Magnetite Aggregates Research Articles

Insight into the molecular mechanism of organic pollutants’ adsorption on magnetic ZIF-8 synthesized via a transformational route

This study presents the synthesis of Fe3O4@Zeolite Imidazolate Framework-8 (Fe3O4@ZIF-8), a novel magnetic core–shell adsorbent engineered for enhance adsorption of organic pollutants. The process begins with the formation of spherical magnetite aggregates (i.e., Fe3O4) via a solvothermal method, using polyacrylic acid for stabilization and capping. A ZIF-8 shell is then grown through a sol gel process followed by reaction with 2-methylimidazole, resulting in a crystalline shell approximately 60 nm thick. Characterization techniques, including energy dispersive X-ray analysis and X-ray diffraction, confirm the successful preparation of Fe3O4@ZIF-8. The adsorption capabilities were evaluated using methylene blue (MB) and diclofenac sodium (DCF) as model pollutants. Fe3O4@ZIF-8 demonstrated rapid removal efficiencies, with 98 % removal of MB (6.01 × 10-4 mg·g−1·min−1) and DCF (4.43 × 10-4 g·mg−1.min−1) within 15 and 30 min, respectively, significantly outperforming conventional activated carbon. Thermodynamic studies indicate that the adsorption processes are spontaneous; enthalpic changes drive MB adsorption, while DCF is influenced by entropic factors. Molecular modeling reveals preferential adsorption behaviors on different ZIF-8 facets, with stronger interactions for MB due to π-π stacking and hydrogen bonding. These findings underscore the potential of Fe3O4@ZIF-8 as an effective adsorbent for water purification, highlighting its substantial adsorption capacity (73.2 mg·g−1 for MB and 53.8 mg·g−1 for DCF), stability, and reusability.

Heavy aggregate and different admixtures efffect on parquets: chrome, magnetite, and quartz-based surface hardener

This paper presents the mechanical and micro-structure results of concrete parquet blocks. The blocks were generated by utilizing the same part in the bottom part and by substituting different proportions (40%, 30%, 20%, and 10%) of heavy aggregate like chromite aggregate, magnetite aggregate, normal aggregate, and surface hardener in the upper part. The parquet sample tests were conducted on TS 2824 EN 1338. The test outcomes indicated that utilizing diverse aggregate and chemical materials boosted the abrasion resistance, 40% magnetite and quartz-based concrete parquet block samples demonstrated the best abrasion resistance values. Also, the minimum amount of mass loss was discovered in the samples that possess high water absorption at the freezing-thaw test. The different material substitutions in the sheet of the surface of the concrete parquet block samples altered the tensile strength of the samples, even though they did not bring about an outstanding variation in the compressive strength of the concrete parquet samples.

Microstructure and radiation shielding characteristics of PVA fiber-reinforced ultra-high performance concrete

The application of nuclear technologies simulates the development of radiation shielding materials. Traditional heavy-weight concrete used for radiation shielding is limited in practical construction due to the poor mechanical properties and durability. This study developed a PVA fiber-reinforced ultra-high performance concrete (UHPFRC) with magnetite as heavy aggregates used for radiation shielding. Due to the scientific skeleton design, UHPFRC exhibits superior mechanical properties, with compressive strength and flexural strength reaching up to 121.9 MPa and 23.2 MPa, respectively. The microstructure of UHPFRC was investigated in detail and the results revealed that the incorporation of PVA fibers refined the pore structure of UHPFRC. The interfacial transition zone between magnetite aggregates and cementitious matrix in UHPFRC was much denser than that in traditional concrete due to the low water to binder ratio. The gamma and neutron radiations shielding capacity of UHPFRC were evaluated by the combination of actual measurement and simulation. By introducing light nuclei and refining the pore structure, the incorporation of PVA fibers improved the neutron radiation shielding capabilities of UHPFRC by 5.1%.

Multifaceted Analysis of the Thermal Properties of Shielding Cement-Based Composites with Magnetite Aggregate.

