Study On Value-Added Utilization Of Anshan Iron Ore Tailings With High Silica

Iron ore tailings as a main solid waste in metallurgical industry had 2.5 billion tons in China, which was not only a kind of hazard but a potential secondary resource. Therefore, it has strategic meaning for our country to the complete and value-added utilization of iron ore tailings. In this dissertation, the approach and manner of value-added utilization of Anshan iron ore tailings with high silicon were completely and systemicly studied.Firstly, using iron ore tailings as raw materials, the leaching process of SiO2 were investigated. The main factors, i.e. solid/liquid ratios, reaction temperatures, reaction time, that affect the leaching rate of iron ore tailings in sodium hydroxide were determined, and the digestion kinetics of iron ore tailings in sodium hydroxide was investigated correspondingly. The results showed that the optimum leaching ratio is obtained when the solid/liquid ratio is 1:2 under 110℃for 6h. The leaching kinetics of SiO2 can be represented by the interface reaction model, which was written as the following equation:1—(3—X)2/3+2(1—X)=k2//t. The apparent activation energy calculated for SiO2 leaching is about 14.2 kJ/mol, and the overall leaching rate appears to be controlled by the diffusion in solid. Experiment conditions of decomposition of iron ore tailings with molten salt method were investigated. The results showed that iron ore tailings were mixed with NaOH-NaNO3 and calcined at 500℃for 3 h to yield soluble sodium silicate. The iron ore tailings and NaOH were employed as raw materials, and NaNO3 as salts. The preparation of precipitated silica particle via chemical precipitation using sodium silicate from iron ore tailings and sodium hydroxide as starting materials was successfully demonstrated. The component, morphology and structure of the synthesized particles were characterized by XRD, FT-IR, SEM, TEM and XRF. The chemical structure of precipitated silica was hydrated silicon oxide through FT-IR analysis. The structure of precipitated silica was amorphous by XRD analysis. The SEM and TEM micrograph showed that the shape of precipitated silica particles was nearly spherical, and the average grain diameter was less than 150 nm. The SiO2 purity in the precipitated silica product was 92.3% by X-ray fluorescence analysis. Measured results of chemical and physical properties of precipitated silica as followed:the specific surface area was 114 m2/g, pH in the suspending liquid was 5.5-6.0, and loss on ignition at 1000℃was 6.16%. The product could be comparable with the requirements of HG/T 3061-1999 industrial product standard.Secondly, the mesoporous molecular sieve MCM-41 was synthesized by hydrothermal synthesis method with sodium silicate from iron ore tailings as silica source and hexadecyl trimethyl ammonium bromide (CTAB) as template. The effects of crystallization conditions, i.e. the ratios of CTAB/SiO2, pH values, crystallization time and crystallization temperatures on the formation of MCM-41, were investigated. The synthesized MCM-41 samples were characterized by XRD, BET, DTA-TG, HRTEM, SEM and FT-IR. The mesoporous molecular sieve MCM-41 was formed with CTAB/SiO2 of 0.05-0.6 and pH of 8-11. In the condition of CTAB/SiO2=0.15, the synthesized MCM-41 sample was ordered. The longer the crystallization time, the increase of relative crystallinity of MCM-41. It was favored for the increase of relative crystallinity with prolonging crystallization temperature. The MCM-41 was not formed when the crystallization temperature above 140℃or the crystallization temperature below 25℃. The A3 sample had surface area of 527 m2/g, BJH pore volume of 1.339 cc/g and pore wall thickness of 0.93nm. The pore structure of MCM-41 was well-ordered and symmetrical hexagonal structure, which pore diameter of MCM-41 was changed between 2nm to 3nm. Silicon-oxygen tetrahedron skeletons were confirmed by FT-IR、NMR.The effects of adsorption conditions on the adorption efficiency for Cu2+、Cr6+、Zn2+ and methyl orange (MO) by the MCM-41 absorbents were systemically stuied. The adsorption isothern model and adsorption kinetics medel were also explored.With these parameters increasing, such as the adsorbent time, adsorbent dose, initial concentration and adsorbent temperature, the efficiencies of the Cu2+、Cr6+、Zn2+ and MO were also increased.The adsorption kinetics of MCM-41 absorbents for the Cu2+、Cr6+、Zn2+ and MO were all corresponded to the modified pseudo-second-order equations, and the absorption isotherms was all satisfied to the Langmuir models.Finally, BaO-Fe2O3-SiO2 system glass-ceramics were synthesized from iron ore tailing of Anshan as starting material. Compositions of glass-ceramics, selection of main crystallization and crystallization kinetics were discussed. Utilizing the orthogonal experiment, the optimal formula and heat treatment schedule of foam glass- ceramics were decided. The initial crystalline phase of the sample was BaSi2O5 and Ba2FeSi2O7 as transition crystalline phase changed into BaFe12O19 with increasing of temperature. The final crystalline phases of the glass-ceramics were BaFe12O19 and BaSi2O5. With increasing of crystallization temperature, infrared absorption bands of the sample broaden within the range of 800-700cm-land were splitted within the range of 1100-900cm-1 and 500-400cm-1. It was suggested that the crystallization was accelerated by [FeO4] fundamental unit shifted to [FeO6] in the glass structure and BaFe12O19 as the final crystalline phase was observed. The index of crystal growth is 2.8 and it implies that crystals grow along three dimensional space. The complex dielectric constant and complex permeability dispersion were investigated in 8.2 GHz to 12.4GHz. The results show that maximum dielectric loss is 0.44, but magnetic loss is only 0.017. These new features make the composites be a kind of promising microwave absorber.