The beneficiation of low-grade iron ores to meet the growing demand for iron and steel is an important research topic. However, certain ores do not qualify to be treated in physical separation ...processes, and hence, alternative strategies are being looked into for upgrading their iron content. The objective of this review article is to compile and amalgamate the crucial information regarding the beneficiation of low-grade iron ores using carbothermic reduction followed by magnetic separation, which is a promising technique to treat iron ores with complex mineralogy and liberation issues. Reduction roasting studies done for different types low-grade iron ores including oolitic iron ores, banded iron ores, iron ore slimes and tailings, and industrial wastes have been discussed. The large scale technological advancements in reduction roasting and the possibilities of the application of alternative reductants as substitutes for coal have also been highlighted.
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The depletion of high-grade iron ores has necessitated the beneficiation of low-grade iron ores. Flotation is considered the most efficient operation to upgrade the iron content of fine-grained ores ...that do not respond to gravity or size classification units. Out of several reagents used in iron ore reverse flotation, depressants play a crucial role in selectively making the iron oxides hydrophilic and prohibiting them from reporting to the gangue-rich froth phase. Starch is widely used as the depressant in iron ore flotation. The present paper attempts to highlight different facets of starch as an iron ore depressant. It reviews the important research papers that discuss the origin and chemistry of starch, starch-iron oxide interaction mechanism, and the application of different types of starches and their alternatives in iron ore flotation.
The reduction of iron ore using biomass-based reductants has opened up a new chapter because of its contribution to energy conservation and emission reduction. In this connection, the application of ...waste coconut shells (CS) as the reductant in the reduction roasting-magnetic separation of an iron ore overburden sample is explored. Characterization studies on the overburden having 49% Fe suggest that the sample is mostly a goethitic ore containing kaolinite as the major gangue mineral. A concentrate with 63.2% Fe at an iron recovery of 66.2% has been obtained from the low-intensity magnetic separation of the overburden roasted at a temperature of 800 °C, time of 60 min and a CS to feed ratio of 0.2. Characterization studies indicate the formation of magnetite and hematite under these optimum conditions, whereas roasting at a temperature of 900 °C and a reductant to feed ratio of 0.3 is found to form feebly magnetic phases like wustite, fayalite and complex iron aluminosilicates resulting in poor iron recovery. The thermo-gravimetric analysis studies explain the disintegration of the biomass and reduction of the iron ore thereby validating the reduction sequence as predicted using the characterization studies.
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•Novel application of coconut shell as a substitute to coal based reductants.•Iron recovery from iron ore overbudren using reduction roasting-magnetic separation.•Product with 63% Fe with an iron recovery of 66% from a feed of 49% Fe.•In-depth mineralogical characterization.
This work illustrates the reduction roasting and magnetic separation studies of a complex Indian iron ore with 57% Fe that could not be upgraded to >61% Fe using a flow sheet comprising of the ...conventional unit operations like scrubbing, jigging, magnetic separation or flotation. The sole reason of the poor response to physical beneficiation was mainly attributed to the inadequate liberation of iron as visualized under the reflected light microscope, which revealed the fine dispersion of silica particles within the hematite grains and vice versa. In order to overcome this problem, the ore was subjected to reduction roasting using conventional as well as microwave heating followed by magnetic separation. The effects of different process variables such as reductant concentration, time, and temperature during the process of roasting were studied and subsequently optimized using the Taguchi statistical design. Optical microscopy and X-ray diffraction (XRD) studies of the roasted mass confirmed the formation of magnetite with simultaneous disappearance of the hematite and goethite phases. In the microwave roasting process, the reduction could be achieved in a considerably shorter time as compared to the conventional roasting, and the formation of undesired non-magnetic iron minerals like fayalite was limited as well. In both the processes, it was possible to achieve an iron ore concentrate having 63–65% Fe accompanied by ~85–90% weight recovery.
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•Reduction roasting using conventional & microwave (MW) heating was attempted.•Both routes yield iron concentrates with ~63–64% Fe at ~85% weight recovery.•MW route is promising considering the requirement of less roasting time.•Lesser formation of fayalite in case of microwave roasting is an advantage.