The paper presents and discusses the results of a study of the thermal properties of cement composites with different contents of magnetite aggregate (0%, 20%, 40% and 60% by volume). The effect of grain size on the evaluated thermal properties was also investigated. For this purpose, concrete containing 50% by volume of magnetite aggregate with four different fractions (1-2 mm, 2-4 mm, 4-8 mm and 8-16 mm) was used. Thermal parameters were evaluated on specimens fully saturated with water and dried to a constant mass at 65 °C. The series with varying grain sizes of magnetite achieved thermal conductivity values in the range of 2.76-3.03 W/(m·K) and 2.00-2.21 W/(m·K) at full water saturation and after drying to a constant mass, respectively. In the case of the series with 20% magnetite by volume, the thermal conductivity was 2.65 W/(m·K) and 1.99 W/(m·K) for the material fully saturated with water and dried to a constant mass, respectively. The series with a 60% volume share of magnetite obtained values of this parameter of 3.47 W/(m·K) and 2.66 W/(m·K), respectively, under the same assumptions.

Effect of fibers and boron carbide on the radiation shielding properties of limestone and magnetite aggregate concrete

Research on new composite materials in the field of radiation shielding materials requires adequate means and meticulousness in their manufacture and characterization. In this study, concretes that use elements that theoretically improve their shielding properties are developed, such as fibers and boron-rich additions. Both magnetite and limestone concrete have been manufactured, incorporating steel fibers to improve the linear attenuation coefficient and polyvinyl alcohol to increase neutron scattering cross section. The incorporation of boron carbide is intended to increase the neutron absorption cross section. 5 mixes have been manufactured that have been tested with several gamma radiation sources (570–1280 keV) and with an Am–Be neutron source (111 GBq). The experimental results have been used to validate simulations carried out with MAVRIC® and have led to the modelling of a simplified spent nuclear fuel cask. Boron carbide produces a decrease of more than 50% on the neutron dose rate in contact with the cask. Incorporating PVA fibers supposes gain in neutron attenuation capacity of up to 13%, while fibers have a negligible effect on the photon dose rate.

Microstructure and radiation shielding properties of lead-fiber reinforced high-performance concrete

The increasing application of nuclear technology in medical fields has amplified the demand for radiation shielding materials. Traditional large-volume concrete cannot simultaneously exhibit excellent neutron and gamma-ray shielding capabilities while ensuring superior mechanical properties. This study tailored a novel lead fiber-reinforced high-performance concrete (LFRHPC) with lead fibers and magnetite aggregates, focusing on radiation attenuation. The effect of lead fibers on the mechanical performance, microstructure and radiation attenuation characteristics for LFRHPC was comprehensively evaluated. The results indicate a significant improvement in the mechanical performance of LFRHPC compared to traditional radiation shielding concrete (RSC), due to the scientific skeleton design. Additionally, the pore structure in LFRHPC is refined by incorporating lead fibers. Moreover, the interfacial transition zone (ITZ) between the cementitious matrix and magnetite is improved because of the very low water-to-binder ratio. To assess the radiation attenuation ability of LFRHPC, both direct measurements and simulation models were utilized. The data reveals that the porosity of LFRHPC plays a crucial role in its shielding effectiveness against neutron and gamma radiation. Furthermore, the addition of lead fibers considerably boosts its neutron and gamma-ray shielding attenuation capabilities. In summation, LFRHPC combines excellent mechanical properties and radiation shielding capabilities, making it suitable for construction applications in medical settings.

Role of evaporites in sodium metasomatism and formation of albite-rich rocks in IOCG provinces

