||The total amount of heavy-metal containing hazardous industrial wastes could reach about 40000 tons annually in Taiwan. Some of the wastes such as fly ash form incinerator and EAF dusts from the electric arc furnace steel mills could be turn to re-use material with new technology to meet “zero waste” as international trend as sustainable concept in environmental protection; also, it may reduce the cost of treatment and secondary pollution during the traditional possible secondary pollution. Since the fly ash contains certain amount of heavy metals, hence, is classified as hazardous waste and need good treatment. This research is to find suitable chemicals and conditions to have the ash and EAF dust reacts and forming chemical bond in order to form the re-usable material that also meets the regulatory requirement.
The chemical bond formation is formed after different chemicals add to the waste in this research. With variation of different chemicals, different ratio of additions, different aging period, and the variation of volume reduction and mechanical performance, to find out the optimal conditions for better and more economical treatment.
From the results of various experiments, after chemically bonded heavy metals in the wastes, the solubility is reducing after treatment. The optimal condition is to add 3% of the chemical to fly ash, since the good formation of stable chemical bond of these heavy metals with chemical; it meets the TCLP standard after 28 days of aging process, for example, the dissolve quantity reduced to 0.322 mg/l of Pb. From the XRD study, the bonded heavy metals and calcium salts form a very stable phosphates and complex mineral material. Since the solubility product is very low, therefore, the dissolution is unlikely after treatment. This non-hazardous mineral can be further process in order to increase it mechanical strength; for example, it will reach 150 kgf/cm2 after pressurized process. This kind of material can be re-use with abide the environmental regulation as re-fill, base in road construction, seashore protection, and various application to replace the rock in civil applications.