Abstract
The study aimed to examine the electrokinetic and rheological properties of composite water-coal fuel (CWCF) based on anthracite and P-grade coal in the presence of clay minerals.
The influence of clay mineral additives on the electrokinetic and rheological properties of CWCF was studied. The clay minerals used were montmorillonite, illite, and kaolinite from Ukrainian deposits. The fuel was prepared based on P-grade coal and anthracite. The share of the solid phase (coal) in the suspensions was 62 %. According to the particle size distribution, the bulk of the coal has a size of 30–110 μm with a bimodal distribution. To obtain the CWCF, the coal powder was homogenized with the dispersion medium by wet grinding in a ball mill for 20–25 minutes. The dispersion medium was distilled water. Wet grinding was carried out until particles < 0.25 mm in size were obtained. We obtained a CWCF with a concentration of 62% of the solid phase of coal. Additions of chemicals were not practiced to study the effect of clay minerals in a pure experiment. Clay minerals were added at a concentration of 0.5–3 % by weight of the CWCFs.
Their rheological data were measured using a Rheotest-2 rheometer at a temperature of 20 ºC and the shear-stress/shear-rate data for the CWCF covered a range of 0.1 to 470 s-1.
The sedimentation stability of St was studied at the time of stratification of the CWCF sample in a measuring cylinder. After preparation, a 10-mL sample of the CWCF was placed in a 25-mL glass cylinder. St is equal to the time of the beginning of the suspension stratification in days.
It was established that ξ - the potential of CWCF particles with the addition of clay minerals shifts to the negative region and reaches – 45–50 mV at pH>8. Montmorillonite was found to be most effective additive for controlling the properties of the CWCF. Systems with clay mineral additives demonstrate a pseudoplastic type of flow in the range of shear rates γ 0–100 s-1 and a Newtonian type of flow at higher γ. According to their effect on the increase in apparent viscosity, clay minerals are arranged in the following order: kaolinite, illite, and montmorillonite. The thixotropic properties of the studied systems provide complete restoration of the properties of the CWCF when the shear rate is reduced to 0–40 s-1. Sedimentation stability in the presence of illite and montmorillonite additives reaches 8–14 days. In contrast to illite and montmorillonite, kaolinite has a very weak effect on the properties of CWCF.
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