Behavior of phosphorus enrichment in dephosphorization slag at low temperature and low basicity

At low basicity and low temperature, the dephosphorization behavior and phosphorus distribution ratio(L_P) between slag and molten steel in the double slag and remaining slag process were studied with a 180 t basic oxygen furnace industrial experiment.The dephosphorization slags with different basicities were quantitatively analyzed.At the lower basicity range of 0.9–2.59, both L_P and dephosphorization ratio were increased as the basicity of dephosphorization slag increased.Dephosphorization slag consisted of dark gray P-rich, light gray liquid slag,and white Fe-rich phases.With increasing basicity, not only did the morphologies of different phases in the dephosphorization slag change greatly, but the area fractions and P_2O_5 content of the P-rich phase also increased.The transfer route of P during dephosphorization can be deduced as hot metal → liquid slag phase + Fe-rich phase → P-rich phase.     

Thermodynamic Behavior of Manganese and Phosphorus between Liquid Iron and CaO-MgO-SiO2-Al2O3-FetO-MnO-P2O5 Slags

The thermodynamic behavior of manganese and phosphorus between liquid iron and CaO-MgO-SiO₂-Al₂O₃-Fe_tO-MnO-P₂O₅ ladle slag system was addressed by investigating the thermodynamic equilibria between liquid iron containing Mn and P and the ladle slag at 1873 K. The Mn distribution ratio L_Mn increases with increasing Fe_tO content and decreasing the basicity ((%CaO + %MgO)/(%SiO₂ + %Al₂O₃ + %P₂O₅)) in slag, while the P distribution ratio L_p seems to be increased as Fe_tO content and the basicity increases. The values of L_Mn and L_p decrease by the addition of Al₂O₃ into slag. The expression of the dependence of L_Mn and L_p on the basicity and Fe_tO content in slag was obtained.     

Reduction of chromium oxides in stainless steel dust

The recovery of metal oxides from stainless steel dust using C (graphite), SiFe, and Al as reductants was investigated under various conditions. The apparent distribution ratio of Cr (L'_Crm/s) in the recovered metal and residual slag phases was defined as the major performance metric. The results show that the recovery ratio of metals increases as the ratio of CaO:SiO₂ by mass in the residual slag increases to 1.17. The residual content of metals in the slag decreases as the Al₂O₃ content of the slag is increased from approximately 8wt% to 10wt%. The recovery ratio of Cr increases with increasing L'_Crm/s, and a linear relationship between L'_Crm/s and the activity coefficient ratio of CrO in the slag and the recovered metal phase is observed. The combination of C and SiFe or Al as the reducing agents reveals that Si is the more effective coreductant.     

Desulfurization ability of refining slag with medium basicity

The desulfurization ability of refining slag with relative lower basicity (B) and Al₂O₃ content (B = 3.5–5.0; 20wt%–25wt% Al₂O₃) was studied. Firstly, the component activities and sulfide capacity (C_S) of the slag were calculated. Then slag-metal equilibrium experiments were carried out to measure the equilibrium sulfur distribution (L_S). Based on the laboratorial experiments, slag composition was optimized for a better desulfurization ability, which was verified by industrial trials in a steel plant. The obtained results indicated that an MgO-saturated CaO-Al₂O₃-SiO₂-MgO system with the basicity of about 3.5–5.0 and the Al₂O₃ content in the range of 20wt%–25wt% has high activity of CaO (a_CaO), with no deterioration of C_S compared with conventional desulfurization slag. The measured L_S between high-strength low-alloyed (HSLA) steel and slag with a basicity of about 3.5 and an Al₂O₃ content of about 20wt% and between HSLA steel and slag with a basicity of about 5.0 and an Al₂O₃ content of about 25wt% is 350 and 275, respectively. The new slag with a basicity of about 3.5–5.0 and an Al₂O₃ content of about 20wt% has strong desulfurization ability. In particular, the key for high-efficiency desulfurization is to keep oxygen potential in the reaction system as low as possible, which was also verified by industrial trials.     

