Study on effect of pyridine on rheological properties of lignite water slurry

Coal chemical waste water is often difficult to treat due to its complex composition. Pyridine is a typical component of coal chemical industry wastewater. In order to reveal the effect of pyridine,a typical component in coal chemical wastewater,on the rheological properties of lignite CWS,the concentration,viscosity and slurry fluid characteristics of lignite CWS were tested under the addition of 0-1.3% pyridine. The mechanism of the effect of pyridine on rheological properties of LWS was investigated by various characterization methods. Zeta potential,contact angle,distribution and quantity of surface functional groups,hydrophilic and hydrophobic properties of lignite particles before and after the adsorption of pyridine and dispersant were measured in the single-component adsorption and the two-component adsorption tests. Analytical studies are performed to explain the mechanisms of rheological changes. The results show that with the increase of pyridine addition,the concentration of LWS had little change,but the viscosity increased from 1 050 mPa·s to 1 250 mPa·s,and the yield stress increased from 29 Pa to 40.28 Pa. Besides,the fluidity index increased from 0.686 to 0.976 indicating that the pseudoplasticity decreased with the increase of pyridine addition. The maximum adsorption capacity of pyridine was 10.5 mg/g while the adsorption capacity of dispersant decreased from 5 to 3.5 mg/g. The absolute value of Zeta potential of lignite after the adsorption of dispersant was directly proportional to the concentration of dispersant,while the absolute value of Zeta potential of lignite had little increase with the increase of the concentration of pyridine. In addition,the absolute value of Zeta potential increased from 27.9 to 42 mV in the presence of both dispersant and pyridine. The contact angle of lignite particles before and after pyridine adsorption also decreased from 55.4° to 35.8°.The main reason is that the adsorption of pyridine on lignite particle surfaces reduced the Zeta potential and the contact angle,thus enhancing the negative charge and electrostatic repulsion of the surface. Moreover,due to the competitive adsorption between pyridine and dispersant,the adsorption capacity of dispersant decreased significantly,which results in the decrease of dispersion effect of the dispersant on lignite particles and the increase of viscosity. The analysis results of surface functional groups show that the adsorption of dispersant and pyridine on lignite surface were both physical adsorptions. In the case of two-component adsorption test,the addition of pyridine will also reduce the amount of free water in the hydration film formed by the original dispersant adsorbing lignite particles,thereby increasing the viscosity of the lignite coal-water slurry and reducing the pseudoplasticity.