Mass Transfer Of Phosphorus Research Articles

Influence of BaO on viscosity and structure of CaO–SiO2–FetO–Al2O3–BaO steel slag

ABSTRACT The viscosity of steel slag has an important influence on phosphorus mass transfer in dephosphorization process and slagging–off after dephosphorization. In current work, the viscosity of steel slag was measured and the influence of BaO on viscosity and structure evolution of steel slag was studied. The results showed that the viscosity of steel slag decreased with the addition of BaO. The Fourier transform infrared spectroscopy (FTIR) analysis showed that the degree of polymerisation (DOP) of steel slag is reduced by the addition of BaO. The Raman spectra quantitative analysis revealed that the convertion of Q2 and Q3 to Q0 and Q1 was promoted by the addition of BaO. The X–ray photoelectron spectroscopy (XPS) analysis indicated that the general relative fraction quantity of O0 decreased and that of O2− increased with the addition of BaO. The above analysis are agree well with the results of viscosity measurement.

Study on Mass Transfer of Phosphorus Based on New Hot-Metal Dephosphorization Kinetic Model

To investigate mass transfer of phosphorus in hot-metal dephosphorization process, it is necessary to reduce the deviation of traditional dephosphorization models in fitting accuracy. According to the change in hot-metal phosphorus content during dephosphorization, a new dephosphorization model was established by introducing the concept of “dynamic relative area”. With the help of literature data and comparative analysis of the new and old models, the rationality of the new model was verified. On this basis, in order to reveal the effects of CaO and its derivatives on mass transfer of phosphorus, based on the dephosphorization effect of FetO–CaO–SiO2–CaCl2 slags on high-phosphorus hot metal at 1673 K (1400 °C), the mass transfer process of phosphorus was investigated by calculating, analyzing, and discussing the overall mass transfer coefficients of phosphorus using CaO, Ca(OH)2, and CaCO3 with equal molar amount as fixatives (slag formers) in dephosphorizer respectively. The results show that the overall mass transfer coefficients of phosphorus under the action of Ca(OH)2 and CaCO3 are 0.0216 cm/s and 0.0363 cm/s, respectively, which are significantly lower than 0.0840 cm/s under the action of CaO.

Establishment and test of ‘dynamic relative area’ models for hot-metal dephosphorization and rephosphorization

ABSTRACT The kinetic models of hot-metal dephosphorization and rephosphorization have been widely used in the analysis of phosphorus mass transfer, but most of the existing models deviate greatly from the experimental results. Therefore, to reduce the deviation of traditional models in data fitting, according to the change in hot-metal phosphorus content during dephosphorization or slag phosphorus content during rephosphorization, a new dephosphorization model and rephosphatization model were established by introducing a concept of ‘dynamic relative area’, and their rationality and universality were proved. The results showed that the new dephosphorization model presents obvious advantages in the fitting accuracy of [%P]-time data, but no significant difference is observed between the new and old rephosphorization models. Besides, the RHS-time curve stability of the new dephosphorization model is much higher than that of the old model, while the RHS-time curves of the new and old rephosphorization models show little difference and remain relatively stable.

Dephosphorization of Metallurgical-Grade Silicon by Electromagnetic Levitation

In this work, a dynamic model was established for the dephosphorization of metallurgical grade silicon by levitation refining. Particular emphasis was placed on the transport behavior of phosphorus in the liquid boundary layer, then at the melt surface and finally within the gas phase surrounding the levitated droplet. Within the melt boundary layer, and at the droplet surface, temperature was the controlling factor affecting phosphorus behavior. Within the gas phase, the controlling factors were temperature and gas velocity with temperature showing a more pronounced effect on the phosphorus mass transfer coefficient than gas velocity. The dynamic model shows that the dephosphorization of MG-Si was controlled by phosphorus diffusion within the gas phase. The values calculated from the model for the mass transfer coefficient were in good agreement with dephosphorization data obtained from levitation experiments conducted with metallurgical grade silicon. This work can provide a good foundation for application of electromagnetic levitation technology to the refining of metallurgical grade silicon.

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.

