Low-intensity Magnetic Separation Research Articles

An innovative process for recovery of ilmenite using mineral phase transformation followed by magnetic separation

Recovery of fine ilmenite is challenging, resulting in significant waste of titanium resources. In this paper, the mineral phase transformation technology was proposed to strengthen the surface magnetism of fine ilmenite. The results demonstrated that in the oxidation stage, the suitable oxidation temperature was 700 °C and the oxidation time was 30 min. In the reduction stage, the ideal reduction temperature was 575 °C, the CO concentration was 20 %, and the reduction time was 3 min. Under the optimized roasting conditions, the roasted sample was separated by staged low-intensity magnetic separation, and titanium concentrate with a TiO2 grade of 46.24 % and recovery of 67.62 % was obtained. The XRD, SEM and VSM analysis implied that the oxidation products of ilmenite were hematite and rutile, where hematite was enriched on the surface of the particles and formed a layer of 2–5 μm. After reduction roasting, the hematite layer was directionally transformed into magnetite, which significantly enhanced the magnetism of the particles and created conditions for the recovery of titanium by low-intensity magnetic separation.

Evaluasi Kinerja Alat Pengolahan Wet Belt Low Intensity Magnetic Separator (WBLIMS) Untuk Meningkatkan Kadar dan Recovery Sn di TB Primer Batubesi PT Timah Tbk Kabupaten Belitung Timur

Primary TB Batubesi Site a subsidiary of PT Timah Tbk, processes primary tin feed stockpile and SHP of oxide clay type using various tools, including the Wet Belt Low Intensity Magnetic Separator (WBLIMS). Currently, WBLIMS can only produce tin concentrate with a grade of 0.5-2% and a recovery of 5-8%, falling below the company's target of 8% grade and 15% recovery (XRF Test). This research conducted eight experiments with variations in feed types and rates. The WBLIMS feed from the stockpile has a Sn content of 0.62%, resulting in a tin concentrate with 1.21% Sn and a recovery of 7.05%. On the other hand, the feed from SHP has a Sn content of 0.61%, resulting in a tin concentrate with 0.95% Sn and a recovery of 5.11%. The type and rate of feed affect the increase in Sn grade and recovery. At low feed rates, the feed material yields lower Sn grade and recovery, while at high feed rates, the results are higher. Increasing the feed rate for WBLIMS from the stockpile leads to a decrease in Sn grade and recovery, whereas in the processing of SHP, the Sn grade increases but recovery varies. Experiments F1L1 and F2L3 yield the most optimal Sn grade and recovery, with F1L1 having a Sn grade of 2.28% and recovery of 11.54%, and F2L3 having a Sn grade of 2.87% and recovery of 9.24%. Although not reaching the company's target, these experimental results can enhance the Sn grade and recovery compared to the previous setup.

Enhancing Recovery of Ultra-Fine Magnetite from Low-Iron-Grade Cyanidation Tailings by Optimizing Flow Field Parameters of Low-Intensity Magnetic Separation (LIMS)

The characteristics of iron minerals in cyanidation tailings with a low iron grade were determined via chemical composition analysis, iron phase analysis, and mineral liberation analysis (MLA). The results showed that the cyanidation tailings contained 15.68% iron, mainly occurring in the form of magnetite (19.66%) and limonite (79.91%), in which 16.52% magnetite and 65.90% limonite particles were fully liberated. Most ultra-fine magnetite grains were adjacent and wrapped with limonite to form complex intergrowths, which resulted in low-efficiency magnetite recovery in low-intensity magnetic separation (LIMS) and adversely affected the downstream high-gradient magnetic separation (HGMS) process. Thus, in this work, the optimization of the flow field was proposed to enhance the separation of ultra-fine magnetite from the cyanidation tailings using pilot-scale LIMS separation, and the controllable parameters (including feed flow, separation gap, drum rotating speed, and solid weight) affecting ultra-fine magnetite capture were investigated. Under optimized conditions, a high-grade magnetite concentrate assaying 63.31% Fe with 86.46% magnetite recovery was produced, which, respectively, increased by 0.76% and 15.22%, compared with those obtained from industrial production. In addition, from the flow dynamics simulation, it was found that the magnetite particles in the −6 µm ultra-fine fraction were lost much more easily than those of coarser fractions due to the relatively enhanced hydrodynamic drag force acting on the particles compared with the magnetic force. However, this loss would be effectively reduced with the regulation and control of the flow field. The iron recoveries in the −16~+6 µm and −6 µm fractions of magnetite concentrate increased by 3.66% and 4.42%, respectively, under optimized hydrodynamic conditions. This research outcome provides a valuable reference for the economic and effective utilization of iron resources from such solid wastes.

