Green Pellets Research Articles

Effect of V2O5 on Consolidation, Reduction, and Softening-Melting Behavior of High-Cr Vanadium Titanomagnetite

Vanadium titanomagnetite is an important mineral resource. It is a raw material for ironmaking, vanadium extraction, strategic metal titanium production, and titanium dioxide production. In this study, high chromium vanadium titanomagnetite (High-Cr VTM) and ordinary iron ore were used as raw materials for pelletizing. The effect of V2O5 on the preparation and properties of High-Cr VTM pellets was studied. The influence of V2O5 on the properties of the green pellets, the compressive strength of oxidized pellets, the reduction swelling index and reduction degree, softening-melting behavior, and the migration law of Fe, Ti, and Cr in the reduction process were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that with the increase in V2O5 content, the properties of the green pellets basically showed a trend of first decreasing and then increasing but all met the basic requirements of pelletizing. When the added amount of V2O5 in the pellet was 6%, the compressive strength of the oxidized pellet was the lowest at only 2565 N/pellet but it still met the quality requirements for pellets in blast furnace production. As the dosage of V2O5 increased, the reduction swelling index and reduction degree of the pellets showed a trend of first increasing and then decreasing. The addition of V2O5 can increase the softening initial temperature, softening final temperature, melting start temperature, and dripping temperature of the High-Cr VTM pellets, narrowing the softening interval, and expanding the melting dripping interval. The experimental results provided a data reference for revealing the influence of V2O5 on High-Cr VTM pellets during the blast furnace smelting process.

Consolidation behavior of magnesium-containing pellets prepared by high-silica coarse particle magnetite concentrates

Magnesium-containing pellets were prepared using high-silica coarse particle magnetite concentrate and analyzed the mechanism of magnesium element influences pellet consolidation behavior during green pellet preparation, oxidation preheating, and roasting, and the migration-diffusion behavior of magnesium additives. The addition of magnesium-containing additives reduced the green pellet strength. When using magnesite as an additive to magnesium, the preheating temperature needs to reach above 1050 °C, and the suitable roasting temperature is between 1250 °C–1280 °C. When lightly burned magnesite is used as an additive of magnesium, the preheating temperature needs to reach above 1120 °C, and the suitable roasting temperature range is 1220 °C–1280 °C. MgO in the pellet increases, and the preheating temperature needs to increase. The preheating process of high-silica magnesium-containing pellets mainly occurs based on the decomposition of magnesium-containing additives and solid-phase reactions, and MgO primarily exists in the form of Mg2SiO4 and MgFe2O4 during the roasting and consolidation process.

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

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

Evaluation of sugar cane bagasse hydrothermal liquefaction products for co-gasification with coal as green coal pellet production

This study investigates the production and properties of green coal pellets formed by combining hydrochar and coal in different ratios (3,1, 1:1, and 1:3). It was found that higher ratios of hydrochar to coal resulted in increased mechanical strength of the green coal pellets, highlighting the binding properties inherent in hydrochar. Furthermore, all the green coal and hydrochar pellets exhibited remarkable hydrophobic qualities. Among the different ratios tested, the green coal pellets composed of equal amounts of hydrochar and coal demonstrated the most favourable pyrolysis behaviour based on these indices. The gasification reactivities (R50%) at 1000 °C were measured as 107.9 min−1 for hydrochar pellets, 28.2 min−1 for sugarcane bagasse pellets, and 17.7 min−1 for coal. By blending coal with hydrochar, the green coal pellets exhibited improved pyrolysis and gasification properties compared to coal alone. Notably, the synergistic effect observed in the green coal samples increased with higher ratios of hydrochar.

