Dephosphorization Behavior Research Articles

Behavior of Carbothermal Dephosphorization of Phosphorus-Containing Converter Slag and Its Resource Utilization

Phosphorus-containing converter slag is a common waste in the iron and steel industry, and has the characteristics of high generation and low secondary-utilization values; however, the high-phosphorus content in converter slag limits its ability to be recycled during the steelmaking process. In this study, the dephosphorization behavior of converter slag by carbothermal reduction was studied through experiments and thermodynamic calculations. The results showed that the gas product of the converter slag produced by carbothermal reduction was mainly P2, and that part of P2 entered the iron phase to generate iron phosphate compounds. With the increase in Fe content, the amount of P2 also increased, which may provide a suitable new direction for the production of ferrophosphorus. Based on the carbothermal reduction theory, a new “circulating steelmaking process of converter steel slag gasification” was proposed and applied to Chengde Iron and Steel Group Co., Ltd. (Chengde, China). The industrial production practice showed that the process did not affect the dephosphorization effect of the next furnace, and that the average iron, steel, and slagging-material consumption per furnace was reduced by 4.74 kg and 608 kg, respectively. CO2 emissions were reduced by 4.86 kg, thus achieving the goals of energy saving, environmental protection, and efficient dephosphorization.

Influence of CaO-SiO2-FetO Slag with Low Basicity on Dephosphorization Behavior

Influence of CaO-SiO2-FetO Slag with Low Basicity on Dephosphorization Behavior

Dephosphorization behavior of reduced iron and the properties of high-P-containing slag

Abstract Reduced iron (1.74% P) is produced from oolitic hematite ore by coal-based reduction and magnetic separation. To realize the comprehensive utilization of Fe and P, the dephosphorization behavior of the reduced iron is investigated in the presence of CaO–SiO2–FeO–Al2O3 slag. The P content of the final iron and the P2O5 content of the high-P-containing slag are determined, and the phase composition and P2O5 solubility of the slag are analyzed. The P content can be decreased to 0.2% when the initial slag has a basicity of 3.5 and contains 55% FeO and 6% Al2O3. The phases of the high-P-containing slag are mainly Ca2Al2SiO7, Ca2SiO4, Ca5(PO4)2SiO4, and FeO, and P exists in the form of Ca5(PO4)2SiO4. Excessively high basicity or low content of FeO and Al2O3 results in free CaO, which affects the dephosphorization results. The change rule of the intensity of the Ca5(PO4)2SiO4 diffraction peak agrees well with the dephosphorization indexes, which further verify the accuracy of the dephosphorization experiments. Moreover, the P2O5 content and P2O5 solubility of the high-P-containing slag reached as high as 14.41 and 94.54%, respectively, indicating that it can be used as a phosphate fertilizer.

Mechanism of Phosphorus Enrichment in Dephosphorization Slag Produced Using the Technology of Integrating Dephosphorization and Decarburization

In order to better understand and develop the technology of integrating dephosphorization and decarburization in a single converter (abbreviated as IDDSC), the relevant thermodynamic issues were discussed by calculation. Based on the thermodynamic calculation, the bridges between the phosphorus distribution ratio, temperature, and slag composition were constructed. Besides, the connections between the dephosphorization behavior and the microstructure of slag were also established by investigating four heats of hot metal smelt using IDDSC technology. As a result, the mechanism of phosphorus enrichment in the dephosphorization slag was revealed. Also, the results show that the dephosphorization efficiency increases gradually with increasing slag basicity. While the dephosphorization efficiency increases first and then decreases with the increase of FeO content in slag. There is a competition relationship between P2O5 and FeO in reacting with CaO and SiO2. When CaO/FeO is relatively high, not enough FeO is provided. Thus P2O5 is in priority to react with CaO and SiO2 through [3n + 2](CaO) + 2SiO2 + n(P2O5) = n(3CaO·P2O5)-2CaO·SiO2(s), generating P2O5-rich nC2S-C3P solid solution which promotes the removal of [P] from the hot metal. When CaO/FeO is relatively low, FeO competes over P2O5 in reacting with CaO and SiO2 through a(CaO) + b(SiO2) + c(FeO) = aCaO·bSiO2·cFeO(s), generating CaFeSiO4 instead of P2O5-rich solid solution. As a consequence, the slag with low CaO/FeO shows a poor dephosphorization ability.

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 (LP) 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 LP 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 P2O5 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.