Extraction of vanadium from high calcium vanadium slag using direct roasting and soda leaching

The extraction of vanadium from high calcium vanadium slag was attempted by direct roasting and soda leaching. The oxidation process of the vanadium slag at different temperatures was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The effects of roasting temperature, roasting time, Na₂CO₃ concentration, leaching temperature, leaching time, and liquid to solid ratio on the extraction of vanadium were studied. The results showed that olivine phases and spinel phases in the vanadium slag were completely decomposed at 500 and 800℃, respectively. Vanadium-rich phases were formed at above 850℃. The leaching rate of vanadium reached above 90% under the optimum conditions:roasting temperature of 850℃, roasting time of 60 min, Na₂CO₃ concentration of 160 g/L, leaching temperature of 95℃, leaching time of 150 min, and liquid to solid ratio of 10:1 mL/g. The main impurities were Si and P in the leach liquor.     

Effect of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization behavior of glass-ceramics produced from naturally cooled yellow phosphorus furnace slag

CaO-Al₂O₃-SiO₂ (CAS) glass-ceramics were prepared via a melting method using naturally cooled yellow phosphorus furnace slag as the main raw material. The effects of the addition of Fe₂O₃ on the crystallization behavior and properties of the prepared glass-ceramics were studied by differential thermal analysis, X-ray diffraction, and scanning electron microscopy. The crystallization activation energy was calculated using the modified Johnson-Mehl-Avrami equation. The results show that the intrinsic nucleating agent in the yellow phosphorus furnace slag could effectively promote the crystallization of CAS. The crystallization activation energy first increased and then decreased with increasing amount of added Fe₂O₃. At 4wt% of added Fe₂O₃, the crystallization activation energy reached a maximum of 676.374 kJ·mol-1. The type of the main crystalline phase did not change with the amount of added Fe₂O₃. The primary and secondary crystalline phases were identified as wollastonite (CaSiO₃) and hedenbergite (CaFe(Si₂O₆)), respectively.     

Synthesis of steel slag ceramics:chemical composition and crystalline phases of raw materials

Two types of porcelain tiles with steel slag as the main raw material (steel slag ceramics) were synthesized based on the CaO-Al₂O₃-SiO₂ and CaO-MgO-SiO₂ systems, and their bending strengths up to 53.47 MPa and 99.84 MPa, respectively, were obtained. The presence of anorthite, α-quartz, magnetite, and pyroxene crystals (augite and diopside) in the steel slag ceramics were very different from the composition of traditional ceramics. X-ray diffraction (XRD) and electron probe X-ray microanalysis (EPMA) results illustrated that the addition of steel slag reduced the temperature of extensive liquid generation and further decreased the firing temperature. The considerable contents of glass-modifying oxide liquids with rather low viscosities at high temperature in the steel slag ceramic adobes promoted element diffusion and crystallization. The results of this study demonstrated a new approach for extensive and effective recycling of steel slag.     

Effects of additives on the phase transformation,occurrence state,and the interface of the Ti component in Ti-bearing blast furnace slag

The influences of additives on the phase transformation, occurrence state, and the interface of the Ti component in Ti-bearing blast furnace slag were investigated. After oxidation, most of the Ti component in the slag was enriched into the perovskite phase, which served as the Ti-rich phase during the crystallization process. The phase transformation, occurrence state, and the interface of the Ti component were observed to be affected by the addition of different types of agents. During the oxidation process, titanaugite and Ti-rich diopside phases gradually transformed into non-Ti phases (anorthite: CaMgSi₂O₆ and CaAl₂Si₂O₈) in the form of dendrites or columns, which were observed to be distributed at the surface of the perovskite phase. Several more cracks appeared along the grain boundaries of the perovskite phase after the addition of P₂O₅, facilitating the liberation of the perovskite phase. Composite additives combining both an acid and a base, such as CaO + CaF₂ or P₂O₅ + CaF₂, were used. We observed that the disadvantages of using single additives were successfully overcome.     

Numerical modeling and experimental validation of microstructure in gray cast iron

To predict the amount of different phases in gray cast iron by a finite difference model (FDM) on the basis of cooling rate (R), the volume fractions of total γ phase, graphite, and cementite were calculated. The results of phase composition were evaluated to find a proper correlation with cooling rate. More trials were carried out to find a good correlation between the hardness and phase composition. New proposed formulas show that the hardness of gray cast iron decreases as the amount of graphite phase increases, and increases as the amount of cementite increases. These formulas are developed to correlate the phase volume fraction to hardness. The results are compared with experimental data and show reasonable agreement.     