Direct Laser Sintering of Bulk Alumina Using 1070 nm Fiber Laser

Pellets made of α-alumina were sintered by fiber laser irradiation (1070 nm) for 1 min. The optical measurements showed that the laser selectively applied heat around the voids and gaps between grains in the green pellets. Even though the laser can penetrate deep inside the pellets, the heating efficiency is low because alumina poorly absorbs the laser energy. The graphite layer effectively improved the heating efficiency on the irradiated surface at the low-temperature region to “ignite” laser sintering. The microstructure of the sintered pellets was controlled by the microstructure of the green bodies. Porous pellets were obtained from coarse powders and transparent dense pellets from mixtures of coarse and fine powders. The porous pellets showed excellent bending strength owing to the joining of grains by the selective heating of gaps between them. The transparent pellets comprised large alumina single crystals anisotropically formed by spontaneous melt growth under laser irradiation.

Effect of Storage Period on Physical, Sensory and Mechanical Characteristics of Green Fodders Pellets, Dry Fodders Pellets and Concentrates Pellets

Background: Indian farmers are facing shortage of green and dry fodders to feed their livestock during dry period (lean period) which possess a major hurdle in improving livestock productivity. This study delineates, pelleting of green, dry fodders and concentraes in order to meet out the fodder requirement during winter/lean period, which will in turn consequently improve livestock productivity. Methods: The experiments were conducted at Forage Pelleting Unit, Department of Forage Crops in Agricultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu from December 2020 to June 2022 to identify the best suitable fodder crops for pellets production. Three laboratory experiments laid out in completely randomized block design (CRD) were conducted with three replication. Each experiment of pelletisation had different treatments, viz., experiment I with 13 different categories of green fodder, experiment II with 11 different types of dry fodders and experiment III with 9 types of concentrates. Result: The observation of physical characteristics (colour and odour) and sensory characteristics (mould) were noted at regular intervals from date of pelleting, 60 days after pelleting, 120 days after pelleting and 180 days after pelleting. The mechanical characteristics such as pellet durability index (PDI) was recorded by using a tumbling can apparatus. The PDI was remained steady over the period of time. In case of pellets made from certain fodder sources, the colour was not the same and odour was not favourable when the pellets were kept for longer duration (beyond 120 DAP). Except for the agathi pellets, cumbu stover pellets and sorghum grain pellets, all other feed pellets were mold-free.

Authigenic Fe Mineralization in Shallow to Marginal Marine Environments: A Case Study from the Late Paleocene—Early Eocene Cambay Shale Formation

The late Paleocene–early Eocene warm greenhouse conditions, characterized by elevated pCO2 levels in the atmosphere and a dramatic increase in sea surface temperature, prompted abundant authigenic glauconite formation within the shallow marine sediments worldwide by lowering the net sedimentation rate, increasing organic productivity and expanding the oxygen minimum zones to shallow oceans. The early Eocene marginal marine Cambay Shale Formation experienced episodes of marine inundation represented by limestone–green shale alternations. The shales host abundant authigenic light-green, dark-green, and brown pellets. A detailed characterization of the pellets of the Valia and Vastan lignite mines, integrating the sedimentological, petrographical, mineralogical, and mineral geochemical data, suggests two distinct varieties of Fe–silicate formation, viz. glauconite and chamosite. While the glauconitic green pellets are ubiquitous to Valia and Vastan mines, brown chamosite pellets are confined within the basal part of the green shale facies alternating with fossiliferous limestone in the Vastan mine. The glauconites of the Valia mine manifest a ‘nascent’ to ‘slightly evolved’ maturation stage of glauconitization, whereas the glauconites of the Vastan mine represent the ‘evolved’ type. The limestone–green shale alternation in the Valia mine is overlain by a ~4 m-thick spherulitic mudstone facies comprising monomineralic sideritic spherulites, reflecting a pure FeCO3 composition. The glauconites in the Cambay Shale Formation transformed from kaolinite-rich clay pellets under dys-oxic depositional conditions. The increasing anoxicity within the microenvironment, possibly amplified by the rapid oxidation of continent-derived organic matter, facilitated chamosite formation instead of glauconite. The increased freshwater influx into the marginal marine depositional environment resulted in immature, K-poor glauconites of the Valia mine. The formation of siderite spherulites overlying the limestone–green shale alternation relates to the beginning of the regressive phase of sedimentation.

