Wet Low-intensity Magnetic Separation Research Articles

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.

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.

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.

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.

Beneficiation of Iron Oxides from Cupola Furnace Slags for Arsenic Removal from Mine Tailings Decant Water

Large volumes of ferrous metallurgical slags (FMS) are generated annually as waste materials from metal extraction, purification, casting and alloying processes worldwide. Some attempts have been made to use bulk FMS in metal precipitation and concrete works but little success has been achieved because of unstable precipitates and volume expansion of concrete structures. As a result, significant quantities of FMS are still disposed in landfills. This disposal leads to land conflicts and poor environmental practices. The present study focuses on the characterization and separation of iron oxide from selected bulk FMS (Cupola Furnace Slag - CFS) obtained from Ghana into constituent components for use as engineering materials. Quantitative X-ray diffractometry was used to determine the mineralogy of CFS. Iron oxide morphology and spot composition in the CFS were determined using scanning electron microscopy, combined with energy dispersive spectroscopy. The inductively coupled plasma-optical emission spectrometry was used to ascertain the chemical composition of CFS after acid digestion. Wet low intensity magnetic separation technique was employed for beneficiating iron oxides from the CFS. It is shown that the CFS is amorphous and consist of ferrous and non-ferrous material. Results of the investigation confirmed that ferrous materials in the slags can be separated using magnetic separation technique. The study further confirmed that fine grinding (- 75 µm) liberates the magnetic portions of the slag efficiently, and as such, they can be recovered using a low magnetic field. The recovery was 99.04 % and the concentrates obtained from the beneficiation process consist primarily of pigeonite, quartz, magnetite and jacobsite. The beneficiated concentrates have the capacity to adsorb arsenic from mine effluent. This study has demonstrated that, slags can be utilized as secondary resources rather than a waste.

A Phenomenological Model for Particle Kinetics in Drum-type Wet Low-Intensity Magnetic Separation*

Drum-type wet low-intensity magnetic separation (WLIMS) is a versatile technique widely employed in the mining industry for the treatment of iron ores. Its design and operation are rather simple and straightforward. Yet, understanding the process performance from a fundamental point of view still remains a puzzling task due to a number of complex subprocesses involved in the separation. Most of the models for drum-type WLIMS thus are based on empirical approaches. This work presents a modeling strategy that integrates ore properties and equipment characteristics to describe the behavior of iron ore particles. It relies on interpreting a laboratory-scale drum-type wet magnetic separator as a continuously stirred tank reactor. It merges the benefits of phenomenological and empirical modeling to express the particle kinetic rate constants as a function of the separation principles and ore characteristics. Results suggest that the kinetic model satisfactorily reproduces the experimental observations in terms of particle-classified magnetite recovery. The approach is promising for obtaining early information on the behavior of the particles at different stages of the iron ore beneficiation chain, especially for production planning, circuit layout and optimization.

Design optimization and manufacturing of an innovative precise low-intensity magnetic separator based on a multiphysics model

