Slag Phase Research Articles

Dissolution of Al2O3–C bricks in 45 wt% CaO-45 wt% SiO2-x wt% CaF2-(10-x) wt% Na2O slag

The dissolution of Al2O3–C refractories in 45 wt% CaO-45 wt% SiO2-x wt% CaF2-(10-x) wt% Na2O slag was explored by the static test and thermodynamic calculation. The results show that the severe slag penetration into refractories occurs after corrosion test. With the gradual replacement of CaF2 in slag by Na2O, lots of pores are found in the slag phase near the refractory/slag interface due to the formation of gaseous phase from the reaction between Na2O in slag and C in refractories. Compared with the slag without Na2O, the slag bearing 5 wt% Na2O does not accelerate the dissolution of refractory into slag. The possible reason is that the reaction between CaF2 in slag and Al2O3 in bricks is inhibited due to the replacement of CaF2 in slag by Na2O. The dissolution of Al2O3–C refractories is faster in the slag bearing 10 wt% Na2O than that in the slag bearing 5 wt% Na2O, due to the severer Na2O volatilization from the reduction of Na2O in slag by C in refractories, which accelerates the renewal rate of boundary layer between refractories and slag phase. The results indicate that replacing part of CaF2 in mold slag with moderate amount of Na2O does not aggravate the corrosion of submerged entry nozzle consisting of Al2O3–C based refractories.

Desulfurization behavior of Si-killed 316L stainless steel melt by CaO-SiO2-CaF2-Al2O3-MgO slag

The desulfurization behavior of 316L stainless steel (STS316L) melt with the CaO-SiO2-CaF2-Al2O3-MgO slag was investigated with different CaO/SiO2 (=C/S) ratio and CaF2 content at 1873 K. As the C/S ratio increased, the sulfide capacity increased, whereas the sulfide capacity of the high C/S (=1.7) slag was not affected by CaF2 content. The overall mass transfer coefficient (kO) increased with C/S ratio, but was constant above a critical C/S value, and it was also constant across varied CaF2 content at relatively high C/S (=1.7) condition. Since the metal condition of the present study was constant, the change in kO was caused by slag phase mass transfer coefficient (ks) and sulfur distribution ratio (LS), which were affected by the physicochemical properties of the slag. Since desulfurization reaction requires consideration of both kinetic and thermodynamic factors, the ‘logCS2−−logη’ (where CS2− is sulfide capacity and η is viscosity), was proposed as a meaningful physicochemical parameter. If the slag basicity is relatively high, at which the kO is equivalent regardless of slag compositions, the desulfurization reaction is controlled by metal phase mass transfer. However, if the slag basicity becomes lower, at which the kO significantly decreases, the desulfurization reaction is assumed to be controlled by slag phase mass transfer and/or mixed controlled process.

Innovative and sustainable separation and recovery of valuable metals in spent CIGS materials

In recent years, the rapid development of copper indium gallium selenide (GIGS) solar cells makes it necessary to recycle spent CIGS in order to realize circular economy. In this work, a novel and efficient method for comprehensive recovery valuable metals in spent CIGS materials was investigated, mainly including three steps: (1) leaching of spent CIGS with nitric acid to separate indium; (2) precipitating to obtain copper gallium selenite mixture with magnesium oxide as precipitant; (3) calcination of the residue and the precipitation to recover selenium. X-ray photoelectron spectroscopy (XPS) analysis indicates that the valence state of selenium was converted from negative divalent to positive tetravalent after oxidative leaching. In addition, the results of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS) shows that the dissolution of metals in CIGS during leaching were significantly different. Copper and gallium were almost completely leached, while indium entered the slag phase as indium selenite, which achieved the separation of indium. Moreover, the reaction mechanism of leaching was analyzed from the perspective of thermodynamics. After leaching, copper, gallium and selenium can be completely recovered from the leach liquor using magnesium oxide as precipitant. Subsequently, the separation of Se in the residue and precipitates can be achieved at 800 °C for 90 min. Finally, the recovery yields of Cu, In, Ga and Se were 99.23%, 96.82, 98.08% and 96.38% respectively. This research represents an important innovation from the perspective of circular economy and provides a new idea for comprehensive utilization of secondary solar cells.

