Resource recovery of inorganic solid waste for reduction of environmental load

Resource recovery of inorganic solid waste, such as waste incineration fly ash, cupola dust discharged from foundries, and nickel metal hydride battery waste, have been investigated. From results, tobermorite (Al-substituted toberraorite) and zeolitic compounds (zeolites A and P), which exhibit removal characteristics for toxic cations, were prepared from waste incineration fly ash by hydrothermal treatment in the presence of NaOH solution. Pretreatment of waste incineration fly ash with water washing and heating at 800°C was essential for preparing reproducible tobermorite as a major product at 180°C, while pretreatment with HCl solution, in addition to water washing and heating at 800°C, was essential for preparing reproducible zeolites A and P, as major products at 60-120°C. The H₂S sorptive property of cupola dust was induced by spinel-type nanocrystals composed of transition elements in the dust at room temperature in existence of water vapor, and drastically enhanced by NaOH treatments at 80-125°C to extract the spinel-type nanocrystals from amorphous SiO₂ matrix. The further examination revealed that the water adsorbed on the surface of the spinel-type nanocrystals played a role as a sorptive field. The Ni-based compound (w-NiO) was prepared from nickel metal hydride battery waste by a series of acid and base treatments. The CH₄ conversion over w-NiO was superior to that over regent NiO (r-NiO) for the CH₄ dry reforming, and exhibited an unusual behavior. The differences of catalytic activities between w-NiO and r-NiO were attributed to carbon deposition by side reactions and sinterability of the resulting Ni from NiO.