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By He Zhi-jun, Ning Zhe, Pang Qing-hai, Zhang Jun-hong, Zhan Wen-long

In this study, Raman spectroscopy was utilized to investigate the evolution of char structure in pulverized coal (PC) during microwave irradiation. The results indicated that though microwave treatment was carried out at low powers of 132W or 264W, significant variation in char structure was still observed. Char structure turned out to be more irregular firstly under microwave irradiation. However, char structure of superior regularity was obtained with the extension of irradiation time. It can be conclude that short time microwave treatment may facilitate the chemical activity of coal, while long time microwave irradiation on PC may deteriorate its combustion or pyrolysis property.

Jan 1, 2016

By He Zhi-jun, Ning Zhe, Pang Qing-hai, Zhang Jun-hong, Zhan Wen-long

The effect of microwave irradiation on grinding property of coal was studied by using Hardgrove grindability index tester. Superior grindability of coal was obtained to varying extent after microwave irradiation treatment. The variation in microstructure of pulverized coal during microwave irradiation was observed by utilizing scanning electronic microscope (SEM). The results indicated that the different microwave absorbance of minerals and carbon matrix led to cracks on their interface, by which coal particles were further pulverized and therefore the granularity of coal powder was reduced. Due to the different formation process of various coals, bituminite and anthracite are very different in physical and chemical properties. According to the content of coal pulverization, it can found that microwave irradiation has a stronger pulverizing effect on bituminite in comparison to anthracite.

Jan 1, 2016

By E. R. Bobicki

"Low-grade ultramafic nickel ores, while representing a large potential nickel resource, are difficult to process due to their serpentine content. Microwave treatment is proposed as a technique to improve the beneficiation of ultramafic nickel ores by converting the constituent serpentine to olivine. The present paper reviews the microwave heating response of ultramafic nickel ores and resultant changes in mineralogy, as well as effects on grinding and slurry rheology. Beyond nickel extraction, microwave treatment improves the mineral carbon storage capacity of ultramafic ore tailings, providing a potential source of additional revenue via the sale of carbon credits. The combined positive effects, considered in the context of the whole operation, suggest an economically viable process is possible.INTRODUCTIONAs high-grade deposits become depleted, the processing of low-grade ores has become increasingly important. One such resource is low-grade ultramafic nickel ores. While representing a large source of nickel, these ores are difficult to process due to their serpentine content. Serpentine is a phyllosilicate mineral consisting of 1:1 stacked sheets of silica tetrahedra and magnesium hydroxide octahedra. There are three primary polymorphs: lizardite (platy), antigorite (corrugated) and chrysotile (coiled, fibrous). The anisotropic nature and non-spherical morphology of serpentine particles leads to complex rheology. Suspensions of serpentine minerals, especially those of chrysotile, exhibit high viscosity and yield stress, which can have a negative effect on comminution, flotation and dewatering operations. In flotation, serpentine is known to slime-coat pentlandite, a valuable nickel mineral, and form bubble-fibre aggregates that report to the froth, reducing nickel concentrate grade and recovery. Methods used to counteract the effects of serpentine in processing include desliming, the addition of chemical dispersants, salts or acid, and dilution (Bobicki et al., 2014a). Microwave pre-treatment has been proposed as an alternative way to eliminate the deleterious effects of serpentine in ultramafic nickel ore processing by converting the serpentine to olivine via dehydroxylation, which occurs at 600-700oC (Reaction 1). Olivine is isotropic, consisting of isolated silica tetrahedra linked by octahedrally coordinated magnesium ions, and has the same surface potential as pentlandite at the pH of flotation (~pH 9). Furthermore, since olivine is more reactive to CO2 than serpentine, microwave pre-treatment creates an opportunity to store more CO2 in tailings, an attractive option for mining operations looking to increase their bottom line where carbon pricing exists."

