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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.