Hydrothermal Iron-oxide-Cu-Au (IOCG) deposits are important exploration targets for a number of metals of economic importance. Voluminous sodium metasomatism is ubiquitous in most IOCG provinces. The origin of the metasomatic fluid responsible for the formation of albite-rich rocks in such terranes is contentious; both evaporite-derived fluid and magmatic fluid have been advocated. The Singhbhum IOCG province in India is known for hosting several polymetallic deposits from which U, Cu, and apatite-magnetite are mined as principal commodities together with Ni, Au, Ag, Se, Te, Mo, and low-Ti magnetite as by-products. Voluminous albite-rich rocks occur at several sites along the mineralized belt. Metasomatic albite schist comprising predominantly albite and quartz at Pathargora contains tourmaline intricately associated with albite. Based on textures and mineralogical associations, tourmaline is classified as: tur1: coarse nodular tourmaline ± albite ± magnetite aggregate; tur2: disseminated fine-grained tourmaline in a schistose matrix; and tur3: tourmaline + biotite + magnetite + apatite clots. All tourmaline belongs to the alkali group and most to the dravite sub-group. Very low concentrations of Li (avg 3.8 ppm), Zn (avg 6 ppm) and Mn (avg 21 ppm) but high V (avg 2130 ppm) and Ni (avg 306.5 ppm) in tur1 core (tur1c) co-genetic with albite contrast with what is reported in magmatic/magmatic-hydrothermal tourmaline of granitic affinity. The δ11B values of tourmaline are mostly positive, ranging between –4.0 and 9.2 ‰ (avg 4.0 ± 3.0; n = 79); values of tur1 cores are 4.9–9.2 ‰. Previous fluid inclusion studies described the presence of halite and barite daughter crystals in primary fluid inclusions and demonstrated the involvement of a high-temperature (≥450 °C) and high-salinity (≥50 wt% NaCl equivalent) brine in the formation of cores of tur1. Calculated δ11B values of the hydrothermal fluid in equilibrium with tur1c range from 7.3 to 11.5 ‰ (for a crystallization temperature of 450 °C). Based on the textural setting of the tur1c-albite assemblage, geochemical and boron isotope composition of tur1c, and evidence of a high saline brine, we propose that the albite schist is the product of Na-metasomatism by brines that derived major constituents from the dissolution of marine evaporite. The inferred paleo-latitude and geological environment of sedimentation related to the host lithologies are consistent with the evaporitic model. We further suggest that a similar mechanism might have played an important role in the formation of albite-rich rocks in other IOCG provinces where the involvement of evaporite-derived fluids in mineralization/alteration have been demonstrated. Similar major element, trace element and positive boron isotope (1.5–6.3 ‰) composition of tur3 suggest similar source of fluid as that of tur1c, and tur3 formed either during the same alteration event or during a separate fluid pulse. On the other hand, the mode of occurrence, very low trace element concentration and weakly negative to positive δ11B (−4 to 2.3 ‰) value of tur2 suggest their metamorphic origin.

Mafic magma recharge triggered eruption of a long-lived shallow silicic magma reservoir beneath a submarine volcano from the southwestern Okinawa Trough

Abundant submarine volcanoes have been identified in the southwestern Okinawa Trough, yet the duration of shallow magma reservoirs and processes driving their eruptions remains unclear. Here, the texture and in situ element compositions of orthopyroxene and magnetite in the dacite and mafic magmatic enclaves (MMEs) from the FDV-1 submarine volcano were investigated to decipher the duration of pre-eruption shallow silicic magma storage and eruption triggering processes. Both unzoned and zoned orthopyroxene phenocrysts were observed in the host dacite. The rims of zoned and unzoned orthopyroxene have similar compositions with Mg# from 49 to 55, Cr = 2.31–9.26 μg/g, V = 54.10–137 μg/g, and Ni = 16.44–21.19 μg/g, and they are in equilibrium with the rhyolitic matrix, which is consistent with growth in the shallow silicic magma reservoir. In contrast, the high Mg# cores (Mg# = 63–79) in the zoned orthopyroxenes are in equilibrium with basalt, with significant enrichment in Cr (1092–1737 μg/g), Ni (106–181 μg/g), and V (183–295 μg/g), which indicates a recycled (antecryst) origin by mafic magma recharge and magma mixing. Furthermore, the timescales from FeMg interdiffusion in orthopyroxene phenocrysts suggest that the magma mixing is approximately 600 years before eruption. Correspondingly, the shallow silicic magma reservoir beneath the submarine volcano is longevity. The presence of bubble and V-depleted magnetite aggregates in the MMEs suggests that volatile-saturated and oxidized mafic magma recharges into the shallow silicic magma chamber. Moreover, the distinct contents of relatively fast-diffusing Ni in magnetite between the MMEs and host dacite suggest that the mafic magma injection into the silicic magma reservoir and formation of the MMEs must have occurred over very short timescales (< 24 h) before the eruption to inhibit complete re-equilibration. Therefore, this last mafic magma recharge induces destabilization of the long-lived shallow silicic magma reservoir and leads to the dacitic magma eruption.