Jan 1, 2018

By N. M. Can

The effects of microwave treatment on the floatabilities and magnetic susceptibilities of some sulfide minerals, namely, pyrite, chalcopyrite, galena and sphalerite, were studied. Pure mineral samples were prepared in -425+212-µm, -212+106-µm and -106+38-µm size fractions. Microflotation and magnetic separation tests were carried out on the samples after microwave treatment at 600, 950 and 1,300 Watts for 5, 20, 60, 90, 120 and 240 seconds. The maximum temperature values of the samples were measured during the microwave treatment, and possible altera-tions on the mineral surfaces were determined by X-ray diffraction (XRD) analysis. The effects of microwave treatment are discussed based on the result of microflotation and magnetic separation tests. The results revealed that pyrite, chalcopyrite and galena were heated very quickly and that their surface temperatures reached ~700° to 900°C, while the temperature of sphalerite reached only ~130°C. The floatability of pyrite, chalcopyrite and galena were decreased when microwave energy and the duration of treatment were increased, owing to oxidation of the mineral surfaces caused by relatively high temperature. As expected, there was no change in the floatability of sphalerite. The magnetic properties of pyrite and chalcopyrite were improved by the increase in microwave energy and the duration of treatment to such an extent that 90% of the feed separated as magnetic product. But no change was observed in the magnetic properties of galena and sphalerite.

Jan 1, 2007

By S. M. S. Azghdi, K. Barani

The effect of microwave treatment on the surface roughness and wettability of chalcopyrite (CuFeS2 ) and on the chemical composition of its surface was studied. The microwave source was a conventional multimodal oven with frequency of 2.45 GHz and maximum power of 900 W. Pure chalcopyrite specimens and purified chalcopyrite concentrate were used in this study. Analysis using atomic force microscopy showed a decrease in the surface roughness of the chalcopyrite after microwave radiation. This decrease may be due to oxidation of the surface and formation of iron oxide. Moreover, the surface wettability of the chalcopyrite mineral increased with increasing duration of microwave radiation, which was in good agreement with the micro-flotation mass recovery results. The increased wettability of the surface may be attributed to the decreased surface roughness by microwave radiation. Analysis using scanning electron microscope/energy-dispersive X-ray spectroscopy indicate that after microwave radiation, the contents of sulfur and iron increased whereas that of copper decreased on the surface of the chalcopyrite, significantly changing the average atomic number of the chalcopyrite surface.

Microwave pretreatment can improve grindability by weakening brittle particulate material prior to size reduction. The differential thermal expansion experienced by multiphase materials during rapid heating can also promote damage in the grain-boundary region, which may ultimately translate into enhanced liberation. The effect of microwave pretreatment on the breakage characteristics of different ores has been studied using the Ultrafast Load Cell. The energy accumulated during impact (fracture energy) and the particle stiffness have been measured for untreated and microwaved ore samples. It has been observed that microwave pretreatment can weaken brittle multiphase particulate material, as observed by reductions in fracture energy and increase in damage.

Jan 1, 1996

By Harlowe Hardinge, R. C. Ferguson

Laboratory and plant data covering 12 different operations show that lower than "standard" ball mill speeds increase grinding efficiency. In the case of high pulp-level mills, the gain is so great that the increase in capital cost of the larger lower speed mill will pay for itself in less than a year's time.

Jan 1, 1950

By S J. Kim, S W. Kim, L Tomas da Rocha, S Jung

Al2O3 has been regarded as a harmful gangue component in iron ore, especially causing reduction degradation in industrial sintering of iron ore. The current study aimed to utilise low-grade iron ore containing high Al2O3 content in sintering process. In order to counteract the adverse effect of Al2O3 on reduction behaviour of iron ore sinter, mill-scale and calcined dolomite were chosen as FeO- and MgO-bearing materials. Firstly, mill-scale was added to high Al2O3 sinter and addition was optimised as 10 wt per cent, then calcined dolomite was added further. Magnetite and magnesio-ferrite were identified as the major phases in iron ore sinter when adding mill-scale and calcined dolomite. As the dosage of calcined dolomite increased beyond 4 wt per cent of in sinter mix, unreacted MgO particles were observed, which is ascribed to the limitation of MgO dissolution into magnetite matrix. Both mill-scale and calcined dolomite were effective in improving compressive load and Reduction Disintegration Index (RDI) of iron ore sinter although its reduction degree was highly decreased. The addition of both FeO and MgO-bearing materials to high Al2O3 sinter has a potential to improve the sinter quality, also contribute to the recycling of industrial by-product. However, the amount should be optimised in views of phase development and deterioration of reducibility.

