Chemical Composition, Physicochemical Properties, and Morphological Characterization of Granules of AmmoniumNitrate Modified by Serpentinite Additive

Abstract This study investigated the modification of ammonium nitrate (AN) granules with serpentinite (SP) from the Arvaten deposit, Uzbekistan, to improve their physicochemical, morphological, and safety-related thermal characteristics. Serpentinite was introduced into molten AN at AN/SP mass ratios ranging from 100:0.5 to 100:4.0, and the resulting mixtures were granulated under laboratory conditions. The AN-0.025SP formulation, prepared using 2.5 g of serpentinite per 100 g of AN, was selected as the highest serpentinite-containing composition that retained a nitrogen content above 34.0 wt %. This formulation contained 34.07 wt % total nitrogen and 0.80 wt % total MgO. Compared with pure AN, AN-0.025SP exhibited a decrease in caking strength from 5.62 to 2.80 kgf cm–2 and in granule porosity from 22.0% to 7.93%, whereas granule strength increased from 1.32 to 4.72 MPa. DTA/DSC analysis showed that the onset decomposition temperature increased from 211.0 °C for pure AN to 231.6 °C for AN-0.025SP. In contrast, the absolute magnitude of the decomposition thermal effect decreased from 921.1 to 688.6 J g–1. XRD, FTIR, and Raman analyses provided qualitative evidence that nitrate-related structural and vibrational features remained dominant, together with signals attributable to serpentinite-derived Mg-silicate components. AFM indicated changes in local surface topography, while SEM–EDS observations showed a compact granule microstructure and the local presence of Mg- and Si-containing components. Overall, serpentinite acted primarily as a physically dispersed mineral modifier and produced favorable changes in the physicochemical and thermal behavior of AN granules under the applied laboratory conditions. The AN-0.025SP formulation therefore represents a promising candidate for further evaluation as a modified ammonium nitrate fertilizer.

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