ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Separation of urea adducts in the analysis of complex mineral fertilisers

Marcin Sadłowski, Barbara U. Grzmil, Krzysztof Lubkowski, and Kinga Łuczka

Institute of Chemical and Environment Engineering, West Pomeranian University of Technology, Pułaskiego 10, 70-322 Szczecin, Poland

E-mail: Marcin.Sadlowski@zut.edu.pl

Abstract: An investigation of the analytical separation of free urea from its additive compounds with H₃PO₄, HNO₃, CaSO₄ and Ca(H₂PO₄)₂, based on the solubility in butan-1-ol (n-butanol, n-BuOH), is reported. Several methods were tested in order to obtain the best leaching efficiency and solvent utilisation. The urea content was determined using the spectrophotometric method. A simple qualitative determination of urea was also performed using a special type of urea indicator-paper developed during the study. The phase composition of the examined materials was studied using an X-ray powder diffraction method. The urea adducts with phosphoric and nitric acid were found to be soluble in n-BuOH, in a similar way as with free urea. However, the solubility of the urea adducts with CaSO₄ and Ca(H₂PO₄)₂ differs from the solubility of free urea, affording an effective separation of these compounds. The solubility of free urea under defined experimental conditions was estimated to be (1.432 ± 0.043) g of urea in 100 cm³ of n-BuOH. The trace solubilities of urea bound in the adducts CaSO₄ · 4CO(NH₂)₂ and Ca(H₂PO₄)₂ · 4CO(NH₂)₂ were (8.28 ± 0.61) mg and (29.83 ± 0.63) mg of urea in 100 cm³ of n-BuOH, respectively. Partial decomposition of Ca(H₂PO₄)₂ to CaHPO₄ was observed during the leaching process.

Keywords: urea adducts – free and bound urea – fertilisers

Full paper is available at www.springerlink.com.

DOI: 10.1515/chempap-2015-0187

Chemical Papers 70 (3) 315–324 (2016)