Simulation of Classification and Stratification in Double-Deck Roller Screening of Green Iron Ore Pellets using DEM

Simulation of Classification and Stratification in Double-Deck Roller Screening of Green Iron Ore Pellets using DEM

Porous 8YSZ Ceramics Prepared with Alkali Halide Sacrificial Additives.

8 mol% Y2O3-stabilized ZrO2 (8YSZ) ceramics were prepared with KCl and LiF additions to obtain porous specimens with high skeletal density. Thermogravimetric and differential thermal analyses (TG/DTA) were carried out on 8YSZ and on 8YSZ mixed to 5 wt.% KCl or 5 wt.% LiF as sacrificial pore formers that were thermally removed during sintering. The melting and evaporation of the alkali halides were evaluated by differential thermal analysis. Dilatometric analysis was also carried out following the same TG/DTA temperature profile with results suggesting rearrangement of the 8YSZ particles during LiF and KCl melting. The dilatometric data of 8YSZ green pellets mixed to KCl or LiF exhibited an initial expansion up to the melting of the alkali halide, followed by shrinkage due to sintering evolution with grain growth and pore elimination. The time that the alkali halide molten phase was kept during sintering was found to be an important parameter for obtaining 8YSZ-sintered specimens with specific pore content; bulk density and open porosity could then be tuned by controlling the time the alkali halide remained liquid during sintering. Scanning electron microscopy images of the pellet fracture surfaces showed pores that contributed to increasing the electrical resistivity as evaluated by impedance spectroscopy analysis.

Porous Stainless Steel Microsphere Synthesis by a Nonconventional Powder Metallurgy Process Useful in the Cermet-Type Advanced Nuclear Fuel Fabrication

The fabrication of SS (stainless steel)-UO2 cermet-type advanced nuclear fuel pellets suitable for use in power reactors depends on the development of metallic (SS), ceramic (UO2), and cermet (SS-UO2) microspheres with special characteristics. In this work, a nonconventional powder metallurgy process was developed to produce porous SS microspheres aiming to contribute to solve the bottlenecks found in the SS-UO2 cermet pellet manufacturing. SS, UO2, and SS-UO2 microspheres and SS-UO2 cermet pellets were fabricated and characterized (XRD, EDX, EDS, and SEM). Hard (153 ± 5 µm; 132.2 ± 24.7 MPa; 72% TD) and soft (216 ± 10 µm; 1.3 ± 0.4 MPa; 17% TD) SS, hard (176 ± 6 µm; 147.4 ± 25.0 MPa; 99% TD) UO2, and cermet (SS-UO2) microspheres were obtained. The soft porous SS microspheres did not micronize properly in situ, but their high compressibility favors the compaction of the green SS-UO2 cermet pellet; in this pellet, the UO2 microspheres behaved as rigid inclusions. This favored the obtainment of sintered SS-UO2 cermet pellets with high geometric densities (93% TD), excellent metal–ceramic interaction, and the preservation of the physical integrity of the UO2 microspheres. The usage of high fractions of the SS-UO2 cermet microspheres obtained mixed with low fractions of the said soft porous SS microspheres is already under development. This will enable the fabrication of SS-UO2 cermet pellets with a volume fraction greater than 42 vol% UO2, a homogeneous distribution of UO2 microspheres in the metallic matrix, and null connection between them. The oxide–metal reduction mechanisms were discussed. The applicability of the process is already being explored in the manufacture of porous NdFeB microspheres.

