Detection of the assimilation characteristics of iron ores: Dynamic resistance measurements

Resistance in iron ore undergoes a sharp change of up to several orders of magnitude when the sintered solid phase changes to liquid phase.In view of the insufficiency of existing assimilation detection methods,a timing-of-assimilation reaction is proposed,which was judged by continuously detecting the changes in resistance at the reaction interface.Effects of pole position and additional amounts of iron ore on assimilation reaction timing were investigated.The results showed that the suitable depth of pole groove was about 2 mm,and there was no obvious impact when the distance of the poles changed from 4 to 6 mm,or the amount of iron ore changed from 0.4 to 0.6 g.The temperature of sudden change of resistance in the temperature-resistant image was considered to be the lowest assimilation temperature of iron ore.The accuracy of this resistance method was clarified by X-ray diffraction,optical microscope,and scanning electron microscope/energy dispersive spectrometer(SEM/EDS)analyses.

A pilot-scale study of selective desulfurization via urea addition in iron ore sintering

The iron ore sintering process is the main source of SO_2 emissions in the iron and steel industry. In our previous research, we proposed a novel technology for reducing SO_2 emissions in the flue gas in the iron ore sintering process by adding urea at a given distance from the sintering grate bar. In this paper, a pilot-scale experiment was carried out in a commercial sintering plant. The results showed that, compared to the SO_2 concentration in flue gas without urea addition, the SO_2 concentration decreased substantially from 694.2 to 108.0 mg/m^3 when 0.10wt% urea was added. NH_3 decomposed by urea reacted with SO_2 to produce（NH_4）_2SO_4, decreasing the SO_2 concentration in the flue gas.

Disposal of zinc extraction residues via iron ore sintering process:an innovative resource utilization

Zinc extraction residue,a solid waste generated from the treatment of zinc-containing dust in rotary kilns,is commonly stockpiled in steel companies for extended periods.It poses significant disposal challenges and environmental pollution risks.So far,research on the treatment of zinc extraction residues has been slow,inadequate,and sporadic.For this gap,a novel approach was proposed to effectively treat the zinc extraction residue via the iron ore sintering process.It was feasible to add 1 wt.%of zinc extraction residues to the sintering raw materials.The more adequate mineralization reaction resulted in higher yield and tumbler indexes,despite a slight decrease in sintering speed.Although this may result in a slight decrease in sintering speed,the more complete mineralization reaction leads to improved sintering yield and tumbler index.Interestingly,the addition of zinc extraction residues reduced the CO and NO_(x) concentrations in the sintering flue gas.Thus,the iron ore sintering process provided a viable solution for resource utilization and environmentally friendly treatment of zinc extraction residues.

Effect of quaternary basicity on reduction behavior of iron-bearing dust pellets

The treatment of iron-bearing dusts and sludges by the rotary hearth furnace process has the advantage of sufficient utilization of valuable metals and a high impurity removal rate,but the lower strength of the metallized product needs to be addressed.The effects of quaternary basicity R4(w(CaO+MgO)/w(SiO_(2)+Al_(2)O_(3)))on the reduction behavior and physical and chemical properties of metallized pellets,including phase composition,compressive strength,microstructure and soft melting area,were investigated with FactSage thermodynamic software and experiments.The strength of metallized pellets depended on the gangue composition,such as CaO,MgO,Al_(2)O_(3) and SiO_(2),due to the altered chemical composition,physical phase composition,microscopic morphology and stability of the slag phase.The reduction of carbon-bearing pellets was significantly promoted by suitable basicity.The lower basicity(R_(4)<1.4)facilitated the formation of low melting point iron-containing compounds from SiO_(2) and Al_(2)O_(3) with FeO,resulting in increased liquid phase generation,but lower metallization rate,due to the hindered precipitation and growth of iron grains.Interestingly,the higher basicity(R_(4)>1.8)also increased the amount of liquid phase and improved the strength of the pellets,due to the granular iron crystals bonded into sheets.Notably,the main component of the liquid phase in high-basicity conditions was calcium ferrite.Although the additional amount of liquid phase was beneficial to the strength of the metallized pellets,calcium disilicate was formed at R_(4)=1.6,resulting in a reduction in the compressive strength of the pellets to 1521.9 N/pellet.