Effect of particle shape produced from wet ball milling on magnetic separation concentrate by fractal dimension

The particle shape in mineral processing is a function of the comminution mechanism. In this study, the effect of the concentrate particle shape, obtained from the wet ball milling and the low-intensity magnetic separator on magnetite ore is investigated by the fractal geometry approach. The particle shape is described by the fractal dimension, calculated by the divider method. The variable parameters of grinding time, loading ratio, and solid weight percentage were studied here. The fractal dimensions of the particles are obtained between 1.12 and 1.42. When the grinding time is increased from 45 to 65 minutes, the fractal dimension and product grades are increased from 1.19 to 1.42 and from 65.61 to 67.70%, respectively. By increasing the loading ratio from 14% to 22%, the fractal dimension and the product’s grades are increased from 1.17 to 1.38 and from 64.80 to 66.68%, respectively. By increasing the solid weight percentage from 35 to 55%, the fractal dimension and product grades are decreased from 1.32 to 1.12 and from 65.51 to 64.65%, respectively. The results show that the particle shape has a significant effect on the performance of the magnetic separator. It is the findings indicate a direct relationship between the particle fractal dimension and the grade of magnetic separation products.

Mineral Magnetic Modification of Fine Iron Ore Tailings and Their Beneficiation in Alternating Magnetic Fields

In this paper, the properties, mineral magnetic modification, and beneficiation of tailings from the central mining and processing plant in Kryvyi Rih, Ukraine, have been studied. Samples were investigated by X-ray diffraction, X-ray fluorescence, microscopy, and magnetization measurements. The beneficiation was conducted using magnetizing roasting with carbon monoxide followed by dry low-intensity magnetic separation. The effects of chemical, mineral, and granulometric composition on the processing of fine tailings of different sizes sampled at different points of the tailings pond were investigated. Additionally, we proposed a new approach for magnetic separation of fine magnetically modified tailings based on the combination of permanent and alternating magnetic fields. Magnetizing roasting resulted in an enhancement in mass magnetization to 11–62 Am2/kg in comparison with initial values of 0.3–1.5 Am2/kg. After magnetic separation, the magnetic concentrates consisted almost completely of magnetite (with the magnetization of 75–88 Am2/kg) and non-magnetic residues contained major quartz. The content of iron in magnetic concentrates reached 68.5–70.2 wt.% and iron recovery 77–96 wt.%, depending on size fraction. We could conclude that the tailings are represented by fine-grained liberated material that can be effectively upgraded using magnetizing roasting and magnetic separation into two valuable products, such as iron concentrate and quartz powder.

Particle-based characterization and process modeling to comprehend the behavior of iron ores in drum-type wet low-intensity magnetic separation

Drum-type wet low-intensity magnetic separation is a versatile technique traditionally implemented in the mining industry since the mid-19th century. Yet, comprehending the process from a fundamental point of view remains challenging and its implementation still relies on “rules of thumb” that commonly disregard the ore properties and the effects of the operating conditions. This work describes an approach that combines comprehensive particle-based characterization and process modeling to integrate particle properties and equipment characteristics to describe the behavior of an iron ore in a laboratory-scale drum-type magnetic separator. Such a proposal is based on (1) laboratory testing, (2) automated mineralogy for particle-scale ore characterization, and (3) process modeling to compute the particle separation kinetics as a function of the ore intrinsic attributes and the physical principles involved in magnetic separation. This approach proposes the guidelines to obtain early information on the iron ore processing behavior, which represents a promising tool for decision-making at different stages of the beneficiation chain.