Effect of 2CaO·SiO2 particles addition on dephosphorization behavior

AbstractThe effect of the addition of 2CaO·SiO2 solid particles on dephosphorization behavior in carbon-saturated hot metal was investigated. The research results showed that the addition of 2CaO·SiO2 particles have little influence on desilication and demanganization, and the removal of [Si] and [Mn] occurred in the first 5 min with different conditions where the contents of 2CaO·SiO2 particles addition for the conditions 1, 2, 3, 4, and 5 are 0, 2.2, 6.4, 8.6, and 13.0 g, respectively. The final dephosphorization ratios for the conditions 1, 2, 3, 4, and 5 are 61.2%, 66.9%, 79.6%, 63.0%, and 78.1%, respectively. The dephosphorization ratio decreases with the increase of 2CaO·SiO2 particles in the first 3 min. The reason for this is that the dephosphorization process between hot metal and slag containing C2S phase consisted of two stages: Stage 1, [P] transfers from hot metal to liquid slag and Stage 2, the dephosphorization production (3CaO·P2O5) in liquid slag reacts with 2CaO·SiO2 to form C2S–C3P solid solution. The increase of 2CaO·SiO2 particles increases the viscosity of slag and weakens the dephosphorization ability of the stage 1. The SEM and XRD analyses show that the phase of dephosphorization slag with the addition of different 2CaO·SiO2 particles is composed of white RO phase, complex liquid silicate phase, and black solid phase (C2S or C2S–C3P). Because the contents of C2S–C3P and 2CaO·SiO2 in slag and the dephosphorization ability of the two stages are different, the dephosphorization ability with different conditions is different.

Effects of Interfacial Oxygen Potential and Slag Phase Changing during Slag Formation Process on Dephosphorization Behavior

Effects of Interfacial Oxygen Potential and Slag Phase Changing during Slag Formation Process on Dephosphorization Behavior

Dephosphorization Behavior of High-Phosphorus Oolitic Hematite-Solid Waste Containing Carbon Briquettes during the Process of Direct Reduction-Magnetic Separation

In this paper, the process of direct reduction roasting using magnetic separation to produce direct reduction iron (DRI) from high-phosphorus oolitic hematite, using coal slime and blast furnace dust as reductant, is investigated. The possible use of slime coal and blast furnace dust as reductant and the dephosphorization behavior during the process of direct reduction was studied. Experimental results showed that both blast furnace dust and coal slime can be used as reductant under certain conditions in the process. The dephosphorization mechanism of blast furnace dust and coal slime were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM)-energy dispersive X-ray spectroscopy (EDS). A DRI with 91.88 wt. % iron grade, 88.38% iron recovery and 0.072 wt. % P can be obtained with 30 wt. % blast furnace dust as reductant. The program not only used blast furnace dust but also recovered iron from blast furnace dust and high-phosphorus oolitic hematite. The analysis results revealed that phosphorus is distributed in gangue mineral and fluorapatite when blast furnace dust is used as reductant. Phosphorus-bearing minerals were not reduced to phosphorus element when the blast furnace dust was the reductant, but part of the fluorapatite reduced to phosphorus which smelt into metallic iron with coal slime as reductant. This led to a high phosphorus content of DRI. This research could provide support to the idea concept for recycling of carbon-containing solid waste and to assist the effective recovery of refractory iron ore by direct reduction–magnetic separation.

Effect of Adding Mode of Iron Oxide on Dephosphorization Behavior with the Recycling of Decarburization Slag

The recycling of decarburization slag can considerably decrease the slag generation. However, the effect of recycling of decarburization slag, especially the adding mode of iron oxide on dephosphorization process has not been given more consideration. In this research, the effect of adding mode of iron oxide on dephosphorization behavior with the recycling of decarburization slag has been studied. The results indicate that the main phase of dephosphorization slag at different times under two adding modes is composed of FeO, 2CaO · SiO2, 2CaO · SiO2–3CaO · P2O5, Ca3Mg(SiO4)2, and Ca3Fe2O5. But, the content of each phase, especially FeO, 2CaO · SiO2, 2CaO · SiO2–3CaO · P2O5, varies greatly, and the dephosphorization behaviors are significantly different. In the case of initial lump‐sum addition of iron oxide (Pattern A), the dephosphorization is mainly completed in the first 5 min. On the other hand, the dephosphorization is mainly completed from 5 to 10 min in the case of divided addition of iron oxide (Pattern B). The reason for this is the interfacial oxygen potential under the Pattern A is as high as about 1.64 × 10−11 atm, which is about two times higher than that of the Pattern B. And the slag formation path is significantly different between the two adding modes.

