Mechanism Of Phase Transformation And Solidification Of Heavy Metals In Iron Tailings Sintered Brick

The solid waste discharged from iron ore after beneficiation is called iron tailings.With the rapid development of China's steel industry,the emission of iron tailings is increasing as the days passed.The long-term and large-scale accumulation of iron tailings not only occupies land resources,but also brings a series of environmental pollution and safety problems.The secondary utilization of iron tailings as building materials is a hot spot in the field of comprehensive utilization of tailings.In this study,the basic properties of iron tailings were studied.Then the iron tailings were used as the main raw materials to study the preparation process of iron tailings sintered brick and iron tailings sludge brick,and the properties of iron tailings brick were tested and analyzed.The mixing mechanism and phase transformation process of four metal oxides?CuO,PbO,ZnO and CdO?and tailings brick raw materials after sintering at700-1100?for 2 hours were studied,and the migration and transformation mechanism of heavy metals in raw materials during sintering process was proved.The main research results are as follows:The main mineral compositions of iron tailings samples were quartz?SiO₂?,goethite?FeO?OH??,and kaolinite?Al₂Si₂O₅?OH?₄?.Compared with a traditional raw material for sintered bricks-clay,iron tailings have the disadvantages of high iron content,low aluminum and silicon content.However,by added appropriate auxiliary materials,it is completely feasible to use the iron tailings to prepare sintered bricks.The addition of appropriate amount of fly ash,kaolin or sludge from mine drainage works as auxiliary materials made up for the shortage of iron tailings as brick-making raw materials and improved the performance of iron tailings sintered bricks.The best raw material ratio F3?iron tailings:fly ash:kaolin 60:30:10?was obtained.The MU10 standard specified in GB/T5101-2017 can be reached by sintering at 1050?,and the MU30standard can be reached by sintering at 1100?.In this temperature range,the bulk density and water absorption rate of iron tailings brick also meet the best range specified in the standard.Meanwhile,combined with the characteristics of the sludge from the mine drainage plant in Dabaoshan mining area,referring to the preparation process of iron tailings sintered brick,the feasibility of preparing iron tailings sludge brick was preliminarily proved by selecting the sludge from the drainage plant instead of kaolin in the auxiliary materials.The properties of the sintered product with added metal oxides were characterized and analyzed,and the results showed that the main crystalline phases were quartz,cristobalite,hematite,and mullite,because the metal oxides were ascribed to copper ferrite spinel?CuFe₂O₄?,gahnite?ZnAl₂O₄?,zinc ferrite spinel?ZnFe₂O₄?,lead feldspar?PbAl₂Si₂O₈?,and cadmium feldspar?CdAl₂Si₂O₈?.Further analysis indicates that the heavy metals were transited into spinel or silicate structures with favorable efficiency.This indicates a good heavy-metal fixation effect from the structural change after the sintering process.Finally,the leaching experiments of the sintered samples suggest that the metal leaching decreased to a low and stable value when the sintering temperature was higher than 950?,which meets the China standard?GB 5085.3-2007?.The above results indicate that the sintering process facilitates the combination of Cu,Zn,Pb and Cd offering an effective and safe method for the application of materials that contain tailings.