Separation of Iron and Rare Earths from Low-Intensity Magnetic Separation (LIMS) Tailings through Magnetization Roasting-Magnetic Separation.

Low-intensity magnetic separation tailings (LIMS tailings) are a common by-product obtained after magnetite magnetic separation. In this article, various techniques such as chemical analysis, X-ray diffraction, ICP-MS, and Mineral Liberation Analysis (MLA) were employed to investigate the LIMS tailings. The primary iron-bearing mineral identified was hematite and rare earth minerals were monazite and bastnaesite. The main gangue species was fluorite with small amounts of dolomite and amphibole. Due to the weak magnetism of hematite and rare earth minerals, magnetic separation has low efficiency. However, magnetization roasting-magnetic separation is an effective method to recover hematite. The present study focuses on the separation of iron and rare earth from LIMS tailings through magnetization roasting-magnetic separation. The results demonstrate that with a roasting temperature of 650 °C, a roasting time of 60 min, a slurry concentration solid-liquid ratio of 25 : 1, a rough magnetic field intensity of 0.16 T, and a selected magnetic field intensity of 0.10 T, the iron grade in the magnetic concentrate increases to 65.49 % and an iron recovery rate of 65.16 % can be achieved. The XRD patterns of magnetic separation concentrate show that the main mineral phases in concentrate are magnetite (Fe3 O4 ) and fluorite (CaF2 ), which can be removed by grinding and reverse flotation fluorite to obtain a high-grade iron concentrate. The REO grade of magnetic separation tailings is 11.98 %, and its recovery rate is 97.96 %. Consequently, rare earth can be effectively extracted and separated after the subsequent flotation-leaching process.

Arsenic Removal and Iron Recovery from Arsenic-Bearing Iron Ores by Calcification-Magnetic Roasting and Magnetic Separation Process.

Extracting iron while minimizing the health and environmental risks associated with arsenic contamination necessitates the removal of arsenic from arsenic-bearing iron ores to ensure a safe and sustainable supply of this metal for industries. The beneficiation of iron minerals and arsenic-bearing minerals from arsenic-bearing iron ores with a calcification-magnetizing roasting and low-intensity magnetic separation (CMR-LMS) process is investigated in this work. The results show that the process is successful in extracting iron minerals and eliminating arsenic-containing minerals. The roasting involves two key steps: calcification and magnetizing, which change hematite and goethite into magnetite and arsenic-bearing minerals into calcium arsenates. The process's separation efficiency of the CMR-LMS is closely linked to the parameters such as roasting temperature, roasting time, coke, alkalinity, and the liberation of gangue minerals from iron minerals. Through grinding and secondary magnetic separation, the iron minerals and gangue components, as well as arsenic, in roasted sand can be further separated. The optimum procedure results in a high-grade iron concentrate with an iron assay of 65.65%, an Fe recovery rate of 80.07%, and an arsenic content of 0.085%, while achieving a 93.29% As removal rate from the original ore that has 45.32% Fe and 0.70% As.

Low intensity magnetic separation of vivianite induced by iron reduction on the surface layer of Fe(III)[Fe(0)] iron scrap

