Coexistence Theory of Slag Structure and Its Application to Calculation of Oxidizing Capability of Slag Melts

The coexistence theory of slag structure and it's application to calculation of the oxidizing capabilities of slag melts is described. It is shown that the law of mass action can be widely applied to the calculation of oxidizing capabilities of slag melts in combination with the coexistence theory of slag structure.For slag melts containing basic oxides FeO and MnO, their oxidizing capabilities can be expressed by N Fe tO =N FeO +6N Fe 2O 3 , while for slag melts containing basic oxides CaO, MgO, etc., in addition to FeO and MnO, their oxidizing capabilities can be given as N Fe tO =N FeO +6N Fe 2O 3 +8N Fe 3O 4 .

ACTIVITIES OF CaO AND La_2O_3 IN LIQUID CaO-SiO_2-La_2O_3 SLAGS AND SLAG STRUCTURE

The activity of CaO and LaOin the liquid ternary slay CaO-SiO-LaOhas been de-termined by equilibrating Sn with the slag phase in a graphite crucible under l arm of CO at1600C.The experimental results ,showed that the activity of CaO and LaOchanges slowlywhile the ratio of mole fraction.x/x,is less than unit.hut varies sharply while the ra-rio increases from 1 to 1.2.In addition,by equilibrating Sn with the binary slagBO-LaOsaturated witlt solid LaOat three different temperatures,the relation betweenIgγ~0 and I/T is determined as follows:Igγ~0=-20400/T+11.37(1500-1600C)A random network model of molten silicate structure was applied to CaO-SiO-La2O.It was found that the experimentally determined activity-composition curve of CaO arequalitatively reproduced by the curves calculated with the model,but the curves of LaOareconsiderahly different from the calculated ones.It implies that the model used is over-simpli-fied and that the difference in interaction energy between the metal cations of different valenceand silicate anions should be considered.

Applicability of mass action law to sulphur distribution between slag melts and liquid iron

According to the mass action law and the coexistence theory of slagstructure, the calculating models of mass action concentration for CaO-MgO-FeO-Fe_2O_3-SiO_2,CaO-MgO-MnO-FeO-Fe_2O_3-P_2O_5-SiO_2 and CaO-MgO-MnO-FeO-Fe_2O_3-Al_2O_3-P_2O_5-SiO_2 slag melts areformulated and sulphur distribution between the slag melts and liquid iron is treated. It is foundthat CaO, MnO and FeO promote desulphurization, while MgO is detrimental to desulphurization. Inaddition, the sulphur distribution coefficients between the slag melts and liquid iron andpresented.

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.

Metallurgical properties of CaO–SiO_(2)–Al_(2)O_(3)–4.6wt%MgO–Fe_(2)O_(3)slag system pertaining to spent automotive catalyst smelting

The metallurgical properties of the CaO–SiO_(2)–Al_(2)O_(3)–4.6wt%Mg O–Fe_(2)O_(3)slag system,formed by the co-treatment process of spent automotive catalyst(SAC)and copper-bearing electroplating sludge(CBES),were studied systematically in this paper.The slag structure,melting temperature,and viscous characteristics were investigated by Fourier transform infrared(FTIR)spectroscopy,Raman spectroscopy,Fact Sage calculation,and viscosity measurements.Experimental results show that the increase of Fe_(2)O_(3)content(3.8wt%–16.6wt%),the mass ratio of CaO/SiO_(2)(m(CaO)/m(SiO_(2)),0.5–1.3),and the mass ratio of SiO_(2)/Al_(2)O_(3)(m(SiO_(2))/m(Al_(2)O_(3)),1.0–5.0)can promote the depolymerization of silicate network,and the presence of a large amount of Fe_(2)O_(3)in form of tetrahedral and octahedral units ensures the charge compensation of Al^(3+)ions and makes Al_(2)O_(3)only behave as an acid oxide.Thermodynamic calculation and viscosity measurements show that with the increase of Fe_(2)O_(3)content,m(Ca O)/m(SiO_(2)),and m(SiO_(2))/m(Al_(2)O_(3)),the depolymerization of silicate network structure and low-melting-point phase transformation first occur within the slag,leading to the decrease in melting point and viscosity of the slag,while further increase causes the formation of high-melting-point phase and a resultant re-increase in viscosity and melting point.Based on experimental analysis,the preferred slag composition with low polymerization degree,viscosity,and melting point is as follows:Fe_(2)O_(3)content of 10.2wt%–13.4wt%,m(CaO)/m(SiO_(2))of 0.7–0.9 and m(SiO_(2))/m(Al_(2)O_(3))of 3.0–4.0.This work provides a theoretical support for slag design in co-smelting process of SAC and CBES.

