Dissolution behavior of Al_(2)O_(3)inclusions into CaO-MgO-SiO_(2)-Al_(2)O_(3)-TiO_(2)system ladle slags

To investigate the dissolution behaviors of Al_(2)O_(3)inclusions in CaO-5wt%MgO-SiO_(2)-30wt%Al_(2)O_(3)-TiO_(2)system ladle slags,confocal scanning laser microscopy was conducted on the slags with different TiO_(2)contents(0-10wt%),and scanning electron microscopy was performed to study the interfacial reaction between Al_(2)O_(3)and this slag system.The results disclose that the dissolution of Al_(2)O_(3)inclusions does not result in the formation of new phases at the boundary between the slag and the inclusions.In TiO_(2)-bearing and TiO_(2)-free ladle slags,there is no difference in the dissolution mechanism of Al_(2)O_(3)inclusions at steelmaking temperatures.Boundary layer diffusion is found as the controlling step of the dissolution of Al_(2)O_(3),and the diffusion coefficient is in the range of 4.18×10^(-10)to 2.18×10^(-9)m^(2)/s at 1450-1500℃.Compared with the solubility of Al_(2)O_(3)in the slags,slag viscosity and temperature play a more profound role in the dissolution of Al_(2)O_(3)inclusions.A lower viscosity and a lower melting point of the slags are beneficial for the dissolution.Suitable addition of TiO_(2)(e.g.,5wt%)in ladle slags can enhance the dissolution of Al_(2)O_(3)inclusions because of the low viscosity and melting point of the slags,while excessive addition of TiO_(2)(e.g.,10wt%)shows the opposite trend.

Exploring influence of MgO/CaO on crystallization characteristics to understand fluidity of synthetic coal slags

The crystallization has significant influence on fluidity of slag and slag discharge of entrained-flow-bed(EFB) gasifier. The crystallization characteristics and fluidity of five synthetic slags with different MgO/CaO ratios prepared on the basis of the range of oxide contents of Zhundong coal ash were investigated in this study. The results show that with the MgO/CaO ratio increase, the initial crystallization temperature increases, and the main temperature range of crystallization ratio growth moves to higher temperature range gradually which causes Tp25(Tp25is the temperature corresponding to the viscosity of 25 Pa·s)to increase. Mg-rich crystals are formed preferentially than Ca-rich crystals when adding the same amount of MgO and CaO during cooling. The effective slagging operating temperature range decrease from 217 ℃ for the slag with a 0:4 MgO/CaO ratio to 44 ℃ for the slag with a 4:0 MgO/CaO ratio with the MgO/CaO ratio increase. The slags with 2:2 and 1:3 MgO/CaO ratios show similar effective slagging operating temperature range, Tp25and the temperature corresponding to the viscosity of 2 Pa·s.However, compared with the slag with a 1:3 MgO/CaO ratio, the crystallization ratio and rate of slag with a 2:2 MgO/CaO ratio are lower within lower temperature range(1300–1200 ℃), causing its lower critical viscosity temperature and wider actual operating temperature range. Of the five slags, the widest effective slagging operating temperature range and the lowest Tp25of the slag with a 0:4 MgO/CaO ratio due to its low crystallization ratio, and wider actual operating temperature range of the slag with a 2:2 MgO/CaO ratio make the two slags suitable for slag discharge of EFB gasifier.

In situ observation of the dissolution kinetics of Al_(2)O_(3) particles in CaO–Al_(2)O_(3)–SiO_(2) slags using laser confocal scanning microscopy

The dissolution kinetics of Al_(2)O_(3) in CaO-Al_(2)O_(3) SiOslags was studied using a high-temperature confocal scanning laser microscope at 1773 to 1873 K.The results show that the controlling step during the Al_(2)O_(3) dissolution was the diffusionin molten slag.It was found that the dissolution curves of Al_(2)O_(3) particles were hardly agreed with the traditional boundary layer diffusion model with the increase of the CaO/Al_(2)O_(3) ratio of slag.A modified diffusion equation considering slag viscosity was developed to study the dissolution mechanism of Al_(2)O_(3) in slag.Diffusion coefficients of Al_(2)O_(3) in slag were calculated as 2.8×10to 4.1×10m~2/s at the temperature of 1773-1873 K.The dissolution rate of Al_(2)O_(3) increased with higher temperature,CaO/Al_(2)O_(3),and particle size.A new model was shown to be v_(Al_(2)O_(3))=0.16×r_(0)^(1.58)×x^(3.52)×(T-T_(mp))^(1.11)to predict the dissolution rate and the total dissolution time of Al_(2)O_(3) inclusions with various sizes,where vAl_(2)O_(3) is the dissolution rate of Al_(2)O_(3) in volume,μm^(3)/s;x is the value of CaO/Al_(2)O_(3) mass ratio;R_(0) is the initial radius of Al_(2)O_(3),μm;T is the temperature,K;T_(mp) is the melting point of slag,K.