Application of steam injection in iron ore sintering:fuel combustion efficiency and CO emissions

Improving the combustion efficiency of fuels is essential to reducing pollutant emissions in the iron ore sintering process.The sintering bed surface steam-injection technology has attracted significant research interest for its potential advantages in low-energy consumption and low emission.The effect of steam injection on fuel combustion efficiency and CO emission was studied by comparing the thermodynamic response from the sintering process before and after steam injection.The mechanism of improving combustion efficiency was also revealed.The results indicated that the sintering gas medium of H_(2)O-H_(2)-N_(2)-O_(2) with the blown steam improved the heat transfer conditions of fuel combustion and promoted the water gas reaction.The optimum state of steam injection was achieved at 15 min after ignition with 0.02 m^(3) min^(-1).The CO emission reduction is 10.91% compared with the base case.The combustion efficiency was 88.83%,6.15% higher than conventional sintering,and the solid fuel consumption was reduced by 1.15 kg t^(-1).It was indicated that steam injection would improve combustion efficiency and reduce solid fuel consumption.Meanwhile,the steam injection could improve the combustion kinetic conditions in the zone of unburned fuel and low oxygen partial pressure.It was conducive to the reaction of H_(2)O with C and CO to convert the CO of reducing atmosphere to CO_(2),which in turn realized the complete combustion of fuel and CO and improved the efficiency of fuel combustion.

Agglomeration and bonding mechanism of typical metallurgical solid wastes

The agglomeration of solid wastes is a key factor for subsequent utilization,while the difficulty in agglomeration and high cost have become common problems in the recycling process.The disk pelletizing process was adopted,based on the optimization method by liquid binder addition,and the influence mechanism of the ratio of typical solid wastes as blast furnace dust(BFD)and sludge generated by oxygen converter gas recovery(OGS)was explored.Meanwhile,the effect of binder solution concentration on the quality of green pellets was studied.Derived from the contact angle detection and infrared spectrum analysis,the liquid bridge model was established to study the bonding mechanism.The results showed that OGS had stronger adsorption effect with binder,and the hydrophilicity of BFD was better.When the concentration of binder was higher than 0.2 wt.%,the contact angle between the binder and BFD was bigger than that with OGS,while the capillary force between particles reduced with larger contact angle.The increment in the binder concentration increased the viscous force between particles and the maximum separation distance.The ultimate drop strength and compressive strength were related to the type of viscous force,and the compressive strength reflected the strength of the force between particles intuitively,while the drop strength represented the comprehensive forces of green pellets.Reasonable combination of BFD and OGS was available for pelletizing process,while the ratio of BFD should not exceed 32.0%,and binder C was added in the form of solution with the addition amount of 0.4 wt.%,which can reduce the cost of binder by 20–30¥/t.

Preparation and properties of silane coupling agent modified steel slag as functional filler for anti-corrosion coating

The chemical composition and high wear resistance of steel slag(SS)make it a potential alternative to traditional inorganic fillers.3-Aminopropyltriethoxysilane(KH550)modified steel slag(MSS)was successfully prepared,and its application in epoxy(EP)anti-corrosion coating was introduced.Due to the grafting of silane coupling agent functional groups onto the surface of SS,MSS exhibited improved solubility in xylene organic solvent and reduced agglomeration.When the MSS content was 15 wt.%,the contact angle of the MSS/EP composite coating was 101°,and the abrasion was only 0.07 g,compared with 56.2°and 0.13 g,respectively,for the pure EP coating.The corrosion resistance of coatings was investigated by performing the electrochemical test(impedance)after immersion in a 3.5 wt.%NaCl solution.The electrochemical test results showed that the impedance modulus of the 15 wt.%MSS/EP composite coating at low frequency(Z_(f)=0.01 Hz)was approximately 1.08×10^(7)Ωcm^(2),which was two orders of magnitude higher than that of the pure EP coating.

Resource utilization of flue gas calcium-based desulfurization ash:a comprehensive review

Calcium-based desulfurization ash(CDA)is mainly produced in dry and semi-dry flue gas desulfurization processes.The property of CDA is extremely unstable because its main component,calcium sulfite,makes it difficult to be directly applied to the field of building materials.The modification of desulfurization ash can be realized by high-temperature oxidation and wet oxidation.After modification,CDA can be widely used in building materials.Hydrothermal oxidation has broad development prospects because it can complete the oxidation of CDA and the removal of impurity elements at the same time.CDA can be used to prepare high value-added products of calcium sulfate whiskers and ecological rubber fillers.