Characterisation of titania slag produced by a novel process: acidolysis performance

ABSTRACT The sulfuric acid leaching of titania slag produced by semi-molten state reduction of Panzhihua ilmenite concentrate followed by magnetic separation is studied. The titanium-bearing phase of the slag is mainly composed of anosovite (MxTi3-xO5, 0 ≤ x≤2, M represents: Ti, Fe, Mg, Mn, and Al) and M2O3 solid solutions. The titania slag was leached in two stages using sulfuric acid, with the second stage using a stronger acid, a higher acid to solid ratio, and smaller particles to further leach the titanium. The results showed that the overall acidolysis ratio of titanium in the titania slag with additive-free, addition of sodium carbonate, and addition of sodium sulfate is 0.90, 0.81, and 0.89 respectively. It was found that fine grinding of the titania slag is beneficial to the leaching of titanium. The overall recoveries of titanium in the novel process after sulfuric acid leaching for the additive-free, Na2CO3-added, and Na2SO4-added slags are 0.61, 0.76, and 0.79, respectively. The phase and morphology of the raw titania slag and leaching residue related to the leaching behaviour were also characterised.

An Integrated Capture of Red Mud and One-Step Heat-Treatment Process to Recover Platinum Group Metals and Prepare Glass-Ceramics from Spent Auto-Catalysts

Co-treatment for two kinds of hazardous solid waste is an effective method to reduce cost and increase recycle efficiency of value resource. This work developed an integrated process based on capture of red mud (RM) and a one-step heat-treatment process to efficiently recover PGMs from spent auto-catalysts (SAC) and reuse RM simultaneously. Firstly, the iron oxide in RM was reduced to metallic iron to capture PGMs by the reduction process, without the addition of an extra reducing agent, since SAC contained abundant organic volatiles. Then, the mixed waste of SAC and RM was melted under high temperature with additives of CaO and H3BO3. More than 99% of PGMs can be extracted under the optimal conditions of 40–50 wt% of RM addition, 14 wt% of H3BO3 addition, 0.7–0.8 of basicity, 1500 °C of temperature, and 40 min of holding time. In addition, PGM content in obtained glassy slag was less than 1 g/t. The mechanism of iron trapping PGMs was also discussed in detailed, which mainly contained two stages: migration of PGMs and separation of PGM-bearing alloy and slag phases. Besides, the obtained glassy slag was further prepared into glass-ceramic by a one-step heat-treatment process. It was found that the prepared glass-ceramic has good thermostability and an excellent stabilizing effect on heavy metals. Overall, the results indicated that the developed integrated smelting–collection process is an efficient and promising method for the reutilization of SAC and RM.

An experimental study on the phase equilibria of FeOx-saturated iron silicate slags and metallic copper alloys at 1200–1300 °C

The equilibrium phase relations between metallic copper alloys and magnetite/wüstite-saturated iron silicate slags were investigated at 1200–1300 °C and PO2 of 10−10 to 10−6.5 atm. The experiments involved high-temperature equilibration of samples in a controlled CO–CO2 atmosphere, followed by rapid drop quenching and direct measurement of the phase composition using the electron probe microanalysis technique. The equilibrium compositions for the metal and slag phase at different temperatures were displayed as a function of PO2. The present experimental results were compared with data from the literature as well as the thermodynamic assessment using MTDATA thermodynamic software. The present results contribute to the improvement of copper matte and black copper converting and slag cleaning processes.

Potential of Using Waste Incinerator Slag to Sequester Carbon Dioxide

Data on conditions and volumes of slag formation resulting from waste fuel incineration is presented, technological schemes of processing and disposal are made including carbon dioxide fixation. Results of gravitational-magnetic slag enrichment to process polymetallic bulk concentrate are achieved. Granulometric, chemical and mineral composition of fresh and unused slags resulting from waste incineration were measured. Differences of slag material composition depending on grain-size class were identified. Reaction equations of slag carbonization were studied. Reactivity of slag phases with respect to carbonic oxide was assessed. Carbonization potential of unused and fresh slags resulting from waste incineration was calculated depending on grain-size class.

