Fly ash produced by waste combustion is designated as specially controlled waste in Japan due to harmful heavy metals contained in it and is legislated to be processed properly before disposal to landfill. As for technologies for making the fly ash harmless, several methods are recommended for the treatment, but each of them has some problems to be solved. The fly ash from a municipal solid waste incinerator contains large amounts of chlorinated compounds that make the harmful treatment difficult. A complete recycling of waste residue left behind after waste incineration, however, is required to solve the shortage of available final disposal sites. With this background, a new technology needs to be developed, that the heavy metals in the fly ash are removed sufficiently, no harmful heavy metals are leached and the residue ingredients are used effectively. In addition, Japanese government revised the Soil Contamination Countermeasures Law in February 2003 to strengthen the soil environmental evaluation standards. This could also promote the development of above technology. This paper focuses on lead that is particularly emphasized in the law, and proposes an advanced technology to remove lead from the fly ash, discussing the removal mechanism and removing conditions of lead. The newly developed technology is associated with the sintering process using a rotary kiln, and effectively uses only the chlorinated compounds contained in the fly ash to volatilize and remove the heavy metals. The technology achieves satisfactory low level of dioxins as well as prevention of lead leach. The fly ash treated by the technology also has passed a leaching test at pH 4 simulating typical acid rain circumstances.

The larger part of the molten fly ash which is generated when municipal solid waste (MSW) is treated using gasifying and melting furnaces is handled as a specially-controlled waste in the same manner as incineration fly ash (fly ash from stoker-type incinerators), and is disposed of by landfill burial after stabilization treatment by methods designated by the national government, such as chelate treatment or cement fixation. Basically, however, these are not methods which separate out harmful substances. On the other hand, a shortage of landfill disposal sites has also become a major social problem. Therefore, theestablishment of a technology which separates harmful substances such as lead, cadmium, etc. in fly ash as completely as possible, stabilizes the residual trace amounts of heavy metals, and enables recycling of the residue has been desired.In research on a process of this type, the authors constructed a pilot plant (45kg/h) for treatment of molten fly ash and conducted tests of detoxification and conversion to aggregate using several kinds of molten fly ash as raw materials, and carried out technical development of a new roasting treatment technology which enables advanced detoxification of molten fly ash and effective utilization of the residue. The results confirmed that this roasting process possesses sufficient potential for practical application as a treatment for molten fly ash. In the course of this research, (1) the mechanism of chlorination-volatilization of lead (Pb) was clarified, (2) a 99.5% Pb volatilization rate was achieved, and (3) 99.5% volatilization was possible with lead oxide-containing glass (lead glass from end-of-life televisions and computer monitors) by adequately crushing the lead glass and performing mixed roasting treatment with fly ash.

A novel detoxification process for incinerator fly ash was proposed, and the removal mechanism of heavy metals from the fly ash was investigated. The process comprises of roasting the fly-ash extrudates with a rotary kiln, and removes heavy metals by chloridizing volatilization, giving harmless resultant extrudates which contain immobilized heavy metals at trace concentration. The developed roasting technique was unique, as it utilized chlorine originally contained in the fly ash and did not need additional chlorine source. Our detailed investigation proved that appropriate control of bed layer in the kiln could keep reductive atmosphere that should enhance volatilization of metals at either chloride or metals form. The extrudates derived from the process, compared to conventional chelate-solidified ash or to melting solid matter, showed less metals elution at leachate test, as well as contained descended metals content which satisfied the soil environmental standards revised recently.

We had developed new process to treat fly ash generated from municipal incinerators by employing the nonferrous metals refining technology. We clarified the removal mechanism of heavy metals such as lead and cadmium and optimized the conditions based on thermodynamics and metallurgical approaches. We demonstrated by the pilot plant facility with the designed capacity of 100kg/hr that harmful heavy metals like lead are safely removed to trace levels which satisfy the Japanese soil environmental standards. Furthermore, the fly ash treated by this new technology also has passed leaching tests at pH 4 simulating typical acid rain circumstances, so that it can be recycled, for example, as artificial lightweight aggregate. It was also found that volatilized metals collected as secondary ash can be recycled as smelting resources. We could verify at the same time new technology was very conformable as industrial process with developing technologies for materials and equipment. New process will be very useful to fly ash treatment and recycling in the future, as the general technology to treat many types of ashes.

Fly ash generated from a municipal waste incinerator is designated as a specially controlled substance in Japan, and it is obligatory to make it harmless before disposal. In a series of researches, we proposed a new treatment technology to make fly ash harmless, and performed thermodynamic investigations for removing major harmful heavy metals such as lead, cadmium, zinc, and chromium. This paper reports the strengthening mechanism of sintered pellets as treatment residue and the stabilization of minute residual heavy metals, centering on the effects of alkali salt and iron contained in the pellets as well as the effect of sintering in the pellet roasting process. Further, the development of advanced technologies is being required for recycling slag generated as byproducts from various smelting furnaces through effectively dealing with minute residual heavy metals contained in it, aiming at the steady expansion of its applications. This paper also reports the effectiveness of mixed treatment of incinerator fly ash and smelting slag.