Non-magnetic Fraction Research Articles

Geoenvironmental and Health Indices to Assess the Hazardousness of Heavy Metals in Urban Dust in Schoolyards in Murcia, Spain

The aim of this study was to evaluate the possible contamination of urban dust in the schoolyards of 27 schools in an urban area of the city of Murcia (SE Spain). The color and degree of magnetism, as well as the heavy metal content (Cd, Cu, Cr, Ni, Pb, and Zn), were determined to establish the absence or the degree of contamination, if present, using environmental and health indices. It was established that the concentrations of heavy metals in the dust samples followed the order Zn (454 mg kg−1) > Cu (77 mg kg−1) > Cr (68 mg kg−1) > Pb (56 mg kg−1) > Ni (19 mg kg−1) > Cd (0.4 mg kg−1). Dark-colored dust showed the highest concentrations of contaminants associated with medium or high magnetism. An analysis of the magnetic and non-magnetic fractions indicated the highest concentrations of all heavy metals in the magnetic fraction. According to the geoenvironmental indices used, the ecological risk in these schoolyards is moderate overall. Based on the health indices, ingestion is the main route of entry of dust particles into the body, which poses the main health risk for adults and children for all heavy metals. Regarding the hazard index (HI) for all elements and the cancer risk (CR) for children and adults, the results indicate that there is no health risk.

Change in the qualitative composition of non-metallic mineral raw materials as a result of blasting operations

Purpose. The research purpose is to study the change in the qualitative composition of granite before and after blasting operations to determine its compliance with the criteria of marketable products. Methods. X-ray phase and X-ray structural research methods are used to study changes in the mineral composition of granites before and after blasting operations. To separate magnetic and non-magnetic fractions of the selected granite samples, a three-roller RST magnetic separator is used. X-ray phase research is conducted using a DRON-3 diffractometer. Additionally, an analysis of the unit cell dimensions of the quartz crystal lattice was conducted, and the dislocation density along the corresponding crystallographic planes was studied. Findings. It has been determined that after blasting operations, granite mass is redistributed from coarse fractions of 1-20 mm to small fractions of 0-1 mm with an increase in the latter by 4.2%. It has been found that the biotite content decrea-ses naturally and consistently, and the quartz content increases correspondingly in products in the following series: magnetic separator drum (90%, 2%) → lower roller (72%, 14%) → upper roller (55%, 31%) → non-magnetic product (48%, 34%) before blasting operations. Therefore, despite significant differences in the magnetic favorability of these two mineral phases, they are present in all magnetic separation products (with the exception of quartz in the non-magnetic product): magnetic separator drum → lower roller → upper roller. Originality. It has been established that along the crystallographic directions 101 and 211, the maximum gradient of dislocation density increase in the quartz crystal lattice in granite samples before blasting operations is observed during the transition from the lower roller product to the upper roller product, amounting to 1.55·1010 and 6.63·1010 cm-2, respectively. After blasting operations, in granite samples along the same directions, the maximum gradient of dislocation density increase is observed between the upper roller product and the non-magnetic product, amounting to 3.01·1010 and 4.67·1010cm-2. As a result of the thermodynamic impact of blasting operations, the weighted average dislocation density value along crystallographic planes 101 and 211 in the quartz crystal lattice increases by 47.21 and 25.72%, respectively. Practical implications. Understanding the quality characteristics of marketable products after blasting operations will contribute to optimizing the stages of further processing of non-metallic mineral raw materials (two-, three- or four-stage crushing) and expanding the scope of granite applications. This increases its competitiveness in the building materials market by reducing the costs for additional processing with a reduction in the labor intensity of the process.