Аналіз структурно–хімічного стану дуплекс–систем силікати–силіциди лужно–земельних металів. Повідомлення 2. Дуплекс–система SiO2–MgO–CaO: Si–Mg–Ca

A polygonal diagram of the state of the CaO-SiO2-MgO ternary system was constructed in the entire range of concentrations of solid and liquid initial components, which increases the informativeness of polygonal diagrams of the state of metallurgical systems. The obtained results of the SCS analysis of the silicate and silicide phases of the duplex system SiO2–MgO–CaO : Si–Mg–Ca are the scientific basis for the optimization of blast furnace iron refining processes with smelting slags and magnesium alloys. Keywords: polygonal diagram, magnesium slag, silicate and silicide phases of calcium, physicochemical, technological and quantum-mechanical parameters.

Effect of roasting activation of rare earth molten salt slag on extraction of rare earth, lithium and fluorine

A new process was proposed to extract rare earth elements (REEs), Li and F from electrolytic slag of rare earth molten salt by synergistic roasting and acid leaching. Firstly, the thermodynamic analysis of roasting reaction was carried out, then the effects of roasting factors on leaching REEs, Li and F in slag were investigated. In additions, the mineral phase and morphology of molten salt slag, roasting slag and acid leaching slag were characterized, and the migration mechanism of REES, Li and F minerals in roasting and leaching process was analyzed. The results show that the synergistic roasting and activation of molten salt slag by CaO and Al2(SO4)3 are thermodynamically feasible. The optimum roasting conditions are as follows: molten salt slag of 20 g, Al2(SO4)3 of 31.25 g and CaO of 6.25 g, roasting temperature of 1173.15 K and reaction time of 2 h, under this condition, the leaching rates of Nd, Pr, Gd, Li and F are 92.47%, 91.56%, 91.08%, 96.69% and 96.8%, respectively. X-ray powder diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis show that the rare earth fluoride (REF3) in molten salt slag transforms into soluble rare earth oxide (REO) after roasting and activation. After leaching, the leaching residue is mainly strip CaSO4, indicating that REES, Li and F can be fully extracted from molten salt slag.

Solid reactions between CaO–Al2O3 and Si–Ti-containing steel at 1273 K

Solid reactions between Si–Ti-containing steel and calcium aluminates with various CaO/Al2O3 ratios at 1273 K were studied. Particle precipitation zones (PPZs) were observed and analyzed for the composition and thickness. After heating at 1273 K for 10 h, 30 h, and 50 h, the composition of precipitated particles was Ca–Ti–O and TiOx in diffusion couples with a slag phase of CaO·Al2O3 (CA). The precipitates changed into mainly Ca–Si–O when the slag phase was 3CaO·Al2O3 (C3A) or 12CaO·7Al2O3 (C12A7). Elements of calcium and oxygen diffused from the slag phase to the steel phase were proved not to be from the decomposition of calcium aluminates, but ion diffusion under concentration gradients. The thickness of the PPZ increased from 1.5 μm to 14.8 μm with the increase of CaO/Al2O3 ratio of the slag phase and the heating time. The dissolved oxygen at the slag-steel interface calculated by the dynamic model demonstrated that the oxygen delivery capacity of calcium aluminates increased with their CaO/Al2O3 ratios. The evolution path of Ca–Ti–O to Ca–Si–O calculated by FactSage primely explained the precipitation variance of diffusion couples with various slag phases.

Dephosphorization kinetics of high-P-containing reduced iron produced from oolitic hematite ore

Abstract To comprehensively utilize Fe and P in oolitic hematite ore, an innovative method was proposed to enhance P enrichment in the reduced iron during the reduction process. The reduced iron was then converted to low-P-containing molten iron and high-P-containing slag in the presence of CaO–SiO2–FeO–Al2O3 slag. In this study, the P content of the final iron after 0–1,800 s dephosphorization was investigated at different slag composition conditions, and the dephosphorization kinetics of the reduced iron was analyzed. The results showed that the P content of the final iron sample decreased rapidly within 600 s of dephosphorization and became almost constant with increasing dephosphorization time to 1,800 s. The basicity, FeO content, and Al2O3 content also affected the dephosphorization rate of the reduced iron. The apparent dephosphorization rate constant ranged from 1.141 × 10−3 to 2.363 × 10−3 g·(cm2·s)−1, and the overall mass transfer coefficient ranged from 2.47 × 10−3 to 3.38 × 10−3 cm·s−1. The rate-controlling step of the dephosphorization process was the mass transfer of P in both the slag and iron phases. The findings of this study provide a theoretical basis for the utilization of refractory oolitic hematite ore.