A wet low-intensity magnetic separator (LIMS) is the workhorse for winning magnetite from a slurry. However, the issue with optimizing LIMS is the balance between attracting too much material and obtaining mixed grains of extremely low-grade material (less than 20 vol% magnetite) in the concentrates and attracting too little material and losing the fine liberated magnetite to the tailings. In this study, an innovative precise low-intensity magnetic separator (PLIMS) was designed and optimized based on a multiphysics numerical model. The design parameters of the magnetic assembly and operational parameters were designed and optimized by predicting the separation performance and particle dynamic trajectory of the PLIMS. In particular, the remnant flux density of the magnet assembly was designed to gradually increase from low to high along the flow direction of the slurry, so that the magnetic particles were subjected to precise magnetic force during the separation process. When the magnetic force is greater than the competitive forces, the magnetic particles are captured on the surface of the drum. Then, the captured particles with different liberation degrees and particle sizes are taken out of the separation zone via rotating drum one by one and become concentrated products of multiple grades. The aim of the process is to capture the high liberation magnetite into the main concentrates to obtain high-grade concentrate products, while also capture the low-grade intergrowth particles into the minor concentrates as much as possible to obtain higher recovery. Furthermore, this principle of magnetic separation of PLIMS was explained by simulating the dynamic capture process of the magnetic particles.To verify whether the design concept of gradient magnet assembly (GMA) has advantages, another uniform magnet assembly (UMA) with the same remnant flux density of all permanent magnets was designed. Comparative studies of the magnetic field distribution and magnetic separation performance of GMA and UMA show that PLIMS of the GMA has more significant separation performance. Finally, a laboratory-level PLIMS with a drum diameter of 300 mm (ϕ300-PLIMS) was manufactured based on all the optimization studies above. By comparing the experimental results with simulated results, the accuracy of the PLIMS recovery and grade prediction results were verified.

Recovery of iron and phosphorus removal from Gara Djebilet iron ore (Algeria)

Purpose. This research aims to promote the assay of iron and reduce the phosphorus grade of the final DRI. Methodology. A high-phosphorus oolitic iron ore from Gara Djebilet deposit underwent the procedure of coal-based direct reduction (coal-based DR) followed by wet low-intensity magnetic separation (WLIMS). The effects of temperature, periods of time and Na2SO4 dosage on phosphorus removal, metallisation degree and iron recovery rate were tried and optimised. Furthermore, phase changes in iron oxides and the distributing features of phosphorus in both reduced and magnetic materials were investigated as well. Findings. The appropriate addition of sodium sulfate improves the Fe-P separation during the coal-based DR of Gara Djebilet mixed pellets. Originality. Using additives of CaO and sodium sulfate during the coal-based DR-magnetic separation of mixed pellets sourced from Gara Djebilet deposit. Practical value. The results reveal that a final direct reduced powder (DRI) assaying 96 wt% Fe and 0.16 wt% P at a recovery rate of 97.72% was obtained when the ore-coal-CaO mixed pellets were reduced in the presence of 5 wt% Na2SO4 at 1250 C for 30 min. Thus, the coal-based DR could be used as an alternative to the blast furnace (BF) route in the steelmaking industry from refractory iron ores.

Magnetic entrainment mechanism of multi-type intergrowth particles for Low-Intensity magnetic separation based on a multiphysics model

Wet low-intensity magnetic separation (LIMS) is used in the magnetic separation of ferromagnetic minerals. The performance of the separation is controlled primarily by the internal flow in the separator, governed by the process and machine settings. However, a very important factor has been usually ignored in the LIMS process, namely the behavior of the intergrowth particles. The detailed influence of the various condition parameters on the behavior of the particles with different characteristics in LIMS is still not clear. In this study, a two-way coupled multiphysics model was used to simulate the dynamic capture process of the multi-type intergrowth particles and its impact on the performance of LIMS separation. All predictions indicate that the operating parameters and particle properties affect the capture behavior of intergrowth particles, which significantly affects the separation performance of the LIMS. Intergrowth particles play an important role in the process of LIMS. Additionally, the capture time for the intergrowth particles of different particle sizes and liberation degrees to reach the drums’ surface from the initial location are different. Because the capture time of the coarse intergrowth particles is much shorter than that of the ultrafine pure magnetic particles, the coarse particles will preferentially accumulate on the drum to cause a magnetic entrainment phenomenon. The phenomenon of magnetic entrainment facilitates the recovery of intergrowth particles. In LIMS, however, for a high grade and recovery magnetic product, intergrowth particles and high liberation is necessary and excessive grinding of the particles should be avoided.