Jun 19, 2024

By P Holtham, W Valery, P Baguley, A Jankovic

There is a growing interest in magnetite ores because of the increasing demand for this commodity. With these ores, there is significant cost associated with milling the ore to fine sizes using ball mills in closed circuit with hydrocyclones. Cyclone classification efficiency tends to be poor due to the large difference in density between magnetite and gangue. This decreases the grinding circuit efficiency and results in over-grinding of magnetite. The objective of the work described in this paper was to modify the Bond locked cycle milling test procedure to quantify the loss of grinding circuit efficiency due to the mineral density effect. The locked cycle test procedure described here includes a stage of magnetic separation treating the closing screen undersize, which allows simulation of magnetite classification. The effect of classifier efficiency on low-density particles (non-magnetics) was simulated by altering the proportion of closing screen undersize bypass returning to the mill. Using a magnetic separator and a screen in the magnetics stream, different proportions of the magnetic fraction can be bypassed, thus allowing simulation of the effect of particle density on classification efficiency. This laboratory test work has confirmed that the impact of mineral density on cyclone efficiency subsequently has a crucial negative effect on ball mill circuit capacity. The results are in good agreement with reductions in capacity observed in practice. Multicomponent grinding and classification models were also developed in the LIMN software environment and were able to successfully simulate both the industrial and the laboratory ball mill circuit. The test and modelling procedures established in this project could be used for improved design of new magnetite ball mill grinding circuits as well as the optimisation of existing circuits.CITATION:Jankovic, A, Baguley, P, Valery, W and Holtham, P, 2015. Effect of mineral density for milling magnetite ores, in Proceedings Iron Ore 2015, pp 159–164 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 13, 2015

By R. Roufail

"Energy consumption in stirred mills has been studied, in the last couple of decades, on a macro scale. Effective operation and meeting particle size required for downstream operations used to be the main objectives behind energy utilization of stirred mills. In this paper, three energy terms are defined to assist in understanding the breakage mechanism for various types of minerals versus mill operation. The types of minerals studied had diverse physical and mechanical properties that are summarized as specific gravity, hardness and crystal structure. The minerals utilized in this study were quartz and galena. The effect of quartz and galena mix has been addressed as well as Lead-Zinc ore sample from SAG mill discharge. The energy input to the mill is function of the agitator speed, therefore three agitator speeds were evaluated, 1000, 1500 and 2000 RPM, respectively. The energy terms studied are specific energy (kWhr/ton). Effective energy is the ratio between net energy and total energy consumed by the mill. Last type of energy is the specific breakage energy, which is the net energy consumed by the mill per one-micron breakage. Results showed that specific energy and specific breakage rate are functions of mineral type, while effective energy is only function of mill input power (agitator speed).INTRODUCTIONGrinding is the largest energy consuming component of a mineral processing operation and typically consumes about 50% of the total energy used at a mining operation (Botin, 2009). Over the last two decades, stirred mills have been extensively utilized in mineral processing operations due to increased mineralogical complexity of ore bodies. Stirred mills grind particles to less than 10 µm by applying a high power intensity. The technology has been the focus of several research studies to investigate mill energy and grinding mechanisms. Becker, et. al. (2001) studied the relationship between different types of energy including input energy, specific energy, volume/mass specific energies, to stress intensity and final product particle size. Other studies such as by Kwade (1999), Kwade and Schwedes (2002), Blecher et al (1996), Partyka and Yan (2007), Stender et al (2004), focused on mill design and/or stress intensity distribution. Peukert (2004) studied the effect of mechanical properties of the grinding media and ground material on the comminution process."

Jan 1, 2016

By X. P. Zheng

Barium fluorphlogopites were synthesized in the laboratory in order to investigate the effects of composition and crystal parameters on surface properties and floatability. The negative surface charge of mica is determined by the barium content, the crystal cell volume, the distance between layer structure and the Ba-O bond length. The higher barium content, the larger the cell volume and distance between the layer structure and the longer the Ba-O bond, the more negatively charged the surface is and hence the more easily adsorbed to cationic collectors. When an anionic collector (sodium oleate) is used, barium oleate forms on the mica surface and hence chemical adsorption occurs.

