Abstract
For the establishment of a sustainable society, the utilization of ash generated from municipal solid waste incinerators (MSWIs) is an important challenge. The production of slag using a melting process has been a major recycling process in Japan regarding the control of toxic substances such as dioxin and heavy metals, but the ash melting process is expensive and energy-intensive. Therefore, in this study, we focused on accelerated aging technology using exhaust gas from gas engines for the utilization of MSWI bottom ash. As gas engines have been installed to ensure the cessation of operation in an emergency such as a natural disaster or accident, such engines are always used to produce electricity in MSWIs. With this technology, by exposing bottom ash to exhaust engine gas while controlling the ash temperature between 300 and 400°C, the amount of leached heavy metal can be decreased. The advantages of this technology are that it is cheaper and requires less energy than the ash melting process. According to previous studies, accelerated aging resulted in the level of leaching of heavy metals, mainly lead, being lower than the upper limit in environmental standards. However, there remained an insufficient understanding of the mechanism involved. The purpose of this study was thus to investigate the mechanism of stabilization of lead in bottom ash by accelerated aging. After accelerated aging at a temperature of 300°C and an exhaust gas (kg) to bottom ash (kg) ratio of 4:1, bottom ash particles were classified as being over 1 mm in size. Under these conditions, the concentration of leached lead was below the upper limit in environmental standards. It was considered that the lead in bottom ash was not only carbonated but also taken into insoluble minerals, as determined by sequential chemical extraction and X-ray analysis.