Phosphorus (P) recovery through vivianite, which can be found in activated sludge, surplus sludge and digested sludge in the wastewater treatment plants (WWTPs), is a cutting-edge and efficient technology in recent years. However, how to generate and separate vivianite in an effective and economical way with natural iron oxide mineral was still the bottleneck to limit its application. Therefore, in this study, the P recovery efficiency (EP) and vivianite recovery efficiency (EV) of three kinds of iron oxides were investigated. We found that the EP of Akaganeite was 1.83 times and 4.88 times higher than that of Geothite and Hematite. Simultaneously, EV of Akaganeite was 1.64 times and 2.88 times higher than that of Geothite and Hematite. As Akaganeite is main component of rust on the surface of iron scrap, we used Fe(III)[Fe(0)] iron scrap with Fe(0) inside and Akaganeite outside as iron source and electron acceptor for vivianite production and magnetic separation. At the terminal stage (60 day), the P recovery efficiency with 20 g/L Fe(III)[Fe(0)] iron scrap was 36%. Applying a magnetical separator with magnetic field intensity of 0.3 T, vivianite was separated from the solution efficiently and immediately. Low intensity magnetic separation with iron scrap would recover P resources economically with the total cost to be $2.23/kg P, which was much lower than recovery via iron salts. Besides, it provided a significant insights into the P recovery and vivianite separation by reusing Fe waste during wastewater treatment.

A pilot study on recovery of iron from sulfur-bearing hematite ore using hydrogen-based mineral phase transformation followed by magnetic separation

Sulfur is a harmful impurity in iron ore, which seriously affects the subsequent smelting process and product quality. In this study, a novel process of hydrogen-based mineral phase transformation followed by magnetic separation was proposed to treat sulfur-bearing refractory iron ore. The results of pilot-scale experiments showed that in the oxidation heating stage, the sulfur element in the ore was oxidized to form SO2. During the reduction roasting stage, the hematite within iron ore powder was almost entirely transformed into magnetite at a reduction temperature of 520 °C using a gas combination of 45 % H2- 15 % CO- 40 % N2, which significantly enhanced the magnetism of the particles. At this time, iron minerals could be effectively recovered by a grinding and low-intensity magnetic separation process. Under the optimum roasting and magnetic separation conditions, the iron grade of magnetic concentrate reached 66.40 %, the iron recovery was 92.44 %, and the sulfur content decreased significantly from 0.547 % to 0.038 %. The hydrogen-based mineral phase transformation technology showed unique technical advantages and environmental potential in treating sulfur-bearing refractory iron ores.

An Invitation on Characterization of H2-Reduced Bauxite Residue and Recovering Iron through Wet Magnetic Separation Processes

Recovering iron from the bauxite residue (BR) is one of the long-standing challenges in the mining industry. However, there is a substantial lack of information in the literature regarding sample properties and iron extraction by reducing hydrogen. The present study aims at reducing a Greek BR using hydrogen, its characterization, and separating iron by magnetic separation processes. To this end, the reduced sample was characterized using X-ray diffractometry analysis (XRD), X-ray fluorescence spectrometer analysis (XRF), thermomagnetic analysis (TMA), automated mineralogy (AM), and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The effect of particle size (−200 + 100 µm, −100 + 75 µm, and <75 µm) was investigated through a medium-intensity magnetic separation (MIMS, Davis Tube) at 1000–2500 Gauss and a Slon® magnetic separator (1000 G). The effects of solid content (3% and 10% w/w) in a wet low-intensity magnetic separation (WLIMS, 350 G) and a two-stage MIMS followed by WLIMS were investigated. It was revealed that through reduction at 500 °C and 2 h with 20 wt% NaOH under 5 vol.% H2 + 95 vol.% N2, iron oxides and ferric oxyhydroxide (Fe2O3 and FeOOH) were converted into magnetite (Fe3O4), whereas aluminum (oxy)hydroxides (Al(OOH), Al(OH)3) were reacted with Na+ towards sodium aluminates (NaAlO2). The AM observations indicated that only 3% of iron was in the phase of liberated magnetite, and the remaining was associated with Na, Al, and Ti phases with different intensities. The dissemination of iron throughout the matrix of the sample was recognized as the principal challenge in the physical separation processes. It was found that increasing magnetic intensity from 1000 G to 2500 G resulted in improved recovery for all studied particle size fractions in Davis Tube tests. The particle range of −106 + 74 µm was chosen as the most appropriate size to achieve the maximum Fe content of 41%. The results of WLIMS (350 G) showed the maximum Fe grade but revealed less recovery of 52% and 27% at 10% and 3% solid contents, respectively, compared to the Davis Tube trials.