A finite element model to simulate magnetic field distribution and laboratory studies in wet low-intensity magnetic separator

Low-intensity magnetic separators are widely used in the research works and the industry. Advancement in the magnetic separation techniques has led to an expansion in the application of this method in different fields such as enrichment of magnetic mineral, wastewater treatment, and medicine transfer in the human body. In the mineral processing industry, the main application of wet magnetic separation is via drum separators. The design of this separator is based on drum rotation inside a tank media, where a permanent magnet placed inside the drum as an angle form produces a magnetic field. In the present work, the magnetic variables involved (magnetic flux density, intensity of magnetic field, and gradient of magnetic field intensity) were simulated in the drum wet low-intensity magnetic separator using the finite element method and a COMSOL Multiphysics simulator; these variables were further validated through the measured data. A comparison between the simulation and laboratory measurements (of the magnetic field) showed that the mean value of the simulation error in 94 points in 2 sections was equal to 9.6%. Furthermore, the maximum simulation error in the middle of the magnets, as the most important part of the magnetic field distribution in the process of magnetic separation, was in the 6th direction and equal to 7.8%. Therefore, the performed simulation can be applied as a first step to design and construct more advanced magnetics separators.

Dynamic capture behavior of ferromagnetic particles based on fully coupled multiphysics model of particle-fluid interactions

Wet low-intensity magnetic separation (LIMS) is used in the magnetic separation of ferromagnetic minerals. The performance of the separation is controlled primarily by the internal flow in the separator, governed by the process and machine settings. However, these factors change with the properties of the magnetic material and the operating conditions. Therefore, the numerical calculation of the multiphysics coupling separation process of such dynamic captures becomes crucial for wet LIMS. In this study, we present a novel and straightforward fully coupled multiphysics modeling approach for the simulation of LIMS. In this model, particle tracing in the fluid flow module is used to calculate the location and dynamic capture behavior of ferromagnetic particles under the determined magnetic and flow fields. In particular, while calculating the magnetic force, hydrodynamic drag force, gravity, and centrifugal force, the model also inherently retains its ability to simulate the influence of ferromagnetic–particle–fluid interactions.The model is compared with experiments and the particle capture theory, and is demonstrated to be realistic for studying ferromagnetic suspensions in mineral processing applications. The model provides new possibilities to understand and predict the efficiency of mineral separation processes through detailed computational simulations of the effects of the respective operating conditions on the dynamic capture behavior of the particles.

Evaluation and comparison of different machine-learning methods to integrate sparse process data into a spatial model in geometallurgy

A spatial model for process properties allows for improved production planning in mining by considering the process variability of the deposit. Hitherto, machine-learning modelling methods have been underutilised for spatial modelling in geometallurgy. The goal of this project is to find an efficient way to integrate process properties (iron recovery and mass pull of the Davis tube, iron recovery and mass pull of the wet low intensity magnetic separation, liberation of iron oxides, and P80) for an iron ore case study into a spatial model using machine-learning methods. The modelling was done in two steps. First, the process properties were deployed into a geological database by building non-spatial process models. Second, the process properties estimated in the geological database were extracted together with only their coordinates (x, y, z) and iron grades and spatial process models were built. Modelling methods were evaluated and compared in terms of relative standard deviation (RSD). The lower RSD for decision tree methods suggests that those methods may be preferential when modelling non-linear process properties.

Beneficiation Studies of a Rare Earth Ore from the Olserum Deposit

The Olserum deposit located in Sweden hosts an indicated mineral resource of 4.5 million tonnes at 0.6% total rare earth oxides (TREO), exhibiting a relatively high proportion of heavy rare earth elements (HREE). The mineralogy and beneficiation of a composite drill core sample from the Olserum deposit were studied. Monazite and xenotime were found by the mineralogical analyses to be the target minerals for beneficiation of REEs and most (96.9%) of REEs in the ore are carried by monazite (68.5%) and xenotime (28.4%). Because xenotime carries 84.7% of heavy REEs (Y, Gd, Dy) in the ore it is more valuable mineral than monazite. A beneficiation process was developed which includes grinding, wet low intensity magnetic separation (WLIMS) for removal of magnetite and REEs flotation consisting of one stage of roughing and two stages of cleaning. Selective flotation collector of REE minerals and suitable grinding size of feed material were determined by testwork. The REE concentrate and tailings were chemically and mineralogically characterized. The studies of process mineralogy showed that the REE-bearing minerals, monazite and xenotime, and apatite were successfully enriched from the concentrations of 0.6%, 0.31% and 2.6% in the feed to those of 17.0%, 8.9% and 65.0% in the concentrate with the recoveries of 79.0%, 81.3% and 71.0%, respectively.