A Review on the Humic Substances in Pelletizing Binders: Preparation, Interaction Mechanism, and Process Characteristics

Humic acid is inexpensive, and has a wide range of sources and a strong adsorption force with the surface of iron ore, and the size of its adsorption force is affected by some factors such as humic acid concentration, pH of the solution, and metal cations. The modified humic acid pellet binder (MHA) with strong adhesion and high viscosity was obtained through the separation and purification of solid wastes such as lignite and weathered coal and chemical modification treatment and successfully applied in the production process of iron ore pellets. After industrial tests, MHA can significantly improve the strength of green and dry pellets, less residue after high-temperature roasting, less metallurgical pollution, high strength of fired pellets, and can partially or completely replace bentonite.

Novel resource utilization approach of spent catalyst from flue gas denitrification: Preparing high quality titanium-bearing pellets

Spent titanium-based catalyst is a waste generated by the selective catalytic reduction (SCR) denitrification process, whose generation is dramatically increasing in the iron and steel industry year by year. A novel approach was proposed in this work to prepare titanium-bearing pellets by using spent catalyst. The influences of spent catalyst addition on the comprehensive properties of pellets were studied. The corresponding relationship between the change of phase structure and the spent catalyst pellets' strength was investigated. The results demonstrated that the spent catalyst could be adsorbed on the surface of ore particles physically and chemically, improving the adhesion of particles inside the pellet and the hydrophilicity, thus obtaining good comprehensive performance of the green pellets. When adding 5.0 wt% spent catalyst, the bentonite dosage could be reduced by 50%, and the strength of roasted pellets could meet the requirement of large blast furnaces. The consolidation mechanism of the spent catalyst pellets indicated that TiO2 reacted with FeO first to generate FeTiO3 in the preheating process and further oxidized to form Fe2TiO5 in the roasting process. The unreacted TiO2 would appear in the roasted pellets and inhibit recrystallization and polycrystalline growth of Fe2O3 grains, resulting in the reduction of compressive strength. Overall, high-quality titanium-bearing pellets could be obtained when the amount of spent catalyst was less than 5.0 wt%. This study thus provided an alternative route to resource utilization of spent catalysts in iron and steel enterprises.

Study on the drying characteristics of green pellets of ultrafine iron ore concentrate

Ultrafine iron ore concentrate pose challenges like poor pellets formation performance, low-bursting temperature, and a complex drying thermal regime. To examine the drying characteristics of green pellets of ultrafine iron ore concentrate, we employed Weibull distribution function and Dincer model to fit and analyze the corresponding drying curve. The effects of drying temperature and air speed on the strength of dried pellets were also studied. Our findings reveal that the drying process of green pellets of ultrafine iron ore concentrate involves three stages: ascending speed, constant speed, and descending speed. As the drying temperature and air speed increase, the drying time decreases. The coefficient of determination R2 for the fitted Weibull distribution function model ranged from 0.995 to 0.998, while the R2 value for the Dincer model ranged from 0.990 to 0.996. Both fitted models align with experimental data and prove to be effective. According to the Bi values obtained through the Dincer model, raising the drying air speed in the initial stage and the drying air temperature in the subsequent stage of the drying system can efficiently remove moisture, reduce green pellets rupture risk, and maintain productivity. The moisture diffusion coefficient and convective mass transfer coefficient increase with rising temperature and air velocity, following the order of Deff > Dcal > D*eff as determined by the Weibull distribution function, Dincer model, and Fick's second law. Additionally, the activation energy value of ultrafine iron ore concentrate for drying derived from the Arrhenius formula is 4515.60 J/(mol?K). Notably, increasing drying temperature increases the strength of dried particles due to their more compact and dense internal structure. This study offers theoretical support for simulating the drying of green ultrafine iron ore concentrate pellets and provides guidelines for selecting diverse drying conditions and designing drying equipment.

