Removal of Inorganic Salts in Municipal Solid Waste Incineration Fly Ash Using a Washing Ejector and Its Application for CO2 Capture

This study investigated the effects of washing equipment for inorganic salts, such as NaCl, KCl, and CaClOH, to decontaminate municipal solid waste incineration fly ash (MSW-IFA). Based on the feature of hydrodynamic cavitation, the device developed in this study (referred to as a ‘washing ejector’) utilizes the cavitation bubbles. A washing ejector was analyzed under a range of conditions, employing as little water as possible. In hydrodynamic cavitation, the increase in fluid pressure with increasing static pressure is mainly attributed to the increase in particle–bubble collisions via the cavitation flow. The results revealed that the fluid pressure influenced the removal of inorganic salts during cavitation in water. This is because during the washing process from the collapse of cavitation bubbles, the release is achieved through the dissolution of inorganic salts weakly bound to the surface. After treatment by a washing ejector, the removal of soluble salts elements such as Cl, Na, and K was reduced by approximately 90%. Removing the inorganic salts in the IFA altered the characteristics of the Ca-related phase, and amorphous CaCO3 was formed as the cavitation flow reacted with CO2 in the ambient air. Furthermore, the washing effluent produced by washing IFA was found to be beneficial for CO2 capture. The washing effluent was enriched with dissolved Ca from the IFA, and the initial pH was the most favorable condition for the formation of CaCO3; thus, the effluent was sufficient for use as a CO2 sequestration medium and substitute for the reuse of water. Overall, the process presented herein could be effective for removing soluble salts from IFA, and this process is conducive to utilizing IFA as a resource.