Synthesis and performance characterization of an efficient environmental-friendly Sapindus mukorossi saponins based hybrid coal dust suppressant

Abstract

The coal dust produced during coal mining poses a high risk to the safety and health of miners working in coal mines. Water spray with wetting agents is one of the most used ways to control coal dust and most of the wetting agents are composed of chemical surfactants. Further, the extensive use of chemical surfactants is costly as well as exerts damage to environment and human health. Therefore, it is crucial to find and utilize the natural surfactants to develop a greener efficient wetting agent. In this research, Sapindus mukorossi saponins is extracted and blended with various chemical surfactants to prepare a new and efficient saponins-based compounded wetting agent. Surface tension and coal dust wetting time are measured to optimize the best combination of saponins/surfactants compounding and to compare the wetting ability of newly prepared saponins-based compounded wetting agent with pure chemical surfactants as wetting agents. Fourier transform infrared spectroscopy, scanning electron microscope, and surface area analyzer are used to explain the mechanism of wetting agent on the wettability of coal dust. Results show that the critical micelle concentration (CMC) of Sapindus mukorossi saponins extract is 0.51 wt% and the surface tension of CMC is 41.3 mN/m, which indicates a high surface activity. The chemical surfactants dioctyl sodium sulfosuccinate (T) and alkyl polyglucoside (APG) combined with saponins extract as binarily and ternarily have synergically reduced the surface tension and coal dust wetting time. The combination of 0.04 wt% saponins extract, 0.004 wt% APG and 0.02 wt% T at the volume ratio of 1:1:1 is found to be the best saponins-based compounded wetting agent, which can reduce the surface tension to 26.08 mN/m and coal dust wetting time to 9.2 s. The usage of chemical surfactant concentration in the newly developed saponins-based compounded wetting agent is 0.024 wt% while that of current mainstream industrial ones is in the range of 0.1–0.8 wt%. The saponins-based compounded wetting agent reduces the usage of chemical surfactants, exhibits a better wetting ability, and provides a new way for the utilization of Sapindus mukorossi pericarp. When wetting agent is adsorbed to the coal surface, there is 23.81–63.12% increase of oxygen containing groups on coal surface and the formation of hydrogen bonds. As a result, the coal dust becomes more hydrophilic. Therefore, the coal dust particles are easily agglomerated to larger size and rapidly settled by gravity.