Effect of high basicity on compressive strength and microstructure of iron ore pellets containing TiO2

A laboratory study is carried out to characterize the effect of basicity (varying 1.5–3.5) on magnetite iron ore pellets containing TiO2 (content 5%). Green pellets are made by the laboratory scale balling disc and roasted at a horizontal tube furnace with 1220 °C. Thermogravimetric analysis (‘TG’) is used to analyze the thermal decomposition of green pellets. X-ray diffraction (‘XRD’), scanning electron microscope and energy dispersive spectroscopy (‘SEM-EDS’) are utilized to systematically analyze the phase composition, microstructure and elemental distribution of the pellets. The findings show that as the basicity increases the porosity increases first and then decreases while the compressive strength is opposite to porosity to decrease first and then increases. With the increases of basicity, CaO responded with Fe2O3 and TiO2 to form CaFe2O4, Ca2Fe2O5 and CaTiO3. ‘TG’ find basicity has a negative effect on pellet oxidation. Factsage7.1 software shows that with the increase of basicity, the liquid content increases. The ‘SEM-EDS’ result present that CaTiO3 is formed around hematite, impeding the hematite connection, increasing porosity and reducing compressive strength. Being depend on the experimental results, a schematic of the oxidation mechanism is presented, providing the theoretical foundations for the study of high basicity pellets.

Effect of olivine as MgO-bearing flux on low- and high-alumina iron ore pellets

In the present study, the effect of MgO in the form of olivine flux on low- and high-alumina iron ore pellet mineralogy and pellet quality was studied. Green pellets were prepared by varying the MgO content from 0 to 1.5% with a basicity (CaO/SiO2) of 0.30. The pellets were tested for green pellet properties, cold crushing strength (CCS), and reduction degradation index (RDI) and fired at temperatures between 1300 and 1320 oC. An optical microscope with an image analyzer, SEM-EDS, was used to assess the mineralogical phases present in the pellets and the chemical analysis of the mineralogical phases, respectively. The laboratory tests showed that with increasing MgO addition in both low and high alumina pellets, magnesio-ferrite & silicate melt phases increased and the porosity and hematite phases decreased. The decrease in porosity was due to increase in silicate melt formation from the silica in the olivine. With increasing MgO addition, the CCS value of the pellets increased up to an MgO content of 0.9 to 1.1%. Thereafter, the CCS value of the pellets decreased with increasing MgO addition for both low and high alumina pellets. At an MgO content of 0.9 to 1.1%, the CCS value was higher due to the formation of a low melting point magnesio-ferrite phase, which imparted strength to the pellets. For pellets with an MgO level of >1.1, the RDI was within the control limit for both low- and high-alumina pellets. This may be due to a reduction in the porosity of the pellet and a better distribution of the silicate melt phase. Low-alumina pellets showed better physical and metallurgical properties compared to high-alumina iron ore pellets.

Effect of Diluent Amount on Properties of Porous NiAl

Porous NiAl parts were formed by using Ni and Al elemental powders, preformed NiAl as diluent and NaCl particles as space holder (SH). The aim of utilizing preformed NiAl (30%-40%) as a diluent was to preserve the shape of the products. The amounts of the SH NaCl particles in NiAl were 25-50-75 vol.% and their sizes were in 300-500 µm range. Porous NiAl samples were prepared by volume combustion synthesis (VCS). The adiabatic temperatures of the Ni+Al mixtures having 30 and 40% diluent NiAl were calculated as 1638.9 and 1460.8°C, respectively. Formation of NiAl phase was verified by XRD analyses. In the green pellets, the total porosity amount was higher than the added NaCl amount. Also it was slightly higher in the product pellets than in the green pellets before VCS. Compressive strength and microhardness values of the samples which contained 30% diluent NiAl were higher than the samples which contained 40% diluent. Average compressive strength values of the products that were obtained by 25% NaCl and 30 and 40% diluent NiAl additions were 112.0±29.5 and 66.0±20.5 MPa, respectively.