Influence of alumina on mineralogy and environmental properties of zinc-copper smelting slags

An iron-silicate slag, from a zinc-copper smelting process, and mixtures of this slag with 5wt%, 10wt%, and 15wt% alumina addition were re-melted, semi-rapidly solidified, and characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, and X-ray diffraction. The FactSageWM6.2 thermodynamic package was applied to compare the stable phases at equilibrium conditions with experimental characterization. A standard European leaching test was also carried out for all samples to investigate the changes in leaching behaviour because of the addition of alumina. Results show that the commonly reported phases for slags from copper and zinc production processes （olivine, pyroxene, and spinel） are the major constituents of the current samples. A correlation can be seen between mineralogical characteristics and leaching behaviours. The sample with 10wt% alumina addition, which contains high amounts of spinels and lower amounts of the other soluble phases, shows the lowest leachabilities for most of the elements.

Phosphate enrichment mechanism in CaO–SiO_2–FeO–Fe_2O_3–P_2O_5 steelmaking slags with lower binary basicity

The addition of silica to steelmaking slags to decrease the binary basicity can promote phosphate enrichment in quenched slag samples. In this study, we experimentally investigated phosphate enrichment behavior in CaO-SiO2-FeO-Fe203-P205 slags with a P205 content of 5.00% and the binary basicity B ranging from 1.0 to 2.0, where the （%Fe/O）/（%CaO） mass percentage ratio was maintained at 0.955. The experimental results are explained by the defined enrichment degree c, of solid solution 2CaO·SiO2-3CaO·P205 （C2S-C3P）, where R_C2S-C3P is a component of the developed ion and molecule coexistence theory （IMCT）-Ni model for calculating the mass action concentrations Ni of structural units in the slags on the basis of the IMCT. The asymmetrically inverse V-shaped relation be- tween phosphate enrichment and binary basicity B was observed to be correlated in the slags under applied two-stage cooling conditions. The maximum content of PROs in the C2S-C3P solid solution reached approximately 30.0% when the binary basicity B was controlled at 1.3.

Activities of FeO in CaO-SiO2-Al2O3-MgO-FeO slags

Activities of FeO in CaO-SiO2-Al2O3-MgO-FeO slags were determined at 1673 K by electrochemical of the solid electrolyte cell： Mo [Mo＋MoOu[ZrO2（MgO）[Fe＋（CaO-SiO2-Al2O3-MgO-FeO）＋Ag[Fe. The influences of slag compositions and basicity on FeO activities were analyzed. The results reveal that, for slags of fixed （%CaO）/（%SiO2） ratio, MgO and Al2O3 content, there was an increase of FeO activities with increase of FeO content. For slags with constant {（%CaO）＋ （%MgO）}/（%SiO2） ratio, fixed FeO and A1203 content, FeO activities decreased when MgO content increased from 5% to 10%, and increased with the increase of MgO content when it was over 10%. The FeO activities increased when （%CaO）/（%SiO2） ratio changed from 1.03 to 1.30 in the slags of constant MgO, FeO and Al2O3 content.

Study on sulphide capacity of CaO-SiO_2-Al_2O_3-MgO-Fe_tO slags

The sulphide capacity of CaO-SiO2-Al2O3-MgO-FetO slags was studied at 1773 K using gas-slag equilibrium techniques. Utilizing a Pt crucible, the slag was equilibrated with a mixture of gases, namely, CO, CO2, SO2 and N2 to provide the partial pressure of oxygen and sulphur. It was shown that at fixed FetO and Al2O3 contents and a fixed { （%CaO）＋（%MgO）}/（%SIO2） ratio, the sulphide capacity decreases with increasing MgO content. At a constant （%CaO）/（%SiO2） ratio and constant MgO and Al2O3 contents, increasing the FetO content of the slags also results in an increase of the sulphide capacity. The rising basicity of （%CaO）/（%SiO2） from 1.0 to 1.4 at fixed MgO, FetO and Al2O3 contents significantly increases the sulphide capacity.

