Prediction of lime utilization ratio of dephosphorization in BOF steelmaking based on online sequential extreme learning machine with forgetting mechanism

The machine learning models of multiple linear regression(MLR),support vector regression(SVR),and extreme learning ma-chine(ELM)and the proposed ELM models of online sequential ELM(OS-ELM)and OS-ELM with forgetting mechanism(FOS-ELM)are applied in the prediction of the lime utilization ratio of dephosphorization in the basic oxygen furnace steelmaking process.The ELM model exhibites the best performance compared with the models of MLR and SVR.OS-ELM and FOS-ELM are applied for sequential learning and model updating.The optimal number of samples in validity term of the FOS-ELM model is determined to be 1500,with the smallest population mean absolute relative error(MARE)value of 0.058226 for the population.The variable importance analysis reveals lime weight,initial P content,and hot metal weight as the most important variables for the lime utilization ratio.The lime utilization ratio increases with the decrease in lime weight and the increases in the initial P content and hot metal weight.A prediction system based on FOS-ELM is applied in actual industrial production for one month.The hit ratios of the predicted lime utilization ratio in the error ranges of±1%,±3%,and±5%are 61.16%,90.63%,and 94.11%,respectively.The coefficient of determination,MARE,and root mean square error are 0.8670,0.06823,and 1.4265,respectively.The system exhibits desirable performance for applications in actual industrial pro-duction.

Strengthening iron enrichment and dephosphorization of high-phosphorus oolitic hematite using high-temperature pretreatment

The efficient development and utilization of high-phosphorus oolitic hematite is of great strategic significance for the sustainable supply of iron-ore resources in China.In this paper,the mechanism of high-temperature pretreatment for enhancing the effect of iron enrichment and dephosphorization in the magnetization roasting–leaching process was studied by X-ray diffraction(XRD),vibration sample magnetometer(VSM),scanning electron microscopy and energy dispersive spectrometry(SEM–EDS).Compared with the process without high-temperature pretreatment,the iron grade of the magnetic separation concentrate after high-temperature pretreatment had increased by 0.98%,iron recovery rate had increased by 1.33%,and the phosphorus content in the leached residue had decreased by 0.12%.High-temperature pretreatment resulted in the dehydration and decomposition of hydroxyapatite,the dehydration of limonite and the thermal decomposition of siderite,which can produce pores and cracks and weaken the compactness of the ore,improve the magnetization characteristics of roasted ore,and strengthen the iron enrichment and dephosphorization during the magnetization roasting and leaching process.

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.

Reaction mechanism of phosphorus with multi phase fluxes during hot metal dephosphorization

The formation of solid solution combined with tricalcium phosphate and dicalcium silicate could promote a considerable removal of phosphorus from liquid slag to solid during hot metal dephosphorization,and thus the dephosphorization by using multi phase fluxes could significantly decrease the consumption of lime. However,the reaction mechanism of multi phase fluxes has not been understood clearly.In the present study,the phase diagram for the CaO-SiO_2-FeO-P_2O_5 system has been measured with certain oxygen partial pressure at hot metal pretreatment temperature.Comparing with the CaO-SiO_2-FeO system,shrinkage of liquid phase area at higher FeO contents was observed at 1 673 K with oxygen partial pressure of 9.2×10^(-11) atm.

Control of Oxygen Potential and Its Effect on Dephosphorization of Ferromanganese

The relation of Lp(the ratio P content in slag to P content in ferromanganese) and L,(the ratio Mn content in slag to Mn content in ferromanganese) with C content[C]in ferromanganese were tested by means of the equilibrium experiments of P and Mn between ferromanganese and BaO-BaF-MnO slag system.The results show that there exists in ferromanganese an optimum C content[C]* corresponding to maximum Land minimum L> which is closely related to oxygen potential in the system and the activity of P in the alloy.The control limits of oxygen potential in dephosphorization of ferromanganese are then analyzed.The theoretical limits and measures to improve ferromanganese dephosphorization with BaO-based slag are studied comprehensively based on previous research.