Drop strength measurement of green pellet based on drop-rebound mechanism

The construction of blast furnace charge structure based on pellet and the development of short process from non-blast furnace to electric furnace will be an efficient way to accomplish"carbon peak,carbon neutral".Since drop strength is one of the most crucial quality indexes for green pellet,the crack detection in the collision process is an indispensable segment;however,the present crack determination is basically completed manually.Due to a series of problems including high labor intensity and poor detection conditions,it is urgent to develop an accurate,convenient and fast standardized method for drop strength detection.In view of the above issues,combined with plenty of experimental studies,it is found that whether rebound occurs after the collision of green ball can be used as the basis for judging if there are cracks on the surface,and the mechanism of this segment is explained by the energy conversion of collision process that the plastic deformation of the collision is a cumulative process.Each collision will cause a slight displacement of the iron ore particles;until the cumulative displacement exceeds the binding force between the particles,they will slip in a large range,that is,cracks will occur.The drop strength can be detected based on the drop-rebound mechanism determining crack generation during collision process by high-speed cameras,and the method is fully applicable to oxidized pellets with particle size of 8-16 mm though various pellet plasticities and masses increase the difficulty of bounce height monitoring.Based on the drop-rebound mechanism of green pellet,three methods for automatically detecting the drop strength are proposed,which are high-speed camera,photoelectric sensor and pressure sensor methods.

N-doped C-coated MoO_(2)/ZnIN_(2)S_(4)heterojunction for efficient photocatalytic hydrogen production

Designing a heterojunction photocatalyst to improve the separation efficiency of photogenerated electrons and holes is of great significance to improve the hydrogen production efficiency.In this work,we report a rational design to grow ZnIN_(2)S_(4)on Mo-MOF-derived N-doped C-coated MoO_(2)(MOZIS),and it has excellent photocatalytic hydrogen production with triethanolamine(TEOA)as sacrificial agent.N-doped C improves the electron transport efficiency between MoO_(2)and ZnIN_(2)S_(4)·The systematic study shows that MOZIS has good properties to promote the effective separation and transfer of photocatalytic charges,which is attributed to the tight contact interface and good energy band structure between MoO_(2)and ZnlN_(2)S_(4).The optimized nanocomposites have a high hydrogen production efficiency of 10.89 mmol·g^(-1)(4 h)under visible light.MOF-derived N-doped C-coated MoO_(2)is an effective strategy to improve the photocatalytic hydrogen production efficiency of ZnIN_(2)S_(4).

Preparation and properties of flame-retardant rubber composites based on steel slag filler

Ultrafine steel slag powder(shield powder)was prepared by grinding ordinary steel slag with a functional compound.As a substitute for aluminum hydroxide,the shield powder was combined with rubber to prepare flame-retardant composites.Vulcanization tests showed that the incorporation of shield powder enhances the crosslinkage of the composite and speeds up the curing rate.The gaseous products formed in the pyrolysis process are mainly hydrocarbons.Mechanical and combustion tests revealed that the introduction of shield powder improves flame-retardant performance without sacrificing mechanical properties.Specifically,the optimum substitution ratio of shield powder for aluminum hydroxide is 50.0%.In this case,the composite has the highest degree of graphitization and exhibits excellent flame-retardant performance.

Special issue on resources recycling of solid wastes from ironmaking and steelmaking

Driven by the double carbon policy,the iron and steel industry urgently needs to implement a new development concept to strengthen the use of solid waste resources from ironmaking and steelmaking and effectively enhance the economic benefits of recycling resources in order to reduce the accumulation of solid waste resources in the iron and steel industry.The iron and steel production process produces more than 600 million tons of solid waste annually,including metallurgical dust sludge,blast furnace slag and steel slag,etc.From the perspective of environmental friendliness,the efficient utilization of ironmaking and steelmaking solid waste resources through innovative cross-industry technologies is of great significance to the low-carbon,green and high-quality development goals of the iron and steel industry.

Application status and comparison of dioxin removal technologies for iron ore sintering process

The emission of dioxins from the iron ore sintering process is the largest emission source of dioxins, and the reduction in dioxin emission from the iron ore sintering process to the environment is increasingly important. Three approaches to control the emission of dioxins were reviewed： source control, process control, and terminal control. Among them, two terminal control technologies, activated carbon adsorption and selective reduction technology, were discussed in detail. Following a comparison of the reduction technologies, the terminal control method was indicated as the key technology to achieve good control of dioxins during the sintering process. For the technical characteristics of the sintering process and flue gas, multiple methods should be collectively considered, and the most suitable method may be addition of inhibitors ＋ ultra-clean dust collection （electrostatic precipitation/bag filter） ＋ desulphurization ＋ selective catalytic reduction to sufficiently remove multiple pollutants, which provides a direction for the cooperative disposal of flue gas pollutants in future.

