PROLONGED-ACTION MAGNESIUM-BEARING UREA FROM THERMALLY ACTIVATED DOLOMITE: EFFECT OF ADDITIVE CONTENT AND CALCINATION TEMPERATURE ON GRANULE PROPERTIES
- Authors
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B. T Khosimov
Tashkent Institute of Chemical Technology, Tashkent, Uzbekistan
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- Keywords:
- ureadolomite thermal activation slow-release fertilizer prolongation dissolution time hygroscopic point granule strength free calcium oxide full factorial design
- Abstract
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This study quantifies how the amount of thermally activated dolomite added to a urea melt and the temperature at which that dolomite is calcined jointly govern the properties of the resulting granules. Local dolomite ( 27.52 %, 20.24 %, 43.21 %) was calcined at , , , , and 900 °C and introduced into molten urea at ten levels from 0.5 to 5.0 wt %, giving a two-factor full factorial design of 60 compositions plus a dolomite-free control. Dissolution time, melt crystallisation temperature, hygroscopic point, porosity and crushing strength were measured for every composition. Dolomite raised the dissolution time in all 60 cases, from 93.8 s for the control to 94.28–207.62 s, raised the crushing strength to 2.56–3.46 MPa and lowered the porosity below the control value of 5.75 % throughout. Each response was described by an additive linear model in the two factors (–; the interaction term was insignificant, –). Grouping the model residuals by calcination temperature revealed that three independent responses reach an extremum at exactly 700 °C and change sign between and 800 °C, coinciding with the calculated appearance of free and marking the transition of dolomite from a comparatively inert filler to a reactive additive. Four criteria complete activation of the magnesium component, limitation of free , at least 45.5 % total nitrogen and at least 2.5 MPa crushing strength identify a single regime: 2 g of dolomite calcined at 700 °C per 98 g of urea, a product that dissolves 1.38 times more slowly than unmodified urea, is 12.6 % stronger, 9.9 % less porous and contains 45.72 % N and 0.55 % entirely in the active form, with only 0.10 % free . Compared with a urea–formaldehyde system studied under the same criteria it is 6.7 % stronger, carries 4.5 absolute per cent more nitrogen and requires no imported formalin.
This study quantifies how the amount of thermally activated dolomite added to a urea melt and the temperature at which that dolomite is calcined jointly govern the properties of the resulting granules. Local dolomite ( 27.52 %, 20.24 %, 43.21 %) was calcined at , , , , and 900 °C and introduced into molten urea at ten levels from 0.5 to 5.0 wt %, giving a two-factor full factorial design of 60 compositions plus a dolomite-free control. Dissolution time, melt crystallisation temperature, hygroscopic point, porosity and crushing strength were measured for every composition. Dolomite raised the dissolution time in all 60 cases, from 93.8 s for the control to 94.28–207.62 s, raised the crushing strength to 2.56–3.46 MPa and lowered the porosity below the control value of 5.75 % throughout. Each response was described by an additive linear model in the two factors (–; the interaction term was insignificant, –). Grouping the model residuals by calcination temperature revealed that three independent responses reach an extremum at exactly 700 °C and change sign between and 800 °C, coinciding with the calculated appearance of free and marking the transition of dolomite from a comparatively inert filler to a reactive additive. Four criteria complete activation of the magnesium component, limitation of free , at least 45.5 % total nitrogen and at least 2.5 MPa crushing strength identify a single regime: 2 g of dolomite calcined at 700 °C per 98 g of urea, a product that dissolves 1.38 times more slowly than unmodified urea, is 12.6 % stronger, 9.9 % less porous and contains 45.72 % N and 0.55 % entirely in the active form, with only 0.10 % free . Compared with a urea–formaldehyde system studied under the same criteria it is 6.7 % stronger, carries 4.5 absolute per cent more nitrogen and requires no imported formalin.
- References
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[1] M. Skorupka and A. Nosalewicz, “Ammonia volatilization from fertilizer urea—A new challenge for agriculture and industry in view of growing global demand for food and energy crops,” Agriculture, vol. 11, no. 9, art. no. 822, 2021, doi: 10.3390/agriculture11090822.
[2] D. Lawrencia, S. K. Wong, D. Y. S. Low, B. H. Goh, J. K. Goh, U. R. Ruktanonchai, A. Soottitantawat, L. H. Lee, and S. Y. Tang, “Controlled release fertilizers: A review on coating materials and mechanism of release,” Plants, vol. 10, no. 2, art. no. 238, 2021, doi: 10.3390/plants10020238.