Foaminess of Refining Slags System

The experiments on the foaminess of the CaO-MgO-Al2O3 -SiO2 -CaF2 refining slag system have been carried out. The obtained results are as followst (1) relative foaming height linearly increases with the increasing of the flowrate of blowing gas; (2) the proper content of MgO is about 11% when slag basicity B<2.5 and it should lower when slag basicity will be higher; (3) the better content of Al2O3, (MgO)+(Al2O3 ) is 15% and 20 % ～ 26 % respectively at the range of lower basicities; (4) the effect of slag basicity on the foaminess is complex and its optimizing vaiue is 1.9 at the specific contents of MgO, Al2O3 and CaF2.

Kinetics of Reduction of Iron Oxide in CaO-SiO_2-Al_2O_3-Fe_tO Slags with Graphite Powder

The reduction rate of Fe^tO in CaOSiO_2Al_2O_3Fe_tO slags with graphite powder has been determined in an alumina crucible at 1 673-1 823 K. The effects of temperature, slag basicity and Fe_tO content on the reduction rate have also been discussed. Test results show that the reduction rate increases with the increase of temperature or Fe_tO concentration in slags, and the reduction rate has a parabolic relation with slag simple basicity or optical basicity. The maximum reduction rate is observed around CaO/SiO_2=1.5 of molten slags. The reaction order is 1.26 or 1.31, and the reduction activation energy is 126.8 or 129.7 kJ/mol respectively in regard to Fe_tO content or Fe_tO activity calculated by using regular solution model. The reduction rate of Fe_tO in CaOSiO_2Al_2O_3Fe_tO slags with graphite powder is in the range of 0.15×10^-4-0.86×10^-4 molO/cm^2·s.

KINETICS OF REDUCTION IRON OXIDE IN CaO-SiO_2-Al_2O_3-Fe_tO SLAGS WITH CARBON SATURATED IN MOLTEN IRON

The rate of reducing Fet O in CaO-SiO2-Al2O3-Fet O slags with carbon saturated in molten iron has been determined in a graphite crucible in the temperature range of 1673-1773K. The effects of temperature, slag basicity and FetO content on the reduction rate have also been discussed. Test results show that the reduction rate increases with increasing temperature or FEtO concentration in slags, and the reduction rate has a parabolic relation with the simple basicity or optical basicity of slag, the maximum reduction rate being observed at around CaO/SiO2=1.5 of molten slags. The reduction reaction order is 1. 73 or 1.80, and the reduction activation energy is 299.9 or 295.9 kJ/mol in regard to Fet O weight content or Fet O activity calculated by using regular solution model, respectively. The reduction rate of CaO-SiO2-Al2 O3-Fet O slags with carbon saturated in molten iron is in the range of 0.32-3.48 mol-O/cm2·s.

Design and experiment on concentration of phosphorus in factory converter slags

The phosphorus-concentrating phase in the converter slags was designed and simulated by synthetic converter slag.The distribution of phosphorus in factory converter slags was also analyzed by scanning electron microscope(SEM) and X-ray diffraction(XRD).Then factory converter slags were modified by addition of SiO_2 and heated to 1540℃and then cooled to room temperature.The results showed that the phosphorus in the factory converter slags was mostly distributed in two phases:dicalcium silicate (C_2S) and tricalcium silicate(C_3S) by formation of solid solution,and with a little in matrix.Whereas,in the synthetic slags with the basicity close to 3,phosphorus was almost concentrated in phase of C_2S(Pconcentrating phase) in which the contents of P_2O_5 reach to 7.74%.This lays a good foundation for grinding and separation of P- concentrating phase.