Jan 1, 1993

By X. P. Zheng, H. K. Lin

Barium fluorophlogopites were synthesized in the laboratory to investigate the effects of composition and crystal parameters on surface properties and floatability. The negative surface charge of mica is determined by the barium content, the crystal cell volume, the distance between the layer structure and the Ba-O bond length. The higher the barium content, the larger the cell volume and distance between the layer structure, and the longer the Ba-0 bond, the more negatively charged the surface is, and, hence, the more easily adsorbed are cationic collectors. When an anionic collector (sodium oleate) is used, barium oleate forms on the mica surface and hence chemical adsorption occurs.

Jan 1, 1995

By T. Nghipulile, G. Dzinomwa, J. Kurasha, M. Amwaama, B. Mapani, K. Maweja, T. E. Moongo

The effect of mineralogy on the grindability was investigated using three copper ores – two sulphides and one oxide. The dominant copper minerals were identified by optical microscopy and mineral chemistry derived from SEM-EDS analysis. The sample designated sulphide 1 was borniterich, sulphide 2 ore was mainly chalcopyrite, and the oxide ore was predominantly malachite and minor azurite. The gangue minerals were identified using semi-qualitative XRD analysis. Sulphide 1 contained more than 80% (w/w) of quartz compared to about 70% in the other two ores. The Bond work indices were 13.8, 21.6, and 17.3 kWh/t for sulphide 1, sulphide 2, and oxide ore respectively. This suggested that the chalcopyrite-rich ore is the hardest, while the malachite-rich ore has intermediate hardness, and the bornite-rich ore is the softest. The brittleness indices of the ores were calculated using the chemical composition of the gangue, and a good correlation between brittleness indices and Bond work indices was observed, which highlights the importance of the gangue composition in determining the fracture behaviour of the ores. There is scope for further investigation into the relationship between ore mineralogy and comminution behaviour using other breakage characterization techniques.

Mar 30, 2023

By G. Stokreef, B. R. Davis, M. Kadiyski, T. LeBel, Alvear Montenegro, R. Parra, V. Montenegro

A drop tower and methodology were developed to study the impact of mineralogy on the flash combustion behaviour of copper concentrates. Reaction shaft conditions of a flash furnace were simulated using a drop tower reactor and different molar ratios of oxygen gas to sulphur in the feed. Five feeds were tested in the drop tower including pure minerals chalcopyrite and pyrite as well as two mineralogically distinct copper concentrates and a blend of the two. The behaviour of each of these five feeds were evaluated through analysis of the solid combustion products for elemental sulphur, mineralogy and particle size. Desulphurization curves for each of the feeds were produced. It is thought that the desulphurization behaviour of pure minerals can be used to estimate the behaviour of a concentrate and that a blending recipe could be developed, which can optimize the chemical and mineralogical inputs to the flash furnace and guide operations on the optimum furnace conditions. Overall, the drop tower has proven to be a useful tool for studying flash combustion processes. Experimental results suggest that mineralogy has a significant impact on the conditions required for the production of matte with consistent grade. This finding is especially significant for custom smelters, which may see several different blends in a day. INTRODUCTION Flash furnace smelting is a continuous feed, batch tap, pyrometallurgical process that is used to produce copper matte from copper sulphide concentrates. Dried concentrate(s), silica flux, and secondary materials are blended to a target chemical composition, typically given by the Cu/S ratio, before processing. This fine, dried feed is dispersed throughout the heated furnace reaction shaft with an O2-enriched reaction gas. The particles heat up in the shaft of the furnace, ignite and undergo reactions that pre-oxidize the iron sulphide and some of the impurities in the feed. Oxidation reactions in the shaft of the furnace desulphurize the feed and produce an SO2-containing off gas. The reacted particles fall into the furnace settler and separate into a Cu-rich matte and an iron-silicate slag, while the SO2-containing off gas is carried out of the furnace for heat and dust recovery, as well as H2SO4 production. Some concerns during operation of the furnace are dusting, over or under oxidation of the feed, and a stable flame.