Beneficiation of a low-grade iron ore by combination of wet low-intensity magnetic separation and reverse flotation methods

Beneficiation of a low-grade iron ore was investigated by combination of the low-intensity magnetic separation and reverse flotation methods. The main constituents of the representative sample were 36.86% Fe, 8.1% FeO, 14.2% CaO, 13.6% SiO2, and 0.12% S based on the X-ray fluorescence, titration, and Leco analysis methods. The mineralogical studies by the X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron probe micro-analyzer, and Fe/FeO titration methods showed that the ore minerals present in the representative sample were magnetite, hematite, and goethite, and the main gangue minerals were calcite and quartz. The effects of the operating parameters including the feed size, solid content, and drum rotation speed were investigated on the performance of the wet low-intensity magnetic separation (WLIMS). The optimum operating conditions of WLIMS were determined to be feed size = 135 μm, solid content = 40%, and drum rotation speed = 50 rpm. Under these conditions, a concentrate of 62.69% Fe grade and 55.99% recovery was produced. The tailing of WLIMS with an iron grade of 28.75% was upgraded by reverse flotation with fatty acids as the collector. The effects of five parameters on two levels were investigated using the 25-1 fractional factorial design in 16 experiments. The optimum flotation conditions were determined to be pH = 12; dosage of collector, 1 kg/t; dosage of Ca2+ as activator, 4 kg/t; and dosage of starch as depressant, 1 kg/t. Under these conditions, a concentrate of 53.4% Fe grade and 79.91% recovery was produced.

Geometallurgical characterisation of Leveäniemi iron ore – Unlocking the patterns

As part of a geometallurgical program for the Leveäniemi iron ore mine, the Davis tube was used as proxy to classify ore types, predict iron recoveries in wet low-intensity magnetic separation (WLIMS), and to estimate liberation of mixed particles. The study was conducted by testing 13 iron ore samples with a Davis tube and a laboratory WLIMS. Ore feed was studied for modal mineralogy and liberation distribution with Automated Scanning Electron Microscopy. Data analyses to detect the patterns and data dependencies were done with multivariate statistics: principal component analysis, and projection to latent structures regression. Results show that a simple index (XLTU) based on mass pull in the Davis tube is capable of easy classification of magnetite ores. Using Davis tube mass pull and iron recovery, together with iron and Satmagan head grades may predict iron recovery in WLIMS. Also, the variability in Fe-oxides liberation pattern for magnetite semi-massive ores can be explained with the chemical composition of the Davis tube concentrate. It is concluded that the Davis tube test is better used only for marginal ores, since iron oxide minerals tend to be fully liberated in high-grade magnetite massive ores after grinding. The developed models may be used in populating a production block model.

Recovery of iron and lead from a secondary lead smelter matte by magnetic separation

A secondary Pb smelter matte with a total Fe grade of ca. 50% (as FeS, Fe3O4, FeO and metallic Fe), shows good potential for being used as a secondary Fe source. However, requirements for Fe ore are: a total Fe grade >60% and a sulphur content as low as possible. Therefore, further treatment steps are necessary to increase the Fe content in the matte. Dry low intensity, wet low intensity and wet high intensity magnetic separation experiments were performed on different particle size fractions of the matte. Mineral liberation analysis (MLA) was performed to explain different behaviours of Pb in the different size fractions during magnetic separation. Moreover, oxidizing roasting at 600 °C was carried out to transform FeS to Fe2O3, which is the more prefered form of Fe for pig iron production. Results show that by combining low and high intensity magnetic separation and oxidizing roasting, material with a total Fe grade of 61% (as oxide) can be recovered in the magnetic fraction representing circa 50% of the initial weight of the sample. Moreover, the sulphur content was reduced from initial 20 to 4% in the final magnetic fraction. Further reduction in sulphur content would require an additional desulphurization step.

