and ammonium dihydrogen phosphate molar ratio is equal 0.8:0.2. Changing the molar ratio of 0.5:0.5 to 0.8:0.2, and with increasing temperature, various shaped crystals have developed in the remaining aqueous solutions with a morphology shifting from sharp needles to tetragonal prism.