The Effect of Sulfur Concentration in the Metal on the Mass Transfer of Phosphorus in Bloated Metal Droplets

In Basic Oxygen Steelmaking, metal droplets created by the impact of the oxygen jet will swell due to internal decarburization when they react with oxidizing slag in the emulsion zone. In this study, the dephosphorization behavior of bloated metal droplets containing different sulfur concentrations is investigated in the temperature range from 1813 to 1913 K using X‐ray fluoroscopy coupled with constant volume pressure change measurements and chemical analysis of quenched samples. The results show that higher sulfur droplets (>0.017 wt%) have a much longer incubation period for swelling than those with lower sulfur (<0.017 wt%). Due to this different swelling behavior, the dephosphorization rate for high sulfur droplets is found to be not heavily affected by the experimental temperature compared to the case of lower sulfur droplets. Employing a mixed control model including mass transfer and chemical reaction, the effect of temperature on dephosphorization kinetics is further discussed. The mass transfer coefficient in the metal, km, is found to increase slightly with increasing temperature for droplets with 0.021 wt% sulfur. It is also found that lower rates of CO formation result in less stirring in the droplet and lower mass transfer rates of phosphorus for high sulfur droplets.

The Influence of Sulfur on Dephosphorization Kinetics Between Bloated Metal Droplets and Slag Containing FeO

The bloating behavior of metal droplets and the dephosphorization behavior of bloated droplets at 1853 K (1580 °C) were investigated using X-ray fluoroscopy coupled with constant volume pressure change measurements and chemical analysis of quenched samples. The effect of sulfur content on dephosphorization kinetics was studied during the decarburization period. The slag foamed during the reaction forming a foamy layer over a dense layer. After a short incubation period, the droplets became bloated due to internal decarburization. The bloated droplets floated from the dense slag into the foamy slag. The behavioral changes are directly related to the effect of sulfur on the incubation time for swelling. The dephosphorization reaction was very fast; droplets with low sulfur contents experienced phosphorus reversion shortly after entering the foamy slag, while those with higher sulfur content took a longer time to swell and went through reversion before they entered the foam. The dephosphorization rate and maximum phosphorus partition were higher at lower CO evolution rates because the dynamic interfacial oxygen potential increased with the decreasing oxygen consumption rate. The rate controlling step for dephosphorization was initially a combination of mass transport in both the metal and the slag. As the iron oxide in the slag was depleted, the rate control shifted to mass transport in slag.

鲕状赤铁矿高温快速还原试验研究

采用内配碳球团高温快速还原-磁选工艺处理国内某高磷鲕状赤铁矿，系统研究了C/Fe比、还原温度、还原时间、二元碱度、添加剂配比对还原过程中金属化率、脱磷及磁选等指标的影响，并对其提铁脱磷行为进行探讨。研究表明，在适宜的条件下还原-磁选，可获得铁品位94.06%、铁回收率91.37%的铁精矿，总脱磷率由自然碱度、无添加剂条件下的35.49%提高到91.79%，铁精矿的磷含量由2.03%降低到0.25%。部分磷被还原成气态挥发，大部分磷被还原后与金属铁结合，磁选难以脱除；提高碱度，形成高熔点物质可抑制一部分磷与铁反应，加入钠盐添加剂可提高精矿铁品位并抑制磷灰石的还原。 Based on the characteristics of high phosphorus oolitic hematite, the studies were done by short time reduction at high temperature and magnetic separation for carbon-bearing pellets. The effects of C/Fe ratio, reduction temperature, reduction time, binary basicity, and additives on the concentrate indexes on metallization ratio and dephosphorization behavior were studied. The results show that the iron concentrate, assaying 94.06% Fe and 0.25% P with iron recovery of 91.37% and dephosphorization of 91.89%, was conducted under the optimum conditions. The iron concentrate, assaying 2.03% P with dephosphorization of 35.49%%, was conducted under natural basicity and no additives. During the reduction roasting, some phosphorus was volatilized in the form of P gas. For the pellets without adding additives, most phosphorus formed phosphorus iron compounds with metallic iron, which was difficult to remove. When the additives were employed and the basicity was increased, most phosphorus was absorbed in the high melting substances, and removed by magnetic separation.

Removal of Phosphorus in Metallurgical Grade Silicon Using Electron Beam Melting

The effects of melting condition on the dephosphorization behavior in metallurgical grade silicon (MG-Si) by electron beam melting (EBM) were investigated in this study. Experiment results showed that phosphorus content decreased by evaporation with the increase of melting time, and evaporation rate increased with the increase of electron beam power. Phosphorus content decreased to below 0.1 ppmw by EBM treatment at 21 kW for 1800 seconds. The dephosphorization reaction was found to follow the first order kinetics. Dephosphorization rate was controlled by free evaporation.

Dephosphorization Treatment of High Phosphorus Iron Ore by Pre-reduction, Air Jet Milling and Screening Methods

This paper proposes a novel process for the pre-treatment of high phosphorus iron ore by pre-reduction, air jet milling and screening methods. The dephosphorization behavior was evaluated as a function of such parameters as the milling gas kinetic energy, Ek and specific energy consumption, Esp. At a fixed milling gas kinetic energy, the dephosphorization treatment behavior was highly dependent on the solids feed rate and the degree of sintering of the pre-reduced phases. The proposed pre-treatment process involves a pre-reduction process by carbonaceous materials at 1200°C, and air jet milling using Ek of 325.24 kJ and Esp of 3.24 kJkg–1h followed by fine screen separation using a 25 μm screen size.

