الفهرس 
Introduction
SUMMARY AND CONCLUSIONOnly 14 pages are availabe for public view
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Abstract
This study is aiming to evaluate and upgrade Marwit El-Sweiqat and Marwit Rod El Leqah quartz samples from the Eastern Desert of Egypt for hi-tech industrial applications. Field study of the two areas show that Marwit El Sweiqat quartz body is giant hydrothermal quartz vein related to the younger granitic phase in the area. The macroscopic contaminations appear to be iron oxide, sulfides, granitic fragments and mica pockets. While Marwit Rod El Leqah quartz body is mainly pegmatitic quartz and hosted by granodiorite. It was contaminated by iron oxides, opaque minerals, dendritic manganese and granitic rafts in addition to fresh feldspar xenocrysts.
Microscopic investigation for thin and polished sections from some selective collected rock samples from both areas reveal that the samples are composed mainly of quartz grains with minor minerals and fluid contaminations. The present mineral impurities are ordered in abundance as iron oxide, muscovite, feldspars, rutile and zircon. In addition to Submicron tourmaline impurities are detected in Marwit Rod El Leqah quartz. Muscovite appears as secondary mineral that is resulted from alteration of biotite. Muscovite impurities show alteration to opaque iron oxide minerals especially in Marwit rod El Leqah quartz samples. Mineralogical evaluation by reflected light microscope and XRD analysis of the quartz samples of Marwit rod El Leqah reveal the presences of hematite and sulfide impurities. Most of the mineral impurities are located mainly along the quartz grain boundaries or filling micro-fractures. Fluid inclusions are present in planar orientation i.e. secondary in type and concentrate along the micro-fractures or between the boundaries of the quartz grains which may enhance their liberation after primary comminuation.
Marwit El Sweiqat quartz shows high deformation characters, such as more lattice imperfections compared to Marwit Rod El Leqah quartz. This appears in the bulging recrystallization, undulose extinction, ribbon textures, sub-grain boundaries, and secondary twinning, deformation bands, crystalline index (1.22) and (1.65), respectively. This may reflect the increasing in the degree of fineness as well as the higher specific surface area of the ground El Sweiqat quartz compared to Rod El Leqah quartz. This may also explain its relatively higher chemical reactivity than Rod El-Leqah quartz.
The geochemical studies of the samples of the two deposits reveal that both are of medium purity type according to the international classification, where they contain average silica content 99.447% and 99.387% for Marwit El Sweiqat and Marwit Rod El Leqah, respectively. The chemical analysis of the crude samples match the specification of some important applications such as heat bricks and ferrosilicon alloys, but don’t match the requirements of high technical applications such as ellite silicon and solar cells.
The native quartz samples are contaminated by some solid minerals, silicate melt inclusions, fluid inclusions, and some structural impurities as well. Oxides of iron, alumina, calcium, magnesium, potassium, sodium, and manganese appear to be the dominant impurities. Marwit Rod El Leqah quartz appears to be more contaminated with such impurities due to the abundance iron oxide lenses, fresh orthoclase, calcic plagioclase and submicron tourmaline crystals. Most of the present impurities are paramagnetic in nature. The detected feldspar minerals are commonly altered to sericite.
The trials to upgrade the two quartz sample is conducted by testing their amenability to be cleaned from most of the accompanied minerals impurities by dry high intensity magnetic separation. Frantz isodynamic Tester is used to follow up the samples behavior when exposed to the magnetic attraction with different intensities. The results reveal that the purity of the quartz samples can be improved to great extent after high intensity magnetic separation.
Response surface methodology in conjunction with the central composite rotatable design is used to optimize the magnetic separation using the “Magnaroll” separator. This is carried out by optimizing the main working variables of the separator, namely the splitter angle and the belt speed. The upper and the lower limits of the variables are selected after series of exploratory tests to be from 200 rpm to 250 rpm for the belt speed and from 84o to 95o for the splitter angle. The feeding material mode is also studied. This is attained by testing the quartz samples as one overall feed -0.6+0.1 mm or by splitting into two fractions; coarse fraction (-0.6 + 0.3 mm) and fine fraction (-0.3 + 0.1 mm). This is conducted to study to what extent the separation efficiency may be improved by separating a feeding material with a very closed particle size distribution.
The mathematical model equations of quadratic polynomial model are derived from the Design Expert software (version 6.0.5). Such equations are of second order response functions which represent the weight %, the Fe2O3 and Al2O3 contents, and their reduction % in the clean quartz products are expressed as the main responses. Predicted values obtained using the model equations are good agreed with the observed values for all the fractions, where R2 value is higher than 0.9 for all the required responses.
The effect of the operational variables and their interactions on the required responses, the predicted models values are presented as quadratic and 3D response surface graphs. The resulted graphs show increasing in the Fe2O3 reduction % with decreasing the levels of both the belt speed and the splitter angle in case of all the separating samples. The same behavior is repeated for the Al2O3 Reduction % in case of the overall sample and the coarse fractions, but the behavior is reversed in the case of separating the fine fraction of the two quartz deposits.
The experimental tests reveal that the optimum separation conditions are 85o (splitter angle) and 200 rpm (belt speed) for the overall sample and the coarse fraction, where the Fe2O3 reduction% reach 99% and 98%; and Al2O3 reduction% reach 98% and 98.4% for Marwit El Sweiqat quartz and Marwit Rod El Leqah, respectively. In case of the fine fraction splitter angle 85o and belt speed 200 rpm are the optimum conditions for Fe2O3 reduction%, but for Al2O3 reduction%, the splitter angle 95o and belt speed 250 rpm are the optimum conditions. where the splitter angle 95o or 90o and the belt speed 225 rpm are the optimum separating conditions for maximum removal of Fe2O3 and Al2O3.
The optimum experimental conditions is concordant with the predicted optimum conditions from the quadratic model programming with some suggestions to enhance the removal efficiency of Al2O3 to 99% for Ov.S. and 98.1% for C.S at splitter angle 86.9o, 85.15o and belt speed 200.7 and 217.27 respectively. In case of the F.S fraction, Splitter angle 85.59 and belt speed 212.6 rpm are predicted to increase the separation efficiency of Fe2O3 from 97.76% to 97.93%.
Marwit El Sweiqat quartz show relatively higher response for Fe2O3 reduction, while Marwit Rod El Leqah quartz show higher response for Al2O3 reduction. This may be explained after the differences in the nature and abundance of the present impurities, specially the state of the iron oxide, liberation of pyritic inclusion, degree of replacement of muscovite by iron oxide and degree of alteration of the granitic rafts.
The idea of splitting the original quartz samples -0.6+0.1 mm into two portions -0.6+0.3 mm and -0.3+0.1 mm does not improve the RER magnetic separation. This is may be attributed to the stacking of the fine particles on the separating belt due to static charges that reduce both the quality and quantity of the final end product.
It could be concluded the application of the dry high intensity magnetic separation using the Magnaroll separator is a successful technique to produce high quality quartz concentrates hat match the specification of high technical applications. It is important to mention here that this technique, is conducted under a dry base which, is a very promising especially in case of arid areas like those quartz deposits under investigation in this study.
Finally, it is great to mention that the quality of the upgraded quartz end-products are matching the advanced industrial application and are ranked as medium purity quartz according to the international classification and as high purity quartz according to the local classification.