Effect of metallurgical dust on NO emissions during coal combustion process

NO emissions from coal combustion are receiving significant attention in recent years. As a solid waste generated from metallurgical industry, metallurgical dust （MD） contains a large amount of metal oxides, such as Fe2O3, CaO, SiO2 and Al2O3, as well as other rare metal oxides. The influence of MD on the NO emissions and the mechanism of the coal com- bustion systems were analyzed. The results show that the peak values of NO emission decrease with the increase in MD mass percent, and the curve of NO emission can be divided into two stages including rapid generation （400-600 ℃） and slow release （800-900 ℃）. The reduction of NO is significantly affected by temperature, volatile components, 02 and CO. CO has a significant catalytic action which can deoxidize NO to N2. The results obtained by X-ray diffraction and scanning electron microscopy indicate that multiple components in MD, such as FegTiO15, Fe2O3 and TiO2, can react with NO to produce TiN. Besides, the alkali metals in MD, such as Na, K and Ca, may catalyze NO precursor to inhibit NO emission. These results indicate that MD is cheap and highly efficient in controlling NO emissions during coal combustion processes.

Low-temperature oxidation behavior and mechanism of semi-dry desulfurization ash from iron ore sintering flue gas

The low-temperature wet oxidation behavior of semi-dry desulfurization ash from iron ore sintering flue gas in ammonium citrate solution was investigated for efficiently utilizing the low-quality desulfurization ash. The effects of the ammonium citrate concentration, oxidation temperature, solid/liquid ratio, and oxidation time on the wet oxidation behavior of desulfurization ash were studied. Simultaneously, the oxidation mechanism of desulfurization ash was revealed by means of X-ray diffraction, Zeta electric resistance, and X-ray photoelectron spectroscopy (XPS) analysis. Under the optimal conditions with ammonium citrate, the oxidation ratio of CaSO_(3) was up to the maximum value (98.49%), while that of CaSO_(3) was only 8.92% without ammonium citrate. Zeta electric resistance and XPS results indicate that the dissolution process of CaSO_(3) could be significantly promoted by complexation derived from the ammonium citrate hydrolysis. As a result, the oxidation process of CaSO_(3) was transformed from particle oxidation to SO_(3)^(2−) ion oxidation, realizing the rapid transformation of desulfurization ash from CaSO_(3) to CaSO_(4) at low temperature. It provides a reference for the application of semi-dry desulfurization ash and contributes to sustainable management for semi-dry desulfurization ash.

Physicochemical properties of coconut husk activated carbon modified by Fe(N0_(3))_(3)and Mn(N0_(3))_(2)

Fe-loaded activated carbon(AC)has high surface acidity and more active sites,while manganese-loaded AC has high oxygen content.Coconut husk AC modified by Fe-Mn was studied with the aim of revealing the modification mechanism.First,HNO_(3)AC was prepared using the nitric acid immersion method.Second,Fe-Mn/AC was prepared using the Fe(N0_(3))_(3)and Mn(N0_(3))_(2)sequential immersion.The effects of HNO_(3),Fe(N0_(3))_(3),and Mn(N0_(3))_(2)on the pore texture and surface chemical characteristics of carbon materials were examined by scanning electron microscopy,Brunauer-Emmett-Teller(BET)analysis,X-ray diffraction and Fourier-transform infrared spectroscopy.The surface topography,pore structure,active material,and functional groups of AC,HNO_(3)/AC,and Fe-Mn/AC were systematically studied.The following results were obtained.The surface of HNO_(3)AC has more ditches and air voids;the micropores of HNO_(3)AC are deformed and flattened compared to those of AC.The surface of Fe-Mn/AC exhibits an accumulation phenomenon.MnFe_(2)O_(4)and FeMn_(2)O_(4)formed more pore structures.AC and HNO_(3)AC have numerous micropores.The higher loading quantity of Fe-Mn results in bigger specific surface.The active components of Fe-Mn/AC-1,Fe-Mn/AC-2,Fe-Mn/AC-3,and Fe-Mn/AC-4 are MnFe_(2)O_(4),MnO_(0.43)Fe_(2.57)O_(4),Mn_(3)O_(4),and ot-Fe_(2)O_(3)>respectively.The surface functional groups of AC and HNO_(3)AC are oxygen-containing functional groups.The effect of Fe-Mn modifying conditions on functional group species is rare;however,Fe/AC has more oxygen-containing functional groups.These research findings can aid in the desulfurization and denitrification of the Fe-Mn/AC catalyst.