Microstructure and properties of mullite-based porous ceramics produced from coal fly ash with added Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Using coal fly ash slurry samples supplemented with different amounts of Al₂O₃, we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach, which is a popular method suitable for industrial application. The microstructure, phase composition, and compressive strength of the sintered samples were investigated. Mullite was identified in all of the prepared materials by X-ray diffraction analysis. The microstructure and compressive strength were strongly influenced by the content of Al₂O₃. As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40, the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased. A further increase in the Al₂O₃ content resulted in a decrease in the compressive strength of the sintered samples. The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material.     

低碱度脱磷渣在转炉少渣冶炼中的作用

以SGRS工艺为基础,研究了低碱度脱磷渣在转炉少渣冶炼中的作用.根据少渣冶炼物料平衡原理,脱磷阶段结束炉渣碱度控制越低,相当于转炉回收利用的Ca O量越多,能够实现的钢液去Si量也越多.同时实验结果表明,随着脱磷渣碱度的降低,炉渣的熔化性能逐渐改善,带来脱磷阶段结束转炉倒渣量不断增加以及脱磷渣金属铁含量不断降低的有益效果.当脱磷渣碱度在1.2~1.8范围时,脱磷渣半球点温度基本控制在1 380℃以内,脱磷渣中的游离Ca O质量分数控制在0.7%左右的较低水平,同时转炉脱磷阶段结束转炉倒渣量基本可控制在8 t(210 t转炉)或5 t(100 t转炉)以上.     

合成精炼渣对钢水脱磷作用的研究

采用CaO-Al2O3-MgO-BaO-CaF2渣系,在实验室内依据冶金热力学和动力学理论进行热模拟实验,对不同量的原料配比进行了精炼渣的脱磷实验,系统的分析了初始磷含量、碱度、光学碱度、BaO、CaF2等因素对脱磷能力和脱磷反应速率的影响。研究表明,BaO部分取代CaO时,脱磷率高,碱度小于30,光学碱度小于0.9,CaF2在16%-18%,脱磷率高。     

转炉利用石灰石造渣炼钢的试验研究

基于对石灰石分解机理的分析,研究了炼钢过程中利用石灰石代替石灰进行造渣时炉内富余热量的变化,发现当采用全部石灰进行冶炼时,铁水加入比(质量分数)可达到86.1%左右,随着石灰石加入量的增加,废钢比降低,吨钢富余热量减少,石灰加入量降低.若全部采用石灰石进行造渣,铁水比最高可达到97.0%.在此基础上,利用60 t转炉研究了炼钢过程采用石灰石完全代替石灰进行造渣炼钢的冶金效果.实验发现：与采用石灰造渣炼钢相比,当采用石灰石进行造渣炼钢时,吹炼至4 min时的炉渣TFe质量分数为21.87%,碱度为1.22;随着吹炼时间增加,炉渣TFe含量降低,碱度上升至3.0以上.炼钢过程脱磷更加稳定且脱磷率提高了2.6%;平均终渣碱度为3.52,能满足冶炼的脱磷要求;渣量大幅度降低,从而降低了钢铁料消耗;吹炼时间略有延长,终点熔池温度基本保持不变.研究结果为调整炉料结构、降低生产成本提供了新的方法和思路.     

高磷铁水脱磷渣枸溶性

参照实际转炉脱磷炉渣,配制了不同F、P2O5、FeO和MgO含量及碱度的渣样,用化学分析方法测试了不同组分对渣中磷的枸溶率的影响规律.结果表明:当脱磷渣中含有F时,P主要与F形成氟磷灰石,使得磷的枸溶率随渣中F含量的升高而急剧降低,当不含氟时枸溶率可达92.5%,当氟质量分数达到0.5%时枸溶率已降低到50%以下;随碱度增加,由于渣中Ca2+含量增加,破坏了硅氧网络结构,使得枸溶率有所上升;渣中MgO含量升高,由于Mg2+在熔融冷却过程中会抑制β--Ca3(PO4)2晶体的析出,而β--Ca3(PO4)2中磷不易为质量分数为2%的柠檬酸液溶出,而使枸溶率有所升高;随渣中P2O5含量升高,由于P5+与O2-形成络离子,P5+位于O2-密集形成的间隙中,不易溶出,使得枸溶率有所下降;渣中FeOn升高,枸溶率随之降低.     

