Process Optimization and Pollution Control of Heavy Metal Hazardous Waste High Temperature Co-treatment

Author:Yue Yang

Supervisor:qian guang ren zhou ji zhi


Degree Year:2019





Waste incineration fly ash,electroplating sludge,pickling sludge and hazardous waste incinerator slag are heavy metal hazardous wastes dominated by inorganic components.Heavy metal hazardous wastes have the characteristics of complex components,high pollutant content,difficulty in volume reduction and reduction,etc.Heavy metal hazardous wastes have become a difficult problem for the reduction and management of inorganic hazardous wastes.At present,heavy metal hazardous wastes are mainly safely landfilled after solidification treatment,or through the production process of building materials such as cement kiln co-processing.However,safe landfill wastes land resources and is prone to secondary hazards.The co-processing of cement kiln requires pretreatment,which is prone to secondary pollution of pretreatment wastewater Therefore,it is necessary to establish a technical system for co-treatment processing of heavy metal hazardous wastes with controllable pollution control,controllable pollutant distribution and reusable disposal products.According to the characteristics of heavy metal hazardous waste components,this paper utilizes the advantages of high content of Si and A1 in hazardous waste incinerator slag,combined with the melting point control technology of glass industry and the melting characteristics of Ca-Si-Al three-phase system,and will electroplating sludge and acid.Heavy metal hazardous wastes such as sludge washing,incineration fly ash,and hazardous waste incinerator slag are grouped.By regulating the optimization of Ca-Si-Al three-phase ratio design in multi-waste mixing system,the melting point regulation of the mixed system and the formation of amorphous glass in the slag are realized,and the solidification of heavy metals in the glass matrix is promoted.In the high-temperature co-disposal process of incineration fly ash heavy metal sludge,the large amount of chlorine salt in the incineration fly ash is easy to form the volatile characteristics of heavy metal chloride salt,and the heavy metal volatile enrichment and recovery is realized.In the high-temperature sintering process,by controlling the formation of new mineral phases such as CaAl407,CaSiO3 and Ca2Al2SiO7,the minerals are relatively stable and lattice-bound and stable.By introducing a reducing agent to create a high-temperature reducing atmosphere,the transition metal simultaneous reduction and separation in the high-temperature melting co-disposal process is realized.At the same time,X-ray diffraction analysis,polarized light microscopy analysis,electron microscopy microstructure analysis and other means to evaluate the solid metal solidification stability mechanism of high-temperature co-processing products of heavy metal hazardous wastes,and to explore the relationship between the microstructure of high-temperature co-processing products and heavy metal leaching and chemical forms.The main conclusions of the study are as follows:(1)When the fly ash/leachate sludge mixing ratio is 4:1,the high content of salt in the fly ash promotes the disintegration of the floe in the sludge,destroys the microbial extracellular polymer in the sludge,and promotes the transformation of the combined water in the sludge.The leaching concentrations of heavy metal Zn,Pb and Cu decreased to 0.63-0.82 mg/L,0-0.05 mg/L,0.14-0.23 mg/,respectively,after the fly ash/leachate sludge mixed granules were sintered in the grate and the second combustion chamber respectively.L and 0.31-0.44 mg/L,0-0.02 mg/L and 0.05-0.11 mg/L,the leaching concentration is in line with the groundwater level III standard.Before and after the sintering of the mixed particles,the proportion of heavy metals in the form of unstable F1 decreased by 12%-19%,and the proportion of stable forms F3 and F4 increased by about 20%.In the grate sintering and secondary combustion chamber sintering process,the volatilization rate of heavy metals reached 70%and 90%,respectively,and the compressive strength of sintered bodies reached 5.7 MPa and 6.3 MPa.When 3%calcium fluoride and 3%phosphate were added to the fly ash/leachate sludge granules,the leaching concentrations of heavy metals Zn and Cu in the sintered body decreased to 0.32 mg/L,0.02 mg/L,and 0.19 mg/L,and 0.03 mg/L respectively.The volatile rate of heavy metals is reduced by 7%-15%.The co-solvent calcium fluoride was added in two sintering modes to increase the compressive strength by 0.1 MPa and 0.3 MPa,respectively.Sodium phosphate has no significant effect on the sintering strength of the particles.