Several Treatment Methods On The Recycling Of Electric Arc Furnace Fly Ash, MSWI Ash And Sewage Sludge

In this study, several treatment methods on the recycling of electric arc furnace (EAF) flyash，municipal solid waste incineration（MSWI）ash and sewage sludge were carried out basedon the disposal and reuse of those waste solids.Firstly, thermal treatment equipment was employed to treat the EAF fly ash. ThePCDD/F and PBDEs contents/concentrations in the EAF fly ash, cullet, slag, ingot, coolingunit, filter and PUF cartridge were all determined. The congener profiles were then derivedand analyzed, while the fate of the PCCD/Fs and PBDEs was discussed based on massbalance calculations. The results showed that the total PCDD/F I-TEQ in the EAF fly ash was1414ng I-TEQ/kg, revealing that it exceeded the soil pollution standard (1000ng I-TEQ/kg).After treatment of EAF fly ash at1450°C, the total contents of PCDD/Fs and I-TEQ in theEAF fly ash can be effectively reduced and the metal contents were sucessful to be recoveredas the ingot. The PCDD/Fs I-TEQ in the emission was lower than the value of relativeemission standards after the emission was treated with the air pollution control devices(APCDs). Moreover, the total PBDE content in EAF fly ash was50128ng/kg. After thethermal treatment at1450°C, the amount of PBDEs in EAF fly could significantly reduce andthe PBDEs existed in the slag and ingot also were less than in the natural ground soil. Thetotal PBDE concentration in the flue gas was much lower than the content in all the otherplants when it was installed the APCDs. In addition, the reformation of PCDD/F and PBDEcongeners was found in the cooling unit through de novo synthesis and precursorcondensation. The results of the mass ratio and Pearson correlation analyses suggested thatthe ratio of log PBDEs/(log PCDD/Fs) could be used to evaluate the emissions from one tothe other (PCDD/Fs and PBDEs) from the emission sources. Therefore, the thermal treatmentmethod presented in this work not only enhanced the dechlorination/debromination of thehigh-chlorinated/brominated congeners, but also decomposed the aromatic rings of PCDD/Fsand PBDEs. But most of all, it recovered the metal from the EAF fly ash.In addition, the characteristics of the MSWI fly ash and bottom ash which had beenproduced from the incinerator located in South China were investigated. The results showedthat the size distributions of the highest particle mass content in the fly ash was located at theparticle size below0.28mm, while that in the bottom ash was located at the particle sizelarger than0.28mm. The main components and its characteriation of the MSWI fly ash andbottom ash were detected by XRD and XRF. The results showed that main components andcrystal phases of them were similar to those of other areas of China and abroad. The contents of Cd, Cr, Cu, Pb and Zn in the MSWI fly ash and bottom ash exceeded the regulatorythreshold value of the Ⅲ kind soil in accordance with GB15618-1995. The total contents ofPAHs in different particle sizes of bottom ash had a range of43.42-247.14ng/g, revealing thatit was similar to those in the European regional. However, it was lower than some areas ofChina. The leaching concentrations of Pb was exceeded the regulatory threshold value inChina which was listed in accordance with GB5085.3-2007when it used distilled water asleaching agent, while the leaching concentrations of Cd was exceeded the regulatory thresholdvalue when it used2#solution as leaching agent. Moreover, the leaching concentrations of allthe heavy metals in the bottom ash were lower than the regulatory threshold criteria values inChina (GB5085.3-2007) when it used distilled water and2#solution as leaching agents.Therefore, we recommend that the bottom ash can be reutilization as construction material,but its the environmental safety and influences need to be further evaluated.Moreover, the evaluation and test of adsorption dye from aqueous solutions by theoriginal and modified MSWI fly ash were investigated. The fly ash was used to remove theMethylene Blue from aqueous solutions. The maximum amount of MB on to the original flyash was0.692mg/g when their the particle size of the was below0.076mm, which showedthat it lower than those of using coal fly ash as adsorbent for the removal of MB. Moreover, itcould be found that the Pb content in the fly ash could be completely removed and itsadsorption capacity could be obvious improved when the fky ash was treated with a0.5mol/Lacetic acid solution at the L/S ratios of4,6and8. The concentrations of Pb, Cr and Cd in theMB solutions after adsorption processes were below the regulatory threshold values in Chinawhich were listed in accordance with GB5085.3-2007. In addition, the adsorption isothermdata were well fitted by both Langmuir and Freundlich models, and the seconded-orderkinetic model perfectly fitted for the MSWI fly ash systems. According to the results of BET,XRD, SEM-EDS and FT-IR, it revealed that the BET surface area of acetic acid solutiontreatment fly ash was four times than that of original fly ash. This was due to the impurities insurface of original fly ash could be removed by acetic acid solutions and formed the smallerpores, leading to the increasing of BET surface and increase the dye removal percentage.The leaching characteristics and particle size distributions of polybrominated diphenylethers (PBDEs) in the bottom ash of two municipal solid waste incinerators (MSWIs A and B)were measured and discussed. The results showed that industrial waste in the municipal wastecontained commercial PBDE mixtures and they were not completely destroyed during theincineration process. The size distribution of the PBDE content in the bottom ash of bothMSWIs was mainly in the range of0.25to1.0mm, with the larger particles predominating. Moreover, the PBDE concentrations in the leachate for MSWI A and B ranged from0.684to1.23ng/l. The mean normalized leaching ratios of the individual PBDE congeners in thebottom ash in MSWIs A and B were5times more than the levels found in the leaching test forone raw plastic material (ND-HIPS) and three different TV housing samples. Therefore, thepotential leaching of PBDEs to the around during reutilization of bottom ash from MSWIsmust be carefully considered. We suggest that the bottom ash may be reutilization asconstruction material with different particle sizes.Finally, the effects of using dried sewage sludge as additive on cement property in theprocess of clinker burning were investigated in this part. The results indicated that the majorcomponents in the eco-cement clinkers were similar to those in ordinary Portland cement. Theflexural and compressive strength and setting time of eco-cement pastes, scanning electronmicroscope (SEM) micrographs, XRD characterization analysis, heavy metal leachability andchanges of element content of eco-cement clinkers are also investigated. The X-ray diffractionpatterns of all the clinkers showed that the major components present in the eco-cementclinkers were C3S, C2S, C3A, C4AF and that the phase formation of Ca54MgAl2Si16O90wasidentified in all the clinkers. The C2S (α-C2S or β-C2S) phase formation and peaks increasedwith increases in sewage sludge. Investigations by SEM gave evidence of the C2S (α-C2S orβ-C2S) phase formation increasing with increases in sewage sludge content while the C3Sstructures decreased. Particularly, the microstructure of the mixture in the clinker containing15.0%sewage sludge was significantly different in that it displayed a larger amount of poredistribution. Moreover, all the eco-cement pastes had both delayed initial setting times andfinal setting times. The early flexural strengths of all the eco-cement pastes were lower thanthat of the plain paste, whereas their compressive strengths only were a little lower than theplain paste. The more sewage sludge that was added to the raw meals, the lower the flexuralstrengths of the eco-cement pastes. However, there was no significant effect on all thestrengths at later curing ages. This might be primarily attributed to the increased amounts ofC2S in the eco-clinkers and the minor elements carried from the sewage sludge. In addition,the concentrations of Ti, Ba, Zn, Cr, Cu, Ni and Pb in the clinkers increased with the sewagesludge addition into the raw meals, while Mg, Sr obviously decreased, and Al, Fe, Mn slightlydecreased. Finally, the leaching concentrations of all types of eco-cement clinkers met thestandard of current Chinese regulatory thresholds.