No abstract

Vitrification was used to convert hazardous metal-bearing fly ash from municipal solid waste (MSW) incineration into useful products in this work. In addition to volume/mass reduction, some parameters such as basicity, metal leachability, density, porosity, water absorption, and compressive strength of the slags and ingots vitrified from fly ash and fly ash/additive (bottom ash and cullet) mixtures (at 1450 °C for 1.5 h) were investigated. The more the bottom ash or cullet added to the fly ash, the lower the specimen basicity, leading to a more amorphous glassy matrix. Amorphous glassy slags were obtained when the specimen basicity was around 0.24-1.24. All slags were in compliance with the limits of TCLP (Toxicity Characteristic Leaching Procedure) in Taiwan, United States, and Japan. The vitrification process reduced the leaching amount and ratio of Cr and Pb, significantly lowered the leaching ratio of Cd, but raised the leaching ratios of Zn and Cu. The slag metal leachability (particularly for Cu) was mainly influenced by the metal content in slags, not the slag (crystal or glassy) structure or basicity. After vitrification, an over 50% specimen volume reduction was achieved and most of the specimen mass moved to the slag phase. The ingots, mainly consisting of Fe, also met Taiwan and U.S. TCLP requirements and were suitable for a higher purity metal recovery. The slags and ingots were approximately 2-and 6-fold as dense as the specimens before vitrification, respectively. The slags were found to have very small porosities, low water absorptions, and high compressive strengths (>550 kg/cm 2 ), so they may be considered as candidate materials for waterproof and construction.

No abstract

This work investigated the vitrification of hazardous electroplating sludge containing 140 mg/g Cr with/without bottom ash or cullet conditioning to lower specimens' basicities to 0.97-1.17 or 0.18-0.23, respectively. The conditioning was found to enhance the smooth/glassy appearance of slags but no ingot was obtained. Cr was >98% retained in the vitrified slags. Cr2O3 dominated in crystalline structure for the slag vitrified from the sludge, but this domination gradually shifted to Fe2SiO4/Fe3O4/SiO2 or SiO2 crystalline with increasing addition of bottom ash or cullet into the sludge, respectively. Compared to the raw sludge, the sludge-vitrified slag displayed lower leaching concentrations for most metals (particularly Cr (2.54 mg/L)), and smaller leaching ratios for Ag, Cr, and Cu (1.35, 0.02, and <0.01%, respectively) but greater ones for Cd, Pb, and Zn (3.83, 2.46, and 0.36%, respectively). The Cr leaching ratios were approximately 0.01% for the slags vitrified from the conditioned sludge. Independent of the slag basicity and crystalline structure, metal leaching quantity increased but leaching ratio decreased with increasing slag metal content. The slag compressive strengths were improved to >14.7 MPa at the mixing ratios > or = 2/1 and 1/1 for bottom ash/sludge and cullet/sludge, respectively. Fulfilling the criteria of Toxicity Characteristic Leaching Procedure (TCLP), all the slags were recyclable.