How magnetism-based fractional spinels contribute to the bioavailability of geogenic chromium in serpentine soils of Taiwan

Serpentine soils are highly rich in geogenic chromium (Cr), typically associated with spinel minerals. The high resistance of these minerals to weathering has raised concerns regarding their contribution to Cr bioavailability in serpentine soils. This study collected soil horizon samples from two pedons (Entisol and Ultisol) in eastern Taiwan and applied a two-step magnetic separation method to divide the bulk soils into strongly magnetic (SM), weakly magnetic (WM), and nonmagnetic (NM) fractions. The basic characteristics of the bulk soils were examined. To characterize the mineralogy and geochemistry of the fractions and determine their quantitative contribution of bioavailable Cr in serpentine soils, we analyzed their mineral composition, magnetic properties, and elemental composition and valence by using various spectrometric techniques, such as X-ray diffraction, electron probe microanalysis, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, as well as vibrating sample magnetometry. The results indicated the main Cr-bearing minerals were magnetite and chromite in the SM and WM fractions, with minor occurrences in layer silicates, such as serpentine and chlorite, in the NM fraction. The total Cr content decreased in the following order: SM > WM > NM. The SM fraction had the lowest weight proportion, and this proportion was lower for the Ultisol than the Entisol. This observation indicated that the weathering of Cr spinels is associated with the substantial cation substitution of Al, Ca, Mn, and Ni for Fe and Cr in broken mineral grains and increases in the Fe(III) and Cr(VI) concentrations in magnetite. The SM fraction, mainly consists of magnetite and chromite, exhibited the highest concentration of bioavailable Cr extracted by 0.1 M HCl. However, the Cr-bearing layer silicates represented the largest potential pool of bioavailable Cr in the bulk soils because the weight proportion of the NM fraction was higher than those of the other fractions and increased during pedogenesis.

Enhancements of magnetic properties and compacted density for Fe-based amorphous soft magnetic composites via hot compacting under an ultra-low pressure

Amorphous FeSiBCCr soft magnetic composites (FeSiBCCr-SMCs) with high compacted density (ρc) and excellent magnetic properties has been successfully hot-compacted under an ultra-low pressure of 160 MPa. The thermoplastic deformation of amorphous powders within the supercooled liquid region can give rise to the increase of ρc and the reduction of non-magnetic pores fraction for the SMCs. This situation is conductive to the decrease in resistance of domain wall motion during magnetization process of SMCs, and finally contributes to the improvement of SMCs’ soft magnetic properties. Under the recommended conditions with the compaction temperature (Tc) of 475 ℃, the pressure holding time (th) of 6 min, and the molding pressure (Pm) of 160 MPa, the FeSiBCCr-SMCs’ ρc increases by 28.8 % to 6.53 g/cm3, the corresponding effective permeability (μe) increases by 3.39 times to 73.1, while its total core loss (Pcv) reduces by 57.4 % to 275.3 kW/m3 at 100 kHz, 0.05 T compared with those of the SMCs prepared at Pm=600 MPa, Tc=25 ℃.

Analysis of structural, dielectric, magnetic and impedance spectroscopy of ZnO/CuFe2O4 nanocomposites

The nanocomposites of ZnO/CuFe 2 O 4; abbreviated as (ZnO) x /(COF) 1-x (x; 10 ∼ 50 wt%) were prepared by powder mixing method. The x-ray diffraction pattern revealed the formation of nanocomposites (NCs) with inverse spinel structure of COF and hexagonal wurtzite structure of ZnO. The scanning electron microscope analysis depicts the nano-plates like morphology, non-homogenous mixing and agglomeration of particles. The dielectric properties and impedance spectroscopy of NCPs were measured by LCR meter in the frequency range of 1 kHz to 2 MHz. There is decrease in the real and imaginary parts of dielectric constant (ε′ and ε″) were observed with frequency, which is explained by Maxwell–Wagner’s polarization mechanism. The real and imaginary parts of impedance (Z′ and Z″) also show decreasing trend with frequency owing to increase in hopping of charge carriers that result in enhancement of a.c. conductivity (σ a.c ). The impedance spectroscopy shows a semicircular arc at higher frequency which is attributed to the conduction from grains. Finally, the vibrating sample magnetometer result showed the change in the magnetic nature of NCPs; as saturation magnetization (M s ) and coercivity (H c ) decreases substantially with incorporation of non-magnetic ZnO weight fractions.