Jan 1, 2019

By Bahjat Khoshaba, Bern Klein, Haixing Yan, Libin Tong, Andrew Bamber

"When a conductive or magnetic particle was put into an electromagnetic field introduced by an electromagnetic sensor, the particle can influence the electromagnetic field which can be used to characterize this particle. The electromagnetic technology based on eddy current theory was explored to investigate its potential in both the separation of minerals and the pre-concentration of a base metal ore. Samples tested in the study included the minerals obtained from Ward’s Science and the low grade copper ore particles obtained from Mount Polley Mine. The effects of mineral type, sensor frequency, particle size, particle position on the sensor surface, and particle lift-off on the magnitude and phase of the electromagnetic spectra were investigated. The electromagnetic spectra of various minerals show that it is possible to separate chalcopyrite or magnetite from tested minerals, simply based on the magnitude of the spectra. The spectra of the ore particles were determined by the mineral in the particles with the strongest signal. The effect of the pre-concentration of the low grade copper ore is determined by the association of chalcopyrite with magnetite. Direct sorting is the mechanism in the separation of mineral particles, while indirect sorting is the mechanism for low grade ores.INTRODUCTIONSensor-based sorting technologies include radiometric, X-ray transmission, X-ray fluorescence, near infrared, photometric, inductive, microwave heating and so on. Sorting not only discards barren rocks away from the concentrator but also recovers metal bearing that would be lose to the waste dump. The benefits of pre-concentration using sensor-based sorting are achieved on reduced energy consumption for comminution and reduced water usage on a volume per weight of metal basis (Bamber, 2008; Gunson, Klein, Veiga, & Dunbar, 2012; Kleine & Wotruba, 2010; Knapp, Neubert, Schropp, & Wotruba, 2014; Kobzev, 2014; Lessard, de Bakker, & McHugh, 2014; Mazhary & Klein, 2015; Robben, Wotruba, Robben, von Ketelhodt, & Kowalzcyk, 2013). Amongst others, high frequency electromagnetic sensors were developed for ore sorting at MineSense Technologies Ltd. and are subject of this paper. Improving the understanding of ore heterogeneity is the basis for developing a successful semi-bulk or bulk sorting systems by incorporating the sensors in the material handling equipment (MineSense Technologies Ltd., 2016). The present study focuses on the bulk sorting potential and bulk sorting mechanisms of the electromagnetic technology in the pre-concentration of minerals or ores."

Jan 1, 2016

By A. K. Alzo?ubi

Block toppling in natural rock slopes has been under investigation since the 1970?s. De Freitas and Watters (1973) introduced the term ?toppling? to describe the movements of rock slopes by rotation in steeply dipping beds. The Lornex pit case history from British Columbia (Canada) was chosen to study the effect of mining on the stability of toppling rock slopes. A discrete element approach that allows fracturing of intact material was applied successfully to model the composite rock slide-rock topple movement. Three main movement modes were observed in the field and the numerical model; the sliding of the top of the slope exposed normal scarps, the toppling at the middle part of the slope exposed obsequent scarps facing opposite to the slope face, and dilation of the rock caused by fracturing at the toe formed loose material. The development of the rupture surface at the toe of the slope was traced and did not evolve into a continuous rupture surface throughout the slope both in the field and the numerical simulation. Good agreement was achieved between the deformations recorded in the field and the numerical simulation.

Jun 1, 2012

By Robert H. Raring

Viewed abstractly, a mill may be defined as a mineral processing facility located somewhere between the mine and the tailings storage area, Just how mining operations and the demands of tailings storage affect mill design is, the subject of this paper. At the outset, it will be readily acknowledged that no two installations can, or ever will be the same. At one extreme is the bucket line dredge where the distance between the ?mine? and the tailings area is measured in terms of tens of feet. At the other extreme, the large open pit copper mines are frequently spread across twenty, miles or so of countryside with the ore moving to the mill, as exemplified by the operations at Bingham Canyon, Ray, or Ruth - the "upstream" counterparts of Garfield, Hayden and McGill. In each of these cases, mill location was largely determined by requirements for tailings storage and/or water supply.

