Preparation And Mechanism Of Fired Bricks And Tiles With Low-silicon Iron Tailings From Wtbesern Huel

Iron tailings as waste residues generated from the process of iron ore dressing is a kind ofmajor industrial solid wastes. The rapid development of iron and steel industry has led to theincreasing amount of iron tailings. The majority of iron tailings have been abandoned andstockpiled for a long time, not only taken large areas of land, but also resulted in environmentalpollution and safety problems. With the increasing awareness of environmental protection andsustainable development, iron tailings as secondary resources have been attached importance byall countries in the world, the utilization of iron tailings have widely received attention,especially, reuse in producing building materials is nowadays worldwide being investigated.This dissertation deals with the techniques of preparing fired bricks and porcelain tiles withthe low-silicon iron tailings from western Hubei province of China as the main raw materials,based on comprehensive analysis of the basic characteristics of tailings. Then, the properties andmicrostructure of the final fired samples were systematically investigated, the firing process andmechanism were probed. The research contents and results of the tests are summarized as thefollowing:1. The basic characteristics of the tailings were systematically studied. The results indicatedthat the tailings had similar properties with clay, with these advantages such as fine particles,good plasticity and easy drying. But it contained too high iron content and too low silica andalumina content for producing fired bricks and porcelain tiles,on the other hand the fired tailingsamples showed high bulk density and fired shrinkage. Through suitable formulation, it ispossible to prepare fired bricks and porcelain tiles using the iron tailings.2. Fired bricks were made with the low-silicon iron tailings from western Hubei as the mainmaterials together with clay and fly ash, the suitable process conditions and formulation wereinvestigated, the comprehensive properties of tailing bricks from large-scale test were measured.The results showed that the addition of clay and fly ash improved the brick quality. Therecommended mass ratio was the tailings: clay: fly ash=84:10:6, the optimum conditions werefound to be forming water content and forming pressure were respectively in the range of12.5¹5%and20²5MPa, the drying system were100¹05℃for6⁸h, the optimumtemperature system were found to be that the heating rate was about6℃/min, the firingtemperature and holding time were in the range of980¹030℃and2³h. Under theseconditions, the mechanical strength, water absorption and bulk density of the fired specimenswere20.03²3.60MPa,16.54¹7.93%and1.85¹.90g/cm3, respectively. The results oflarge-scale test were consistent with the bench-scale test, and the other physical properties anddurability were well conformed to Chinese Fired Common Bricks standards (GB/T5101-2003). 3. The samples of tailing fired brick were characterized, the mechanism of formingproperties and microstructures of the bricks were analyzed, and the firing process was discussed.The results showed that the main mineral phases of the products were hematite, quartz, feldsparand apatite, which formed the main framework of fired specimens, were principally responsiblefor the mechanical strength of bricks. Part of feldspar phases reacting with quarts andaluminosilicate formed eutectic solution, which filled with among the crystals and promoted thecompactness of bricks. The brick samples showed the typical grain and bond microstructure, andcrystalline phases were embedded in glassy matrix forming strong entirety, which promoted thegood properties of bricks. Moreover, the firing process was concluded to four stages as drying,heating, firing and cooling. The diffusion predominated in firing process, while some meltingliquid generated in the latter stage of firing, which played an important role to the vitrificationand solid-phase reaction of bricks.4. The unglazed porcelain tiles were prepared using the iron tailings instead of parts oftraditional materials, the suitable formulation range of forming ceramics and the optimumprocess conditions were determined, and the properties of tiles were presented. Results indicatedthat the suitable formulation of the iron tailings substituting completely feldspar should beaddition tailings55⁶5wt.%, kaolin20²5wt.%, quartz sand10²0wt.%, the chemicalcompositions range of green body were SiO₂37⁴4%,Al₂O₃14¹6%,Fe₂O₃25²9%,CaO+MgO4⁵%,K2O+NaO0.7⁰.8%and loss on ignition8.0⁹.5%. The tailing porcelain tilescould achieve full vitrification at about1200℃, revealed a sintering interval of more than40℃.The optimum process conditions were found to be that forming pressure30MPa, firingtemperature1200℃and holding for15min. The obtained porcelain tiles as eco-friendlyproducts were well conformed to the requirements about drying press poecrlain tiles in Chinesestandard specifications Ceramic Tiles (GB/T4100-2006) and Specifications for EnvironmentalLabeling Products-Ceramic Tiles (HJ/T297-2006).5. The microstructures of the tailing porcelain tiles were discussed, the mechanism of theiron tailings addition could lower the firing temperature and promote the firing densification, andthe main reasons of narrowing densification interval were analyzed, in addition the feasiblesolutions are proposed, the fired process and densification mechanism of porcelain tiles wereprobed.Results revealed that the tiles featured good degree of sintering, high crystallinity with mainmineral phases as residual quartz, hematite, cristobalite, together with small amount anorthite andmullite, and presented in dense glassy and crystalline phase solid solutions with low porosity,which contributed to the densification and full vitrification of porcelain tiles.The high content of Fe₂O₃and CaO in tailings reacted with quartz and aluminosilicate andformed eutectic solution at lower temperature, which promoted the densification of porcelain tiles. Furthermore, Fe₂O₃crystallized form the liquid phases in cooling and were uniformity embeddedin glassy phases, which favored the mechanical strength and hardness of the tiles. The firedprocess of the tailing tiles could be divided into four stages as low temperature heating, oxidizingand decomposing, high sintering and cooling, at last the densification porcelain tiles withmultiphase structure were formed.Through the above research, the feasibility of making fired bricks and porcelain tiles usingthe low-silicon iron tailings was proved, not only resolved the problem of utilizing this kinds oftailings, but also would offer a new resources for building materials, with the double effects ofenvironmental protection and resources saving. Meanwhile,the comprehensive investigation oftailings characterics provided the scientific proof for tailings utilization, the mechanism researchenriched the theoretical systems and offered the theoretical basis for the application anddevelopment of the utilizing low-silicon tailings technologies.