•Quaternary ammonium based IL’s attempted as collectors for quartz flotation.•Effect of alkyl chain length assessed through XPS and molecular modelling.•IL–quartz interaction governed by van der ...Waals and electrostatic forces.•IL with 6 carbon in alkyl chains gives the maximum coverage and floatability.•IL’s are found to be better than conventional quartz collectors.
Application of quaternary ammonium based ionic liquids (IL’s) as flotation collectors of quartz has been investigated. Effect of number of carbon atoms in the four identical alkyl chains of the IL’s has been studied. The adsorption behaviour of the IL’s on the quartz surface is ascertained through FTIR, XPS and molecular modelling. The FTIR peak at 2900cm−1 indicates the adsorption of the IL’s onto the quartz surface, which is further substantiated by the appearance of the N (1S) peak in the X-ray photoelectron spectra (XPS). Curve splitting data of C (1S) suggests the maximum adsorption for the IL tetrahexylammonium iodide (THEX). Flotation results of pure quartz using ionic liquids are found to be better compared to the conventional collectors such as dodecylamine (DDA) or cetyltrimethylammonium bromide (CTAB). It is possible to float 92–100% quartz by using a THEX concentration of 4.8 × 10−5M. IL collectors are further applied in the flotation of a low grade banded hematite quartzite (BHQ) iron ore with ∼38% Fe. It is possible to achieve an iron concentrate of 63.6% Fe at 63.2% recovery by using THEX as the collector. Molecular simulations using the COMPASS forcefield explains the IL–quartz adsorption mechanism comprising of both electrostatic and van der Waals forces. Floatability of quartz has been correlated with the surface coverage and adsorption energy calculations. The IL’s used here are found to be better quartz collectors than the conventional ones as they show better collecting efficiency in lower dosages. Flotation using these IL’s does not require frothers which is an added advantage compared to the conventional collectors.
Induration of ilmenite pellets by oxidation is an essential step in the pelletization process since it decides the physical and metallurgical properties of the pellets. In this regard, the induration ...parameters such as temperature and roasting time have been optimized to obtain good quality ilmenite pellets made of concentrates obtained from low-grade ilmenite ores of Odisha, India. The oxidation temperature of 900 °C at a short roasting time of 15 min has been found suitable to achieve recommended requirements of various pellet properties such as cold compressive strength, porosity, metallization, tumble, and abrasion indices. X-ray diffraction and microstructural analysis indicate that the recrystallization of hematite in the oxidation process improves the mechanical strength of the pellets. In contrast, the formation of ferric pseudobrookite phase at 1000 °C and 1100 °C oxidation temperatures impairs the pellet strength.
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•The readiness of the ilmenite pellets for the reduction process was assessed through induration studies.•Different metallurgical properties were analyzed as a function of temperature and time.•Desirable pellet properties were attained at a temperature of 900 °C and a period of 15 min.•The phases changes occurred during induration were clarified using in-depth XRD, SEM, and EPMA analyses.•The oxidation mechanism of ilmenite pellets was correlated to the pellet consolidation.
•Plane wave periodic DFT study of oleate-iron oxide interaction.•Magnetite-oleate complex is more stable than hematite and goethite.•Flotation recovery of magnetite is more compared to the other two ...oxides.
Comparative studies of oleate interaction with hematite, magnetite and goethite using density functional calculations are presented. The approach is illustrated by carrying out geometric optimization of oleate on the stable and most exposed planes of hematite, magnetite, and goethite. Interaction energies for oleate-mineral surface have been determined, based on which, magnetite is found to be forming the most stable complex with oleate. Trend as obtained from the quantum chemical calculations has been validated by contact angle measurements and flotation studies on hematite, magnetite and goethite with sodium oleate at different pH and collector concentrations.
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•TOMAS, an ionic liquid is used in quartz flotation for the first time.•Flotation recovery of quartz with TOMAS is better than that with DDA.•Consumption of TOMAS is much lesser than ...DDA.•Adsorption of TOMAS on quartz confirmed by zeta potential, FTIR and XPS.•Molecular modeling supports stronger adsorption of TOMAS with quartz.