Applicability of law of mass action to distribution of manganese between slag melts and liquid iron

According to the law of mass action and the coexistence theory of slag structure, the distribution of manganese between MnO FeO SiO 2 and MgO MnO FeO SiO 2 slag melts as well as liquid iron was analyzed. It is shown that K ′ Mn and K MnO are only dependent on temperature and don’t change with basicities and compositions of slag melts. So the distribution of manganese between the above mentioned slag melts and molten iron obeys the law of mass action. But analysis of experimental results from other sources shows that K ′ Mn and K MnO really change with basicities of slag, which is probably arisen from not approaching equilibrium under low basicity slag melts.

A novel process for comprehensive utilization of vanadium slag

Traditional processes for treating vanadium slag generate a huge volume of solid residue and a large amount of harmful gas,which cause serious environmental problems.In this study,a new process for the comprehensive utilization of vanadium slag was proposed,wherein zeolite A and a V2O5/TiO2 system were synthesized.The structural properties of the as-synthesized zeolite A and the V2O5/TiO2system were characterized using various experimental techniques,including X-ray diffraction,X-ray fluorescence,scanning electron microscopy,and infrared spectroscopy.The results reveal that zeolite A and the V2O5/TiO2 system are successfully obtained with high purity.The results of gas adsorption measurements indicate that the prepared zeolite A exhibits high selectivity for CO2 over N2 and is a candidate material for CO2 capture from flue-gas streams.

Application of Air-cooled Blast Furnace Slag Aggregates as Replacement of Natural Aggregates in Cement-based Materials：A Study on Water Absorption Property

The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7 d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.

Leaching behavior and microstructure of phosphorus in converter slag

Converter slag is a by-product of the steelmaking process and contains a large amount of Ca,Fe,P and other elements.If the phosphorus in the converter slag can be effectively extracted,the resulting phosphorus can be used as a phosphate fertilizer.Phosphorus in converter slag is mainly enriched in 2CaO·SiO_(2)-3CaO·P_(2)O_(5)(C_(2)S-C_(3)P)solid solution and is easily dissolved in water.Therefore,acid leaching method was used to dissolve the solid solution to extract phosphorus in converter slag,so as to realize the recycling of phosphorus resources in converter slag.The leaching behavior of three actual converter slags from different steel mills in acid leaching solutions composed of citric acid,sodium hydroxide,hydrochloric acid and deionized water was studied by X-ray diffraction,scanning electron microscopy combined with energy dispersive spectrometry,Fourier transform infrared spectroscopy and Raman spectroscopy to reveal the change in object image structure as well as SiO_(4) and PO_(4) tetrahedron before and after acid leaching.The results show that only a small amount of phosphorus in converter slag with too low basicity is enriched in C_(2)S-C_(3)P solid solution,resulting in poor leaching effect.When the converter slag has a high basicity,the removal effect of phosphorus is 70.64%-81.88%.In addition,when the basicity of converter slag is roughly the same,the dephosphorization effect of slag with high FeO content is relatively poor.And acid leaching will cause depolymerization behavior of SiO_(4) and PO_(4) tetrahedron,so that the mole fraction of Q0(Si)(asymmetric stretching vibration of Si-O bond in SiO_(4) tetrahedron with bridge oxygen number of 0)and NBO/Si(non-bridging oxygen in silicate tetrahedra)will increase.Phosphate-containing solids can be obtained from the solution after acid leaching through static precipitation,and the solids have the potential to make phosphate fertilizers.