Development of 3D printed heavyweight concrete (3DPHWC) containing magnetite aggregate

The main objective of this study is to develop 3D printed heavyweight concrete (3DPHWC) to produce elements with a dry density of up to 3500 kg/m3 by replacing natural aggregate (SA) with magnetite aggregate (MA) up to 100%. A comprehensive systematic study was conducted to thoroughly assess mixtures' mechanical properties, physical proficiency, fresh properties, and printing qualities. The inclusion of MA exhibited the desired fresh properties required for 3D printing and promising physical and mechanical properties. Evaluation of the mechanical properties of designed 3DPHWC indicates that replacing SA with MA increases both cast and printed samples' strengths. The 3D printed M100 sample achieved higher 28 days flexural and compressive strengths by 18 % and 20%, respectively, compared to printed control mix (M0). Micro-CT study correspondingly demonstrated improvements in the composites' porosity, pore size, and pore morphologies. The linear attenuation coefficients (LACs) and half-value layer (HVLs) for slow neutron and gamma-ray were measured to assess radiation shielding characteristics. A significant performance improvement was obtained for slow neutrons by introducing the magnetite aggregate. Unlike slow neutrons, no significant difference was observed between cast and printed samples against γ-rays. Moreover, the effect of porosity on the shielding performance was discussed.

Laboratory evaluation of microwave heating and skid resistance of pavement friction surfacing using calcined bauxite and magnetite aggregates

A high friction surface treatment (HFST) with magnetite (MT) aggregates instead of conventional calcined bauxite (CB) aggregates as microwave absorbers were prepared in this paper. The deicing properties by microwave heating and long-term skid resistance of HFST with different proportions of CB and MT aggregate were evaluated. The deicing properties by microwave heating of HFST were determined by electromagnetic characteristics, heating surface temperature, and microwave deicing time (MDT) tests. The long-term skid resistance of the HFST was characterized by conducting dynamic friction coefficient and mean profile depth (MPD) tests after long-term polishing using a three-wheel polishing device. The results showed that the electromagnetic characteristics of HFST were enhanced greatly by the addition of MT. The microwave heating efficiency of HFST was enhanced by the increase of MT substitution rate, which further enhanced its microwave deicing efficiency. The microwave deicing efficiency of HFST with MT substitution rate of 25% was 1.4 times that of HFST with MT substitution rate of 0%. Long-term skid resistance of HFST was reduced by the addition of MT, however, HFST with MT substitution rate of 25% also maintained a terminal μ40 and μ60 above 0.7, which can provide higher friction comparable with other high friction aggregate such as taconite, basalt, emery and flint. To improve the deicing properties by microwave heating and maintain high skid resistance, 25% MT replacement rate in HFST is recommended.

A Study on the Heating and Deicing Performance of Microwave-Absorbing Asphalt Mixtures.

Road icing in winter brings challenges to traffic safety, and microwave heating and deicing technology is an effective method with the advantages of high efficiency and environmental protection. Magnetite has been widely used as a microwave-absorbing material in pavement. In this paper, magnetite powder formed by crushing natural magnetite and high-purity Fe3O4 powder after purification were mixed to replace mineral powder, and the magnetite aggregate was used to replace the limestone aggregate with the same particle size to enhance the asphalt mixtures' microwave absorption capacity. The effect of microwave heating time and microwave power on the heating of the asphalt mixtures was studied, and the heating performance of different thicknesses of the asphalt mixtures under microwave radiation was evaluated. The heating performance of the mixtures under different initial temperatures and ice layer thicknesses was also assessed. The results showed that the addition of the magnetite powder-Fe3O4 powder and the magnetite aggregate significantly enhanced the heating performance of the asphalt mixtures by microwave heating. The replacement of the magnetite powder-Fe3O4 powder, the microwave heating time, and the microwave power had positive effects on the heating efficiency of the asphalt mixtures. Moreover, the thinner asphalt mixtures had a better heating performance. The heating and deicing performance of the mixtures decreased with a decline in initial temperature. As the ice thickness increased, the deicing time of the specimen surface to reach 0 °C also increased.

