Phosphorus In Slag Research Articles

Least Squares Twin Support Vector Machines to Classify End-Point Phosphorus Content in BOF Steelmaking

End-point phosphorus content in steel in a basic oxygen furnace (BOF) acts as an indicator of the quality of manufactured steel. An undesirable amount of phosphorus is removed from the steel by the process of dephosphorization. The degree of phosphorus removal is captured numerically by the ‘partition ratio’, given by the ratio of %wt phosphorus in slag and %wt phosphorus in steel. Due to the presence of multitudes of process variables, often, it is challenging to predict the partition ratio based on operating conditions. Herein, a robust data-driven classification technique of least squares twin support vector machines (LSTSVM) is applied to classify the ‘partition ratio’ to two categories (‘High’ and ‘Low’) steels indicating a greater or lesser degree of phosphorus removal, respectively. LSTSVM is a simpler, more robust, and faster alternative to the twin support vector machines (TWSVM) with respect to non-parallel hyperplanes-based binary classifications. The relationship between the ‘partition ratio’ and the chemical composition of slag and tapping temperatures is studied based on approximately 16,000 heats from two BOF plants. In our case, a relatively higher model accuracy is achieved, and LSTSVM performed 1.5–167 times faster than other applied algorithms.

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.

Effect of MgO and MnO on Phosphorus Utilization in P-Bearing Steelmaking Slag

AbstractIn order to recycle the phosphorus in P-bearing converter slag and make it used as slag phosphate fertilizer, the effect of MgO and MnO in P-bearing steelmaking slag on phosphorus existence form, P2O5 solubility and magnetic separation behavior were researched systematically. The results show that the phosphorus in slag is mainly in the form of n2CaO · SiO2–3CaO · P2O5 (for short nC2S–C3P) solid solution in the P-rich phase for CaO-SiO2-FetO-P2O5-X (X stands for MgO and MnO, respectively). And the increasing of MgO and MnO content has no influence on precipitation of nC2S–C3P solid solution in slag, MnO and MgO mainly enter into RO phase and base phase to form MnFe2O4 and MgFe2O4, which has little effect on the P2O5 content of P-rich phase, so which has little effect on the degree of phosphorus enrichment and phosphorus occurrence form of the P-bearing slag. And adding MgO and MnO into CaO-SiO2-P2O5-Fe2O3 slag system can break the complex net structure formed by Si–O on certain degree, and also hinder the precipitation of β-Ca3(PO4)2 crystal with low citric acid solubility during the melting–cooling process. Therefore, adding appropriate MgO and MnO content into slag can improve the slag P2O5 solubility, but the effect of different amounts of MgO and MnO on the P2O5 solubility has little difference. Meanwhile, adding MgO and MnO into slag can improve the metallization of slag and magnetism of iron-rich phase, make the magnetic substances content increase and separation of phosphorus and iron incomplete, so it is adverse to phosphorus resources recovery from P-bearing slag by magnetic separation method. In order to recycle the phosphorus in P-bearing converter slag, the MgO and MnO content in the P-bearing slag should be controlled in the steelmaking process.

Influence of Al2O3 modification on phosphorus enrichment in P bearing steelmaking slag

In order to effect enrichment of phosphorus in converter slag, phosphorus enrichment was researched by Al2O3 melting modification, the Al2O3 modification process is discussed according to the thermodynamic analysis, and phosphorus rich phase was separated from experimental slag by magnetic separation. The results show that gehlenite (Ca2Al2SiO7) and high phosphorus solid solution (n′C2S–C3P) are generated by the continuous reaction of n2CaO.SiO2–3CaO.P2O5 (nC2S–C3P) solid solution precipitated in the slag with Al2O3 at 1623K. The early precipitated solid solution (nC2S–C3P) is reduced with increasing content of Al2O3, and even disappeared. If the addition of Al2O3 is increased or excess in the slag, the high phosphorus solid solution (n′C2S–C3P) that was generated by the above mentioned reaction will continue to react with Al2O3 to produce gehlenite, then the phosphorus content in the phosphorus rich phase is increased. Through magnetic separation the amount of non-magnetic substance of no. 2 slag after modification is raised 26·88% compared to the original slag, the distribution ratio of P2O5 is raised from 0·96 to 4·61, and the amount of separated non-magnetic substance is 68·47% of the total no. 2 slag, 84·57% of the phosphorus in slag is entered into collected non-magnetic substance, thereby most phosphorus element was recycled.

