study on conditions of hydrothermal treatment method for recycling of municipal solid waste incinerator bottom ash

The capacity of landfill sites for municipal solid waste incinerator (MSWI) bottom ash has decreased in recent years, and the construction of new landfill sites is difficult because of protests from nearby residents. Thus, it is required to develop technologies that promote effective use of bottom ash. If bottom ash is to be recycled as construction materials e.g., it is important to prevent environmental pollution, considering changes of mineralogical characteristics of bottom ash over a long period of time on site. The purpose of this study is to clarify the conditions of hydrothermal treatment to generate secondary minerals to stabilize heavy metals in bottom ash. Bottom ash was mixed with SiO2, Al(OH)3 and Mg(OH)2 considering chemical composition of hydrothermal clay minerals. These solid specimens were mixed with water at a liquid/solid ratio of five. The reaction temperature was 200ºC, and reactions were performed for 120 hours. Generation of kaolinite/smectite mixed-layer clay mineral was found in the samples after treatment of the mixture of bottom ash, SiO2, and Mg(OH)2. To confirm the effect of hydrothermal treatments, leaching test at various pH level were performed on some samples. Each sample was leached at five different pH values in the range 4−12 in pH-stat system at a liquid/solid ratio of 10L/kg. Experiments were run for six hours. Concentration of heavy metals (Cu, Pb, Zn, Cr, Cd) in filtrates were analyzed with ICP emission spectroscopy. The results of leaching tests showed that the hydrothermal treatment of bottom ash without the additives reduced the leaching of heavy metals ,but the treatments with the additives did not reduce successfully.