含铁尘泥高碱度内配碳球团自还原过程中脱硫和脱磷研究

在竖式碳管炉中进行含铁尘泥高碱度内配碳球团的还原试验,并通过改变温度、配碳比和碱度对含铁尘泥还原过程中的脱硫和脱磷进行研究。结果表明,高碱度内配碳球团在高温下快速还原制备金属铁粒的脱硫率高于97%,铁粒中硫含量最低达到0.007%,而脱磷率一般为25%~35%,最高达到38.52%。随着温度和配碳比的升高,铁粒的脱硫率和脱磷率均增加;而随着碱度的增加,铁粒的脱硫率和脱磷率均先增大后减小。     

高磷铁水预处理环保脱磷渣系的相图计算和实验研究

采用FactsageTM软件对以B2O3、K2O、MnO2、TiO2代替CaF2助熔的4种高磷铁水预处理脱磷渣系在1 623 K时的相图进行计算,发现相图中的多数区域都有液态渣出现.根据计算相图制定脱磷实验的配渣方案,实验过程中观察到的化渣情况与计算相图提供的信息基本一致.     

Slag formation path during dephosphorization process in a converter

The slag formation path is important for efficient dephosphorization in steelmaking processes. The phosphorus capacity and the melting properties of the slag are critical parameters for optimizing the slag formation path. Regarding these two factors, the phosphorus par-tition ratio was calculated using the regular solution model (RSM), whereas the liquidus diagrams of the slag systems were estimated using the FactSage thermodynamic package. A slag formation path that satisfies the different requirements of dephosphorization at different stages of dephosphorization in a converter was thus established through a combination of these two aspects. The composition of the initial slag was considered to be approximately 15wt%CaO–44wt%SiO2–41wt%FeO. During the dephosphorization process, a slag formation path that fol-lows a high-iron route would facilitate efficient dephosphorization. The composition of the final dephosphorization slag should be approxi-mately 53wt%CaO–25.5wt%SiO2–21.5wt%FeO. The composition of the final solid slag after dephosphorization is approximately 63.6wt%CaO–30.3wt%SiO2–6.1wt%FeO.     

不锈钢渣凝固过程中物相转变的热力学分析

采用热力学软件FactSage6.2，研究不锈钢渣凝固过程中的物相转变规律.结果表明:降低碱度和添加Al₂O₃含量均能降低硅酸二钙的析出温度，抑制硅酸二钙的产生，并促进黄长石相的生成.不锈钢渣中尖晶石相的含Cr量随着碱度的降低而增加，当碱度从1.6降到1.0时，Cr质量分数从24.93%增加到48.27%，同时凝固过程液态渣中的铬元素含量随着碱度的降低也有所减少.添加10%的Al₂O₃，有利于尖晶石相的析出，且随着温度的降低，Al³⁺逐步取代尖晶石中的Cr³⁺，尖晶石相中的Cr质量分数也由30.39%(1500℃)降低至13.88%(1300℃).     

含TiO_2熔渣与铁液之间钛的行为

探讨了含TiO_2熔渣与铁液之间钛的行为,结果表明在试验条件下,钛从熔渣向铁液内迁移时受钛离子在渣中扩散的控制,整个迁移过程的表观级数为准零级,表观活化能为62kcal/mol,讨论了渣中TiO_2含量,碱度,温度等因素对钛迁移量和迁移速度的影响,发现炉渣碱度对钛迁移影响具有两重性:若渣中TiO_2含量较高时(TiO_2>25％),提高碱度将减少钛的迁移量和迁移速度;反之,若渣中TiO_2含量较低时(TiO_2<25％),提高碱度却增加钛的迁移量和迁移速度。     

调质高炉渣纤维化过程析晶行为的热力学研究

以Ca O-Mg O-Si O_2-Al_2O_3四元渣系为研究对象,利用Factsage 6.4热力学软件,研究冷却过程中黄长石等高熔点矿相的析出热力学现象,解析碱度、Mg O和Al_2O_3含量等因素对不同组分调质高炉渣中晶相析出的影响规律。结果表明:随着碱度的增加,析晶温度逐渐升高,液相量逐渐减少,黄长石的析出量先增加后减少,当碱度为1.2时黄长石的析出量达到最大;随着Mg O含量的增加,析晶温度逐渐升高,1 275~1 420℃黄长石的析出量逐渐增加,液相量逐渐减少,1 240~1 275℃黄长石的析出量逐渐减少,液相量逐渐增加;随着Al_2O_3含量的增加析晶温度逐渐增加。