Sigma phase embrittlement-induced failures of heat-resistant stainless steel traveling grate links

Traveling grates (TG) are used as beds over which green pellets are subjected to a series of thermal cycles, namely preheating, induration, and firing to make the pellets suitable for charging in the blast furnaces of an integrated steel plant. In this work, chronic failures of TG links after a service life of 2.5–3 years are investigated. A comparative analysis of failed, used and new TG links was carried out. Fractography of the failed link revealed an intergranular brittle fracture near the surface followed by a transgranular fracture with a signature of decohesion in the bulk of the fracture surface. Microstructural analysis revealed the presence of pre-existing grain boundary chromium carbides (Cr23C6) in the new (unused) link, which can facilitate easy crack initiation and propagation. Furthermore, failed and used TG link revealed the presence of extensive precipitation of needle-like sigma phase confirmed by a combination of X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy techniques. Such precipitation of the sigma phase occurs during exposure to a susceptible high-temperature range. The presence of the sigma phase is known to embrittle the austenitic stainless steel and such embrittlement is confirmed by a significant increase in hardness and decrease in Charpy impact toughness of failed and used TG links compared to the new TG link. Thermodynamic and kinetic simulations confirmed a high susceptibility of the existing alloy composition to extensive sigma phase precipitation in a wide temperature range. A new alloy composition with higher nickel (∼30 wt%) and free from tungsten is proposed to reduce the susceptibility towards in-service embrittlement induced by sigma phase precipitation.

Improvement of Sinter Productivity and Qualities by Placing Low Slag Green Pellet at Lower Layer of Sinter Packed Bed

Improvement of Sinter Productivity and Qualities by Placing Low Slag Green Pellet at Lower Layer of Sinter Packed Bed

Mechanical Properties of Hydroxyapatite Ceramic Prepared from Micropowder and Nanopowder

In this work, hydroxyapatite ceramics were prepared from hydroxyapatite micropowder and nanopowder. The hydroxyapatite nanopowder was obtained from natural buffalo bone by using a high speed vibro-milling machine for 2 hour. The green compacted pellets of all HA powders were subsequently sintered at 1200, 1250, 1300 and 1350°C for 3 hour and then the physical and mechanical characterizations as well as microstructural evaluation have been carried out. It was found that the optimum sintering temperature were 1250°C by fabricated from nanopowder which gave the HA nanoceramic with the maximum bending strength of 78.6±2.6 MPa. This is about 200% higher than that of the sample which fabricated from HA micropowder.

Prediction of Green Properties of Flux Pellets Based on Improved Generalized Regression Neural Network

In order to improve the quality of magnesia flux pellets and meet the production needs of the iron and steel industry, a pellet formation experiment was carried out. The effects of alkalinity R, SiO2 mass fraction, MgO mass fraction on the green pellets’ burst temperature, compressive strength, and falling strength were studied. The results showed that with the increase in alkalinity, the bursting temperature of green pellets decreases, but has no obvious effect on the compressive strength or drop strength; with the increase in SiO2 content, the bursting temperature of green pellets decreases gradually, and the green pellets’ strength also decreases slightly; with the increase in MgO content, the compressive strength of green pellets shows an upward trend, while the falling strength gradually decreases, and the burst temperature of green pellets shows a trend of rising first and then decreasing. The change trend is coupled with the software test data amplification method algorithm, based on the search algorithm of longicorn (MBAS), to expand a small amount of experimental data. Through data analysis and algorithm comparison, an improved generalized regression neural network (CFA-GRNN), based on culture firefly, was proposed to establish an optimization model for green pellet performance prediction. CFA uses the weights in the input layer and hidden layer of GRNN, the weights in the hidden layer and output layer, the threshold of the hidden layer and the threshold of the output layer as codes for optimization. The evolutionary goal is to obtain the most appropriate and optimal neural network structure. The results show that the MBAS algorithm, combined with the experimental research, can expand the effective data to 1000 pieces. Secondly, the green pellets’ burst temperature, compressive strength and falling strength predicted by the improved generalized regression neural network are in good agreement with the real values, and the average relative errors were 1.88%, 3.18% and 3.62%, respectively. The error analysis shows that the improved model algorithm has higher accuracy, meets the classification of pellets, and can be used to guide the production of pellets.