Thermodynamic Study on BaO-CaO-CaF_2 Slags for Dephosphorization of Molten Steel

The molten steel was dephosphorized by high basic BaO-based slags (BaO-CaO-CaF_2) to achieve ultra low phosphorus level. The dephosphorization ability of the BaO-CaO-CaF_2 slags was tested. The phosphate capacity of this slag system at 1 620 ℃ varied from 10^(18.03) to 10^(19.11) with an activity coefficient of P_2O_5 ranging from 10^(-19.47) to 10^(-18.09). The effect of BaO content, initial phosphorus content and oxygen potential of molten steel on dephosphorization was discussed. The phosphorus pick-up by the BaO-based slags was studied.

The Effect on Activated Sludge of Chemical Coagulants Applied in Synchronization Dephosphorization

Combined with the practical experience of wastewater treatment plant, the chemical coagulants have inhibition effects on microorganism activity, with the influence degree of PAC (polyaluminium chloride) > AlCl3> Fe2(SO4)3. In synchronization dephosphorization, the inhibition rates of PAC in 10 ppm and 20 ppm are 11.9% and 33% respectively;while the inhibition rates of AlCl3 and Fe2(SO4)3 in 20 ppm are 15.8% and 8.5% respectively, compared with 9.6% and 5.4% in 10 ppm. Backwash wastewater from sand filter after adding coagulants has no direct inhibition effect on microorganism, but it results in inorganic components increase in active sludge. By taking North STP as an example, the VSS/SS ratio reduced from 0.65 after coagulants application to 0.54.

Structure Characterization and Dephosphorization Effect Analysis of Oyster Shell-silica Micropowder Waste Water Dephosphorization Materials

In this work,the effects of pH value of waste water and initial concentration of phosphorus on dephosphorization materials were investigated.The materials were prepared by shaping,sintering and hydrothermal reshaping oyster shell and silica micro-powder.Different concentrations of phosphorus-contained waste water were simulated with potassium dihydrogen phosphate solution,the effect of dephosphorization was tested with phosphomolybdenum blue spectrophotometer method,and the crystal phase and microstructure of materials were characterized by XRD and SEM methods. It was indicated that dephosphorization was completed in 6 h when the initial phosphorus concentration in waste water was lower than 15 mg/L, and the dephosphorization time prolonged as the increase of phosphorus concentration. It was observed that the pH value of waste water influenced dephosphorization significantly, and neutral subalkalic environment favored dephosphorization. When the pH value was 11, the efficiency of dephosphozation was the greatest. For waste water with an initial concentration of 20 mg/L, the dephosphozation rate is close to 100% in8 h.

Vacuum Treatment for Simultaneous Desulphurization and Dephosphorization of Hot Metal and Molten Steel

The vacuum treatment for simultaneous desulphurization and dephosphorization of hot metal and molten steel with pre-melted CaO-based slag was carried out.For pre-treatment of hot metal,both desulphurization and dephosphorization are improved with the increase of CaO in slag,but deteriorated with the increase of CaF2 in slag.The average desulphurization and dephosphorization rate is 68.83 % and 78.46 %,respectively.For molten steel,the substitution of BaO for CaO in slag has minor effect on simultaneous desulphurization and dephosphorization.The desulphurization and dephosphorization rate is higher than 90% and 50% respectively with the lowest final sulfur and phosphorus mass percent being 0.001 2% and 0.010%,respectively.The overall effect of simultaneous desulphurization and dephosphorization of molten steel is better than that of hot metal.

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 partition 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% SiOz-41wt%FeO. During the dephosphorization process, a slag formation path that follows a high-iron route would facilitate efficient dephosphorization. The composition of the final dephosphorization slag should be approximately 53wt%CaO-25.Swt% SiO2-21.5wt%FeO. The composition of the final solid slag after dephosphorization is approximately 63.6wt%CaO-30.3wt%SiO2-6. 1wt%FeO.