Revisiting sustainable resources in the combustion products of alumina-rich coal: Critical metal (Li, Ga, Nb, and REY) potential of ash from the Togtoh Power Plant, Inner Mongolia, China

Coal fly ash has gained much attention as a potential alternative source for extracting critical metals such as Li, Ga, Nb, and lanthanides and yttrium (REY). This study investigates their distribution characteristics and modes of occurrence in alumina-rich fly ashes from the Togtoh Power Plant in Inner Mongolia, using various analytical methods. The objective was to provide a reference for the pre-enrichment of critical metals in fly ash. Lithium is primarily present in the glass phase, and its concentration is extremely low in the crystalline phases. Lithium is mainly concentrated in “pure” aluminosilicate glass, and is present but at a low level in Ca-rich aluminosilicate glass. Gallium is primarily present in the glass phase and in corundum, while Nb mainly exists in submicron zircon particles surrounded by Si-Al-Ca glass. Lanthanides and yttrium primarily occur in the glass phase and in crystalline phases, including an intermediate phase composed of the three end-member minerals of the gorceixite-crandallite-florencite series, as well as in monazite, crystalline forms of iron oxides and REY oxides. The Li concentrations in the alumina-rich fly ashes range from 562 to 894 μg/g for Li2O, from 43.9 to 81.9 μg/g for Ga, from 58.7 to 70.6 μg/g for Nb2O5, and from 258 to 450 μg/g for REY oxides, respectively, indicating their substantial potential for resource recovery. Especially, the 2nd row fly ash has the highest contents of these metals, allowing for direct extraction without the necessity for complex pre-processing. Physical separation can further enrich Li, Ga, Nb, and REY in the fly ash. In particular, particle size separation enriches these elements in the < 20 μm size range and magnetic separation enriches Li, Ga, Nb, and REY (except Ce) in the non-magnetic fraction. However, Ce is significantly enriched in the magnetic fraction compared to the original fly ash.

Iron Removal from Low-Grade Pyrophyllite Ore by Microwave Irradiation and Dry Magnetic Separation

Owing to its unique properties, pyrophyllite is an economical alternative to many minerals in different applications. The presence of iron-bearing minerals in Saudi pyrophyllite hampers its industrial uses. The aim of this study was to examine the removal of iron from Saudi low-grade pyrophyllite ore using two approaches. The first approach involves dry high-intensity magnetic separation, whereas the second approach involves microwave pretreatment of the ore before dry magnetic separation. For the first approach, the studied operating parameters were roll speed; feed rate, field intensity, and feed particle size. For the alternative approach, microwave treatment followed by dry magnetic separation, the microwave irradiation time and the magnetic field intensity were studied. The results show that the combined microwave treatment and dry separation method could provide high-purity pyrophyllite for filler industries. Microwave irradiation for 30 min was optimal to change impurity phases (i.e., pyrite, hematite) into ferromagnetic phases in microwave-treated pyrophyllite samples. At a magnetic field intensity of 2000 Gauss, the 30 min microwave-irradiated pyrophyllite sample achieved an iron recovery of 11.2% in non-magnetic fractions, with a removal efficiency of 89% with an alumina recovery of 91.31%.

Design of highly stable Co3O4/RGO/CoFe2O4 hybrid nanocomposites with multiple nanointerfaces for enhanced supercapacitor performance

In this study, we developed a novel hybrid electrode nanomaterial composed of Co3O4, CoFe2O4, and reduced graphene oxide (RGO) for electrochemical supercapacitor applications. The hybrid nanocomposite of Co3O4/RGO/CoFe2O4 was prepared using a modified chemical oxidation process and the phase formation of the composites was evidenced by X-ray diffraction (XRD). The grain size for Co3O4 and CoFe2O4 was estimated as 12 nm and 22 nm. For Co3O4/CoFe2O4 the reduced grain size of 19 nm for CoFe2O4 was observed and further it was reduced with RGO up to 15 nm. The bare Co3O4 exhibited a hexagonal plate-like morphology, whereas the bare CoFe2O4 showed mostly a spherical morphology. The reduced saturation magnetization for the hybrid electrode material due to the non-magnetic fraction of Co3O4 and RGO was observed to be 21 emu/g compared to the bare CoFe2O4 (77 emu/g). The Co3O4/RGO/CoFe2O4 electrode exhibited enriched electroactive sites and enhanced diffusion pathways, achieving a high specific capacity of 235C g − 1 at 5 A g − 1 with excellent durability.. This work highlights the significant charge storage potential of the Co3O4/RGO/CoFe2O4 hybrid, making it a promising candidate for advanced energy storage systems.