Evaluation of gamma and neutron radiation shielding properties of the GGBFS based geopolymer concrete

Superior characteristics of the ground granulated blast furnace slag (GGBFS) based geopolymer concrete (GGC) compared with the ordinary Portland cement (OPC)-based concrete (OPCC), have made it a more preferable choice for being used in the radiation shielding. The aim of this study is to investigate the radiation shielding properties of the GGC containing different contents of magnetite aggregates in separate and cover-layer forms. In this study: 1)gamma and neutron attenuation capacities of one-layer samples, including the OPCC containing 100 % normal-density aggregates, the GGC containing 0 % to 100 % magnetite aggregates and the steel fiber reinforced GGC containing 100 % magnetite aggregates have been evaluated, 2)the OPCC containing 100 % normal-density aggregates specimens have been covered with 5 cm layer of the concretes studied at the first stage to investigate their effects on radiation attenuation and 3)a comparison between a two-layer specimen and an equivalent mixed sample has been conducted. The main results obtained are: a)when the ordinary aggregates are replaced by the magnetite ones from 0 to 100 volume percentages, the parameters such as the linear attenuation coefficient (μ) and the removal cross section (ΣR) are respectively increased from 0.14225 to 0.18055 cm−1 and from 0.116086 to 0.143864 cm−1 in the GGC, b)adding 1.5 vol% of steel fibers to the GGC containing 100 % magnetite aggregates leads to increase in μ and ΣR respectively equal to 2.697 % and 6.5819 %, c)for gamma radiation, ratios of the transmitted rays to the incident ones in sample covered with the GGC containing 100 % magnetite aggregates and the specimen covered with the GGC containing 100 % ordinary aggregates have been obtained respectively equal to 0.197563 and 0.250297. For neutron radiation, these ratios have been obtained equal to 0.261019 and 0.346008, respectively and d)radiation attenuation capacity of the two-layer specimen has been obtained higher than that of its equivalent mixed sample.

Structural performance of reinforced concrete beams with 3D printed cement-based sensor embedded and self-sensing cementitious composites

Cementitious composites containing conductive functional fillers can achieve self-sensing and continuous monitoring of the damages and cracks through piezoresistive characteristics defined as the electrical resistivity change under external deformation. Previous studies developed two types of self-sensing cementitious composites expressing superior piezoresistive characteristics, as well as good linearity, repeatability, and sensitivity. This research further investigates the flexural damage sensing capability of the developed self-sensing cementitious composites by applying them to reinforced concrete beams. The 3D printed self-sensing cementitious composites containing carbon fibre (CF) at 0.7 wt% and activated carbon powder (ACP) at 0.25 wt% were tested as the embedded sensors in this study. Mould cast self-sensing cementitious composites developed by 100 wt% of magnetite aggregate (MA), 0.3 wt% of CF, and 0.05 wt% of carbon nanotube (CNT) were examined in bulk form. The corresponding fractional change in resistivity (FCR) was attained on the tension face of the reinforced concrete beams when subjected to flexural loading. Experimental findings suggest that the embedded 3D printed cement-based sensors in beam elements can contribute to the load-carrying capacity of the reinforced concrete beam, achieving an average load of yielding at 88.65 kN and a maximum loading capacity of 111.09 kN, which is 10% and 12% higher compared with the controlled reinforced concrete beam, respectively. In terms of sensing performance, both 3D printed self-sensing cementitious composites in sensor form and mould cast self-sensing cementitious composites in bulk form could reflect stress and strain changes and detect crack formation in reinforced concrete beams, which demonstrate gage factors at 318 and 527, respectively. However, 3D printed cementitious sensors are more effective when reinforced concrete beams are severely damaged. In terms of self-sensing cementitious composites in bulk form, the randomly distributed CF and CNT could provide a more pronounced crack and damage sensing capability, with fluctuations that can be observed at both low and high levels of damage.

Investigation on electromagnetic pulse shielding of conductive concrete

Electromagnetic radiation is generated naturally or artificially by weapons capable of affecting the power grid and modern electronic devices; this poses a threat to a nation's defence, hospitals and communication systems. This study focused on designing and developing electromagnetic interference (EMI) shielding cement-based concrete using locally available materials. The shielding effectiveness (SE; in dB) of conductive concrete was assessed using a newly designed and fabricated metallic testing chamber with a monopole antenna (1.46 GHz) and a vector network analyser. A maximum SE of 36 dB was achieved experimentally in conductive concrete with magnetite and graphite aggregates and 2% steel fibres. The developed conductive concrete has a higher (around three times) SE than normal concrete with a similar range of compressive strength. A simulation study was carried out to predict the SE of the developed conductive concrete with the aid of CST Microwave Studio simulation software and validated with experimental results. The durability of the conductive concrete was assessed; it was observed to have low permeability and porosity. The research outcomes of this study form a stepping stone towards the design and development of conductive concrete against EMI.