Effects of oxygen potential and flux composition on dephosphorization and rephosphorization of molten steel

The dephosphorization experiments of low phosphorus containing steel by CaO-based and BaO-based fluxes were carried out. The effects of the oxygen potential in molten steel and the BaO content in the slag on dephosphorization and rephosphorization of molten steel were analyzed. The results showed that the dephosphorization ratio of more than 50% and the ultra-low phosphorus content of less than 0.005% in steel were obtained by the three kinds of dephosphorization fluxes as the oxygen potential of molten steel higher than 400×10^-6. Rephosphorization of molten steel was serious as the oxygen content of molten steel lower than 10×10^-6. BaO-based fluxes can improve the dephosphorization effect and reduce the phosphorus pick-up effectively under the condition of weak deoxidization of molten steel （the oxygen potential is about 100×10^-6）, but can not prevent rephosphorization under the condition of deep deoxidization of molten steel （the oxygen potential less than 10×10^-6）.

Dephosphorization mechanism of prolonged sludge age SBBR treating saline and high-phosphorus wastewater

Prolonged sludge age sequencing batch biofilm reactor (SBBR) without sludge discharge appears high performance phosphorus removal in treating saline and high-phosphorus wastewater,which cannot be explained by traditional biological dephosphorization theory. The new path and mechanism of phosphorus removal was discussed on the phosphorus balance of phosphorus removal system without sludge discharge. Phosphorus balance in sludge was studied on 26 running cycles of the phosphorus reduction system. The results show that there is only 0.12 mg/g poly-P in sludge at the end of each reaction period,not phosphorus uptake by polyphosphate-accumulating organisms (PAOs). It is found that 41.8 mg/L of external phosphorus gets lost per day averagely,and 155 mg of internal phosphorus in sludge gets lost. The matrix bound phosphine in sludge achieves 36.04 mg/kg measured by alkaline digestion,and there is 18.44 mg/kg in +1 valence state,a intermediate,in sludge. This implies that the phosphorus removal system of prolonged sludge age SBBR without sludge discharge is a phosphate reduction,and the path of dephosphorization is phosphate→hypophosphite→phosphine.

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 150μm,while Fe and Fe2O3 have neglectable effect on the dephosphorization of the monazite.

Investigation on Dephosphorization of Stainless Steel

The principle of the dephosphorization for stainless steels differs from that of other low alloy steels, which should not only decrease phosphorous content efficiently but also keep the concentration of Cr almost lossless. In these cases, two techniques can be selected. The strategy for oxidational dephosphorization is illustrated in terms of “the selective oxidation among elements ［Cr］, ［P］ and ［C］. So there are two critical W［C］ values. If the real W［C］ locates between these two critical values, the dephosphorization process will be optimized. The optimized region deduced theoretically coincides with the reported range very well. The experiment of reductional dephosphorization was carried out in a sealed reactor. The dephosphorization degree reached 55.4 %—78.0 % when the original phosphorous content was 0.04 %—0.05 %. The processing parameters and the way to avoid pollution were suggested. So this process seems to be possibly adopted in industrial scale.

Kinetic study on deep dephosphorization treatment of liquid steel by BaO-based fluxes

Laboratory study was carried out on deep dephosphorization of liquid steel byBaO-based fluxes at 1600°C to achieve ultra low phosphorus level in the steel. A dynamic model ofdephosphorization of Liquid steel by BaO-based fluxes was established. According to the model, thecontrolling step of dephosphorization by BaO-based fluxes was the mass-transfer of phosphorus insteel phase under the condition of low phosphorus liquid steel. It is estimated that the apparentrate constant of dephosphorization by BaO-based fluxes was 0.4xl0^(-3)-8.2xl0^(-3) g/(cm^2 centre tos) and the mass-transfer coefficient of phosphorus in bulk steel was 0.025-0.04 cm/s.

Influence of temperature and Fe_(2)O_(3)on phosphorus recovery from dephosphorization slag by reduction

The reduction and recovery of P_(2)O_(5)in dephosphorization slag were examined to establish a new recycling process for dephosphorization slag.The dephosphorization slag is obtained from the dephosphorization furnace in the duplex converter process,and the content of P_(2)O_(5) in the dephosphorization slag can reach 9 wt.%.The dephosphorization slag is considered to be a prospective resource of phosphorus due to its high content of P_(2)O_(5).To explore the effects of temperature and Fe2O3 content in slag on phosphorus recovery from dephosphorization slag,the experimental slag was reduced by carbon powder in a resistance furnace.The results show that the temperature and content of Fe2O3 in slag have a significant effect on the reduction in P_(2)O_(5),and the reduction and recovery ratios of P_(2)O_(5) in slags increase with the increase in the experimental temperature and content of Fe_(2)O_(3),reaching 94.41%and 83.09%,respectively.It has been indicated that phosphorus recovery from dephosphorization slag using carbothermic reduction has significant environmental and economic benefits.