Increasing Silicate Grade in Crude Ore

Luossavaara-Kiirunavaara AB (LKAB) operates an iron ore mine, three concentration plants and three pelletising plants in Kiruna, Sweden. The current methods of separation at the beneficiation plants are low intensity magnetic separation (LIMS) and reverse flotation (i. e., apatite is floated and magnetite depressed), where the wet LIMS stage is regarded as the crucial part of the separation of silica from the ore. It is increasingly important to understand the Kiirunavaara high-grade iron ore deposit from a mineral processing perspective as well as from a mineralogical and geochemical perspective as the production in the mine is advancing towards deeper levels with higher concentrations of SiO2 in the ore. The mineral processing parameters such as the natural breaking characteristics, specific energy consumption and degree of liberation of magnetite and silicate minerals are equally important. The intergrowth of magnetite with actinolite is of particular importance for understanding the processes in the processing plants in Kiruna and the flotation behaviour of silicate minerals. The iron ore deposit at Kiirunavaara consists mainly of magnetite and apatite, with an average grade of 63.8% Fe and 0.4% P (estimated from the 3D resource model, LKAB) and with varying, but mostly small, amounts of gangue minerals, mostly silicates and carbonates. Based on mineralogical investigations, actinolite and phlogopite and in many cases also chlorite, titanite, quartz and albite are the most significant SiO2-bearing minerals in the ore. Currently, the high-grade iron ore deposit of Kiirunavaara has in situ a low grade of silica of approximately 3% SiO2. However, the SiO2 grade is expected to increase in the deeper parts of the deposit. It can be assumed that the silicate mineralogy and the SiO2 grade in the crude ore undoubtedly impact the SiO2 content of the final products, i. e. the iron ore pellets and/or iron ore fines. This results in new challenges and requirements for the production at LKAB. Within the framework of the completed “Silica in the Mine” project, which was an important research and development area for LKAB for several years, the entire production chain from “the mine to the mill” and from “the mill to the final product” was evaluated in several subprojects. Important information was gained from the results of these subprojects in order to better understand the problem of the increasing and fluctuating SiO2 grades in the crude ore and magnetite concentrate. To study the reduction of the SiO2 content additionally in the magnetite concentrate obtained by WLIMS, a reverse cationic flotation laboratory test programme was initiated in the early spring of 2016. This flotation test work was based on the investigation carried out at the mineral processing laboratory at the Geological Survey of Finland (GTK). To obtain additional information about the problem of SiO2 and the behaviour of individual silicates during mineral processing, an extensive large-scale sampling programme will be carried out at the different stages of the process at the beneficiation plants (KA1, KA2, KA3) at the Kiirunavaara site.

