Effect of Sapropel Dispersion on the Colloidal-Chemical Properties and Structure of Urea-Sapropel Heterogeneous Dispersion Systems

Abstract

Aims: The aim of this study was to determine the effects of sapropel dispersion on the colloidal-chemical, rheological, and structural properties of a heterogeneous urea-sapropel dispersion system and to substantiate their role in controlled nitrogen release. Study Design: An experimental laboratory study was conducted to evaluate the colloidal-chemical, rheological, and structural properties of a heterogeneous urea-sapropel dispersion system. Place and Duration of Study: The study was conducted at Bukhara State Technical University and Navoi State University of Mining and Technologies from 20 January to 1 June 2026. Methodology: Urea-sapropel granules containing sapropel of different particle sizes were prepared. Dried sapropel was separated into six fractions within the 0.063-1.000 mm range and incorporated into urea at mass ratios of 100:1-100:10. The granules were produced using a melt-granulation method. The dissolution time of the granules in water, crystallisation temperature, and density and viscosity of the melts were determined. Samples prepared using the 0.25 mm sapropel fraction were further characterised by scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS) and Brunauer-Emmett-Teller/Barrett-Joyner-Halenda (BET-BJH) analyses to evaluate their morphological, elemental, and surface-adsorption properties. Results: Increasing the sapropel content and decreasing the particle size increased the dissolution time of the granules and decreased their crystallisation temperature. At a 100:10 mass ratio, the dissolution time was 214.62 s for the 0.063 mm fraction and 193.28 s for the 0.75-1.00 mm fraction. The corresponding crystallisation temperatures were 110.88 and 121.57 °C, respectively. For the 0.25 mm sapropel fraction at a 100:5 mass ratio, the melt viscosity was 2.491 mPa·s at 130 °C, and the temperature range of 138-142 °C was identified as suitable for granulation. The 100:5 sample exhibited a specific surface area of 1.10 m2/g, a total pore volume of 0.0021 cm3/g, and an average pore diameter of 12.5 nm. Conclusion: Control of sapropel particle size and content enabled regulation of the dissolution, crystallisation, and rheological properties of urea-sapropel granules. The 0.25 mm sapropel fraction, a 100:5 urea-to-sapropel mass ratio, and a temperature range of 138-142 °C were identified as suitable conditions for the granulation process. These findings support the feasibility of using local sapropel to produce organo-mineral nitrogen fertilisers with controlled dissolution characteristics.