Separation of phosphorus from dephosphorization slag modified by alkaline oxide by HCl leaching

Dephosphorization slag is one of the bulk solid wastes generated from steelmaking.If P is effectively removed from dephosphorization slag,a phosphate source which can substitute for phosphate rocks is obtained;meanwhile,the tailings can be reutilized as a feedstock in steel plant.To realize the integrated utilization of dephosphorization slag,selective leaching was applied for removing the P-bearing mineral phase from dephosphorization slag.Alkaline oxide was added as the slag modifier and HCl was selected as the acid lixiviant.The P selective leaching from dephosphorization slags modified by Na_(2)O or K_(2)O was studied at different pH values.By modification,the mass fraction of P in the_(2)CaO∙SiO_(2)–3CaO∙P_(2)O_(5)phase increased,indicating that it was in favor of P_(2)O_(5)enrichment.As the Na_(2)O or K_(2)O content increased,the P leaching ratio from slag increased at pH 4,reaching about 80%,and that of Fe was nearly zero.Na_(2)O and K_(2)O modification played a similar role in enhancing the P leaching.The effect of alkaline oxide modification became weak at pH 3,and the slag without modification also realized a good P selective leaching in the HCl solution.To facilitate the P removal,the leaching of Fe from dephosphorization slag needs to be restrained.

Analysis of Steel Slag Treatment Process and Comprehensive Utilization

As a by-product of steel enterprises,steel slag has a huge output and is rich in valuable minerals,but its comprehensive utilization rate is very low.The article mainly introduces the hot splashing method,hot sealing method,and drum method for the treatment of steel slag outside the furnace,and compares and analyzes the advantages and disadvantages of the production operation process and steel slag treatment process.At the same time,it also introduces the residual slag+double slag process and gasification dephosphorization slag circulation steelmaking technology for steel slag treatment inside the furnace,providing direction for steel enterprises to clean and comprehensively utilize steel slag.

Double Slag Operation Dephosphorization in BOF for Producing Low Phosphorus Steel

A study on the production of low phosphorus steel by double slag operation in 210 t converter was carried out. A phosphorus content of less than 0.005% （mass percent） was obtained before tapping. About 80% phosphorus could be removed by the first slag after 5 min. High Fe^3＋ content and high basicity in the first slag were in favor of dephosphorization. On the other hand,Fe3＋ content had less effect on dephosphorization during second slag treatment. In the second slag period,the fraction of dephosphorization increased with the increase of basicity up to a basicity of 6. Further increase of basicity of the second slag had very little effect on dephosphorization. The tapping temperature had great impact on dephosphorization. It was impossible to get phosphorus less that 0.005% when the tapping temperature was higher than 1 943 K. The optimum operation conditions were suggested. On the basis of these conditions,the amount of the second slag and the effect of the remaining first slag were estimated.

Effect of Modification Treatment for Reduction of Dephosphorization Slag in Hot Metal Bath

To extract the valuable elements from the steel slag, a novel approach has been proposed by modification treatment to provide the stronger driving forces and accelerate the reduction. Three types of dephosphorization steel slags were reduced using carbon-saturated iron bath to extract iron and phosphorus simultaneously. During the process of reduction, slag composition, temperature, and original P2O5 content were investigated respectively. Slag modification treatment, adding either silica or alumina to vary the slag composition, was proven to accelerate the reduction of dephosphorization slag. The equilibrium time can be shortened from 60 to 30 min. Slag modification also allowed the reduction reaction to occur at lower temperature. After slag modification, the original P2O5 content in slag presents a slight difference on reduction process. Almost half of the reduced phosphorus was vaporized within 5 and 20 min. As more and more FeO was reduced, CO gas generation decreased, and evaporation amount of phosphorus therefore decreases.