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 HNO 3 extraction method. For this purpose, solubility diagrams, polytherms, were constructed of the ternary CO(NH 2 ) 2 –Zn(NO 3 ) 2 –H 2 O and NH 4 NO 3 –Zn(NO 3 ) 2 –H 2 O 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(NO 3 ) 2 effect was observed at the decomposition temperature of CO(NH 2 ) 2 during thermal analysis. Two crystalline phases of NH 4 NO 3, namely III and IV, were observed and the corresponding transition temperature decreased with increasing Zn(NO 3 ) 2 concentration in solution. Zn extraction in the form of soluble Zn(NO 3 ) 2 was performed from the white pigment industrial waste and optimal extraction parameters including HNO 3 concentration, stoichiometric amount and temperature were determined. These included a 60 °C solution temperature, 55% HNO 3 concentration and 140% of stoichiometric HNO 3 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(NO 3 ) 2 were obtained and their physicochemical properties were measured.
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Baltrušaitis et al. (2015) studied this question.
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