An Assessment of the General Applicability of the Relationship Between Nucleation of CO Bubbles and Mass Transfer of Phosphorus in Liquid Iron Alloys

The current paper seeks to demonstrate the general applicability of the authors’ recently developed treatment of surface renewal during decarburization of Fe-C-S alloys and its effect on the mass transport of phosphorus in the metal phase. The proposed model employs a quantitative model of CO bubble nucleation in the metal to predict the rate of surface renewal, which can then in turn be used to predict the mass-transfer coefficient for phosphorus. A model of mixed transport control in the slag and metal phases was employed to investigate the dephosphorization kinetics between a liquid iron alloy and oxidizing slag. Based on previous studies of the mass-transfer coefficient of FeO in the slag, it was possible to separate the mass transfer coefficient of phosphorus in metal phase, $$ k_{m} $$ , from the overall mass-transfer coefficient $$ k_{{\text{o}}} . $$ Using this approach, $$ k_{m} $$ was investigated under a wide range of conditions and shown to be represented reasonably by the mechanism proposed. The mass-transfer model was tested against results from the literature over a wide range of conditions. The analysis showed that the FeO content in the slag, silicon in the metal and the experimental temperature have strong impact on, $$ k_{m} $$ , almost entirely because of their effect on decarburization behavior.

Correction to: Dephosphorization Kinetics between Bloated Metal Droplets and Slag Containing FeO: The Influence of CO Bubbles on the Mass Transfer of Phosphorus in the Metal

An error occurred in the Table VI of this paper. The values used in this paper for diffusivity of phosphorus in the metal phase were incorrectly entered in Table VI. The values should be as listed in the following table.

Dephosphorization Kinetics between Bloated Metal Droplets and Slag Containing FeO: The Influence of CO Bubbles on the Mass Transfer of Phosphorus in the Metal

Dephosphorization kinetics of bloated metal droplets was investigated in the temperature range from 1813 K to 1913 K (1540 °C to 1640 °C). The experimental results showed that the overall mass transfer coefficient, \( {k_{\text{o}}} \), decreased with increasing temperature because of decreasing phosphorus partition ratio, \( {L_{\text{P}}} \). It was also found that the mass transfer coefficient for phosphorus in the metal, \( {k_{\text{m}}} \), had the highest value at the lowest temperature [i.e., 1813 K (1540 °C)] because the formation of smaller CO bubbles increased the rate of surface renewal, leading to faster mass transport. Meanwhile, metal droplets without carbon were also employed to study the effect of decarburization on dephosphorization. The results show that although decarburization lowers the driving force significantly, \( {k_{\text{m}}} \) (6.2 × 10−2 cm/s) for a carbon containing droplet is two orders of magnitude higher than that for carbon free droplets (5.3 × 10−4 cm/s) because of the stirring effect provided by CO bubbles. This stirring offers a faster surface renewal rate, which surpasses the loss of driving force and then leads to a faster dephosphorization rate.

Evaporation Behavior of Phosphorus from Metallurgical Grade Silicon via Calcium-Based Slag Treatment and Hydrochloric Acid Leaching

Phosphorus removal from metallurgical grade silicon by CaO-SiO2-CaCl2 slag treatment, HCl leaching, and vacuum refining was investigated. The effect of different compositions of slag was evaluated. The calcium concentration in slag-treated silicon increased with increasing CaO/SiO2 mass ratio of slag, decreasing the evaporation efficiency of phosphorus in molten silicon. The total phosphorus removal efficiency changed from 93.0% to 98.3% when the slag-treated silicon was treated with HCl before vacuum refining. The final concentration of phosphorus in silicon was 0.43 ppmw. This is because phosphorus was removed from metallurgical-grade silicon as follows: Phosphorus reacts with slag at the silicon/slag interface and forms Ca3(PO4)2 and Ca3P2, most of which diffuse from the interface to the slag phase. The remaining Ca3(PO4)2 and Ca3P2 reduce the phosphorus removal efficiency by altering the activity coefficient of phosphorus in molten silicon. HCl leaching enhanced the phosphorus removal efficiency by removing the remaining Ca3(PO4)2 and Ca3P2. Therefore, the mass transfer of phosphorus from metallurgical-grade silicon was accelerated.

Mass transfer of phosphorus in high-phosphorus hot-metal refining

Mass transfer of phosphorus in high-phosphorus hot-metal refining was investigated using CaO-FetO-SiO2 slags at 1623 K. Based on a two-film theory kinetic model and experimental results, it was found that the overall mass transfer coefficient, which includes the effects of mass transfer in both the slag phase and metal phase, is in the range of 0.0047 to 0.0240 cm/s. With the addition of a small amount of fluxing agents Al2O3 or Na2O into the slag, the overall mass transfer coefficient has an obvious increase. Silicon content in the hot metal also influences the overall mass transfer coefficient. The overall mass transfer coefficient in the lower [Si] heat is much higher than that in the higher [Si] heat. It is concluded that both fluxing agents and lower [Si] hot metal facilitate mass transfer of phosphorus in liquid phases. Furthermore, the addition of Na2O could also prevent rephosphorization at the end of the experiment.

