Profesora Patricia Vargas Colegio Fe y Alegría.

Lateritic ore is earthy in luster and limonitic red in color, yellow with white patches. Goethite-Lateritic ore mainly contains goethite, hematite (as subordinate mineral), kaolinite, gibbsite and quartz. Goethite which is common in lateritic profile/ surfaces of iron ore deposits is abundant in all the samples. Ore microscopic studies reveal presence of colloform and cavity filling texture. There are extensive vein filling by goethite precipitation.

From mineralogical study, it is evident that the ore has two distinct types of valuable minerals i.e. i) crystalline hematite with disseminated inclusions (Fig.6.8e) and microcrystalline hematite particles with microcrystalline goethite (Fig.6.8d). Vitreous goethite, being hard and crystalline is abundant in the sample (Fig.6.8e). Most of the lateritic samples show high degree of porosity. These pores are the most favorable sites for clay deposition (Fig. 6.8h), which is mainly responsible for the high alumina content in this ore rendering it difficult for use in iron making without rigorous beneficiation. These cavities are also partly filled by gibbsite and kaolinite (Fig.6.8b). Spongy hematite and martite partly or wholly transformed to goethite and later concreted by goethite precipitation along the wall of the tubular pores. This ore also exhibits multiple joint and fracture surfaces along which the clay and goethite precipitation takes place (Fig.6.8c). Goethite replaces hematite indifferent degrees (Fig.6.8c& f). Kaolinite occurs in intimate association with goethite but free quartz grains are uncommon indicating that silica is available in the form of kaolinite. Majority of the kaolinite grains are embedded with iron hydroxide minerals i.e. goethite. Gibbsite is the predominant alumina contributing mineral and occurs intimately intermixed with goethite. Gibbsite & clay minerals are present as microcrystalline to cryptocrystalline aggregates. Colloform texture of weathered goethite is observed in Fig.6.8b. Free quartz is rarely observed.

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Goethite changes to limonitic clay due to dissolution and re-precipitation. Goethite occurs as massive mass occasionally with secondary hematite. Goethite and clay at places occur as oolitic or pisolitic grains cemented together (Fig.6.8 a). Small highly altered relicts of martite ore fragments are common within goethite. Goethite partially dehydrates to hematite. The clay bearing laterite contains clusters of gibbsite grains in the voids and fine kaolinite needles in the nodules and pisoids.

XRD pattern reveals that lateritic ores mainly comprise of hematite, goethite and clay minerals (Fig. 6.7). SEM observation of goethite-lateritic ore shows that goethite is the common mineral (Fig. 6.6). It is formed under oxidizing conditions as a weathering product of iron bearing-minerals. The alumino-silicates are intricately associated with goethite and are very difficult to remove from the ore.

SEM observation of goethite-lateritic ore shows that goethite is the common mineral (Fig. 6.6). It is formed under oxidizing conditions as a weathering product of iron bearing-minerals [62]. The alumino-silicates are intricately associated with goethite and are very difficult to remove from the ore.

A number of images were processed and the conclusion drawn was most of the iron bearing minerals are fully or partially weathered (Fig.6.6A) resulting in substitution of most of the iron oxides with Al in mineral grains (Fig.6.6B). At point b (Fig.6.6B), it is free of silica which can be substantiated from EDX. At the same time it is porous and rich in alumina. This substitution can normally happen in goethite grains which are resulted due to the weathering of iron oxide particles.

A very low grade Goethite-lateritic ore collected from Barsua iron ore deposits of Eastern India. The sample contains 38.19% Fe, 9.48%SiO2, 19.97 Al2O3. Goethite- In the present work attempts have been made to understand and characterize the lateritic iron ore to ascertain the feasibility of their beneficiation for value addition.

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The weight percentage distribution of goethite-lateritic ore sample in respect of various size fractions is shown in Table.6.4. From size measurement it is evident that the ore is coarse in nature at the same time, the finer fraction (<150) accounts for 13% indicating significant amount of slime generation during washing. The coarser fraction requires suitable grinding for proper liberation. The Fe assay is almost uniform over the entire size range.

Liberation analysis of goethite-lateritic ore shows (Table 6.1) that in coarser fractions percentage of interlocking is very high which decreases with decreasing particle size. Low free hematite content and higher gangue contents indicate very low grade of this type of iron ore. Complex interlocking nature of the particles shows that the liberation can be achieved below 150 mm size. Achieving high purity concentrate in beneficiation of this ore is likely to

be quite difficult due to the complexity of interlocking. Proper comminution is required to break the interlocking and attain good liberation in this case.

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Table. 6.4: Size distribution and size-wise chemical analyses of Goethite-Lateritic ore & Iron ore slime

Goethite-lateritic ore Iron ore slime

ParticleSize, μm Wt % Fe Assay Particle Size, μm Wt % Fe Assay

2000 40.24 42.32 +1mm 19.89 56.08 1000 10.60 41.64 -1+500 6.59 52.04 853 5.87 39.07 -500+250 5.26 54.15 600 8.72 38.24 -250+200 4.72 54.52 500 4.08 38.43 -200+150 7.53 57.35 300 5.74 37.64 -150+100 4.52 58.36 200 2.23 37.35 -100+75 8.53 59.73 150 6.40 37.39 -75+66 3.13 60.76 100 1.68 37.72 -66+50 4.11 61.82 75 2.07 37.20 -50+37 3.09 62.80 66 0.62 35.45 -37+25 4.54 54.23 <66 11.75 33.70 <25 32.92 50.83 Composite 100 38.19 Composite 100

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Fig. 6.6 SEM photomicrographs of goethite-lateritic ore

B A Fe Fe Fe Fe Al Si Fe Fe Al Fe Fe Fe Al

94 2 0 3 0 4 0 5 0 6 0 7 0 8 0 0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 G o H m H m K K H m H m H m K Intensity G o Q _K Q Q H m G b G o D e g r e e s 2 - t h e t a

Fig. 6.7: XRD patterns of Goethitic-Lateritic ore (a) ore fraction shows presence of hematite and goethite.

6.1.3.1 Distinguished features

In case of lateritic iron ores, the iron bearing grains are highly weathered due to surface weathering of the bulk ore in the deposit. The iron occurs mainly in hydroxy form as goethite interlocked with kaolinite and gibbsite. The liberation analysis illustrates that the impurities are concentrated at finer size fraction, which contains ferruginous clayee material such as kaolinite etc. These ores must be upgraded by thorough and proper processing after adequate comminution to attain liberation. The concentration criterion [146] for these ores is found to be less than 2.5. Therefore, simple gravity separation will not be much effective. These ores may be upgraded by using advanced gravity separation techniques in the first stage. Further purification may be achieved using wet high intensity magnetic separation. If this stage also fails to achieve the required grade, froth flotation to remove the gangue may be tried at the final concentration stage.

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Fig.6.8: Photomicrographs of Goethite- Laterite iron ore (a) Gibbsitic clay (reddish black) bounded by goethite (grayish white), characteristic of Lateritic ore (b) colloform goethite with clay (c) joint and fracture surface along which goethite and clay precipitation takes place (d) microcrystalline hematite with microcrystalline goethite (e) vitreous goethite (f) cavity filling by goethite

precipitation (g) Vein filling by goethite precipitation (h) Highly porous goethite & cavities are filled up by clay

Goethite Goethite Clay

Goethite

Hematite

Goethite Goethite

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