Source removal of iron and aluminum impurities over vanadium in phosphate-sulfate complex anionic leaching system of the black shale

BackgroundThis work aims at achieving the source removal of Fe and Al impurities during the pressure leaching process of black shale, which is beneficial to the subsequent purification and enrichment of V. MethodsPhosphate ions were introduced into the sulfate single anionic leaching system (SSLS) to form the phosphate-sulfate complex anionic leaching system (PSCLS) of the black shale, which enhanced the complexing capability of the leaching system and enabled more of Fe and Al impurities to get transformed into complex precipitates. Significant findingsThe results show that the intervention of phosphate ions reduced the leaching efficiencies of Fe and Al by 82.1% and 47.3%, respectively. Due to the difference in affinity for phosphate and self-hydrolysis capability, Fe and Al impurities were converted into stable precipitates of iron phosphate hydroxide (Fe4(PO4)3(OH)3) and aluminum phosphate (AlPO4), respectively. As a result, Fe and Al impurities leached with V re-enter the slag phase, thus realizing the source removal of Fe and Al impurities.

Relationship between interaction under non-load condition and softening & melting behaviour of typical blast furnace feed

ABSTRACT The evolution of slag phases and interaction between sinter and acid pellet in cohesive zone were systematically investigated, as well as the relationship between microstructure, thermal calculation and S&M behaviour. The results indicate that both ‘component interaction’ and ‘formation interaction’ will be hindered before the formation of liquid phases. The effect of network iron at the interface on the interaction is more apparent than that of the relative position of materials. The main slag phases detected at the interface are FeO–CaO–SiO2, FeO–CaO–MgO–SiO2, FeO–CaO–Al2O3–SiO2 and FeO–CaO–MgO–Al2O3–SiO2. The relationship between interaction without load and S&M behaviour has been revealed through breaking down the complex process into the reaction between P–P, S–S and P–S. The main area that affects the pressure drop in cohesive zone is the melting region. Mixed burden is beneficial to enhance the interaction and promote the melting behaviour.

Selective Leaching of Inert Mineral Product and the RO Phase in Steel Slag with Acetum to Improve Total Fe Content.

The chemical and mineral components of the leaching residues obtained during the leaching of inert mineral product (IMP) and two samples of divalent metal oxide continuous solid solution (RO phase) by acetum at 20 °C were analyzed to reveal the selective leaching characteristics of the chemical and mineral components in steel slag, and clarify the leaching rates and differences of MgO and FeO in the RO phase. The results indicated that the content of total Fe (TFe) in the leaching residue increased, whereas the contents of CaO, SiO2, and MgO decreased during the leaching of the inert mineral product by acetum. Fe3O4 was insoluble in acetum. The leaching rates of the RO phase and metallic Fe were very low, while those of calcium silicate (C2S + C3S) and dicalcium ferrite (C2F) were quite high. MgO and FeO in the RO phase continuously leached over time, and the leaching rate of MgO reached 1.9 times that of FeO. Therefore, during the leaching of the RO phase by acetum, the FeO content increased, whereas the MgO content decreased. In conclusion, acetum leaching can effectively improve the TFe content of the RO phase and the inert mineral product.

Characterization of SiC and Si3N4 inclusions in solar cell Si scraps and their motion at the Si/slag interface

The separation of SiC and Si3N4 inclusions from solar cell Si scraps to the slag phase during slag refining is essential to the recovery and production of high-purity Si. This study characterized the SiC and Si3N4 inclusions in solar cell Si scraps, which formed large clusters with complex shapes. According to the experimental and theoretical investigations, the inclusions with large diameters were found to be conducive to passing through the Si/slag interface and then being retained in the slag phase. The favorable conditions such as positive overall wettability, high operating temperature, low viscosity slag, and prolonged-time can promote the small inclusion removal from molten Si scraps.