Processing of Ilmenite Concentrate with High Chromium Content

The results of research on the processing of ilmenite concentrate from the Obukhovskoye deposit are presented in this article. As the concentrate has a high chromium content, the study involved converting the iron into metal and the titanium into slag through the addition of soda. Positive results were obtained during the smelting of the ilmenite concentrate, and a one-stage smelting mode was established. This mode involved an increase in the temperature up to 1700 °C, with a heating step of 10 °C/min and using an argon supply. The holding time at this temperature was 30 min, followed by cooling to 700 °C in argon. The optimal parameters for sintering the non-magnetic fraction with soda and leaching the sinter with water and hydrochloric acid solution were also determined.

Enhancing Rare Earth Element Recovery from Coal Ash Using High-Voltage Electrical Pulses and Citric Acid Leaching

The study investigates the application of high-voltage electrical pulses (HVEP) as a pretreatment to enhance the leaching efficiency of rare earth elements (REE) from coal ash (CA) produced from the combustion of Ekibastuz Basin coal in Almaty, Kazakhstan. HVEP treatment was applied to the finest (&lt;40 µm) non-magnetic fraction of CA under controlled conditions, optimizing discharge current, voltage, and treatment duration. Leaching experiments with 1 M citric acid at various solid-to-liquid ratios, temperatures, and durations were conducted on both treated and untreated samples. Results indicated that HVEP-treated CA significantly improved REE recovery rates compared to untreated samples, with optimal conditions achieving 74% cerium, 79% yttrium, and 77% lanthanum recovery. The leaching of untreated CA under the specified conditions allowed no more than 28% REE to be extracted into the solution. The leaching process was found to follow first-order kinetics, with the chemical reaction of metal dissolution being the rate-limiting step.

The Waelz Slag from Electric Arc Furnace Dust Processing: Characterization and Magnetic Separation Studies.

The Waelz slag generated during electric arc furnace dust processing is an iron-rich product with significant amounts of iron, zinc and copper. About 600-800 kg of the Waelz slag is generated per ton of the dust processed. The Waelz slag samples from two different plants were thoroughly characterized using inductively coupled plasma optical emission spectroscopy (ICP-AES), X-ray diffraction analysis (XRD), chemical phase analysis, Mössbauer spectroscopy and other supporting methods. The phase distribution of iron, zinc and copper was determined in the Waelz slag samples. Low-intensity wet magnetic separation was tested for the iron recovery from the Waelz slag samples. It was found that the Waelz slag samples have complex chemical and mineralogical compositions, which can impede the selective recovery of valuable elements. The obtained results indicate that the chemical and mineralogical composition of the Waelz slag samples has a considerable effect on the magnetic separation indexes. The experiments showed that the iron concentrates with Fe contents of 73% and 46.8% with the metallization degrees of 87.2% and 57.5% and the iron recovery degree of 54.8% and 52.9% were obtained at optimal conditions for two different samples, respectively, without selective segregation of Cu and Zn in the magnetic or non-magnetic fraction.

Economic heavy minerals in the stream sediments of wadi Shaàb, southern coast of the Red Sea, Egypt; characterization and upgrading for investigation of their potential recovery

The southern coast of the Red Sea is one of the most promising areas for the occurrence of economic minerals. Therefore, studying the characterization and evaluation of these minerals in the Wadi Shaàb Quaternary sediments and investigating their ability to concentrate and physically separate using economical and ecofriendly techniques is the main goal of this work. The results showed that the representative sample contains an average of 0.06% ilmenite, 0.08% zircon, 0.07% rutile, 0.07% leucoxene, 0.008% cassiterite, 0.004% xenotime, 0.0004% monazite, 0.022% almandine garnet, and 0.46% magnetite. The recovery of economic heavy minerals was applied using a combination of wet-gravity technique via shaking table and magnetic separation using high intensity magnetic separator. The results demonstrated the success of gravity separation in raising the grade from 7.63% to 45.03% in a yield of 13.74% out of the original sample, and also valuable metallurgical recoveries that greater than 89% for tabling multi-stages (rougher and scavenging) was obtained. Concentrated mineral fractions of magnetite, ilmenite, almandine, heavy silicates, and the non-magnetic fraction bearing zircon and rutile were obtained using a high intensity magnetic separator at different ampere range