Study on the blending behavior of asphalt binder in mixing process of hot recycling

The blending behavior of aged and virgin asphalt binder is one of the most critical problems in the mixing process of hot recycling. To accurately measure the participation degree of aged asphalt and optimize the mixing process of hot recycling, a series of laboratory tests were designed by using magnetite aggregate and thin-layer chromatography with flame ionization detection (TLC-FID) for the first time. In this study, 24 different lab-mixing conditions were deliberately adopted to investigate the impact on the DoB of aged and virgin asphalt binders, including mixing amount of RAP, mixing amount of rejuvenating agent, mixing time, mixing temperature, mixing orders and the thickness of asphalt film. The results indicated that the aged and virgin asphalt cannot be completely blended in the mixing process and DoB is only about 40–60 % in general. The DoB decreases with the increase of asphalt film thickness and it decreases by 30 % when asphalt film thickness is 9 µm. DOB increased with the content of RAP and rejuvenating agent up to 70 % which same as mixing sequence. Although the mixing time and temperature can promote DOB, the mixing time and temperature should be controlled within 240 s and 170 °C, otherwise the accuracy of DOB will be affected.

Ispitivanje mehaničkih svojstava i svojstava smanjenja zračenja običnog i teškog betona s različitim agregatima i vodocementnim omjerima

This paper presents the results of comprehensive laboratory work conducted for investigating the mechanical and radiation attenuation characteristics of heavyweight concrete produced with pyrite, chromium, and magnetite aggregates and normal weight concretes produced with three different water/ cement (w/c) ratios. Various experiments were conducted to determine the compressive strengths, ultrasound transmission velocities, experimental elasticity modules, and mass attenuation coefficients of these concretes. Heavy and normal weight concretes exhibited similar behaviour in terms of compressive strength and elasticity modules. In heavyweight concretes, with increased w/c ratios (by keeping the amount of water constant and decreasing the amount of cement), the corresponding density increased due to the increase in the amount of high-density aggregates rather than cement in the composition of concrete. Thus, heavyweight concretes produced with a high w/c ratio and low strength can absorb more X-rays. Mass attenuation coefficients converge in heavy and normal weight concretes with different densities at high energy levels.

Synchronous sequestration of cadmium and fulvic acid by secondary minerals from Fe(II)-catalyzed ferrihydrite transformation

As consequence of the dual demands for pollution control and carbon (C) fixation in soils, Fe(II)-catalyzed mineral transformation may be a promising method to simultaneously immobilize heavy metals or organic matter (OM), but the underlying mechanisms remain unclear. Here, the synchronous sequestration mechanism of cadmium (Cd) and fulvic acid (FA) during Fe(II)-catalyzed the transformation ferrihydrite with C/Fe molar ratio of 0.21 were examined. Mineral phase analysis revealed that increasing the Fe(II) concentration (1–5 mM) favored the transformation of lepidocrocite and goethite to magnetite, and ferrihydrite transformation rate increased with increasing Fe(II) concentration. Color overlays and line profiles of elements depicted that Cd was dominantly adsorbed on the lepidocrocite and goethite surfaces. A positive correlation between the quantity of nonextractable Cd and magnetite further indicated that Cd may be sequestered by magnetite. Meanwhile, FA molecules were adsorbed on goethite surfaces and magnetite aggregates, and incomplete structure of lepidocrocite provide spaces for immobilizing C. Newly formed iron (Fe) (oxyhydr)oxides may immobilize Cd through surface binding, structural substitution, and physical encapsulation. The OM bound to the newly formed Fe (oxyhydr)oxides was rich in aromatic and carboxyl functional groups, which was beneficial for binding Cd, whereas the presence of Cd promoted the generation of nano pore spaces or defects and consequently enhanced FA sequestration. Therefore, Cd immobilization and FA sequestration can be synchronously achieved during the phase transformation. The findings provide a profound insight into various nanoscale mechanisms accounting for the fate of Cd and FA coupled with mineral transformation. The findings also are very helpful for developing strategies for simultaneously immobilizing heavy metals and C in soils.

