Influence of sulfate on MSWI ash for cement sintering

摘要

In the viewpoint of zero-waste management policy, MSWI ashes were pretreated and reused as alternative cement raw materials in this research. MSWI ashes were samples, pretreated and mixed according to the compositional equations. Sintered clinkered were analyzed with R1R technique. The interferences in MSWI ashes were investigated accordingly.rnThe results show that the compositional effect should be taken into consideration first. The lime saturation ratio, silica ratio and alumina ratio should be fulfilled in the raw mix recipe. In addition, the interferences brought in by the MSWI ashes, e.g. chlorine and sulfate should be taken into consideration. For example, water-washing could remove mostly 90% of the chlorine in the fly ash, and therefore the result in RIR show that tricalcium silicate (C_3S), the major crystalline in cement clinker, could be presented. Nevertheless, sulfate is not as easily removable as chlorine. RIR shows that 3.65% and above of SO_4~(2-) -S content could react with calcium oxide and form γ-CaSO_4 phase (gypsum). The crystalline phase (gypsum) could inhibit the formation of C_3S and therefore the cement sintering would stop as gypsum, dicalcium silicate (C_2S) and free lime. Though, the RIR also show that sulfate tolerance level in MSWI bottom ash raw mix is higher than the other two MSWI ashes. Partial results indicate that the soluble/ insoluble phase would be the possible factor, and further experiments are needed to clarify the relationship between sulfate species in MSWI ashes and cement sintering.