Effect of Al_(2)O_(3)/SiO_(2) mass ratio and CaO content on viscosity and structure of slag for pyrometallurgical processing of spent automotive catalysts

The effect of Al_(2)O_(3)/SiO_(2) mass ratio and CaO content on the viscosity and structure of the CaO-Al_(2)O_(3)-SiO_(2)-6MgO-1.5ZrO_(2)-1.5CeO_(2) slag was investigated.The results show that with the increase in Al_(2)O_(3)/SiO_(2) mass ratio,the viscous flow units within the slag gradually change from Si-O-Si to Al-O-Al and Al-O-Si.Furthermore,the substitution of Al_(2)O_(3) for SiO_(2) leads to the transformation of Si-O bonds towards weaker Al-O bonds,which weaken the bond strength of the aluminosilicate networks,thus leading to a decrease in the viscosity of slag.The increase in CaO content effectively promotes the depolymerization of the aluminosilicate networks,resulting in a significant decrease in the viscosity of the slag.The slag with Al_(2)O_(3)/SiO_(2) of 0.7-1.5 and CaO of 30 wt.%shows promise as the reference slag system for the Fe-collection smelting of spent automotive catalysts due to its good comprehensive performance.

Physicochemical properties and structure of titania-containing metallurgical slags: a review

The titanium industry can hardly bypass the titania-containing slags,and the slag physicochemical properties are essential in the metallurgical reactor design and process control.The TiO_(2)–FeO-based slags and TiO_(2)–SiO_(2)–CaO-based slags are the main metallurgical slag systems in the titanium resource utilization processes.To elaborate the role of TiO_(2) in the physicochemical properties of titania-containing metallurgical slags,the physicochemical properties including titanium redox ratio,liquidus temperature,viscosity,electrical conductivity,density,surface tension,thermal conductivity,and sulfide capacity were critically reviewed.Moreover,the property prediction models were briefly introduced with regards to the limitations of the existing models.The property prediction models are still required to evolve since not all properties of titania-containing slags can be well modeled.As the slag structure has an intimate relationship with slag properties,the structural details of the titania-containing slag were investigated by using a combination of spectroscopic technologies,but the knowledge of the slag structure was not fully ascertained.The potential research fields related to the physicochemical properties and structure of the titania-containing slags were also suggested.

Effect of SiO_(2) and B_(2)O_(3) on crystallization and structure of CaF2–CaO–Al_(2)O_(3)-based slag for electroslag remelting of ultra-supercritical rotor steel

Regarding development of the dedicated slag for electroslag remelting,crystallization characteristics of the slag exert a strong influence on the initial solidification of liquid metal in mold and surface quality of as-cast ingot.The crystallization behavior of CaF_(2)-CaO-Al_(2)O_(3)-based slag with varying SiO_(2)and B_(2)O_(3)contents and their correlation with the slag structure were investigated.Increasing SiO_(2)(0.24-8.95 mass%)and B_(2)O_(3)(0-3.20 mass%)contents lowers the crystallization temperature and suppresses the crystallization of the slag melts,as well as decreases the sizes of the crystalline phases.The crystalline phases precipitated during continuous cooling of the slag melts are faceted 11CaO·7Al_(2)O_(3)·CaF_(2),faceted or spherical CaF_(2),and non-faceted MgO·Al_(2)O_(3)(or MgO)in sequence irrespective of the SiO_(2)and B_(2)O_(3)contents of the slag.The polymerization degree of slag melts increases with increasing either SiO_(2)or B_(2)O_(3)contents.The crystallization of the slag melts is increasingly retarded with increasing the SiO_(2)and B_(2)O_(3)contents of the slag caused by increased component diffusion resistance originating from increased polymerization degree of the slag melts.