An Investigation on Reduction of Calcium Added Bauxite Residue Pellets by Hydrogen and Iron Recovery through Physical Separation Methods

This study investigates the properties of H2-reduced calcium-added bauxite residue, self-hardened pellets, and the feasibility of iron recovery through electrostatic and magnetic separation methods. The oxide pellets are prepared via a mixing of bauxite residue, calcite, and quicklime. The self-hardened pellets are reduced at 1000 °C with hydrogen gas flow for 120 min. The chemical composition, phase identification, and microstructural observations are executed using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. The porosity and strength of the self-hardened pellets are performed by the Mercury intrusion porosimetry and tumbling tests, respectively. The separation of iron is examined through a dry electrostatic technique, and in wet conditions, i.e., via Davis Tube and low-intensity magnetic separation (WLIMS). The effect of the magnetic field (0.1, 0.25, and 0.32 T) is tested on two different particle size fractions (−212 + 106 µm and −106 + 74 µm). It is found that most of the iron oxide in the bauxite residue is converted to metallic iron, which corresponds well with both XRD and SEM results. The Carpco electrostatic tests indicate that this approach is inefficient for the studied type of material because of the intensive association of iron with the rest of the components leading to transferring it to the middling rather than to conductive product. However, both the Davis Tube and WLIMS approve a reasonable improvement in the Fe content from 22% to 37% with acceptable recoveries. The results of the Davis Tube show that there is an optimum magnetic field and particle size for maximization of Fe grade and recovery. Finally, further suggestions are highlighted for the physical beneficiation of studied bauxite residue with the purpose of maximizing iron grade and recovery.

Producing magnetite concentrate from iron tailings via suspension magnetization roasting: A pilot-scale study

ABSTRACT In the process of iron ore beneficiation, a considerable amount of iron was lost to the tailings, resulting in the waste of resources and environmental pollution. In this study, an innovative technology of pre-concentration followed by suspension magnetization roasting and low-intensity magnetic separation (PSRM) was used to recover iron from iron tailings. The iron grade of the roasted feed ores was increased from 15.68% to 33.19% by pre-concentration process. Subsequently, the suspension magnetization roasting was performed to transform the weak magnetic minerals into magnetite, and magnetite concentrate was obtained via low-intensity magnetic separation. The effects of feeding rate, roasting temperature, reducing gas CO flow rate, and fluidizing gas N2 flow rate during suspension magnetization roasting were investigated, and the pilot-scale equipment was conducted for 72 h continuously under the optimum roasting conditions. The phase transformation and magnetic property variations of the minerals before and after roasting were analyzed by X-ray diffractometer (XRD) and vibrating sample magnetometer (VSM), respectively. The results showed that an iron concentrate with iron grade of 63.04% and total iron recovery of 48.40% was obtained under the optimum roasting conditions: feeding rate of 111.70 kg/h, roasting temperature of 550°C, CO flow rate of 4.0 m3/h, and N2 flow rate of 2.0 m3/h. The hematite and siderite in tailings were transformed into magnetite with an average magnetic conversion rate of 86.46%. This innovative PSRM technology provides an important reference for the resource utilization of solid waste and the recovery of iron from iron tailings.

Fluidization magnetization roasting of limonite ore using H2 as a reductant: Phase transformation, structure evolution, and kinetics

As a rich iron ore resource, limonite ore is seldom utilized due to and lack of mature processing methods. In this paper, fluidization magnetization roasting and low-intensity magnetic separation were used to process limonite ore. A concentrate with an iron grade of 59.92% and an iron recovery of 87.26% was obtained under these optimum roasting conditions: a temperature of 525 °C, a roasting time of 10 min, and a H 2 concentration of 20%. X-ray diffraction, vibrating sample magnetometry, and scanning electron microscopy were used to study the reduction mechanism. The results indicated that the reduction product characteristics greatly changed after roasting. The reduction kinetics followed the nucleation model A 2 , and the activation energy was 29.62 kJ/mol. This study will provide some guidance for limonite ore utilization. • An efficient and green method to recovery iron minerals from refractory limonite ore. • H 2 was used as a reducing agent to reduce refractory limonite ore. • The reduction kinetics was calculated during the process.