Optimization of Low Phosphorus Steel Production With Double Slag Process in BOF

To produce the steel with phosphorus less than 0.007% (mass percent), the double slag process has been optimized in basic oxygen furnace (BOF). Dephosphorization and decarburization arc performed in sequence in the same converter. Deslagging is conducted twice, each at the end of dephosphorization and decarburization, by tilting the BOF. Production was tested in a 180 t BOF. Mass percent of phosphorus in steel at BOF blow end has been made to as low as 0.0042% after optimizing operational parameters. Factors affecting dephosphorization performance were studied. Before intermediate deslagging, dephosphorization is determined by the mass transfer of phosphorus from metal/slag interface to bulk slag phase rather than equilibrium thermodynamic conditions. After intermediate deslagging, dephosphorization is determined by the equilibrium thermodynamic conditions such as slag composition and temperature.

Phosphorous Enrichment in Molten Adjusted Converter Slag: Part II Enrichment Behavior of Phosphorus in CaO-SiO 2-FeO x-P 2O 5 Molten Slag

The enrichment behavior of phosphorus in CaO-SiO 2-FeO x -P 2O 5 slag was studied by making an investigation on the distribution of phosphorous content in the CaO-SiO 2-FeO x -P 2 O 5 molten slag. The research results showed that the 2CaO • SiO 2 solid particles existing in molten slag were the condensation sites for the phosphorus enrichment. The enrichment process of phosphorus in the molten slag can be recognized as three substeps: mass transfer of phosphorus from bulk slag to the surface of 2CaO • SiO 2 particle, superficial solid solution reaction of phosphorus around the 2CaO • SiO 2 particle, and diffusion of phosphorus through the product layer of 2CaO • SiO 2-3CaO • P 2O 5 solid solution to the inner of 2CaO • SiO 2 particle. Moreover, higher temperature is favorable to the phosphorous enrichment from molten bulk slag to the 2CaO • SiO 2 particles.

Mass Transfer of Phosphorus in Silicon Melts Under Vacuum Induction Refining

An experimental investigation into the mass transfer of phosphorus in molten silicon under vacuum induction refining has been carried out. In a pilot-scale experiment, in the temperature range 1773 K (1500 °C) to 1873 K (1600 °C) and a vacuum of 0.1 to 0.035 Pa smelting for 7200 seconds (2 hours), phosphorus is decreased from 15 ppmw to 0.08 ppmw, which achieved the target for solar-grade silicon of less than 0.1 ppmw. Lab-scale experiments are used to determine the effects of vacuum, refining time, and temperature on the rate of mass transfer of phosphorus during vacuum refining. Hardly any phosphorus was removed when the vacuum pressure is greater than 100 Pa. Mass-transfer coefficients are nearly independent of pressure at 1783 K (1510 °C) when pressures are below 0.1 Pa and are highly correlated with vacuum pressures above 0.1 Pa. A model of vacuum refining of inductively stirred silicon melts is discussed to explain the transfer path of phosphorus out of the melt.

Modeling nutrient in-stream processes at the watershed scale using Nutrient Spiralling metrics

Abstract. One of the fundamental problems of using large-scale biogeochemical models is the uncertainty involved in aggregating the components of fine-scale deterministic models in watershed applications, and in extrapolating the results of field-scale measurements to larger spatial scales. Although spatial or temporal lumping may reduce the problem, information obtained during fine-scale research may not apply to lumped categories. Thus, the use of knowledge gained through fine-scale studies to predict coarse-scale phenomena is not straightforward. In this study, we used the nutrient uptake metrics defined in the Nutrient Spiralling concept to formulate the equations governing total phosphorus in-stream fate in a deterministic, watershed-scale biogeochemical model. Once the model was calibrated, fitted phosphorus retention metrics where put in context of global patterns of phosphorus retention variability. For this purpose, we calculated power regressions between phosphorus retention metrics, streamflow, and phosphorus concentration in water using published data from 66 streams worldwide, including both pristine and nutrient enriched streams. Performance of the calibrated model confirmed that the Nutrient Spiralling formulation is a convenient simplification of the biogeochemical transformations involved in total phosphorus in-stream fate. Thus, this approach may be helpful even for customary deterministic applications working at short time steps. The calibrated phosphorus retention metrics were comparable to field estimates from the study watershed, and showed high coherence with global patterns of retention metrics from streams of the world. In this sense, the fitted phosphorus retention metrics were similar to field values measured in other nutrient enriched streams. Analysis of the bibliographical data supports the view that nutrient enriched streams have lower phosphorus retention efficiency than pristine streams, and that this efficiency loss is maintained in a wide discharge range. This implies that both small and larger streams may be impacted by human activities in terms of nutrient retention capacity, suggesting that larger rivers located in human populated areas can exert considerable influence on phosphorus exports from watersheds. The role of biological activity in this efficiency loss showed by nutrient enriched streams remained uncertain, because the phosphorus mass transfer coefficient did not show consistent relationships with streamflow and phosphorus concentration in water. The heterogeneity of the compiled data and the possible role of additional inorganic processes on phosphorus in-stream dynamics may explain this. We suggest that more research on phosphorus dynamics at the reach scale is needed, specially in large, human impacted watercourses.