Effect of nickel oxide additive on smelting mechanism of chromium-bearing vanadium titanomagnetite pellets

The effect of nickel oxide additive on the smelting behaviors of chromium-bearing vanadium titanomagnetite pellets(CVTP)was investigated while analyzing the transfer behavior of nickel in iron and slag.The results show that when NiO added to CVTP increases from 0 to 6 wt.%,softening start temperature increases from 1148 to 1212℃,and the softening end temperature increases from 1280 to 1334℃;the melting start temperature increases from 1318 to 1377℃,and the dripping temperature decreases from 1558 to 1521℃.The pig iron comprises a compound of Fe-Ni-C.The slag structure depolymerizes with increasing nickel addition.The softening-melting behaviors of CVTP,the reduction of nickel into pig iron,and the depolymerization of slag structure indicate the feasibility of producing nickel-iron alloy through the blast furnace process.

Viscosity prediction on iron-bearing slags during pyrometallurgical recycling: structure-based modeling of CaO-‘FeO’-MgO-Al_(2)O_(3)-SiO_(2) system and its subsystems

A structure-based modeling of the CaO-‘FeO’-MgO-Al_(2)O_(3)-SiO_(2) system and its subsystems was investigated based on iron extraction nickel slagaluminum dross.Parameters optimization in the present model indicated that the coefficient of free O^(2-)in FeO,a_(O_(FeO)^(2-)),on the lengths of network linkage had the largest value and O_(FeO)^(2-)(free O^(2)-in FeO)had the largest mobility.The coefficients of bridging oxygen(a_(Si-O-Al) and a_(Al-O-Al))were lower than those of nonbridging oxygen and free oxygen(O^(2-)).Viscosity prediction for the CaO-‘FeO’-(8 wt.%)MgO-Al_(2)O_(3)-SiO_(2) system was conducted at a fixed slag basicity,which indicated that the predicted viscosity changed monotonously with the FeO content.However,the non-monotonous evolution with Al2O3 content reflected the amphoteric behavior of Al2O3.In addition,the performances of the present model in predicting viscosity binary(‘FeO’-SiO_(2))to quinary(CaO-‘FeO’-MgO-Al_(2)O_(3)-SiO_(2))system were analyzed and a comparison with the established models was made.

A Kinetic Study on the Control of Nitrogen in Molten Slag and Metal

Nitrogen can easily contaminate molten steel during the steelmaking process and due to the low nitrogen capacity in slag, it is difficult to remove entrapped nitrogen from liquid steel. Degassing is often done to the steel at secondary steelmaking to lower the nitrogen content, but the control can often be kinetically limited by the steel grade and also the slag composition. Thus, a fundamental understanding of nitrogen dissolution into molten slag and metal including the rate of nitrogen dissolution can help in controlling nitrogen content in the final product.The kinetics of nitrogen dissolution in the molten calcium aluminate based slags and in molten steel with various element additions was investigated by measuring the 14N-15N isotope exchange reaction using a mass spectrometer at 1873 K.Results show that effect of elements on the rate constant of nitrogen dissolution such as Ni in Fe is relatively minimal similar to molybdenum. The surface rate constant of nitrogen dissolution in liquid Fe-10%Ni alloy was found to be 3.77×10-5 (mol/cm2·s·atm).The rate constant of nitrogen dissolution in the CaO-Al2O3-CaF2 slag was found to be wedge shaped, which decreased with increasing CaF2 to about 20 mol% followed by an increase through the rest of the CaF2 composition range. This was related to the effect of CaF2 on the structure of Al-O bonds for this slag.

Effect of basicity and Al2O3 on viscosity of ferronickel smelting slag

The effect of the Al2O3 content and basicity (the molar ratio of MgO to SiO2) on the viscosity of a SiO2-MgO-FeOAl2O3-CaO slag was studied to fully understand the smelting process of the ferronickel alloy. Experimental results show that the slag is a mixture of liquid and solid phases at the experimental temperature. The viscosity decreased as the basicity increased and increased as the Al2O3 content increased. To determine the effect of the Al2O3 content and basicity on the structure of the molten slag, Raman spectroscopy was performed on the slag sample, which was quenched from the high temperature with water. The Raman spectra showed that the fractions of the polymerization structural units decreased significantly as the basicity of the slag increased, resulting in a decrease in the apparent viscosity. However, Al2O3 acts as a network former in the slag system, thereby making the slag structure further polymerized and increasing the viscosity.

