small gangue ball mill in tanzania

small gangue ball mill in tanzania

If the gangue mineral in an iron ore is predominantly quartz, reverse flotation is usually used in the cleaning stage to improve the concentrate grade. Figure 9.13 presents a typical flow sheet for processing an oxidized iron ore containing about 30% Fe using a combination of SLon magnetite separators and reverse flotation. The ore is mainly composed of magnetite, hematite, martite, and quartz. It is very difficult to produce a high-quality iron ore concentrate by magnetic separation alone for this type of iron ore. The ore is first ground using ball mills down to about 90% -75 μm. Drum LIMS are then used to take out the magnetite particles, while drum MIMS (0.4 T middle-intensity magnetic separators) are used to recover the martite grains. SLon magnetic separators are subsequently used to recover the hematite grains. The magnetic products from the LIMS, MIMS, and SLon are combined to generate the feed for reverse flotation, which produces the final iron ore concentrate

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From the plant operating results for this flow sheet, an iron ore concentrate containing 67.5% Fe was produced from a run-of-mine ore containing 30.5% Fe, at a mass yield to the iron ore concentrate of 35.7%, an iron recovery of 78.9%, and a tailings grade of 10.0% Fe

Details of the common iron ore and associated gangue minerals found in many iron ore deposits and iron ore products are given in Table 2.1. The three most common iron ore minerals are magnetite, hematite (the spelling “hematite” is preferred here over “haematite”), and goethite, which together account for an estimated > 99% of the iron minerals contained in world seaborne-traded iron ores in 2012

gangue mineral - an overview | sciencedirect topics

Magnetite (Fe3O4) is a common iron ore mineral in iron ore deposits of metasedimentary and magmatic origin. Magnetite has an inverse spinel structure and is partly altered in near-surface environments to hematite or kenomagnetite (Waychunas, 1991)

Hematite is commonly thought to form from oxidation of magnetite in the near-surface environment although Ohmoto (2003) demonstrated that the transformation of magnetite to hematite or vice versa can also be achieved via a pH shift without a redox reaction. Martite is a commonly used textural term to denote hematite pseudomorphs after primary magnetite where the octagonal outlines of many of the original magnetite grains are preserved (Morris, 1985). The term “kenomagnetite” was introduced by Morris (1980, 1985) to describe metal-deficient spinel phases between magnetite and maghemite

Goethite is an iron oxyhydroxide (α-FeOOH), believed to be the most common iron ore mineral in sedimentary and near-surface, altered metasedimentary iron ore deposits. The three most common forms of goethite are brown, yellow ochreous, and dark brown vitreous goethites (Table 2.1). Many seaborne-traded iron ores are mixtures of hard brown goethite and yellow ochreous goethite with hematite (Figure 2.1). The yellow ochreous form of goethite is often incorrectly referred to as “limonite.” Limonite is a discredited mineral name according to the Commission on New Minerals and Mineral Names of the International Mineralogical Association (Nickel and Nichols, 1991) and its continued use should therefore be discouraged. Yellow ochreous goethite often contains amorphous material and high (2–9%) levels of Al2O3 and SiO2, although there is some debate on the extent to which the latter two oxides are present as submicron inclusions of contaminant minerals or substituted as elemental Al and Si into the crystal lattice

Figure 2.1. Ternary mineralogy plot for various seaborne-traded iron ore products from Western Australia (Pilbara) and Brazil. Note the normative mineralogy has been calculated from assay and normalized to 100%, with goethite abundance calculated from loss on ignition at 371 °C and goethite type and abundance confirmed from polished section microscopy

gangue mineral - an overview | sciencedirect topics

Hydrohematite (Fe(2 − x)/3(OH)xO3 − x) is a defect solid solution structure where OH− ions replace oxygen atoms and charge balance is achieved by octahedral Fe3 + ion vacancies (Wolska and Szajda, 1985; Wolska and Schwertmann, 1989). The presence of hydrohematite is often inferred, but its presence is difficult to prove, especially where colloform goethite is interpreted to have been partially dehydrated to hematite

While, in rare cases, in some countries, iron may be extracted from the iron-bearing minerals pyrite and siderite, they are not considered here to be economically viable iron ore minerals since they result in unacceptable environmental emissions of SOx and CO2, respectively, during subsequent agglomeration and high-temperature processing

