Distribution Characteristics Of Rare Earth Elements In Incineration Fly Ash From Municipal Solid Waste

How to deal with urban domestic garbage in an efficient and clean way has longbeen one of the most difficult problems in China and the world.In recent years,the waste incineration treatment has been in line with the principle of treatment of reduction,harmlessness and resource utilization of solid waste,so it has developed rapidly.However,in the process of waste incineration,the rare earth elements in them will migrate and transform,and will be enriched in fly ash,which may cause many potential hazards.And because of the wide application of rare earth elements,its demand has increased year by year.Analysis and study of rare earth elements in waste incineration fly ash and their utilization as much as possible can not only reduce the environmental damage caused by rare earth mine development,but also reduce the content of harmful substances in fly ash and reduce environmental pollution.In this paper,the municipal solid waste incineration fly ash is studied.Firstly,themorphology and structure characteristics of waste incineration fly ash are analyzed by scanning electron microscopy?SEM?.X-ray powder diffraction?XRD?technology is used to determine the phase distribution characteristics.Microwave digestion technology and ICP-MS accurately detected the distribution characteristics of 15 rare earth elements in waste incineration fly ash.Finally,Tessier separation and extraction method was used to analyze the morphological characteristics of rare earth elements in fly ash and to identify waste incineration fly.The migration and transformation of different forms of rare earth elements in ash.In order to provide a scientific basis for the rational treatment and efficient reuse of municipal solid waste incineration fly ash.Research indicates:?1?The fly ash?FA1?of a bag garbage collector in a municipal solid wasteincineration plant in Beijing is evenly distributed,with fine particles and simple types,mostly spherical floc aggregates.These particles have small pores and a smooth surface;a municipal waste incineration plant in Beijing The ash silo fly ash?FA2?is mainly composed of amorphous flocculent particles,which is dense inside,with small particles attached to the surface,many pores and rough surface.The ash silo fly ash?FB3?of a domestic waste incineration plant in Shanxi is rich in shape.In addition to the round particles,there are polygons,strips,blocks,sheets,etc.,and there is a high porosity between the particles,and the surface is rough.In general,there are few intact crystals in fly ash,mostly in the form of polycrystalline polymers and amorphous forms,indicating that the structure of waste incineration fly ash is more complicated.?2?The main mineral components in fly ash include SiO₂?CaCO₃?CaSO₄?Ca₂Al₂SiO₇?Fe₂O₃?Fe₃O₄?Al₂O₃?Al₂SiO₄ and the like.In addition to the above main mineral composition,there are also NaCl,KCl,MgSiO₃,CaO,Mg₂SiO₄,NaAlSiO₄,MgAl₂Si₃O₁₀,Ca?OH?₂,BaSO₄,FeO,FeS₂,NaSO₄ and the like.The content of the glass phase is as high as58%.SiO₂ can be clearly detected in all three fly ash samples,reflecting the poor solubility of SiO₂ in the incineration process.?3?A qualitative detection method for rare earth elements in fly ash by microwavedigestion/ICP-MS was established.The detection limits of 15 rare earth elements ranged from0.0002 to 0.0043 mg/kg.The precision of the method?RSD,n=6?was 0.94%².86%,and the correlation coefficients were all greater than 0.9996.The contents of the three kinds of fly ash samples were:The FA1 content was 177.9362 mg/kg,the FA2 content was 55.9468 mg/kg,and the FB3 content was 1602.6016 mg/kg.The content from high to low was FB3>FA1>FA2.The content of 15 rare earth elements in the FB3 sample is higher than that in the other two samples.?4?The content of light rare earth elements in the three kinds of fly ash samples ishigher than that of heavy rare earth elements,and the proportion of total rare earth content in fly ash is more than 80%.The enrichment of 15 rare earth elements in fly ash is quite different.The content of Ce is the highest among the three fly ash samples,followed by La,Y and Nd.?5?The content of residual ash in the three fly ash samples was the highest,followed by the iron-manganese oxide combined state and the lowest carbonate combined state.The distribution of different rare earth elements in the five forms was basically the same.The rare earth elements having a higher content are Ce,La,Nd,Gd,Y,etc.