Ball milling coupled cascade magnetic separation to recover valuable metals from alkali disaggregation copper smelting slags

Due to the lack of effective reduction and recycling methods, copper smelting slags (CSS) containing a large number of valuable metals are stockpiled. This work proposed a novel strategy of ball milling coupled cascade magnetic separation to achieve recovery of magnetite and ferrite and enrichment of Cu and Zn in alkali disaggregation CSS. The Fe grade of recovered magnetite reached as high as 72.43%, and 15.51% of Cu and 16.63% of Zn were recovered efficiently as spinel ferrites. Simultaneously, 70.54% of Cu and 58.18% of Zn were enriched in non-magnetic fraction. Compared with primary magnetic fraction, the grade of Fe in the secondary magnetic fraction increased by 19.19%. Additionally, compared with the control, the recovery efficiency and the grade of Fe in the magnetic products after ball milling increased by 52.11% and 49.20%. The main mechanisms were as follows: (1) The significant dissociation of Fe3O4 from non-magnetic impurities and the transformation of Cu and Zn to ferrite were promoted by ball milling. (2) The separation efficiency of weak magnetic ferrite and Fe3O4 was improved by cascade magnetic separation. Therefore, the proposed strategy could provide a green and sustainable solution for CSS processing.

Extraction of Fe and Al from red mud using carbothermic reduction followed by water leaching

Red mud, a solid byproduct from bauxite ore processing for Al2O3 production, encompasses valuable industrial metals, including Fe and Al. The objective of the present study was to investigate the feasibility of an integrated route for the efficient use of red mud for the multistep extraction of Fe and Al. Carbothermic roasting was performed in the presence of Na2CO3 to reduce iron oxide to metallic iron. Optimal roasting conditions (reductant dosage: 1 g, temperature: 900 °C, time: 120 min, and charge ratio 10:5:1) yielded a 95.6 % recovery of the magnetic fraction. Applying a magnetic gradient of 0.1 T resulted in a 92.5 % recovery of metallic iron. Subsequent water leaching, performed under optimal conditions (time: 120 min, temperature: 70 °C, pulp density: 10 %), achieved a 98.5 % leaching efficiency of Al from a nonmagnetic fraction, with and without sodium carbonate, demonstrating 26 % efficiency. Incorporating sodium salt during carbothermic roasting facilitated the reduction of iron oxide to metallic iron and activated alumina for leaching. Finally, a value-added Al product, AlPO4, was precipitated from the leachate. This approach primarily attempts to contribute to a more circular economy, reducing waste and minimizing the environmental impact.

Prevention of Silica Gel Formation for Eudialyte Study Using New Digestion Reactor

This work includes a combined hydrometallurgical treatment of a eudialyte ore sample with a subsequent preparation of leaching residue using mechanical separation methods. Hydrometallurgical treatment contains dry digestion with sulphuric acid at room temperature and filtration of the obtained product. The objectives of adopting these procedures are to test a new digestion reactor in order to prevent silica gel formation from the eudialyte ore. The obtained results revealed that silica gel formation is prevented during dissolution with sulphuric acid. A high leaching efficiency of light rare earth elements (La, Ce, Nd, Y) was reached using the dry digestion process with sulphuric acid, where the starting molarity was 12 mol/L. After the filtration process, magnetic separation is studied as the main method to recover weakly magnetic minerals like amphiboles and pyroxenes from the leaching residue in the magnetic fraction and feldspars in the nonmagnetic fraction. A new combined research strategy was developed for the production of different concentrates such as the one bearing Zr, Hf, and Nb.