Beneficiation of Oolitic Iron Ore Sourced from Gara Djebilet using Coal-Based Direct Reduction prior to Magnetic Separation

A process involving coal-based direct reduction followed by wet low-intensity magnetic separation is presented in this paper with the objective of promoting the Fe content and reducing the P assay of phosphorus-rich oolitic iron ore. A final direct reduced iron powder assaying 92.5 wt% Fe and 0.2wt % P at a recovery rate of 95.9% was obtained when a mixture of ore-coal-CaO was reduced at 1200°C during 60 min in the presence of 7.5% sodium sulfate. In addition, microscopic analyses reported that the oolitic texture was completely destroyed, and most of the iron occurred in the metallic state. These findings suggest the ease utilisation of the ore mined from Gara Djebilet in the steelmaking industry as a substitute to scrap steel in electric arc furnace.

Recovery of Scandium, Aluminum, Titanium, and Silicon from Iron-Depleted Bauxite Residue into Valuable Products: A Case Study

Bauxite residue is a high-iron waste of the alumina industry with significant contents of scandium, aluminum, and titanium. This study focuses on the recovery of Sc, Al, Ti, and Si from iron-depleted bauxite residue (IDBR) into valuable products. Iron depletion was carried out using reduction roasting followed by low-intensity magnetic separation to enrich bauxite residue in Al, Ti, and Sc and reduce an adverse effect of iron on scandium extraction. Hydrochloric high-pressure acid leaching, aluminum precipitation by saturation of the acid leachate, solvent extraction of scandium using di(2-ethylhexyl) phosphoric acid (HDEHP) and tributyl phosphate (TBP), alkaline leaching of the acid residue with subsequent silica precipitation were used to obtain appropriate selective concentrates. As a result, scandium concentrate of 94% Sc2O3, crude alumina of 93% Al2O3, titanium concentrate of 41.5% TiO2, and white carbon of 77% SiO2 were prepared and characterized. Based on the characterization of the treatment stages and the obtained valuable products, the prospect for the application of the suggested flowsheet was discussed.

Efficient Utilization of Siderite- and Hematite-Mixed Ore by Suspension Magnetization Roasting: A Pilot-Scale Study

Steel is an important industrial raw material and plays an important role in industrial construction. Studying the efficient utilization of complex refractory iron ore with large reserves is of great significance to ensure the strategic safety of China’s iron and steel industry. Focusing on the typical mixed iron ore of siderite (FeCO3) and hematite (Fe2O3), this paper analyzes the possible ways of magnetization roasting from the perspective of thermodynamics and highlights that oxidation–reduction roasting is an easy way to realize industrial application. On this basis, a pilot-scale test of suspension magnetization roasting followed by low-intensity magnetic separation is carried out by using a newly developed suspension magnetization roasting furnace. The effects of roasting temperature, CO consumption, and N2 consumption on the magnetization roasting process are investigated, and 24 h continuous tests are carried out. Here, we find continuous suspension magnetization roasting followed by low-intensity magnetic separation can obtain a total iron grade of over 56% with an average value of 57.18% and a total iron recovery rate of over 91% with an average value of 92.22%. Product analysis shows that after SMR, iron minerals such as siderite and hematite transform into magnetite, with a substantial increase in magnetism, which is conducive to the separation of iron ore. The results provide a reference for the development and utilization of siderite- and hematite-mixed iron ore.