[3] K. R. M. Ibrahim, F. E. Babadi, and R. Yunus, “Comparative performance of different urea coating materials for slow release,” Particuology, vol. 17, pp. 165–172, 2014, doi: 10.1016/j.partic.2014.03.009.
[4] Y. Guo, Y. Shi, Q. Cui, X. Zai, S. Zhang, H. Lu, and G. Feng, “Synthesis of urea-formaldehyde fertilizers and analysis of factors affecting these processes,” Processes, vol. 11, no. 11, art. no. 3251, 2023, doi: 10.3390/pr11113251.
[5] L. Hermida and J. Agustian, “Slow release urea fertilizer synthesized through recrystallization of urea incorporating natural bentonite using various binders,” Environmental Technology & Innovation, vol. 13, pp. 113–121, 2019, doi: 10.1016/j.eti.2018.11.005.
[6] M. Hauer-Jákli and M. Tränkner, “Critical leaf magnesium thresholds and the impact of magnesium on plant growth and photo-oxidative defense: A systematic review and meta-analysis from 70 years of research,” Frontiers in Plant Science, vol. 10, art. no. 766, 2019, doi: 10.3389/fpls.2019.00766.
[7] R. Härdter, M. Rex, and K. Orlovius, “Effects of different Mg fertilizer sources on the magnesium availability in soils,” Nutrient Cycling in Agroecosystems, vol. 70, no. 3, pp. 249–259, 2004, doi: 10.1007/s10705-004-0408-7.
[8] Z. Lu, F. Degryse, J. Wu, C. Huang, Y. Yu, M. J. McLaughlin, and F. Zhang, “Slow- and fast-release magnesium-fortified macronutrient fertilizers improve plant growth with lower Mg leaching loss,” Journal of Soils and Sediments, vol. 24, no. 4, pp. 1507–1515, 2024, doi: 10.1007/s11368-024-03752-7.
[9] C. Rodriguez-Navarro, K. Kudlacz, and E. Ruiz-Agudo, “The mechanism of thermal decomposition of dolomite: New insights from 2D-XRD and TEM analyses,” American Mineralogist, vol. 97, no. 1, pp. 38–51, 2012, doi: 10.2138/am.2011.3813.
[10] L. C. Resio, “Dolomite thermal behaviour: A proposal to establish a definitive decomposition mechanism in a convective air atmosphere,” Open Ceramics, vol. 15, art. no. 100405, 2023, doi: 10.1016/j.oceram.2023.100405.
[11] L. Huang, Z. Yang, and S. Wang, “Influence of calcination temperature on the structure and hydration of MgO,” Construction and Building Materials, vol. 262, art. no. 120776, 2020, doi: 10.1016/j.conbuildmat.2020.120776.
[12] P. M. Schaber, J. Colson, S. Higgins, D. Thielen, B. Anspach, and J. Brauer, “Thermal decomposition (pyrolysis) of urea in an open reaction vessel,” Thermochimica Acta, vol. 424, no. 1–2, pp. 131–142, 2004, doi: 10.1016/j.tca.2004.05.018.
[13] N. Rahmanian, S. Naderi, E. Supuk, R. Abbas, and A. Hassanpour, “Urea finishing process: Prilling versus granulation,” Procedia Engineering, vol. 102, pp. 174–181, 2015, doi: 10.1016/j.proeng.2015.01.122.
[14] A. Benzaouia, H. Belbsir, S. Kounbach, S. Laassiri, A. Laamaoui, R. Labiad, and R. Benhida, “Exploring the influential factors of granular fertilizer caking: a comprehensive review,” Chemical Papers, vol. 79, no. 3, pp. 1269–1301, 2025, doi: 10.1007/s11696-024-03856-x.
[15] C. E. Weir and E. R. Lippincott, “Infrared studies of aragonite, calcite, and vaterite type structures in the borates, carbonates, and nitrates,” Journal of Research of the National Bureau of Standards – A. Physics and Chemistry, vol. 65A, no. 3, pp. 173–183, 1961.
[16] Z. Piasek and T. Urbański, “The infra-red absorption spectrum and structure of urea,” Bulletin de l’Académie Polonaise des Sciences, Série des Sciences Chimiques, vol. 10, no. 3, pp. 113–120, 1962.