転炉型溶銑脱燐時の上吹き酸素による酸化鉄生成挙動の基礎検討

The effects of hot metal temperature, oxygen gas flow rate from a top lance and argon gas flow rate from an injection lance on iron oxide formation and dephosphorization rates in hot metal were investigated with 3 kg- and 200 kg-scale furnaces. The results were summarized as follows.1) Iron oxide formation rate increased with lower hot metal temperature, higher oxygen gas flow rate and lower argon gas flow rate.2) A kinetic model was developed to estimate the iron oxide formation on hot metal, and a mathematical model for hot metal dephosphorization has been made based on the aforementioned model of iron oxide formation and the coupled reaction model.3) Dephosphorization and the formation rate of iron oxide in 200 kg-scale tests agreed well with those were obtained by the mathematical model.4) Oxygen activity at slag/metal interface obtained by the mathematical model agreed with the equilibrium oxygen activity with FeO in slag.5) In the early stage of dephosphorization, the gas flow rate of the bottom blowing need to be lower in order to enhance the iron oxide formation. In the late stage of dephosphorization, that needs to be higher in order to enhance the mass transfer of phosphorus in hot metal.6) Industrial hot metal dephosphorization tests were carried out with a 350 t-scale top and bottom converter. The conditions of top blowing oxygen and bottom blowing nitrogen have been improved by adopting the mathematical model in order to increase the iron oxide content in slag. It has been possible to increase dephosphorization efficiency without fluor spar at lower hot metal temperature (below 1300°C) by improving the blowing conditions.

Effect of slag/metal interfacial tension on kinetics of dephosphorisation

The effect of interfacial tension on the kinetics of the dephosphorisation of iron has been investigated. X-ray monitoring of the shape of a molten iron droplet in liquid slag showed that there was a marked reduction in the interfacial tension γms during periods of rapid mass transfer and an increase in γms as the mass transfer process slowed down, similar to that observed for desulphurisation. The dephosphorisation kinetics was found to be first order with respect to phosphorus in the liquid iron and implied that, for the system studied, mass transfer of phosphorus in the slag phase is the rate controlling step.

Nonequilibrium segregation of phosphorus in the system silicon dioxide-silicon

A model of diffusion-segregation impurity redistribution in the system SiO2-Si during the thermal oxidation of silicon is developed, taking into account the nonequilibrium character of the segregation process at the moving phase boundary. The temperature dependence of the mass transfer of phosphorus and its mass-transfer coefficient at the SiO2-Si interface are determined by the numerical analysis of experimental data.

Behaviour of Intracellular Polyphosphate in the Biological Phosphate Removal Process

In this study the functions of the intracellular polyphosphate in the biological phosphorus removal process were investigated from biological point of view. The STS method was used for the determination of polyphosphate and the fractionation of the intracellular phosphorus compounds. The lowmolecular polyphosphate and the highmolecular polyphosphate can be determined separately in this method. The radiotracer experiments were performed in which 32P-labeled orthophosphate was used as a tracer. The chemical analyses of phosphorus and the radioactivity measurement were made simultaniously in the course of the anaerobic oxic process. From the results of a radiotracer experiment the mass transfer of phosphorus among the phosphorus compounds was calculated. It was suggested that the lowmolecular polyphosphate served as the energy source under the anaerobic conditions and that the highmolecular polyphosphate served as the phosphorus source for the growth reactions. Some models for the phosphorus transfer in the high phosphorus accumulating microorganisms were proposed.