A Study On Hydrothermal Process To Stabilize Heavy Metals From MWI Fly Ash With Silicon-aluminum

This study aims to use the hydrothermal method to treat medical waste incineration fly ash with external silica-alumina source added. Experiments study the various additives and hydrothermal conditions which affect the stabilization. The use of XRF elemental analyzer, XRD crystal analyzer, SEM-EDS, ICP-MS and other equipment to test the fly ash and wastewater with characteristics such as element content, crystal characteristics, surface morphology, the concentration of heavy metals in wastewater, toxic leachate experimental study.The use of XRF, SEM-EDS and XRD analysis of the medical waste incineration fly ash characteristics of elements, surface morphology and crystal properties, and the use of EPA implementation of the solid particles of heavy metals leaching toxicity test standard (TCLP Method1311EPA) to study the heavy metal leaching characteristics of fly ash. The heavy-metal leaching experimental results have different concentration, the concentration of Zn is the largest leachate, and its leaching value exceeds the standard value.In the hydrothermal treatment experiments, it found that high Al and Si element content, high reaction temperature and high reaction time can improve the heavy metals stabilization effect. For the reason that characteristics of MSI fly ash has low silicon-aluminum content, a high-silicon aluminum content of MSWI fly ash, coal fly ash and bentonite are add to assist the hydrothermal experiments. Some zeolite crystals (such as Katoite [Ca3Al2(SiO4)(OH)s], Al-tobermorite-11A [Ca5(Si, Al)6O16(OH)10], Analcime-C[Na(Si2Al)O6-H2O], etc.) have been synthesized, thereby increasing the stability of fly ash, and the heavy metal pollutions in fly ash are greatly reduced.Experiments added sodium metasilicate (Na2SiO3) and sodium aluminate (NaAlO2) as the Si-Al additives, using hydrothermal to remove the heavy metal in the simulated wastewater, at the same time, stabilizing the fly ash. When the reaction temperature reaches275℃， the removal rate of heavy metals (eg. Mn2+，Ni2+, Cd2+, Pb2+, Zn2+and Cu2+) in wastewater can reach95%or more. The toxicity characteristic leaching of treated fly ash is also greatly reduced. Secondary applied research of using fly ash for the removal of heavy metals in waste water provides a theoretical basis. Through this study, a more cost-effective treatment process is formed to stabilizing heavy metal in medical waste incineration fly ash.