Search

The method of continuous treatment with Na2CO3 solution, HF solution, and CO2 was proposed for the regeneration of the exhausted activated carbon (EAC) produced in the sintering flue gas purification process. In order to obtain the optimal operation conditions, the effect of key parameters such as Na2CO3 solution concentration, HF solution concentration, and CO2 activation temperature on the sulfur conversion rate and regeneration efficiency was analyzed. Also, the N2 adsorption, Brunauer-Emmett-Teller analysis, scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, X-ray fluorescence, and Fourier transform infrared spectroscopy were adopted to investigate the deactivation reason and the change of the physical-chemical properties. The results showed that the deactivated EAC was mainly due to the deposition of inorganic compounds such as CaSO4, SiO2, and KCl to block the pores. Continuous treatment with Na2CO3 solution and HF solution could remove the inorganic compounds effectively. CO2 activation treatment further developed the blocked porosity and decreased the surface acidity. The optimal conditions for the regeneration of EAC were a Na2CO3 concentration of 0.5 mol/L, an HF concentration of 0.8 mol/L, and a CO2 activation temperature of 1073 K with the activation time of 1 h, corresponding to the specific surface area of 607.91m2/g. In the fourth regeneration cycle, the adsorption performance during the successive adsorption-regeneration process could still maintain a high level and the regeneration efficiency was 95.31%.

The effect of MgO on the carbothermal reduction of FeTiO3 has been investigated using isothermal experiments. x-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) techniques were used to reveal the reduction mechanism of FeTiO3 doped with MgO. The results showed that MgO could promote the reduction of FeTiO3. After doping with MgO, solid solution of Mg2+ in the FeTiO3 unit cell formed a new phase (Fe1–x,Mgx)2TiO4. With increase of the MgO content, the stability of the FeTiO3 lattice and the (Fe1–x,Mgx)2TiO4 structure decreased while the reaction activity increased, facilitating formation of FeTi2O5 and (Fe1–2x,Mg2x)TiO3 and aiding reduction of (Fe1–x,Mgx)2TiO4 to the orthogonal system (Fe1–2x,Mg2x)TiO3. When the content of MgO exceeded 4%, large amounts of magnesium–titanium compounds were generated and subsequently covered unreacted particles. Meanwhile, the contact area between unreacted particles and reducing agents decreased, thereby weakening the promoting effect of MgO.

The viscosity, melting proprieties, and molten structure of the high-Al silicon&ndash, manganese slag of SiO2&ndash, CaO&ndash, 25 mass% Al2O3&ndash, MgO&ndash, MnO&ndash, K2O system with a varying MgO and K2O content were studied. The results show that with the increase in MgO content from 4 to 10 mass%, the measured viscosity and flow activation energy decreases, but K2O has an effect on increasing those of slags. However, the melting temperature increases due to the formation of high-melting-point phase spinel. Meanwhile, Fourier transform infrared (FTIR) and X-ray photoelectron spectra (XPS) were conducted to understand the variation of slag structure. The O2&minus, dissociates from MgO can interact with the O0 within Si&ndash, O or Al&ndash, O network structures, corresponding to the decrease in the trough depth of [SiO4] tetrahedral and [AlO4] tetrahedral. However, when K2O is added into the molten slag, the K+ can accelerate the formation of [AlO4] tetrahedra, resulting in the increase in O0 and O&minus, and the polymerization of the structure.

The effect of TiO2 on the viscous behaviours of mineral wool melts containing CaO−SiO2−Al2O3−MgO-TiO2 were studied at acidity coefficient Mk in the range of 1.0–1.6 and TiO2 content in the range of 0–6wt%. Based on the experimental data, the critical temperature and activation energy were calculated to analyse the changes in viscosity flow. The morphology and phase of slag were clarified by scanning electric microscopy with energy dispersive spectroscopy and X-Ray diffraction. Fourier transformation infrared and Raman spectra were used to obtain information about the variations in melt structure. The results showed that the viscosity decreased with increasing TiO2 content. The critical temperature (Tcr) was 1537–1645K, and it was relatively stable when the acidity coefficient Mk is 1.3. The activation energy decreased from 182.27, 178.48, 162.75 kJ/mol to 146.67, 139.28, 127.64 kJ/mol with increasing acidity coefficient Mk, respectively. With increasing TiO2 content, the fraction of main crystal phases (CaSiO3) decrease and form perovskite (CaTiO3). In addition, relationships are found to exist between the viscosity and structure of melt. The formation of Ti-O or O-Ti-O bonds weakens the stability of molten slag, and the number of bridging oxygen decreases from 1.85 to 0.65.

The effects and reduction mechanisms of carbothermic reduction of vanadium&ndash, titanium&ndash, magnetite were studied by adding various mass fractions of CaF2 ranging from 0%, 1%, 3%, 5% to 7%. The results showed that the proper CaF2 addition could strengthen the carbothermic reduction of vanadium&ndash, magnetite while the excessive amounts will weaken the promotive effect, hence the appropriate dosage was determined to be 3 mass%. The CaF2 was favorable for the carbon gasification reaction, where it increased the partial pressure of CO inside briquette and caused the lattice distortion of vanadium&ndash, magnetite. The reaction improved the reduction process and accelerated the reduction rate. The appearance of 3CaO&middot, 2SiO2&middot, CaF2 and other complex compounds with low melting point facilitated the aggregation and growth of the slag and the iron, which increased the concentration of iron grains and the aggregation level of the slag.

In order to promote the application of Ti-bearing blast furnace slag in mineral wool manufacture, the viscosity, thermal stability and structure of melt were studied in this paper. And the concept of “Extreme Heat Release of Slag (EHRS)” was firstly proposed to quantify the thermal stability of melt. The results showed that slag viscosity decreased with the increase of TiO2 content in the range of 0wt% to 6wt% at acidity coefficient (Mk) of 1.0~1.6. TiO2 reduced the heat capacity of melt, but increased the EHRS. And when the Mk was 1.3, the EHRS was relatively large. The variation of activation energy of viscous flow had a good agreement with that of viscosity. In addition, TiO2 acted as network modifier in the melts, which decreased the average number of bridging oxygens from 2.93 to 2.71. Ti4+ mainly existed in the form of [TiO4] 4– monomers and O–Ti–O in chain or sheet units, resulting in the decrement of slag stability. At the Mk of 1.3, increasing TiO2 content to 6wt% would beneficial for the production of fibers with uniform diameter and length.