Value-added utilization of copper slag to enhance the performance of magnesium potassium phosphate cement

Copper slag, a byproduct of the production of copper metal, is difficult to be reused as supplementary cementitious material in the ordinary Portland cement due to the low content of active amorphous alumino-silicate and the high content of crystalline phases. This study proposes a high value-added utilization approach of copper slag to enhance the early performance of magnesium potassium phosphate cement (MPC). MPC is an expensive rapid repair material with excellent early mechanical property. The experimental results show that the addition of 40% copper slag lead to more than 30% growth of the 1 day's compressive strength of MPC mortar. The crystalline phases in copper slag, especially the fayalite (Fe2SiO4), could react and strongly increase the content of hydrates in MPC system. The reaction products of copper slag in MPC are mixtures of magnesium silicate hydrate (MSH), vivianite (Fe3(PO4)2•8H2O) and Fe-hydrotalcite (Mg4Fe2(OH)14·3H2O). The novel approach proposed in this study to reuse copper slag as a reinforcing agent of MPC not only consumes solid waste but also improves the performance and reduces the cost of high-end rapid repair materials of concrete.

Interaction mechanism between arsenate and fayalite-type copper slag at high temperatures

The interaction mechanism between sodium arsenate and fayalite-type copper slag at 1200 °C was investigated through XRD, XPS, HRTEM, TCLP and other technical means and methods. The results indicated that the proportions of sodium arsenate in the slag and flue gas phases were approximately 30% and 70%, respectively. The addition of sodium arsenate depolymerized the fayalite structure and changed it from a crystalline state to an amorphous state. The fayalite structural changes indicated that the [AsO4] tetrahedron in sodium arsenate combined with the [SiO4] tetrahedron and [FeO4] tetrahedron through bridging oxygen to form a silicate glass structure. The TCLP test results of the samples before and after the high temperature reaction of fayalite and sodium arsenate showed that after high temperature reaction, fayalite could effectively reduce the leaching toxicity of sodium arsenate, reducing the leaching concentration of arsenic from 3025.52 to 12.8 mg /L before and after reaction, respectively.

Microstructure Evolution and Improved Permeability of Ceramic Waste-Based Bricks.

The resource and large-scale utilization of waste ceramic materials, magnesium slag, and coal gangue are one of the important ways for the sustainable development in metallurgy, coal, and other related enterprises. In this paper, waste ceramic materials were used as aggregates; coal gangue and magnesium slag were used as mixed binder; and the all solid-waste-based permeable bricks with excellent performance were prepared by forming pressure at 5 MPa. The mechanical properties and water permeability of the all-solid-waste-based permeable bricks were evaluated. The results proved that the porous channel of permeable brick is mainly composed of waste ceramic materials with a particle size of 2–3 mm. Pore structures below 200 μm were mainly composed of fine aggregate and mixed binder. Using 60% coarse aggregate, 20% fine aggregate, 10% coal gangue, and 10% magnesium slag as raw materials, the all-solid-waste-based permeable bricks were obtained by pressing at 6 MPa and sintering at 1200 °C, which exhibited the best performance, and its water permeability, compressive strength, and apparent porosity were 1.56 × 10−2 cm/s, 35.45 MPa, and 13.15%, respectively. Excellent water permeability, compressive strength, and apparent porosity of the all solid-waste-based permeable bricks were ascribed to the high content of connecting open pores, and closely adhesive force were ascribed to the porous microstructure constructed by the grading of waste ceramic materials and the tight conjoined points of the liquid phases in coal gangue and magnesium slag at a high sintering temperature.

Chromium enrichment in different crystalline phases of Cr-containing slag under various basicities and equilibrium temperatures

Chromium enrichment in different crystalline phases of Cr-containing slag under various basicities and equilibrium temperatures

Numerical investigation of particle motion at the steel—slag interface in continuous casting using VOF method and dynamic overset grids

The capillary interactions are prominent for a micro-sized particle at the steel—slag interface. In this study, the dynamics of a spherical particle interacting with the steel—slag interface is numerically investigated using the volume of fluid method in combination with the overset grid technique to account for particle motion. The simulations have shown the particle’s separation process at the interface and successfully captured the formation and continuous evolution of a meniscus in the course of particle motion. A sensitivity analysis on the effect of different physical parameters in the steel—slag—particle system is also conducted. The result indicates that the wettability of particle with the slag phase is the main factor affecting particle separation behavior (trapped at the interface or fully separated into slag). Higher interfacial tension of fluid interface and smaller particle size can speed up the particle motion but have less effect on the equilibrium position for particle staying at the interface. In comparison, particle density shows a minor influence when the motion is dominated by the capillary effect. By taking account of the effect of meniscus and capillary forces on a particle, this study provides a more accurate simulation of particle motion in the vicinity of the steel—slag interface and enables further investigation of more complex situations.