Proceedings of the Annual Conference of The Japan Society of Waste Management Experts

Polysulfide agent was found to stabilize heavy metal from ash. Polysulfide ions ,Sn2- (n=2 to 5), slowly produces Sn-1 and S2-. Sulfur and alkali agent were reacted in a pressurized test tube placed in an oven, giving polysulfide agent solution (sulfur content: 0.104 mgS/mL ). The property of the agent was compared with an existing sulfide agent NaHS solution(sulfur content: 0.992 mgS/mL ). The ability of polysufide agent to surpress Pb was slightly higher than NaHS. The emission of toxic , H2S, was also evaluated. The potential of H2S gas emission from NaHS was as high as 9.8% at pH 9, while that of polysulfide agent was only 0.062% at pH 9. The polysulfide agent is promising a low cost agent for metal stabilization with comparable ability with existing sulfide reagent and without of fear of toxic H2S gas emission.

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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.

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Due to the lack of industrial and municipal dumping yards in Japan, it is very important to make efficient use of municipal and industrial slag. If we use industrial waste slag for aggregates of concrete and road bed to efficient use, we always afraid of dissolution of heavy metals components (e.g. Pb, Cu, Ba, Cr, Ni, etc.). In this study, we investigated chemical bond structure of heavy metal components in industrial waste slag to assure the chemical safety of the industrial waste slag. Therefore we tried to analyze the chemical composition, IR spectrum and leaching experiment of slag and synthesized Pb glass to clear that the heavy metal elements are strongly (covalent) or weakly (ionic) bonded in slag. The results were that the parts of Si site in -Si-O-Si- bone structure of industrial waste slag were homogenously displacement by heavy metal components (especially Pb). Therefore, heavy metal components (especially Pb) may be bound covalently into -Si-O-Si- bone structure. The industrial waste slag would be chemically sable as well as urban waste slag, except for extremely acid and condition (pH=2).

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When melted slag is effectively used as a fine aggregate for concrete, the high-speed, centrifugal grinding down by friction processing is effective for the improvement of the grain degree and the grain shape.It turned out that a slaggy quality was influenced because of confirmed the quality of the operating condition in this case and slaggy manufactured the melt by the presence of the rotational speed and the spray water.

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