ABSTRACT
The micro-sintering method was used to determine the sintering basic characteristics of iron ore with Zn contents from 0 to 4%, the influence mechanism of Zn on sintering basic characteristics of iron ore was clarified by means of thermodynamic analysis and first-principles calculations. The results showed that (1) increasing the ZnO and ZnFe2O4 content increased the lowest assimilation temperature (LAT) but decreased the index of liquid phase fluidity (ILF) of iron ore. The addition of ZnS had no obvious effect on LAT but increased the LIF of iron ore. (2) ZnO and ZnFe2O4 reacted with Fe2O3 and CaO, respectively, during sintering, which inhibited the formation of silico-ferrite of calcium and aluminum (SFCA). The addition of ZnS accelerated the decomposition of Fe2O3 in the N2 atmosphere; however, the high decomposition temperature limited the oxidation of ZnS, so the presence of ZnS had a slight inhibitory effect on the formation of SFCA. (3) The Zn concentrated in hematite or silicate and less distributed in SFCA and magnetite in the form of solid solution; meanwhile, the microhardness of the mineral phase decreased with the increase in Zn-containing solid solution content. As the adsorption of Zn on the SFCA crystal surface was more stable, the microhardness of SFCA decreased more. The decrease in microhardness and content of the SFCA bonding phase resulted in a decrease in the compressive strength of the sinter.
ABSTRACT
In order to increase the utilization rate of stainless steel slag, reduce storage needs, and mitigate environmental impacts, this study replaces a portion of limestone with varying amounts of stainless steel slag in the calcination of Portland cement clinker. The study primarily examines the influence of stainless steel slag on the phase composition, microstructure, compressive strength, and free calcium oxide (ƒ-CaO) content of Portland cement clinker. The results show the following: (1) Using stainless steel slag to calcine Portland cement clinker can lower the calcination temperature, reducing industrial production costs and energy consumption. (2) With an increase in the amount of stainless steel slag, the dicalcium silicate (C2S) and tricalcium silicate (C3S) phases in Portland cement clinker initially increase and then decrease; the C3S crystals gradually transform into continuous hexagonal plate-shaped distributions, while the tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF) crystal structures become denser. When the stainless steel slag content is 15%, the dicalcium silicate and tricalcium silicate phases are at their peak; the C3S crystals are continuously distributed with a relatively dense structure, and C3A and C4AF crystals melt and sinter together, becoming distributed around C3S. (3) As stainless steel slag content increases, the compressive strength of Portland cement clinker at 3 days, 7 days, and 28 days increases and then decreases, while ƒ-CaO content decreases and then increases. When the stainless steel slag content is 15%, the compressive strength at 28 days is at its highest, 64.4 MPa, with the lowest ƒ-CaO content, 0.78%. The test results provide a basis for the utilization of stainless steel slag in the calcination of Portland cement clinker.
ABSTRACT
To elucidate the behavior of fluoride evaporation in an electroslag remelting process, the non-isothermal evaporation of the low-fluoride CaF2-CaO-Al2O3-MgO-TiO2-(Na2O-K2O) slag is studied using thermogravimetric analysis. The evaporation law of the melted slag is further verified using thermodynamic calculations. Fourier transformation infrared (FTIR) spectroscopy is used to evaluate the change in slag structure. It is discovered that the principal evaporating substances are CaF2, KF, and NaF, while the evaporation of MgF2, AlF3, and AlOF is less. KF evaporates absolutely in the early stage of the reaction, and CaF2 evaporates in a large proportion during the late reaction period. At 1500 °C, the order of vapor pressure is KF > CaF2. When K2O and Na2O are added to the residue sample at the same time, the evaporation ability of KF is stronger than that of CaF2 and NaF. As the K2O content increases from 0 to 8.3 wt%, evaporation increases from 0.76% to 1.21%. The evaporation rates of samples containing more K2O and those containing more Na2O are 1.48% and 1.32%, respectively. Under the same conditions, K2O has a greater effect on evaporation than Na2O. FTIR results show that the addition of K2O depolymerizes the network structure and that K2O can depolymerize the network structure better than Na2O.
ABSTRACT
The coal tends to be affected by the water vapor from quenching coke process in the pyrolysis process during the coal carbonization process and in turn causes the variation of physicochemical properties of semicoke. The preparation of semicoke based on different pyrolysis temperatures and water vapor content was carried out in order to investigate the influence of water vaper on physicochemical properties of the pyrolytic semicoke, combined with specific surface area analysis and thermal analysis to study the pore structure and combustion properties of semicoke. The morphology of the semicoke and the alteration rule of carbon-containing functional groups were analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy. The result indicates that adding an appropriate amount of water vapor (40%) instead of excess (60%) in the pyrolysis process (800 °C) is beneficial to the increase of the proportion of fixed carbon and the removal of volatile and ash. The specific surface area and the combustion performance of the semicoke is significantly improved when the appropriate amount of water vapor was added. The water vapor content has a slight effect on surface functional groups when the temperature ranges from 500 to 700 °C, whereas the higher water vapor content inhibits the improvement of physicochemical properties of the semicoke when the pyrolysis temperature is higher (800 °C). Therefore, the entry of excess water vapor (60%) into the high-temperature pyrolysis section should be avoided in the process of quenching coke or it would have an adverse impact on the performance of semicoke.
ABSTRACT
The isothermal kinetics of fluoride evaporation from CaF2-CaO-Al2O3-MgO-TiO2-(Li2O) slag with varying Li2O content were investigated in the temperature range 1743-1803 K by thermogravimetric analysis. Thermodynamic calculations and viscosity measurements were applied for studying the evaporation mechanism of fluoride. The results showed that the evaporation ratio increases with increasing Li2O content and temperature. The volatile constituents from the molten slags, mainly LiF and CaF2, were detected and their concentrations calculated. The fluoride evaporation is primarily affected by the vapour pressure of LiF and CaF2, viscosity of the slags, and melt-component activities under given experimental conditions. On the other hand, mass transfer of the gas is not the rate-controlling step that affects fluoride evaporation from the slags. The activation energy for fluoride evaporation gradually decreased from 193 ± 11 to 113 ± 3 kJ mol-1 as the Li2O content in the slags increases from 0 to 5.48 wt%. These results hold great theoretical significance for developing low-fluoride slags for electroslag remelting.