Internal flow measurements in pilot scale wet low-intensity magnetic separation

In the mining industry, ferromagnetic particles (e.g. magnetite) are concentrated using wet low-intensity magnetic separation (LIMS). The performance is to a large extent controlled by the internal flow conditions in the separator. In previous work, it was shown how an ultrasound pulse-echo setup can be used to simultaneously measure particle velocity profiles and local solids concentration variations in laboratory conditions.In this paper, a real-world case is demonstrated where the system is installed on one of the wet LIMS at the LKAB R&D facilities in Malmberget, Sweden. For the pilot scale experiments a setup with two ultrasound transducers, mounted at the bottom of the separator tank, is used. The design of experiments method is used to study the effects of the feed solids concentration, drum rotational speed, position of the concentrate weir, and the magnet assembly angle on the measured flow patterns. The results show that it is possible to detect changes in the flow velocity patterns and the local solids concentration, as the operational conditions of the separator are varied.Of the factors studied, the drum rotational speed has the strongest influence on the overall flow velocity in the dewatering zone. Also, the presence of a recirculating flow transporting gangue particles away from the concentrate is confirmed. The factor with the strongest influence on this recirculating flow is also the drum rotational speed, together with the magnet assembly angle. Using this method it is possible to make high quality measurements of internal flow velocity profiles. It is also possible to monitor material build-up on the separator drum, and e.g. detect overload of magnetic material. The insights gained, and the methods developed, have generated new possibilities to control, optimise, and develop the wet LIMS process.

Developing a particle-based process model for unit operations of mineral processing – WLIMS

Process models in mineral processing can be classified based on the level of information required from the ore, i.e. the feed stream to the processing plant. Mineral processing models usually require information on total solid flow rate, mineralogical composition and particle size information. The most comprehensive level of mineral processing models is the particle-based one (liberation level), which gives particle-by-particle information on their mineralogical composition, size, density, shape i.e. all necessary information on the processed material for simulating unit operations. In flowsheet simulation, the major benefit of a particle-based model over other models is that it can be directly linked to any other particle-based unit models in the process simulation. This study aims to develop a unit operation model for a wet low intensity magnetic separator on particle property level. The experimental data was gathered in a plant survey of the KA3 iron ore concentrator of Luossavaara-Kiirunavaara AB in Kiruna. Corresponding feed, concentrate and tailings streams of the primary magnetic separator were sampled, assayed and mass balanced on mineral liberation level. The mass-balanced data showed that the behavior of individual particles in the magnetic separation is depending on their size and composition. The developed model involves a size and composition dependent entrapment parameter and a separation function that depends on the magnetic volume of the particle and the nature of gangue mineral. The model is capable of forecasting the behavior of particles in magnetic separation with the necessary accuracy. This study highlights the benefits that particle-based models in simulation offer whereas lower level process models fail to provide.

Relationship between cation distribution with electrochemical and flotation properties of calcic amphiboles

Reverse cationic flotation is a very efficient method of beneficiation of oxidised iron ores when you need to separate hematite and quartz. This method can be also applied to reduce silica content in the magnetite concentrates obtained by wet low-intensity magnetic separation. However, cationic flotation in this case is less effective due to the presence of Fe–Mg–Al-bearing silicates as amphiboles in magnetite ores. These silicates are concentrated in magnetic products and determine the difficulties of their separation from iron oxides when amines and starches are used as collectors and depressants, respectively. The recalculation of the results of the electron microprobe analysis of five calcic Fe–Mg–Al-bearing amphiboles used to characterise cation distributions in structural units and to obtain structural formulae in accord with stoichiometric limits was conducted. The Mössbauer spectroscopy was used to examine the validity of the empirical estimation of cation distributions in amphiboles. The studied samples are metamorphic pargasite, ferrotschermakite and magnesiohornblende and volcanic kaersutite and magnesiohornblende. The crystallographic analyses of the amphibole samples exhibited their heterogeneous surfaces explaining worse floatability of amphiboles with amines at pH10. The electrokinetic measurements showed that the position of the isoelectric point of amphiboles is related to a substitution of Al3+ for Si4+ in tetrahedral sites and to an amount of Mg2+ cations in octahedral sites. Thus, the amine adsorption onto amphiboles through electrostatic interactions is mainly affected by a distribution of these cations in tetrahedral and octahedral sites of amphiboles. In addition, the effect of starch on the depression of Fe–Mg–Al-bearing amphiboles during flotation can be attributed to the presence of metal ions on the amphibole surface, which are capable of forming strong chemical complexes with starch molecules.