High temperature dephosphorization behavior of monazite concentrate with charred coal

Dephosphorization behavior of monazite concentrate with charred coal at high temperature was investigated. It is found that the roast temperature is the main factor for the dephosphorization of the monazite. The high dephosphorization efficiency can be reached at the temperatures ranging from 1 200 to 1 400 °C. When the monazite pellets, made by pressing mixture of the monazite, charred coal and water into mould, were roasted at 1 400 °C for 2 h, 98% of phosphorus was removed from the monazite pellets. The roast time has little effect on the dephosphorization efficiency. Meanwhile, the particle size of the charred coal also has great influence on the dephosphorization efficiency of the monazite, and it is better to control particle size around 150 (m, while Fe and Fe 2O 3 have neglectable effect on the dephosphorization of the monazite.

High temperature dephosphorus behavior of Baotou mixed rare earth concentrate with carbon

Based on the carbothermal reduction technology applied in industry, the dephosphorization behavior of Baotou mixed rare earth concentrate (Baotite) with carbon at high temperature was investigated. The experimental results showed that both the charred coal and the coking coal were effective carbonaceous reductants for the dephosphorization of the Baotite. Among them, the charred coal was more suitable for the dephosphorus due to its high carbon content and lower volatile and ash. When the rare earth pellets, made by pressing the mixture of the Baotite, charred coal and water in mould, were roasted at 1500 °C for 2 h, its dephosphorus rate was as high as 98%. Roasting temperature was a main factor for the dephosphorus rate, and roast time was the second one. The size of both charred coal and coking coal also had influence on the dephosphorus, and was better less than 150 μm.

Al<SUB>2</SUB>O<SUB>3</SUB>含有焼結脱りん剤による溶銑脱りん挙動

Al<SUB>2</SUB>O<SUB>3</SUB>含有焼結脱りん剤による溶銑脱りん挙動

Phosphorus Distribution Ratios between CaO-SiO2-FetO Slags and Carbon-saturated Iron at 1573 K.

In response to recent industrial demands for refining hot metals without using halides at the lowest CaO consumption, the possibility of hot metal dephosphorization by CaO-SiO2-FetO slags of low CaO content has been assessed in this study. In order to clarify the dephosphorization behavior of hot metals, equilibrium distribution ratios of phosphorus between CaO-SiO2 -FetO slags and solid iron strips have been measured as a function of slag composition at 1573 K, avoiding CO gas evolution if carbon-saturated iron is used. The obtained distribution ratios have been converted to those for hot metals using available thermodynamic data of phosphorus in solid and liquid irons. Phosphorus distribution ratio strongly depends on CaO content but not so much on FetO content of the slag. It increases with an increase in CaO content when FetO content is kept constant, while it slightly decreases when total Fe content is increased from 18-24 to 55 mass% at the (mass%CaO)/(mass%SiO2) rario of around unity. Phosphate capacities have also been estimated using activity data for FeO in this slag system, being considerably affected by CaO content of the slag. They show a good correlation with slag basicity.

溶銑処理温度における石灰系スラグと炭素飽和溶鉄間のりんの分配平衡

In order to thermodynamically understand the dephosphorization behavior of hot metals, the equilibrium distribution of phosphorus between a solid iron strip and CaO-bearing slag was measured in the temperature from 1200°C to 1400°C as a function of slag composition, avoiding the possible violent CO evolution if carbon-saturated iron were used. The obtained result was then converted to the value for the hot metal system using available thermodynamic data of phosphorus in solid and liquid irons.The results are summarized as follows:1) The CaO-SiO2-FeO system has very high dephosphorizing capacity when it is saturated with 2CaO·SiO2.2) The CaO-CaF2-FeO system containing a large amount of CaO and CaF2 has high Lp values, where Lp denotes the distribution ratio of phosphorus between slag and carbon-saturated iron.3) When FeO content is low, the CaO-SiO2-CaF2-FeO system containing a large amount of CaO has very high phosphate capacity.4) Iron oxide decreases the phosphate capacity of basic slags.5) From the laboratory equilibration test of the CaO-bearing slags used in the practical hot-metal treatment, the partial pressure of oxygen at the slag-metal interface is estimated at 10-1410-15 atm, which is ten it Ines as high as that in the soda-ash treat mem. This lies between the one determined by the reaction Fe+1/2O2= FeO and the one by C+1/2O2=CO.