Recycling of ironmaking and steelmaking slags in Japan and China

The mass production of steel is inevitably accompanied by large quantities of slags.The treatment of ironmaking and steelmaking slags is a great challenge in the sustainable development of the steel industry.Japan and China are two major steel producing countries that have placed a large emphasis on developing new technologies to decrease slag emission or promote slag valorization.Slags are almost completely reused or recycled in Japan.However,due to stagnant infrastructural investments,future applications of slags in conventional sectors are expected to be difficult.Exploring new functions or applications of slags has become a research priority in Japan.For example,the utilization of steelmaking slags in offshore seabeds to create marine forests is under development.China is the top steel producer in the world.The utilization ratios of ironmaking and steelmaking slags have risen steadily in recent years,driven largely by technological advances.For example,hot stage processing of slags for materials as well as heat recovery techniques has been widely applied in steel plants with good results.However,increasing the utilization ratio of basic oxygen furnace slags remains a major challenge.Technological innovations in slag recycling are crucial for the steel industries in Japan and China.Here,the current status and developing trends of utilization technologies of slags in both countries are reviewed.

Electroreduction Kinetics for Molten Oxide Slags

The oxygen-ion conductor, the reducing agent, and the molten oxide slag containing electroactive matter were used as constituent of a galvanic cell. Metal was directly electroreduced from molten slag using a short-circuit galvanic cell. The following galvanic cell was assembled in the present experiment： graphite rod, [-O]Fe-C saturated ｜ZrO2 （MgO） ｜ Cu（1） ＋ （FeO）（slag） , and molybdenum wire. The FeO electroreduction reaction was studied through measuring short circuit current by controlling factors such as temperature, the FeO content in molten slags, and the external circuit resistance. An overall kinetics model was developed to describe the process of FeO electroreductiono It was found that the modeled curves were in good agreement with the experimental values. The new oxide reduction method in the metallurgy with controlled oxygen flow was proposed and the metallurgical theory with controlled oxygen flow was developed.

Effect of the CaO/SiO2 mass ratio and FeO content on the viscosity of CaO–SiO2–“FeO”–12wt%ZnO–3wt%Al2O3 slags

An effective process for recycling lead from hazardous waste cathode ray tubes（CRTs） funnel glass through traditional lead smelting has been presented previously. The viscous behavior of the molten high lead slag, which is affected by the addition of funnel glass, plays a critical role in determining the production efficiency. Therefore, the viscosities of the CaO–SiO_2–＂FeO＂–12wt%ZnO–3wt%Al_2O_3 slags were measured in the current study using the rotating spindle method. The slag viscosity decreases as the CaO/SiO_2 mass ratio is increased from 0.8 to 1.2 and also as the FeO content is increased from 8wt% to 20wt%. The breaking temperature of the slag is lowered substantially by the addition of FeO, whereas the influence of the CaO/SiO_2 mass ratio on the breaking temperature is complex. The structural analysis of quenched slags using Fourier transform infrared（FTIR） spectroscopy and Raman spectroscopy reveals that the silicate network structure is depolymerized with increasing CaO/SiO_2 mass ratio or increasing FeO content. The [FeO_6]-octahedra in the slag melt increase as the CaO/SiO_2 mass ratio or the FeO content increases. This increase can further decrease the degree of polymerization（DOP） of the slag. Furthermore, the activation energy for viscous flow decreases both with increasing CaO/SiO_2 mass ratio and increasing FeO content.

Corrosion mechanism of magnesia-chromite refractories by ZnO-containing fayalite slags: Effect of funnel glass addition

An efficient approach for lead extraction from waste funnel glass through the lead smelting process has been proposed. To clarify the effect of funnel glass addition on the degradation of magnesia-chromite refractories by ZnO-containing fayalite slag, the corrosion behavior of magnesia-chromite refractories in lead smelting slags with different funnel glass additions from 0wt% to 40wt% was tested. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) was used to acquire the microstructural information of the worn refractory samples. Experimental results showed that the corrosion of magnesia-chromite refractory consisted predominantly of the dissolution of MgO into slag. ZnO and FeO reacted with periclase and chromite to form (Zn,Fe,Mg)O solid solution and (Zn,Fe,Mg)(Fe,Al,Cr)2O4 spinel, respectively. With the addition of funnel glass, the solubility of MgO increased whereas ZnO levels remained stable, thereby resulting in a reduced Mg content and an elevated Zn and Fe content in the (Zn,Fe,Mg)O solid solution and the (Zn,Fe,Mg)(Fe,Al,Cr)2O4 spinel. Considering the stability of the (Zn,Fe,Mg)O solid solution layer and the penetration depth of the slag, the optimal funnel glass addition for lead smelting was found to be 20wt%.