Performance assessment of an innovative precise low-intensity magnetic separator

An innovative precise low-intensity magnetic separator (PLIMS) was developed for recovering low-grade magnetite. The effects of the key parameters on the separation performance of the PLIMS in recovering magnetite were investigated. The results indicated that the drum rotation speed and feed particle size played major roles in enhancing the grade of the concentrate and the recovery. Additionally, the performances of the PLIMS and selected conventional low-intensity drum magnetic separators (CLIMSs) and Davis tube testers (DTTs) were compared. The comparison revealed that the performance of the PLIMS was consistent with that of the DTT in terms of the grade of the concentrate and the recovery. In addition, the PLIMS had a higher iron grade with fewer gangue particles and higher recovery compared with the CLIMS.For the PLIMS, the remnant flux density of the magnet assembly was designed to gradually increase from low to high along the flow direction of the slurry. In the entire magnetic separation process, the magnetic force acting on the captured magnetic particles is always the most minor magnetic force required to achieve precise magnetic separation, which results in improved selectivity. Furthermore, the advantage of the PLIMS is that seven concentrates can be obtained by one magnetic separation. Therefore, the newly developed PLIMS simplifies the magnetic separation process and produces multiple products, and the grade of the concentrate can be flexibly controlled. It has a high recovery and can create various high-, medium-, and low-grade concentrates.

Mineralogical Study of Low and Lean Grade Iron Ore Fines during Slow and Rapid Reduction Roasting

Abstract The present study focuses on the mineralogical aspects and roasting of iron ore (Fe: 55.4%) fines in both fixed bed and fluidized bed roaster. Goethite is the dominant mineral phase in this low-grade iron ore containing hematite, silica and alumina. Such ore was roasted at a constant temperature of 900°C, with non-coking coal of 20% at residence time ranging from 15 to 60 minutes at intervals 15-minute in the fixed bed and 2 to 8 minutes at intervals 2-minute in the fluidized bed reactor. Non-coking coal was utilized as a reductant in the reduction reaction. A high-grade iron ore concentrate was subsequently extracted using Low Intensity Magnetic Separation (LIMS) from the roasted ore. Phase changes in both cases were different due to the difference in the mechanism of reduction. In the fixed-bed reduction roasting phase, transformation occurs as Goethite – Hematite – Magnetite – Wustite, whereas in a fluidized bed, it has followed Goethite – Hematite – Magnetite – Maghemite route. The maghemite phase formed during the fast reduction process due to reoxidation of the reduced magnetite. The wustite phases are reported in the nonmagnetic fractions during LIMS, lowering the yield. On the other hand, the maghemite phase is reported to the magnetic portions. It has a simple cubic structure like magnetite, which increases the yield in the fast reduction roasting process. The results show that 65.85-grade iron ore can be obtained after 30 minutes of residence time with a recovery of 51.5% from the fixed bed and 62.17-grade iron ore can be obtained after 4 minutes of residence time with a recovery of 53.2 % from the fluidized bed.

Particle-based characterization and classification to evaluate the behavior of iron ores in drum-type wet low-intensity magnetic separation

Magnetic separation is a versatile technique widely used in the mining industry. Drum-type wet low-intensity magnetic separation (WLIMS) represents the backbone of the iron ore upgrading circuits since the mid 19th century. However, it has been traditionally applied through guidelines that commonly disregard the ore properties and their interaction with the operating conditions to influence the final process selectivity. This work describes a three-stage methodology to achieve the comprehensive characterization and classification of an iron ore, seeking to recognize links between the ore properties and operating conditions, and their influence upon the process performance. This methodology integrates 1) laboratory testing, 2) particle-scale characterization of the ore and products from separation trials, and 3) data analysis to identify and categorize the particle attributes that control their behavior in a laboratory-scale magnetic separator. Dry sieving, Saturation Magnetization Analyzer (SATMAGAN) and Mineral Liberation Analysis (MLA) represent the basis to collect quantitative particle-level information for clustering the ore into classes of unique nature. The further determination of the volumetric magnetic susceptibility by particle class, together with the relative probability of particle capture, provides valuable insight on the ore magnetic behavior. The calculation of particle-classed partition coefficients resulted practical to assess the process selectivity in terms of particle attributes and operating conditions. The methodology proposes guidelines to comprehend the behavior of an ore from a particle-scale perspective. Moreover, the acquired data can be used for geometallurgical and process modeling, which represent promising forecasting tools to support decision-making in plants.