A novel process for extracting bismuth from high iron content copper smelting dust by magnetic separation and leaching process

In this study, an efficient method for extracting bismuth from copper smelter flue dust with high content of iron was proposed. In this method recovery of bismuth from copper flue dust was carried out after copper and iron separation. To separate copper from dust, this material was leached with water and dilute sulfuric acid (0.6 M). Magnetic separation was performed with field intensities of 0.1 T and 0.4 T to separate iron in the leaching residue. 70 % of bismuth is placed in the non-magnetic fraction. The non-magnetic fraction of this separation was leached with (1.4 M) H2SO4 + (1 M) NaCl solution to recover bismuth. In optimal conditions, more than 98 % of bismuth in the non-magnetic fraction is leached. Bismuth precipitation from this solution was done by adjusting the pH to 2.5 with the ammonia solution. Impurities such as; Pb, Fe, As, and Cu were precipitated with bismuth in this condition. Lead was removed as a PbCl2 compound by leaching the precipitate with 6 M hydrochloric acid. Other elements were leached in this chloride environment and entered the solution phase. Bismuth was separated from this leaching solution by hydrolysis in the form of BiOCl. The purity of the BiOCl product was about 95 %. This substance can be used in photocatalyst and solar cell industries.

Indonesian Tungsten Mineralogy and Processing Concept

Tungsten minerals which are major as Wolframite and Scheelite mineral are by-product minerals of Tin mineral known as Cassiterite. Tin minerals are mostly found in Bangka Island which is one of the islands in the Southeast Asian tin belt that makes Indonesia the largest Tin (Sn) producer in the world. This research aims to characterize the mineralogy of Tungsten and associated minerals for potential mineral processing to gain the Tungsten concentrates. The Tungsten minerals were collected from the eastern edge of Klabat Granite in Toboali District, South Bangka. The Tungsten minerals were magnetically separated up to 14000 Gauss. The magnetic and non-magnetic fractions were identified to analyze the associated mineral of Tungsten with SEM analysis. The associated minerals in the Tungsten mineralization system in Toboali were found along with Silicates, Oxides, Sulphides, and Carbonates where Silicates dominated up to 91.8% of the non-magnetic minerals while Wolframite presence up to 0.9% in the non-magnetic fraction. At magnetic fraction found that Silicates dominates also up to 84.6% while Wolframite existed at 1.1%. The results of element deportment in the non-magnetic fraction show that Tungsten is associated with iron minerals and also in liberated form. The potential Tungsten mineral is Wolframite (Fe,Mn) WO4 in the magnetic and non-magnetic fraction. Mineral locking at P100 size 18.8 μ. shows that 84.4% Wolframite was locking with 3 (three) other minerals, 10.4% locking with 2 (two) other minerals, and only 4.8% Wolframite was 100% free in the magnetic fraction while in non-magnetic fraction P100 size 31.5 μ 77.5% Wolframite was locking with 3 (three) other minerals 18.3% locking with 2 (two) other minerals and only 4.2% Wolframite was 100% free. The processing concept is to liberate Tungsten from the associated minerals either with comminution or a combination of roasting alkali and leaching process and concentrate it up to marketable Tungsten concentrates.

Co-encapsulation of organic polymers and inorganic superparamagnetic iron oxide colloidal crystals requires matched diffusion time scales.

Nanoparticles (NPs) that contain both organic molecules and inorganic metal or metal oxide colloids in the same NP core are "composite nanoparticles" which are of interest in many applications, particularly in biomedicine as "theranostics" for the combined delivery of colloidal diagnostic imaging agents with therapeutic drugs. The rapid precipitation technique Flash NanoPrecipitation (FNP) enables continuous and scalable production of composite nanoparticles with hydrodynamic diameters between 40-200 nanometers (nm) that contain hydrophobic superparamagnetic iron oxide primary colloids. Composite NPs co-encapsulate these primary colloids (diameters of 6 nm, 15 nm, or 29 nm), a fluorescent dye (600 Daltons), and poly(styrene) homopolymer (1800, 50 000, or 200 000 Daltons) with NPs stabilized by a poly(styrene)-block-poly(ethylene glycol) (1600 Da-b-5000 Da) block copolymer. Nanoparticle assembly in FNP occurs by diffusion limited aggregation of the hydrophobic core components followed by adsorption of the hydrophobic block of the stabilizing polymer. The hydrodynamic diameter mismatch between the collapsed organic species and the primary colloids (0.5-5 nm versus 6-29 nm) creates a diffusion-aggregation time scale mismatch between components that can lead to nonstoichiometric co-encapsulation in the final nanoparticles; some nanoparticles are composites with primary colloids co-encapsulated alongside organics while others are devoid of the primary colloids and contain only organic species. We use a magnetic capture process to separate magnetic composite nanoparticles from organic-only nanoparticles and quantify the amount of iron oxide colloids and hydrophobic fluorescent dye (as a proxy for total hydrophobic polymer content) in the magnetic and nonmagnetic fractions of each formulation. Analysis of the microstructure in over 1100 individual nanoparticles by TEM imaging and composition measurements identifies the conditions that produce nonstoichiometric composite NP populations without co-encapsulated magnetic iron oxide colloids. Stoichiometric magnetically responsive composite NPs are produced when the ratio of characteristic diffusion-aggregation time scales between the inorganic primary colloid and the organic core component is less than 30 and all NPs in a dispersion contain organic and inorganic species in approximately the same ratio. These rules for assembly of colloids and organic components into homogeneous composite nanoparticles are broadly applicable.

