| With the continuous advancement of urbanization in China,the output of sewage and is increasing year by year,which has brought tremendous pressure to Chinese industrial treatment of sewage and sludge.As a by-product of the sewage treatment process,there are also a large number of potentially toxic substances,while the sludge contains more calorific value.The traditional sludge treatment method with landfill as the main and compost supplementation not only wastes the heat value of the sludge itself,but also brings great harm to the environment.In this context,the research on sludge incineration and co-firing of sludge with coal is receiving increasing attention.In this research,the combustion of sludge alone and the mixture of sludge with low-rank coal were carried out through the settling furnace system.At the same time,microwave digestion instrument,ICP-AES,XRF,XPS,XRD and other test methods were used to explore heavy metals(Zn,Mn,Cr)migration and conversion rules in the combustion process of sludge and blending of sludge and low-rank coal.At the same time,in order to achieve the fine utilization of combustion ash,the collaborative extraction of Zn,Mn,Cr in ash was also studied by multiple methods.(1)When the sludge is burned alone,the enrichment rate of Zn in the combustion ash decreases with increasing temperature.Increasing temperature promotes the volatilization of Zn.The enrichment rate of Zn in the ash during O2/CO2 combustion is significantly higher than that in the air atmosphere,because ZnCl2 formation is suppressed.The enrichment rate of Mn in ash increases as the temperature rises.MnO captured by the aluminosilicate is promoted.The enrichment rate of Cr in the ash increases with the temperature increase.The temperature increase promotes the capture of Cr vapor by Fe2O3 and CaO.The partially reducing atmosphere caused by high concentration of CO2 during O2/CO2 combustion promotes the enrichment of Mn and Cr in the ash.(2)The enrichment rate of Zn in ash increases with the increase of water content in sludge.The higher the temperature,the more intense the effect of water content to promote the increase of Zn enrichment rate in ash.The enrichment rate of Mn in sludge ash increases with the increase of water content.With temperature increase,the accelerating effect of Mn enrichment in the ash is weakened by water.The enrichment rate of Cr in sludge ash increases with the increase of water content.The addition of water promotes the enrichment of Cr in the ash during sludge combustion.And with temperature increase,the promotion of water enhances.(3)The blending of low-rank coal during sludge combustion has a positive effect on the enrichment of Zn,Mn,Cr in ash.The enrichment rate of Zn Mn,Cr in ash increases with the increase of the low-rank coal blending ratio.The enrichment rate of Zn and Mn is greatly affected by the blending ratio change of Xiheishan coal The enrichment rate of Cr is greatly affected by the blending ratio of Xiaolongtan coal.The blending ratio increase of Tianchi coal obviously affects the enrichment of Zn,Mn and Cr.Therefore,the industrial application of the blending of sludge and low-rank coal is of great significance in the control of heavy metals(Zn,Mn,Cr).(4)At the studied temperature of 800?,900? and 1000?,the enrichment rate of Zn,Mn,Cr in the ash increases with the temperature increases.Temperature increase has a promoting effect in the solidification of Zn,Mn and Cr when the sludge is mixed with low-rank coals.In addition,the enrichment rates of Zn,Mn,and Cr decrease during co-firing of sludge and coal with the increase of water content.The addition of water is not conducive to enrich heavy metals Zn,Mn,and Cr in ash during co-firing of sludge and coal(5)The water bath and acid leaching method,microwave extraction method and hydrothermal extraction method were used to synergistically extract Zn,Mn and Cr from ash.It is found that hydrothermal method has the highest energy consumption,while the extraction rate of Zn,Mn and Cr is the lowest.The energy consumption of water bath and acid leaching method is significantly lower than hydrothermal method.The extraction efficiency of the three heavy metals is higher,especially Cr.The microwave extraction method has the lowest energy consumption,and the extraction rates of Zn and Mn are higher than the water bath and acid leaching method,although the extraction rate of Cr is only 40.28%.Considering the energy consumption and extraction rate,the microwave extraction method is the most ideal extraction method for Zn,Mn,Cr in ash. |
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