Effect of Al_(2)O_(3) content on the viscosity and structure of CaO-SiO_(2)-Cr_(2)O_(3)-Al_(2)O_(3) slags

The effect of Al_(2)O_(3) content on the viscosity and structure of CaO-SiO_(2)-Cr_(2)O_(3)Al_(2)O_(3) slags was investigated to facilitate recycling of Cr in steelmaking slags.The slags exhibit good Newtonian behavior at high temperature.The viscosity of acidic slag first increases from 0.825 to 1.141 Pa·s as the Al_(2)O_(3) content increases from 0 to 10wt%and then decreases to 1.071 Pa·s as the Al_(2)O_(3) content increases further to 15wt%.The viscosity of basic slag first increases from 0.084 to 0.158 Pa·s as the Al_(2)O_(3) content increases from 0 to 15wt%and then decreases to 0.135 Pa·s as the Al_(2)O_(3) content increases further to 20wt%.Furthermore,Cr_(2)O_(3)containing slag requires less Al_(2)O_(3) to reach the maximum viscosity than Cr_(2)O_(3)free slag;the Al_(2)O_(3) contents at which the behavior changes are 10wt%and 15wt%for acidic and basic slags,respectively.The ac-tivation energy of the slags is consistent with the viscosity results.Raman spectra demonstrate that[AlO_(4)]tetrahedra appear initially and were replaced by[AlO_(6)]octahedra with further addition of Al_(2)O_(3).The dissolved organic phosphorus content of the slag first increases and then de-creases with increasing Al_(2)O_(3) content,which is consistent with the viscosity and Raman results.

Effect of Al2O3 on the viscosity of CaO-SiO2-Al2O3-MgO-Cr2O3 slags

We investigated the effect of Al2O3 content on the viscosity of CaO-SiO2-Al2O3-8wt%MgO-1wt%Cr2O3(mass ratio of CaO/SiO2 is 1.0,and Al2O3 content is 17wt%-29wt%)slags.The results show that the viscosity of the slag increases gradually with increases in the Al2O3 content in the range of 17wt%to 29wt%due to the role of Al2O3 as a network former in the polymerization of the aluminosilicate structure of the slag.With increases in the Al2O3 content from 17wt%to 29wt%,the apparent activation energy of the slags also increases from 180.85 to 210.23 kJ/mol,which is consistent with the variation in the critical temperature.The Fourier-transform infrared spectra indicate that the degree of polymerization of this slag is increased by the addition of Al2O3.The application of Iida’s model for predicting the slag viscosity in the presence of Cr2O3 indicates that the calculated viscosity values fit well with the measured values when both the temperature and Al2O3 content are at relatively low levels,i.e.,the temperature range of 1673 to 1803 K and the Al2O3 content range of 17wt%-29wt%in CaO-SiO2-Al2O3-8wt%MgO-1wt%Cr2O3 slag.

Dissolution of Al_2TiO_5 inclusions in CaO-SiO_2-Al_2O_3 slags at 1823 K

Al-Ti-O inclusions always clog submerged nozzles in Ti-bearing Al-killed steel.A typical synthesized Al2TiO5 inclusion was immersed in a CaO-SiO2-Al2O3 molten slag for different durations at 1823 K.The Al2TiO5 dissolution paths and mechanism were revealed by scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS）.Decreased amounts of Ti and Al and increased amounts of Si and Ca at the dissolution boundary prove that inclusion dissolution and slag penetration simultaneously occur.SiO2 diffuses or penetrates the inclusion more quickly than CaO,as indicated by the w（CaO）/w（SiO2） value in the reaction region.A liquid product （containing 0.7-1.2 w（CaO）/w（SiO2）,15wt%-20wt% Al2O3,and 5wt%-15wt% TiO2） forms on the inclusion surface when Al2TiO5 is dissolved in the slag.Al2TiO5 initially dissolves faster than the diffusion rate of the liquid product toward the bulk slag.With increasing reaction time,the boundary reaches its largest distance,the Al2TiO5 dissolution rate equals the liquid product diffusion rate,and the dissolution process remains stable until the inclusion is completely dissolved.