Basic Research On Resource-utilization Of Ferrous Dust And Municipal Solid Waste Incineration Fly Ash Through Co-thermal Treatment

Ferrous dust containing Fe and C is a solid waste produced in ironmaking&steelmaking process,but the existence of Zn,Pb,K,Na made it difficult to be reused by ironmaking&steelmaking process.Reduction is commonly used for removing Zn,Pb,K,Na.However,the high reducing temperature(>1250℃)and large usage of reducing agent increase the difficulty of disposing.Municipal solid waste incineration fly ash is a kind of high calcium chloride waste,which can provide calciumcontaining flux for ironmaking&steelmaking process.When co-disposing ferrous dust and municipal solid waste incineration fly ash through thermal treatment,Fe and Ca can be recycled,and Cl can react with Zn,Pb,K,Na at lower temperature.Then Zn,Pb,K,Na can be removed in form of chlorides and enriched.At the same time,dioxins can be degraded.Therefore,in this article,the method of co-disposing ferrous dust and municipal solid waste incineration fly ash through thermal treatment was proposed,which can recycle valuable components in ferrous dust and municipal solid waste incineration fly ash,and realize the harmless treatment of municipal solid waste incineration fly ash.The method is of great significance for the construction of eco-friendly ironmaking&steelmaking industry and city.In this article,blast furnace dust,converter sludge and municipal solid waste incineration fly ash were investigated.Their basic physico-chemical characteristics and high-temperature reaction behavior were researched:①In blast furnace dust and converter sludge,zinc and lead mainly existed in the form of zinc ferrite(ZnFe2O4)and lead ferrite(PbFe10O16).While in municipal solid waste incineration fly ash,zinc chloride(ZnCl2)and lead chloride(PbCl2)are the mainly phase.Main phase of alkali metals in ferrous dust and municipal solid waste incineration fly ash are chlorides.② Due to the high content of carbon in blast furnace dust,Zn,Pb,K,Na were reduced under 1200℃ and their removing rate were 96.51%,99.32%,93.88%and 88.25%,respectively.Due to the low content of carbon in converter sludge,removing rates of Zn,Pb,K,Na in converter sludge were 36.01%,83.57%,72.90%and 72.41%,respectively,after roasting under 1200℃.Due to the high content of chlorine,removing rates of Zn,Pb,K,Na in municipal solid waste incineration fly ash were 81.11%,94.41%,95.93%and 84.64%,respectively,after roasting under 1200℃.Reaction behavior of ferrous dust co-disposing with and MSWI fly ash was revealed:Carbon content,chlorine content and calcium content are key factors affecting the removal of Zn,Pb,K and Na during co-thermal disposing process;As the content of chlorine and carbon increased,removing rates of Zn,Pb,K,Na firstly increased and then flatten.The increase of calcium content can promote the removal of Zn and alkali metals,while for Pb,its removing rate firstly increased and then decreased.The mechanism of reactions promoting the removal of Zn,Pb,K,Na during co-disposing process was revealed:During the co-thermal disposing process,calcium in municipal solid waste incineration fly ash displaced the zinc and lead in ZnFe2O4 and PbFe10O16(ZnFe2O4+CaO→ZnO+CaFe2O4,PbFe10O16+5CaO→PbO+5CaFe2O4),and ZnFe2O4 and PbFe10O16 decomposed under relatively lower temperature.ZnO and PbO formed.Carbon in ferrous dust promote the chlorination reaction between chlorine in municipal solid waste incineration fly ash and ZnO,PbO(ZnO+C+O2+CaCl2→ZnCl2+CaO+CO2,PbO+C+CaCl2+O2→PbCl2+CaO+CO2).Migration paths of Zn,Pb,K,Na during co-disposing process were found:ZnFe2O4→ZnO→ZnCl2(g),PbFe10O16.→PbO→PbCl2(g),KCl/NaCl→KCl(g)/NaCl(g);Adjust the content of chlorine,carbon and calcium oxide through mixing ferrous dust and MSWI fly ash in an optimized ratio.After co-disposing,the roasting temperature can be reduced to 1100℃,removing rates of Zn,Pb,K,Na were above 90%.The technology of co-thermal treatment was developed.Appropriate ratio is determined,namely blast furnace dust:MSWI fly ash=87:13,blast furnace dust:converter sludge:MSWI fly ash=63:17:20.The process route of strong mixing-pelletizing-drying-high temperature roasting was proposed.Under condition of blast furnace dust:converter sludge:MSWI fly ash=63:17:20,pelletizing water content 13%,drying temperature 150℃,drying time 15min,roasting temperature 1100℃,roasting time 30min,the large-scale test was carried out.The removing rates of Zn,Pb,K and Na are 95.22%,97.81%,93.52%and 91.40%,respectively.And the calcium ferrite containing 47.54%Fe and 20.17%Ca was obtained,and alkali/heavy metal contents meet the requirements of recycling in smelting process as well.Zn,Pb,K and Na can be enriched in dust,in which the contents of Zn,Pb,K,Na were 37.34%,1.64%,13.22%and 10.86%,respectively.The purpose of resource utilization of ferrous dust and MSWI fly ash is realized.