| Textile dyeing sludge has strong harmfulness because of its large production capacity,complex composition and long retention time of pollutants.At present,sludge incineration technology has the advantages of minimizing sludge volume,killing bacteria and pathogens and recovering energy in the process of disposal,so it is generally considered that incineration is one of the best feasible technologies for the disposal of textile dyeing sludge at home and abroad.Textile dyeing sludge has low calorific value and incineration can produce bottom ash by-products containing a lot of heavy metals.In addition,the bottom ash itself is in metastable state.Heavy metals in the bottom ash carrier will release to the environment through solid-liquid reaction under specific conditions,which will cause serious environmental problems.At the same time,biomass has the advantages of high calorific value,large storage capacity,wide source,clean and renewable.Therefore,the co-incineration of printing and dyeing pollution and biomass is an ideal treatment technology for textile dyeing sludge.However,the effects of biomass excipients on combustion characteristics of textile dyeing sludge,heavy metals in bottom ash and their mechanisms are still unclear.In this paper,rice husk and ramie biomass were selected as auxiliary materials of textile dyeing sludge.The combustion characteristics of textile dyeing sludge and biomass were studied,and the feasibility of energy utilization was discussed.At the same time,the influence of biomass auxiliary materials on the characteristics of heavy metals in mixed bottom ash was deeply explored,and its internal mechanism was revealed.Its main research contents are as follows:(1)Taking textile dyeing sludge,rice husk and ramie as the research objects,through the analysis of raw materials,it was found that the volatile and fixed carbon content of textile dyeing sludge was low,only 40%,while the volatile and fixed carbon content of rice husk and ramie was high,about 90%.The content of C and H in textile dyeing sludge is lower than that in rice husk and ramie,and the content of N and S is higher than that in rice husk and ramie.Compared with textile dyeing sludge,rice husk and ramie have the characteristics of high volatile matter,low ash content,high hydrocarbon organic matter and low emission of nitrogen and sulfur oxides.They are ideal clean fuels.The total amount of Cr,Cu,Ni and Zn in textile dyeing sludge is much higher than the risk control standard of soil pollution in agricultural land.The leaching value of Cr in textile dyeing sludge exceeded the standard value stipulated in "Hazardous Waste Identification Standard".The leaching value of Cu,Ni and Zn all exceeded the comprehensive discharge standard of sewage.It can be seen that textile dyeing sludge has a great potential threat to the environment.Rice husk and ramie are two kinds of biomass excipients which are clean and harmless to the environment.(2)Combining the theoretical calorific value and Si/Al ratio of biomass and textile dyeing sludge,the feasibility of energy conversion of textile dyeing sludge and biomass was discussed.The blending process of textile dyeing sludge with rice husk and ramie biomass was simulated by thermogravimetric experiment.The results showed that the introduction of biomass was beneficial to increase the calorific value of textile dyeing sludge,but because the introduction of biomass would cause slagging problem,the dosage should be strictly controlled within 50%.The introduction of biomass excipients such as rice husk and ramie can effectively improve the ignition performance,maximum combustion rate,comprehensive combustion performance,burnout characteristic index and combustion stability of textile dyeing sludge.Moreover,there is obvious synergistic effect between textile dyeing sludge and biomass additives,which promotes the combustion performance.When the content of rice husk is 20% and ramie is 40%,the gain effect is the most significant.(3)The total amount and leaching characteristics of target heavy metals in the mixed fly ash of textile textile dyeing sludge and biomass auxiliary materials(rice husk and ramie)were studied.The effect of biomass auxiliary materials on heavy metals in the bottom ash of textile textile dyeing sludge was discussed with the leaching rate as an evaluation index.The results showed that the total amount of heavy metals in the bottom ash of textile dyeing sludge increased significantly after incineration,while the leaching value decreased significantly.With the addition of rice husk/ramie additives,the total amount of heavy metals in the mixed-firing bottom ash gradually decreased and the leaching concentration of heavy metals further decreased.The Cu and Ni of the mixed-firing rice husk ash reached or were lower than the comprehensive sewage discharge standard,while the Cu,Ni and Zn of the mixed-firing ramie ash were far below the standard threshold.Comparing the leaching rates of different heavy metals in different ash samples,it was found that the rice husk blending system had a greater impact on the leaching rate of Cu,with a maximum reduction of 33%,while the ramie system had a greater impact on the leaching rate of Cr,Ni and Zn,with a maximum reduction of 50%.In addition,when the content of rice husk/ramie reached 40%,the leaching characteristics of heavy metals were basically stable.(4)Coupled with the morphological distribution of heavy metals in bottom ash,mineral composition and micro-morphology of bottom ash,it was found that incineration of textile dyeing sludge was beneficial to increase the content of target heavy metal residues,and the content of Ni and Zn residues was up to 94% and 88%.The addition of rice husk and ramie further promotes the increase of residue content in mixed bottom ash,that is,the combustion of textile dyeing sludge and biomass is beneficial to the stabilization of heavy metals in bottom ash.The risk assessment of ecological analysis shows that the heavy metals in the mixed fly ash are in a low pollution or risk-free state,and the potential ecological hazards to the environment are relatively weak.The results of XRD and scanning electron microscopy show that the formation of zeolite minerals in rice husk fly ash inhibits the leaching of heavy metals and promotes their transformation to a stable state,while the formation of iron-calcium garnet and iron-magnesium-chromium minerals in Ramie fly ash also passivates heavy metals,and the latter reacts directly with Cr to form a stable mineral phase.The stabilization of heavy metals in rice husk and ramie ash is related to aluminosilicate,iron and magnesium minerals and calcium salts.A large number of porous and fibrous structures appeared in the scanning electron microscopy of rice husk and ramie ash,which formed a larger space channel,increased the specific surface area of bottom ash,and increased the active sites of heavy metals in contact with minerals. |
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