Quartz is by far the most common iron ore gangue mineral overall, whereas clays (kaolinite and gibbsite) predominate in weathered supergene altered and near-surface exposures of ore deposits, while minnesotaite and stilpnomelane are the most common silicate minerals in unweathered iron formation deposits. There are many other major to minor gangue minerals associated with iron ore deposits including many different silicates (including amphiboles and chlorites), carbonates (siderite and ankerite), sulfides (e.g., pyrite), and oxides (e.g., pyrolusite)

gangue mineral - an overview | sciencedirect topics

Morris (1980, 1985, 1987) recognized that while the mineralogy of many iron ore deposits is relatively simple, the ore textures are typically quite complicated and are directly related to deposit ore genesis. Furthermore, Clout (2005) provided evidence that it is these complex textures and not mineralogy alone that control metallurgical process performance from crushing to screening, beneficiation and agglomeration (sintering or pelletizing) of fine ores or concentrates, and lump burden behavior in the blast furnace. Differences in iron ore chemistry, texture, mineralogy, and physical properties are directly related to iron deposit types

Valuable metals can occur in different minerals and in trace quantities in gangue minerals. Instrumentation used to quantify elements include electron probe micro analysis, Laser Ablation ICP-MS, dynamic Secondary Ion Mass Spectrometry, and micro-pixie. (Which instrument to employ is mainly dependent on the ore type and the mineral assemblage.) Coupling with automated mineralogical analyses, the distribution of metals among the minerals can be quantified

As an example, consider a Cu-Ni deposit. Commonly, Ni is carried by the sulfides pentlandite, millerite, and violarite, but can also occur in small amounts (a few ppm to ~1 wt%) in the lattice of ferromagnesian minerals (e.g., olivine), Fe-oxides pyrrhotite, and other minerals. Figure 17.11 illustrates the distribution of Ni from two deposits. For Deposit-1, 90% of the Ni is in sulfide form and is considered recoverable. For Deposit-2, only about 72% of the Ni is hosted by the sulfides, where the balance is hosted by the gangue minerals. These results will impact the resource calculations and overall economics of a project. This information can be incorporated in geometallurgical models to help define the ore’s amenability to concentration. Instrument and technique advances continue to push these analyses to ever smaller particles (Brodusch et al., 2014)

gangue mineral - an overview | sciencedirect topics

Deposits related to granite include: (1) true veins composed of ore and gangue minerals in granite or adjacent (meta-) sedimentary rocks and (2) disseminated mineralization in granite as episyenite bodies. Uranium mineralization occurs within, at the contact or peripheral to the intrusion. In the Hercynian Belt of Europe and other parts of the world, these deposits are generally associated with peraluminous, twomica granite complexes (leucogranites). Resources range from small to large and grades vary from low to high. Two subtypes are distinguished based on their spatial setting with respect to the pluton contact, endogranitic deposits within the granite and perigranitic deposits in the adjacent country rocks

Microbial processing can be used for removal of sulfide minerals such as pyrite and chalcopyrite from gangue minerals such as quartz and calcite present in mill tailings. It is well established that presence of the above types of sulfides in tailings is responsible for the formation of acid mine drainage (AMD) and heavy metal contamination of water bodies. Prior removal of acid-forming sulfides from waste ores and tailings before disposal is an efficient method for the prevention of AMD and water pollution

Bioremoval of pyrite and chalcopyrite from quartz and calcite using bioflocculation in the presence of P. polymyxa has been reported. In the neutral pH range, pyrite and chalcopyrite exhibited the highest bacterial cell adsorption, followed by calcite. Quartz exhibited the lowest cell adsorption. Flocculation studies indicated that pyrite and chalcopyrite settled very rapidly (selectively flocculated) in the presence of bacterial cells, unlike calcite and quartz (Tables 10.12 and 10.13). Selective flocculation of sulfide minerals can be brought about through interactions with either bacterial cells or their metabolic products which contain exopolysaccharides and proteins

gangue mineral - an overview | sciencedirect topics

Sulfide minerals such as pyrite–chalcopyrite can be effectively removed from calcite and quartz through microbially induced selective flocculation. Interaction with bacterial cells or bioproteins promoted selective flotation of quartz from pyrite–chalcopyrite

Mineralogically, iron ore fines are characterized by the occurrence and abundance of different iron and gangue minerals and their associations and textures. The importance of ore mineralogy was demonstrated by recent modeling work that concluded that the inclusion of ore textural information can significantly improve model prediction of sinter quality (Donskoi et al., 2007, 2009)