Jan 1, 1961

By Yang Guangqing, Shao Jiugang, Zhang Jianliang, Wan Dan, Fu Yuandi, Guo Hongwei

"Resource of metallurgical coke is becoming scarce, and although coke can be partially replaced by pulverized coal injection, there are many restrictions for further increase in coal ratio. Mixed charge of ore and lump coal from top to replace more coke was studied in this paper. Softening-melting property of the burden was affected by charge of lump coal. Softening-melting properties of mixed charge of ore and coke, mixed charge of ore and lump coal were tested respectively. Results show: the property of the burden mixed with coke is superior to the burden mixed with lump coal; lump coal would not deteriorate softening-melting property of the burden and some of them can even improve softening-melting property of the burden. Top charge of lump coal would not deteriorate softening-melting process, and this should be a new way to increase coal consumption to decrease coke rate.IntroductionThe blast furnace is still the predominant process for the reduction of iron ore and will probably remain so for the next decades. Metallurgical coke is becoming scarce and expensive, so the cost of hot metal can be decreased by reducing the consumption of metallurgical coke[l]. Coke can be partially replaced by pulverized coal injection, currently the highest rate of pulverized coal reached 266kg/tHM, most of blast furnace PCR is about 150kg/tHM, and it is very difficult to further increase of PCR. Nut coke is charged into blast furnace mixed with iron ore, not only for improving utilization of metallurgical coke, but also for lowering the coke rate. Presently the majority of blast furnaces in the world use nut coke although its amount is very different: from 10-20 to 70--100 kg/tHM and more[2-4].The effect ofnut coke in blast furnace is extensively researched, and the main conclusions recommend: to improve gas permeability of cohesive layer in blast furnace, to promote reduction of iron burden, protect metallurgical coke from the solution in the shaft due to higher reactivity of nut coke. There is no special requirement for the strength of nut coke[5-8]. Nut coke is also used for sintering fuel, which may lead to the shortage of the nut coke charging into blast furnace. So lump coal mixed with iron ore is considered to be charged into the blast furnace, not only to reduce the cost of grinding coal, but also to increase the use amount of coal."

Jan 1, 2013

By Mei-le He, Min Chen, Xiang Shen, Lei Xu, Lei Liu, Nan Wang, Xue-liang Yin

In the current study, Al2O3-MgO-CaO refractories were prepared at 1400-1600 by the addition of MnO micro-powders, and the effect of MnO addition on densification behavior of the refractory was discussed. The results showed that the doped MnO dissolved to MgAl2O4 phase, and promoted the growth of MgAl2O4 grains by the formation of MgAl2O4 solid solution. As a result, the dense microstructure was obtained, with the apparent porosity decreased from 19.2% to 5.4% and the bulk density increased from 2.78g/cm3 to 3.15g/cm3 after firing at 1600 for 2h by the addition of 4% MnO. In addition, a texture microstructure was observed, which is considered to be favorable to improve mechanical properties and the service life of Al2O3-MgO-CaO system refractories.

Jan 1, 2016

By George Breyer

DURING the past 25 years the steelmaker has experienced some difficulty in producing steel to meet the standards established by the metallurgist. In contrast to the past, when a chemical specification of broad limits was the only requirement, he now has to employ such tests as microscopic, macroscopic, tensile, impact, Magnaflux and even X-ray and supersonic. The development of these tests has more than set the pace for a manufacturing process of which the exactness still hinges to an important degree on the ability of the furnace operator. In our efforts to produce steel, and especially alloy steel, to meet the exactness of modern engineering specification, many factors must be taken into account. It is not sufficient to make a good heat of steel in the furnace and then be satisfied that the job is done, since there are many pitfalls between the furnace and the finished product. The literature abounds with information on melting practices, deoxidation methods and slag control, but the lack of positive information about what happens when the steel is teemed into molds is quite evident. Such questions as what is the proper mold size, shape and thickness; which is the best mold coating; what is the best rate of pour for any given steel, and what is the effect of cooling rates on quality, are still answered by opinions. It is acknowledged that a poor heat of steel cannot be improved in the pouring pit. On the other hand, a good heat can be ruined by improper handling after it leaves the furnace.

Jan 1, 1947