Life Cycle Assessment on the Regeneration of Municipal Solid Waste Incinerator Fly Ash as the Feedstock in the Brick Manufacturing

Incineration have been popular used in the modern city to handle the municipal solid waste, while the fly ash (FA) produced from the incineration plant, contains of heavy metals and dioxin, is sill a troublesome matter. Landfilling followed by solidification is commonly adopted in many countries, nevertheless, it still exist long term environmental and healthy risk; regeneration by melting process is generally used in Japan, while it is expensive since consumed much energy and need huge bottom ash to adjust the basicity. Sintering is a cheaper recycling method than melting, and brick is one of the typical products. Washing is a necessary pretreatment operation for the recycling of FA, which will remove most of the harmful salts during the sintering process. Milling is a helpful operation for the sintering, which will not only reduce the particle size to promote the quality of sintering product, but also provide mechano-chemical mechanism to enhance the Pb stabilization by phosphoric acid. In this study, FA was washed twice by liquid/solid ratio 5, wet-ball-milling in 10 min with proper quantity of cullet and phosphoric acid, substituting 20% of the feedstock clay, compress molding, and then oven heat at 900 degrees C. The result showed that, the quality of the product satisfied the standard of ordinary brick in Taiwan, the dioxin was below the detection limit and the destruction was > 99.9%, the Pb evaporation during the sintering was lower than 20%. The result of life cycle analysis (LCA) by Simapro program shows that the use of phosphoric acid was the largest loading to the environment; the second one was the energy consumption during the sintering. Dioxin and heavy metals risk to the health were only trace. When change the stabilizing agent to spent phosphoric acid, the environmental loading will be limited.