Origin of Podiform Chromitites in the Sebuku Island Ophiolite (South Kalimantan, Indonesia): Constraints from Chromite Composition and PGE Mineralogy

The presence of PGM associated with the podiform chromitites in the Jurassic–Cretaceous ophiolite of Sebuku Island (South Kalimantan, Indonesia) is reported for the first time. Two types of chromitite have been recognized; one with high-Cr composition (Cr/(Cr + Al) &gt; 0.7) occurs in the deep mantle, the other, high-Al (Cr/(Cr + Al) &lt; 0.6), is located close to the Moho transition zone. The TiO2-Al2O3 relations indicate affinity to IAT and MORB, for the high-Cr and high-Al chromitites, respectively. However, both are believed to have formed by mantle/melt reaction and differentiation of a magma characterized by an initial IAT composition related to an SSZ. Primary magmatic inclusions (&lt;10 μm) of laurite characterized by Ru/Os chondritic ratio are the only PGM found in the high-Cr chromitites, indicating crystallization from undifferentiated magma, at low fS2 in the mantle. In contrast, the high-Al to chondrite, suggesting the increase of fS2 in the evolved melt. Besides laurite, the high-Al chromitite contains a complex assemblage of secondary PGM (Pt-Fe, garutiite, iridium, ruthenium–magnetite aggregates, zaccariniite and unnamed Ru and Mn oxides). These secondary PGM have an irregular shape and occur exclusively in the chlorite matrix sometimes associated with Mn-Ni-Fe-Cr hydroxides. They are interpreted to have formed by desulfuration of primary interstitial PGM sulfides or to have precipitated from secondary fluids during low T alteration. The relative abundance of PPGE in the high-Al chromitite is interpreted as a result of PGE fractionation during differentiation of the parent melt of the chromitites.

Effect of aggregate and fibre types on ultra-high-performance concrete designed for radiation shielding

This research examines the properties of ultra-high-performance (UHPC) and heavyweight radiation shielding concrete (UHPHSC). Several types of heavy-weight fine aggregates (sand, magnetite, hematite ilmenite and barite) were used to achieve these properties. In addition, the different types of fibres (steel fibre, lead fibre and basalt fibre) with a volume fraction of 2% were used. The fresh properties of workability and density, and hardened properties of compressive strength, splitting tensile strength, flexural strength, and water permeability were studied. Radiation attenuation was measured at two different gamma-ray energies at 137Cs0.662 and 60Co 1.173 (MeV) sources. Linear attenuation coefficient, half-value layer and tenth-value layer were evaluated. UHPHSCs were exposed to different temperatures at 22 °C, 250 °C, 500 °C and 750 °C to study their effect on the compressive strength and the mechanical shielding properties of gamma rays. The highest density of concrete, 3850 kg/m3, was achieved using magnetite aggregate and steel fibre. Although the highest compressive strength of 180.6 MPa was achieved using Ilmenite aggregate and steel fibre, the best radiation protection properties were achieved using lead fibre and magnetite aggregates.

Study on the electromagnetic property and microwave heating efficiency of concrete with magnetite aggregate

As an excellent absorbing material, natural magnetite with high microwave heating capacity may be used for deicing cement concrete road. In order to remove ice and snow on road surface quickly and effectively, in exploration of the microwave deicing technology, 6 kinds of concrete with different magnetite aggregate content were prepared with magnetite gravel as the absorbing material, and the influence of magnetite aggregate on mechanical properties, electromagnetic properties, microwave heating efficiency and microwave deicing efficiency of concrete was investigated. The results showed that magnetite aggregate improved both compressive strength and flexural strength of concrete significantly, and also enhanced its electromagnetic properties, microwave heating efficiency and microwave deicing efficiency greatly. For the concrete with magnetite aggregate, when the height of waveguide port was 55 mm, the microwave heating efficiency was optimal. With the increase of magnetite aggregate content, the microwave heating efficiency of concrete increased gradually. After the addition of magnetite aggregate, the dielectric loss capacity of concrete was improved obviously, and the magnetic polarization loss capacity was improved to a certain degree. The improvement in microwave heating efficiency of concrete with magnetite aggregate was closely related to the increase of imaginary part of the complex dielectric constant. Magnetite gravel can be used as aggregate and absorbing material of cement concrete for efficient microwave deicing.