Determination method of high-temperature characteristics of iron-ore sintering based on n(Fe2O3)/n(CaO)

The high-temperature characteristics of iron ores play important roles in optimizing ore proportion of sintering,which are tested by using iron-ore fines and analytical reagent CaO as raw materials.Two calculation methods of CaO addition amount based on binary basicity(basicity method)and n(Fe2O3)/n(CaO)(mole ratio method),respectively,were employed to evaluate the liquid phase fluidity(LPF)and the capability of calcium ferrite formation(CCFF)of iron ores.The results show that the rule of LPF of iron ores under the mole ratio method is different from that with basicity method.The LPF measured by basicity method has a linear positive correlation with the SiO2 content,and there is no linear relationship between LPF and Al2O3 content or mass loss on ignition,which are inconsistent with the results of the previous study.And the results of CCFF with low SiO2 content(<3 wt.%)or high SiO2 content(>7 wt.%)based on basicity method cannot reflect the true CCFF.The mole ratio method could successfully solve this problem by reducing the effect of CaO addition amount changes caused by SiO2 content of iron ores.

Preparation of Chromium-iron Metal Powder from Chromium Slag by Reduction Roasting and Magnetic Separation

Chromium slag（CS）has become one of the most hazardous solid waste containing chromium and iron.Based on its characteristics,the technology of reduction roasting and magnetic separation was employed to treat CS.The major impurity element of CS is magnesium and it exists in magnesium ferrite phase,which is hard to recover iron in the absence of additives.During reduction roasting,additives（Al2O3and CaF2）could destroy the structure of magnesium ferrite and improve the iron grade and recovery.The final product,i.e.chromium-iron powder,contains 72.54% Fe and 13.56% Cr,with the iron recovery of 80.34% and chromium recovery of 80.70%.

Effects of gangue compositions on reduction process of carbonbearing iron ore pellets

The influence of gangue compositions (mainly composed of SiO2,CaO,MgO and Al2O3)on the reduction kinetics of carbon-bearing iron ore pellets was estimated at 1373-1473 K in N2 atmosphere.The results showed that gangue content and each component distribution affected the pellets reduction process.The reduction rate was found to follow a linear correlation with quaternary basicity R4 [mass ratio of (CaO +MgO)to (SIO2 +Al2O3)]of the carbon-beating iron ore pellets;also,the content of SiO2 solid solution in iron oxide had a significant impact on the reduction rate.At the same reduction temperature,a higher R4 resulted in a lower SiO2 free content,weakening its inhibitory effect on the Boudouard reaction.The reduction temperature of Fe2SiO4 could be reduced by increasing the contents of CaO and MgO,improving the iron oxide reduction as well as the precipitation and growth of the iron grains.The g'angue content and .component distribution showed no effect on the rate-controlling step of the reduction;however,the apparent activation energy of reaction decreased with increasing quaternary basicity.When R4 increased from 0.15 to 0.67,the apparent activation energy decreased from 228.51 to 193.66 kJ/mol.

Visualization of collision and aggregation behavior of particles simulating movement of inclusions in molten steel

Inclusions with sizes less than 1 μm in molten steel are difficult to float up to the molten steel and slag interface owing to their slow terminal velocity. Thus, increasing the size of inclusion is essential for accelerating the removal of inclusions. Polystyrene particles simulating inclusions in molten steel were quantified by direct observation of the particle collision behavior in a turbulent flow in a water model. The box-counting fractal dimension of particles was calculated by processing the binary images of aggregated particles. The fractal dimension of the outer contours of the single plastic particles was smaller than that of the aggregated particles. The fractal dimension was varied from 1.14 to 1.35. When two or more monomer particles collide, the aggregates are separated more easily, as the temperature increases from 40 to 80 ℃. The aggregated particles were loose and easy to separate in the high-temperature aqueous solution. The effect of temperature on the surface tension of liquid and the interracial tension of solid and liquid is obvious. The particles are wetting in the water solution at a temperature more than 60 ℃. The relationship between the velocity of the particles and the fractal dimension of the solid particles with the equivalent diameter was discussed.