Influence of SiO2 modification on phosphorus enrichment in P bearing steelmaking slag

In order to effect enrichment of phosphorus in the converter slag, phosphorus enrichment was researched by slag modification with SiO2. The SiO2 modification process was evaluated thermodynamically, and phosphorus rich phase was separated from experimental slag by magnetic separation. The results show that n2CaO.SiO2–3CaO.P2O5 (nC2S–C3P) solid solution is generated by the reaction of Ca3(PO4)2 phase in the slag with precipitated Ca2SiO4 phase at 1623 K, and Ca2SiO4 in the solid solution is reduced with increasing SiO2; hence, the phosphorus content in the solid solution is increased. If the addition of SiO2 is excessive, the amount of Ca2SiO4 precipitation in the slag is decreased remarkably (and even disappeared), CaSiO3 phase is generated and the generation of nC2S–C3P solid solution is reduced, which is not favourable to phosphorus enrichment. Through magnetic separation, the non-magnetic fraction was increased by 10–74·68% compared with the original slag. The distribution ratio of P2O5 was increased from 2·71 to 5·48. As 84·57% of the phosphorus in the slag is in the collected non-magnetic substances, the work demonstrates that most of the phosphorus is able to be effectively recycled.

Dissolution Behavior of Dicalcium Silicate and Tricalcium Phosphate Solid Solution and other Phases of Steelmaking Slag in an Aqueous Solution

AbstractMost of the phosphorus in slag forms a solid solution of dicalcium silicate (C2S) and tricalcium phosphate (C3P), and the process used to separate this solid solution from the matrix phase is the same technology used to separate P from other valuable elements such as Mn and Cr containing in the matrix phase. Although it is known that the solubility of C2S in an aqueous solution is much greater than that of C3P, the solubility of the solid solution and that of the matrix phase have yet to be investigated. To clarify the possibility of selectively extracting P from slag through a leaching process, the dissolution behaviors of the solid solution at various compositions and that of the matrix phase were investigated. The following results were obtained: The dissolution ratio of Ca to the aqueous solution at pH = 7 was close to 1.0 in the case of pure C2S and decreased greatly with increasing C3P content. The dissolution ratio of P was about 0.1 and did not change relative to the C3P content. When the ratio of C3P in the solid solution was higher than 0.3, hydroxyapatite (HAP) formation was observed in the residue. The dissolution ratio of P increased for 30 min, and after reaching the maximum value, started to decrease owing to the precipitation of HAP. The dissolution ratio of each element from a glassy slag sample (matrix phase) was lower than that from the solid solution at every pH level.In this study, the possibility to extract a solid solution containing P without dissolving the matrix phase was found through the use of an aqueous solution at pH = 7, although the dissolution ratio of P was not sufficiently high.

Quantitative evaluation for effective removal of phosphorus for SoG-Si

Production of solar cells has increased rapidly in recent years, and metallurgical production of solar grade silicon (SoG-Si), has increased compared with more expensive processes such as Siemens process and Cz processes. It is important to understand the thermodynamic behavior of phosphorus in slag for optimized refinement of SoG-Si. In this study, the thermodynamic behavior of phosphorus in the CaO–SiO 2–CaF 2 slag system was investigated at 1773 K for various oxygen potential and slag composition. In addition, evaporation of phosphorus in the reduction process was observed during slag refining by addition of H 2 gas. Experimental results showed that the stability of phosphorus in slag depends on both the O 2−(basicity) content of the slag and the solubility of Ca in silicon, and the dissolution mechanism of phosphorus into slag was derived. Results confirmed that phosphorus and calcium in molten silicon were also removed by acid leaching. The effective removal of phosphorus for SoG-Si using several refining processes was evaluated quantitatively.

Thermodynamic Study for P Reduction from Slag to Molten Steel by using the Microwave Heating

Phosphorus exhibits considerable segregation in steelmaking slag. In order to recover phosphorus from slag to <TEX>$K_3PO_4$</TEX> via molten iron, a carbothermic reaction using microwave heating was suggested recently. The carbothermic reduction of phosphorus from slag to molten iron using microwave heating was carried out at 2073K. However, at this temperature the thermodynamic properties of both slag and molten iron cannot be determined experimentally. Therefore, the computational approach of the so-called CALPHAD method is very useful to understand the transfer of phosphorus from slag to metal and to enhance this reaction. In the present investigation, a theoretical study of the reduction behavior of phosphorus in slag was carried out at much lower temperatures using the recently developed thermodynamic database in the FactSage program. The calculated results showed reasonable accordance with the experimental data; namely, the thermodynamic database could be applied successfully to higher temperature reactions. The current study found that higher temperature and high <TEX>$SiO_2$</TEX> concentration are favorable for the recovery of phosphorus from slag.