Influence of feed mineralogical characteristics on the reduction behavior of low-grade iron ores

Reduction roasting followed by magnetic separation has become a major beneficiation technique to utilize low and lean-grade iron ore resources. However, the fundamentals of the reduction nature of iron ore are complex and largely depend upon the mineralogical characteristics of the raw material. In order to ascertain the complexities involving the phase transformation and reducibility nature of iron ores, experiments were conducted on four mineralogically different iron ores such as crushed fines, slime, BHQ and BHJ samples to examine their responses in terms of recovery and their enrichment in Fe content. The representative samples of each class were undergone through identical experimental conditions (850 °C temperature, 30 min resident time, 10% non-coking coal used as reductant) and it was observed that the crushed fines and slime showed the highest degree of reducibility while the BHQ and BHJ samples responded moderately to the process. Mineralogical characterization of both BHQ and BHJ show the presence of hematite mineral phases in the non-magnetic fractions, indicating the necessity of higher reductant content as well as residence time than the crushed fines and slimes. In essence, the banded ores require a higher temperature and reducing environment than the hematite and goethite-rich feed materials for higher magnetite conversion. In addition, the advantages of reduction roasting followed by magnetic separation process over direct magnetic separation process is highlighted in detail.

Preparation of high-purity SiO2 by S-HGMS coupled with mixed-acid leaching: A case study on hematite tailings from Ansteel, China

Hematite tailings (HTs) are rich in silica and are used as replacements for fine aggregates in the preparation of construction materials. However, there is scope for a more effective utilization of the valuable elements present in HTs. In this paper, a process for preparing high-purity SiO2 using HTs procured from Ansteel (China) is proposed. HTs were treated using the superconducting high-gradient magnetic separation (S-HGMS) technology, where the silica as part of the nonmagnetic fraction was obtained in the form of a high-silica concentrate, which was then subjected to mixed-acid leaching to dissolve impurities to achieve refined purification. The optimum process conditions for S-HGMS were determined, and the response surface methodology was applied to optimize the process parameters of the mixed-acid leaching process. The process indicators of the mixed-acid leaching step included the leaching time, leaching temperature, and molar ratio of the mixed acids. The optimum process conditions for S-HGMS were as follows: the magnetic strength-to-velocity ratio in the weak magnetic separation stage was set to 0.034 T·s/m whereas it was maintained at 0.076 T·s/m in the strong magnetic separation stage; the pulp concentration was 40 g/L, the pulp velocity was 500 mL/min, and the dispersant concentration was 1 mg/g. Under these conditions, the high-silica pulp was processed. The corresponding SiO2 grade increased from 71.788 % to 95.260 %, and its recovery and yield reached 56.330 % and 42.450 %, respectively. The SiO2 content in the sample increased from 95.260 % to 99.961 %. Further, the mechanisms of the S-HGMS and mixed-acid leaching were revealed. The proposed process is environmentally friendly and operationally inexpensive. It can reduce the amount of HTs by 42.450 %, and the obtained high-purity silica product has high economic value and good industrialization prospects.