Phosphorus fixation capacity of CaO-SiO_(2)-Al_(2)O_(3)-MnO-Ce_(2)O_(3) slag based on structural considerations

The phosphorus fixation capacity of some slag systems,such as Ce_(2)O_(3)-containing slag,has hardly been investigated from a thermodynamics view due to the lack of relevant thermodynamic data.Since the macroscopic properties are primarily determined by the microscopic structure,the correlation between phosphorus fixation capacity and slag structure was explored by spectroscopy(XPS),Raman spectroscopy,and ferromanganese dephosphorization experiments.The results show that the predominant species of P^(5+)are Q_(P)^(0)(PO_(4)^(3-))and Q_(P)^(1)(P_(2)O_(7)^(4-))units in the CaO^(-)SiO_(2)-Al_(2)O_(3)-MnO^(-)Ce_(2)O_(3)-P_(2)O_(5)quenched slag,and the phosphorus fixation capacity increases with the Q_(P)^(1)(P_(2)O_(7)^(4-))unit to Q_(P)^(0)(PO_(4)^(3-))unit transformation(the P-O^(0) bond to P-O^(-)bond transformation)since the electron cloud density between P and O atoms increases and the average radius of P-O bonds decreases.Especially,CaO or Ce_(2)O_(3) as a network modifier can release the O_(2)-and promote the P-O^(0) bond to P-O^(-)bond(connected to Ca^(2+),/Ce^(3+))transformation in the quenched slag.Furthermore,the phosphorus enrichment phases in the slow cooling slag are confirmed as nCa_(2)SiO_(3)-Ca_(3)P_(2)O_(8)(nC_(2)S-C3P)and CePO_(4) solid solutions by the scan electron microscopy(SEM),transmission electron microscopy(TEM),and energy-dispersive spectrometer(EDS)methods.The re sults show Ce_(2)O_(3) can depolymerize the polyphosphate structure partially replacing CaO after introducing Ce_(2)O_(3) into CaO based slag because of its strong ability to donate electrons.The above results not only help to understand the dependence of phosphorus fixation capacity on slag composition from a structural view,but also provide the theoretical guidance for optimizing the composition of Ce_(2)O_(3)-containing dephosphorization slag.

Phosphorus Removal of High Phosphorus Iron Ore by Gas-Based Reduction and Melt Separation

A new method （gas-based separation plus melt separation） has been proposed to remove phosphorus of the high phosphorus iron ore which was 1.25 % of phosphorus content and 50. 0% of iron content. HSC chemistry package and the coexistence theory of slag structure were adopted for theoretical analysis. The gas-based reduction was carried out using a fixed bed reactor and the ore sample of 80 g with an average particle size of 2 mm were reduced using CO or H2 at temperature of 1 073 K for 5 hours. 50 g of the reduced sample with 3.0% CaO as additive was then subjected to melt separation in an electric furnace at temperature of 1 873 K under Ar atmosphere. In each run, SEM, EDS, optical microscopic examination and chemical analysis of the reduced ore sample, the metal sample and the slag sample were conducted. Results of all gas-based reduction experiments showed that iron metallization ratios were some 65% and the phosphorus compounds in the ore remained unchanged. It was agreed well with the simula- tions except for the iron metallization rate being less than predicted value; this difference was attributed to kinetics. Results of melt separation experiments showed that P content in metal samples is 0.33% （metal sample from H2 reduction product） and 0.27% （metal sample from CO reduction product）. The phosphorus partition ratios of both cases were less than predicted values. Some P in the metal samples existed as slag inclusion was considered to be the reason for this discrepancy.