| Iron tailings are the major type of industrial waste which are often stockpiled in tailings ponds. They have great harmful influence on surrounding environment. With the depletion of mineral resources and increase of tailings stock, comprehensive utilization of tailings has become a hot issue. Autoclaved aerated concrete is a new type of building material, which has various advantages such as lightweight, fireproof, thermal insulation, anti-seismic, etc. The application of autoclaved aerated concrete in housing construction can decrease energy consumption of building effectively and improve energy efficiency. It is an effective method for handling mineral tailings to apply them for preparation of autoclaved aerated concrete. It can not only consume large amount of mineral tailings, relieve the pressure of construction and maintenance of mine tailings reservoir and open up new avenues for the raw material of the production of aerated concrete simultaneously, but also provide high-quality products for the building materials market.After adding appropriate amount of additives such as silica sand, lime, cement, the lean vanadium-titanium iron tailings of Fuyou company from Pingquan county in Hebei Province can be used as the main siliceous material in preparation of autoclaved aerated concrete. The preparation process of autoclaved aerated concrete with the iron tailings has been studied systematically, which including the ratio of different raw materials, autoclave curing system, etc. Kinetics of autoclave curing reaction process has been explored, and the mechanism of the preparation process has been elaborated.The particle size of vanadium-titanium iron tailings from Pingquan county in Hebei Province is coarse. The content of-0.074 mm fraction and Si O2 composition accounts for only 21.07% and 40.46%, respectively. Experimental result shows that the best ratio of raw materials can be shown as iron tailings: silica sand: lime: cement: gypsum = 32:35:21:10:2. The dosages of aluminum powder is 0.08%. The water-solid ratio is 0.57. The static-stop curing time ranges between 5~6 h. The heating up time of autoclave curing lasts 2h, the thermostatic time and temperature is 8 h and 178?, respectively. Natural cooling method is taken. The average compressive strength and dry bulk density are 3.98 MPa and 622.1 kg/m3, respectively, which are in line with national standard for autoclaved aerated concrete of A3.5B06 specification.By analyzing the autoclave curing reaction process kinetics, reaction rate of raw materials during the thermostatic temperature stage of autoclave curing process is controlled by the diffusion rate of reactants through the hydration layer primarily. Reaction process of the Si O2-Ca(OH)2-H2 O system during the autoclaved curing process can be described with the model of prodution layer diffusion control. The kinetic equation of the autoclaved curing reaction process can be explained as 2/31 -2 / 3x -(1 -x) =0.792 exp(-19269 / RT)t +b.Series of hydrothermal synthesis reactions occur between siliceous and calcareous materials in the environment of high temperature and pressure during autoclave process. Hydration product type transforms from high alkalinity to low alkalinity gradually, while the degree of crystallinity improves constantly and the structure become denser gradually. The main chemical components in autoclaved aerated concrete blocks include tobermorite, CSH(B), hydrogarnet and unreacted silicon. The compressive strength is formed with adhension of flaky tobermorite crystals and CSH gel. |
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