Tricaprylmethyl ammonium salicylate (TOMAS), an ionic liquid has been employed as a collector for the flotation of quartz. The sign reversal of zeta potential of quartz from negative to positive values and increase in contact angle from 80 to 700 by the addition of TOMAS have substantiated the interaction of TOMAS with the quartz surface. The change in morphology as indicated in SEM and two peaks at 2933 and 2857cm−1 owing to the vibrations of CH2 and CH3 as seen in FTIR spectra support the adsorption of the reagent on quartz. The N(1s) peak as observed in the XPS spectra of the quartz treated with TOMAS, and the curve fitting data of C(1s) corroborate the reagent-mineral interaction. A comparative study of adsorption of DDA and TOMAS using classical molecular mechanics also suggests stronger adsorption of the latter on the hydroxylated quartz surface. Flotation studies of quartz at natural pH indicate ∼100% quartz recovery at a TOMAS concentration of 8*10−5M. Flotation of the natural occurring BHQ iron ore containing 38.7% Fe and 43.8% SiO2 concludes that a TOMAS concentration of 3.71*10−5M is sufficient to achieve 67.3% Fe with 66.6% iron recovery. TOMAS stands out as a better quartz collector, when compared with DDA.
The present communication describes a novel application of lime mud, a waste material generated in paper/pulp industries, for the recovery of potash values from mica scraps. Characterization studies ...of the mica scraps using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) indicate the major minerals to be muscovite and quartz while the chemical analysis confirms the presence of K2O to the tune of 7.5%. Lime mud is found to be mostly consisting of calcite and quartz as the major phases. The roast-leach studies using lime mud and NaCl as the additives have been carried out using response surface methodology to optimize the factors for maximizing the potash recovery. Under optimum conditions such as a temperature of 950 °C, a roasting period of 30 min and a ratio of mica: lime mud: NaCl – 1:0.7:0.7, around 99% of the potash value could be recovered. The results, under similar roasting conditions, are found to be comparable to the ones using CaCl2 as the additive. The formation of different phases as analysed using the characterization studies suggests that the mechanism of potash extraction may follow two routes. One of them is the direct reaction of muscovite with CaCl2 (formed due to the reaction of lime mud and NaCl) to form sylvite, anorthite, and kyanite. The other one may be an indirect route in which muscovite at high temperature along with SiO2, forms K-feldspar that further reacts with CaCl2 to give the sylvite phases. It is also noticed that a further increase in roasting temperature to 1100 °C leads to a decrease in potash recovery with the possible reasons being the formation of water-insoluble K-phases like leucite as confirmed in the SEM studies.
•First ever application of lime mud, an industrial waste, in potash extraction from mica scraps.•Roasting mica scraps at 950 °C with lime mud and NaCl followed by water leaching gives 99% potash recovery.•Under optimized operating conditions sylvite is obtained as revealed by XRD and SEM.•Extraction efficiency decreases beyond the roasting temperature of 1000 °C due to the formation of water insoluble K-phases.
The present study explores the application of biomass briquette, produced from the unutilized vegetative remnants, as an alternative reductant for the reduction roasting-magnetic separation of an ...iron ore slime sample assaying 56.2% Fe. The X-Ray Diffraction (XRD) studies indicated tridymite and quartz to be the only crystalline mineral phases present in the biomass briquettes while the Fourier Transform Infra Red (FTIR) spectra identified several organic functional groups representing the biomass. Iron ore concentrates with ∼65% Fe and ∼64% weight recovery were obtained with reduction conditions such as temperature: 650–750 °C, reductant to feed ratio: 0.15, reduction time: 30–45 min and reductant size: −3+1 mm. The analysis of the statistically designed experiments suggested that temperature is the most crucial factor followed by time, reductant to feed ratio and reductant size. Magnetite and hematite were found to be the only major phases present in the magnetic fractions produced from roasting at the optimum conditions. Many feebly magnetic phases like wustite, fayalite and clinoferrosilite appeared at higher temperature and reductant to feed ratios, which was confirmed by XRD, reflected light microscopy and quantitative mineralogical analysis.
•Establishing biomass briquette as a substitute to coal.•First ever usage of biomass briquettes as a reductant of iron ore.•Iron recovery from iron ore slime using reduction roasting and magnetic separation.•Product with ∼64–65% Fe at a weight recovery ∼63–64% from a slime of 56.2% Fe.