Ore mineralogy and textural relationships determine the type and relative abundance of iron oxyhydroxides (e.g., dense, vitreous goethite vs. microporous, ochreous goethite) in an ore, which further determine the LOI components and bulk density of iron ore fines. The LOI components in iron ore fines are released as the temperature increases, leaving behind many secondary pores and cracks. The primary and secondary porosities strongly affect the stability of nucleus particles in contact with the gas and liquid phases. Therefore, the mineralogy and texture of ore particles also play an important role in melt formation and retention of nucleus particles. Figure 14.12 depicts the difference in the stability of typical hematitic and goethitic nucleus particles in a typical Japanese steel mill (JSM) sinter matrix. Ore A is composed largely of fine to very fine-grained microplaty hematite, which forms a moderately to highly microporous network. The microplaty hematite texture in Ore A is physically denser and harder than would otherwise be expected from its microporous microstructure. This explains the low nucleus assimilation rate and the high retention rate of nucleus particles from this ore (Figure 14.12a). Ore C has a uniform texture and mineralogy typical of channel iron deposit iron ores. The ore consists of concentrically zoned pisoliths of dense vitreous goethite, hydrohematite, and ochreous goethite, cemented together by porous vitreous-ochreous goethite. While this ore appears denser with some macropores but low microporosity, it consists predominantly of goethite, which generates large amounts of secondary porosity upon heating. Therefore, at the same firing temperature, the nucleus particles from Ore C are highly reactive and fully assimilated (Figure 14.12c). Ore B has the typical characteristics of a Marra Mamba ore and contains both stable nucleus particles (dense and harder ore textures dominated by martite-goethite associations) and reactive nucleus particles from vitreous and ochreous goethite types (Figure 14.12b). The release of the LOI components also increases the gas volume generated within the sinter matrix, which can result in a frothy texture, particularly where the melt viscosity is high, creating secondary porosity. This can have a negative impact on sinter strength

gangue mineral - an overview | sciencedirect topics

Figure 14.12. Stability of different types of nucleus particles at 1300 °C in the matrix of a typical Japanese steel mill (JSM) sinter blend. Relict ore particles are presented as dense gray particles in (a) and (b). (a) Nuclei from a dense hematitic ore (Ore A in Figure 14.4). (b) Nuclei from a Marra Mamba ore (Ore B in Figure 14.4). (c) Nuclei from a low alumina pisolitic ore (Ore C in Figure 14.4)

Ideally, a sinter structure requires about 30% relict nuclei to avoid excess melting and densification and hence ensure sinter quality. Therefore, it is important when designing a sinter mixture to have an appropriate balance in mineralogy and sizing to maintain a sufficient amount of relict particles in the sinter structure but still generate sufficient sinter melt

In case of sulfide mineralization, biological activity of sulfur- and iron-oxidizing microbes will be facilitated. The presence of basic gangue minerals such as calcite and magnesite will promote higher acid consumption and also influence pH changes affecting bacterial activity. Chemical and biological weathering in situ can provide access paths to solution transport, while slime and clayey formation can retard solution permeation and leaching kinetics

gangue mineral - an overview | sciencedirect topics

Role of chemical reagents, O2, and microorganisms in mineral dissolution needs to be ascertained because the ISL concept includes the application of bioleaching. “In place” bioleaching of uranium had been practiced at Elliot Lake, Ontario, Canada. Deep ore bodies contain indigenous native microorganisms. Occurrence of anaerobic, aerobic, and thermophilic organisms in deep subsurface environments has been well known. Microbial growth in situ needs to be promoted to facilitate efficient biooxidation of the minerals in the presence of leach solutions. This may require providing essential growth components including oxygen and control of other parameters such as Eh, pH, temperature, and metal ion concentrations. Both aerobic (oxidation) and anaerobic (reduction) microbial processes may be stimulated as required. Several strains of acidophiles such as Acidithiobacillus spp., Leptospirillum ferrooxidans, Sulfobacillus sp., and Acidimicrobium sp. were isolated from leachate and ore samples of bore holes from sandstone in situ uranium leach in China [30]. Even though the role of microorganisms on the mobility of uranium under environmental conditions is well established, their impact on ISL remains underexplored. The role of uranium-mobilizing organisms in uranium-contaminated sites has been well studied and utilized for remediation. Such indigenous organisms can also play effective roles in enhancing uranium dissolution in ISL processes. Similarly, for ISL of copper sulfides, native microorganisms in the presence of oxygen can accelerate copper dissolution. Bacterial oxidation could be maintained in the subsurface. It has been shown that the required bacterial cultures can withstand hydrostatic pressures, and it would then become possible to sustain bacterial activity at subsurface leaching depths [31–32]. Besides the beneficial role of subsurface microorganisms, deleterious aspects of some microbes also need to be understood. Some native subsurface organisms are known to cause bacterial plugging of pores impeding permeability. Prevalence of elevated temperatures due to geothermal gradients and exothermic mineral sulfide oxidation reactions on bacterial growth and activity also needs to be considered. Bacterial oxidation for regeneration of ferric ions will be useful for the treatment of raffinate solutions before reinjection into wells. Bioleaching of block-caving remnants was carried out during 1940s at the Miami mine in Arizona

