Ilmenite grain

The lower 3He/4He ratios in the magnetic separates may also be due to the predominance of SEPs, which have a lower 3He/4He ratio < 2.5 x 10 4 (Benkart et al., 1988). Recent studies of lunar ilmenite grains by Nichols, Hohenberg, and Olinger (1994) seem to favor this interpretation they found that the majority of the ilmenite grains were enriched in SEP. 

Nichols, R. H., Jr., Hohenberg, C. M., Olinger, C. T. (1994) Implanted solar helium, neon, and argon in individual lunar ilmenite grains Surface effects and temporal variation in the solar wind composition. Geochim. Cosmochim. Acta, 58, 1031-42. 

In a process variant (Enhanced Acid Regeneration System EARS process), the ilmenite is roasted to convert the titanium component into the insoluble rutile form and to condition the iron component for leaching. The product is then rapidly leached at atmospheric pressure in hydrochloric acid to remove the iron, leaving rutile crystals in the former ilmenite grain. This synthetic rutile (typically 96-98% Ti02) is then washed, filtered, and calcined. The iron chloride leach liquors are processed to regenerate the acid, and the iron oxide pellets can be sold for use by the steel or cement industries. 

Extensive research has been carried out mainly on ilmenite and, to a lesser degree, on flotation of rutile and perovskite. Flotation studies have been performed on titanium minerals from both hard rock and fine-grained sand deposits. 

Synthetic Rutile. In contrast to ilmenite, only a small number of rutile deposits can be mined economically, and the price of natural rutile is therefore high. Consequently, many different processes have been developed to remove the iron from ilmenite concentrates without changing the grain size of the mineral because this is highly suitable for the subsequent fluidized-bed chlorination process. All industrial processes involve reduction of Fe3+ with carbon or hydrogen, sometimes after preliminary activation of the ilmenite by oxidation. Depending on the reducing conditions, either Fe2 + is formed in an activated ilmenite lattice, or metallic iron is produced. 

Northwest Africa Oil (NWA 011) has briefly been described by Afanasiev et al. (2000) and more extensively by Yamaguchi et al. (2002), the source of most information presented here. NWA Oil is composed of relatively coarse, anhedral pigeonite and augite, and fine-grained, mostly interstitial plagioclase with a recrystallized texture, interpreted to indicate that it is a recrystallized breccia. Minor phases are silica, chromite, ilmenite, calcium phosphate, ferroan olivine, troilite, and baddeleyite. Pyroxenes make up... 

Fig. 5a). The cores are dominated by abundant, very fine-grained silicate inclusions (c. 5-10 urn) and a few larger quartz and ilmenite inclusions. 

Garnet morphology. Garnets in calcic pelite 462536 are similar in form in both the amphi-bole-rich and biotite-rich bands. Grains are up to 5 mm in diameter and are characterized by a broad inclusion-rich core and an inclusion-poor rim, with euhedral facets. The inclusions in the core are principally quartz and ilmenite and vary in size from a few micrometres to >100 pm. Smaller (c. 2 mm) euhedral garnets preserve only a small zone of inclusions in their core. The garnet depicted in Figure 7a is from the biotite-rich domain in calcic pelite 462536. 

Viewing the results as a whole they present a closely unified picture, the main differences being the inevitable variations in the composition of samples. The iron was present as either Fe(II) or Fe(0) and no significant concentration of Fe(III) was detected. Separation of individual components was only partly feasible because several minerals were often embedded in a single grain, and, for example, iron metal was seen lining cracks in ilmenite and silicates. 

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