(2)Hazardous waste incinerator slag with silica and alumina content of 24.57%and 18.63%,and waste incineration fly ash and electroplating sludge,etc.When the silica content in the mixed system is more than 30%and the alumina content is more than 10%,the melting point of the mixed system may be lowered to 1300℃.When the amount of fly ash added reached 30%,the maximum volatility of Zn,Pb and Cd in the mixed system reached 41%,96%and 94%,respectively.In the secondary fly ash captured by flue gas treatment,the Zn content reached 6.64%,which is much larger than the average value of the zinc ore industrial grade of 1.39%;the lead content reached 0.62%,exceeding the lowest value of the lead ore industrial grade by 0.5%.The total content of lead and zinc in the secondary fly ash reached 7.26%,which is within the range of 5%-10%of the main lead-zinc deposits in China.After the addition of the reducing agent in the high-temperature melting process,about 85%of Cr,50%of Zn,and 70%of Cu can be reduced.The reduced transition metal element is separated from the slag by gravity in the furnace,and the simultaneous transition metal reduction and separation in the high-temperature melting process is realized.(3)Heavy metal hazardous waste forms mineral phases such as CaA14O7,CaSiO3 and Ca2Al2SiO7 during high temperature sintering.Using density functional theory analysis,heavy metals Zn and Pb can replace the Ca atoms in the above three mineral phases after absorbing 0.05 eV energy to achieve lattice restraint stability.When the heavy metal Cr absorbs 0.005 eV,it can be atomically replaced with A1 in CaAl4O7 to achieve stable solidification of the heavy metal lattice.Heavy metal hazardous waste can be completely melted after proper ratioing,and an amorphous glass body is formed in the molten slag.During the melting process,the surface microstructure of the material changes from a flocculent,massive structure to a planar structure with a smooth surface,and the heavy metal is wrapped and bound in the glass matrix.At this time,the leaching concentrations of heavy metals Zn,Cu,Cr and Ni were 0.63 mg/L,0.14 mg/L,0.03 mg/L and 0.01 mg/L,respectively,which met the groundwater level III standard.The proportion of heavy metals present in unstable forms falls to within 4%.(4)The stabilizing mechanism of heavy metals in wastes in high temperature co-processing products was preliminarily revealed,including stable lattice-bound curing and stable matrix-bound curing.By adjusting the ratio of Ca-Si-Al three-phase system in the high-temperature co-processing raw materials,the formation of new mineral phases such as CaAl4O7 CaSiO3 and Ca2Al2SiO7 in the sintered particles can be controlled,and the replacement of Ca and Al in heavy metals and crystals can be realized,and the lattice can be realized.On the other hand,in the high-temperature melting process,the formation of an amorphous glass matrix having a glass structural characteristic is promoted by a suitable melting condition and a group distribution mechanism.The formation of a dominant mineral phase is stabilized by crystal binding in the molten glass matrix by group partitioning and cooling.The glass matrix wrap binding effect and the dominant mineral phase atom replacement effect are achieved,and the heavy metal glass matrix is bound and solidified stably and the dominant mineral phase is lattice-bound and solidified.Based on the characteristics of heavy metal hazardous wastes,this study used technological innovations such as group distribution and coordinated disposal to construct a synergistic combination of multi-metal waste volatilization to promote enrichment,reduction and separation,lattice-bound solidification stability,and glass matrix solidification stability.Disposal and resource utilization control a new technical system.The mechanism of volatile metal enrichment,reduction separation and solidification stability in high temperature co-disposal process was preliminarily revealed,which provided theoretical basis and engineering demonstration for the promotion and application of high-temperature co-processing technology for heavy metal hazardous waste.