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Phase Composition of Aqueous Urea–Ammonium Nitrate (UAN)–Zinc Nitrate Solutions for Sustainable Reuse of Zinc Containing Industrial Pigment Waste

Baltrusaitis, J., Sviklas, A. M.
ACS sustainable chemistry 2015 v.3 no.5 pp. 950-958
ammonium nitrate, chemical composition, industrial wastes, liquid fertilizers, nitric acid, nitrogen fertilizers, solubility, temperature, thermal analysis, urea, zinc
Sustainable metal recovery from waste is of utmost importance. Zn is a micronutrient that is abundant in many industrial wastes. In this work, the process of converting industrial white pigment waste into a Zn micronutrient containing nitrogen fertilizers was developed utilizing an HNO₃ extraction method. For this purpose, solubility diagrams, polytherms, were constructed of the ternary CO(NH₂)₂–Zn(NO₃)₂–H₂O and NH₄NO₃–Zn(NO₃)₂–H₂O systems to determine the corresponding phase equilibria and solid material chemical composition. Complex salts containing Zn and two and four urea molecules were observed and the catalytic Zn(NO₃)₂ effect was observed at the decomposition temperature of CO(NH₂)₂ during thermal analysis. Two crystalline phases of NH₄NO₃, namely III and IV, were observed and the corresponding transition temperature decreased with increasing Zn(NO₃)₂ concentration in solution. Zn extraction in the form of soluble Zn(NO₃)₂ was performed from the white pigment industrial waste and optimal extraction parameters including HNO₃ concentration, stoichiometric amount and temperature were determined. These included a 60 °C solution temperature, 55% HNO₃ concentration and 140% of stoichiometric HNO₃ amount. This agreed well with the reactive conditions currently used in nitrophosphate fertilizer production potentially enabling direct production of micronutrient containing NP fertilizers without significant technology modification. Sensible compositions of UAN-28 and UAN-30 liquid fertilizers containing Zn micronutrient from industrial grade compounds and pigment waste extracted Zn(NO₃)₂ were obtained and their physicochemical properties were measured.