Magnetic separation takes advantage of the fact that magnetite is strongly magnetic (ferromagnetic), hematite is weakly magnetic (paramagnetic), and most gangue minerals are not magnetic (diamagnetic). A simple magnetic separation circuit can be seen in Figure 1.2.5 [9]. A slurry passes by a magnetized drum; the magnetic material sticks to the drum, while the nonmagnetic slurry keeps flowing. A second pass by a more strongly magnetized drum could be used to separate the paramagnetic particles from the gangue

The usual objective of reducing the size of run-of mine ore pieces is to separate the mineral of interest contained in the ore body from associated gangue minerals. As crushing only does not generally liberate a mineral, further size reduction is usually required. This is achieved by grinding the crushed ore in tubular mills or devices such as pan mills or roller-grinder mills. In tubular mills, a grinding media such as steel balls, rods or hard pebbles imparts the forces required for size reduction. On rotating a mill charged with rocks and grinding media, the entire charge rises against the perimeter of the mill in the direction of motion. On reaching a certain height, part of the charge cascades and falls to the bottom of the mill; the other part tends to slip down but soon travels in the direction of motion of the mill. During this process, the media drops repeatedly onto the rock breaking down its size. Some size reduction also takes place due to abrasive forces. As a result of the combined action of repeated impact and abrasion over time, size reduction takes place and given sufficient time the mineral of interest is liberated

gangue mineral - an overview | sciencedirect topics

Some tubular mills are specially shaped mills, such as the Hardinge Mill, where only the central portion is cylindrical and the ends are shaped like the frustum of a cone. Straight cylindrical mills, however, are the more common. The grinding medium generally used is in the form of balls, rods or cylindrical media called cylpebs. Both steel and ceramic balls are in use depending on the hardness of the rock. For soft ores, pebbles are added or simply autogenously ground with no medium. Both wet and dry grinding is common. Figure 7.1 illustrates the grinding action inside a tubular mill

The media used in the charge generally describes a tubular mill. Thus, the medium could be steel or cast iron balls when the mill is designated as a ball mill, or it could be steel rods where the mill is known as a rod mill. When no grinding medium is charged it is known as an autogenous mill

Improved characterization of lower-grade iron ores is becoming more critical owing to the depletion of world high-grade iron ore reserves. The mineralogy and gangue minerals of the lower-grade iron ores are found to affect the quality of pretreated agglomerates of fine ore (sinters and pellets), which are making up a growing proportion of blast-furnace feedstock (currently ~ 70 % in East Asia)

gangue mineral - an overview | sciencedirect topics

The understanding of lower-grade iron ore mineralogy and the subsequent characterization of lower-grade iron ore are therefore becoming increasingly important to the efficient processing of the ores and the optimization of downstream smelting processes

Using scanning electron microscope (SEM)-based technologies to characterize and quantitatively analyze iron ores and iron ore mineralogy dates back to the invention of the technology in the late 1950s to the early 1960s. The emphasis shifted from the chemical analysis of penalty elements on microprobe systems to quantitative mineralogy on automated mineralogical systems (auto-SEMs) only relatively recently (early 1990s). However, auto-SEMs consistently struggled to differentiate between the most common iron oxides present within iron ore, those being magnetite (Fe3O4) and hematite (Fe2O3), since auto-SEMs traditionally used energy-dispersive spectroscopic (EDS) technology for Fe quantification and furthermore ran at low X-ray counts. Assay reconciliation, by comparing the amount of Fe measured from chemical analyses against the calculated amount of Fe in a sample based on its mineralogy, was thus essential for these systems, in gaining some kind of grasp on the amount of hematite/magnetite in an ore body up until about 2008 and often required further X-ray diffraction (XRD) analysis for confirmation, which with the advent of Rietveld analysis has become more quantitative in recent years

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