Investigation On The Preparation Of High Purity Quartz From Low Grade Silica

Quartz is a kind of mineral resources with stably physical and chemical properties, used in very extensive fields. Ordinary quartz sand are used in glass, ceramics, rubber, foundry and other fields. The high purity quartz sand with SiO2 content more than 99.95%, is mainly used in high-tech industries such as aerospace, biotechnology, high-frequency technology, electronic technology, optical fiber communications, military and other fields. Only natural crystal (1,2 grade crystal) with limited reserves can meet their demands, additionally the rapid development of global semiconductor industry and optical fiber communication makes the resource trend to depletion. Therefore, it become the recent focus that to take use of various means to separation high purified quartz sand from common quartz sand.Quartz purification is an important flotation theoretical and practical task. Quartz often associates with other silicate minerals, mainly feldspars, both are silicate minerals with frame structure, and the surfaces of two minerals after dissociation have very similar characteristics, so the flotation separation of feldspar and quartz is difficult. Currently, the flotation researches of these two minerals are mainly focusing on cation/anion mixed collector to float feldspar from quartz under acidic condition and mixed acid leaching. To abtain high purity quartz, the selection of high grade ore for the purification is required, thus limiting the raw materials of high purity quartz. In order to abtain high purity quartz from ordinary quartz sand, systematic investigation is necessary.Firstly, the search for selectivity activator and inhibitor between feldspar and quartz was carried out through a large number of trials in laurylamine collector system by pure feldspar and quartz minerals flotation. Organic small molecule inhibitors were targeted and screened in laurylamine collector system. Oxalic acid, the high-selective inhibitor for the separation of feldspar and quartz, was found. Good indicators were both achieved under this new reagent system in flotation of artificial minerals and actual ore.It was first discovered that the interactive effects of fine fraction feldspar to feldspar and quartz separation. Rational reagent system was managed to decline the adverse impact caused by interactive function, and the flotation index was improved. Results of actual ore showed that: For the silica from Chaoyang with SiO2 grade 93% under the reagent system of oxalic acid as the regulator, dodecylamine as collector, the index of concentrates achieved: SiO2 grade>98.5% recovery rate>93.01% for the simple-0.5mm+0.1mm size fraction material, SiO2 grade>99.3% recovery rate>85% for-0.1mm+0.037mm size fraction material, SiO2 grade>99.3% recovery rate>75% for the full fraction material, at the grinding fineness-0.044mm 85%; For the silica from Jilin with SiO2 grade 97.32% under the reagent system of oxalic acid as the regulator, dodecylamine as collector, the index of concentrates achieved:SiO2 grade>99.8% recovery rate>85% at the grinding fineness-0.044mm 85%; For the silica from Chifeng with SiO2 grade 97.45% under the reagent system of oxalic acid as the regulator, dodecylamine as collector, the index of concentrates achieved:SiO2 grade>99.2% recovery rate>70% at the grinding fineness-0.044mm 75%.With the help of modern surface testing technology, it was first discovered that the ultimate impact factor on concentrate grade of silica flotation was due to the some fine feldspar adsorpted on the surface of quartz particles still. And the pure quartz minerals and fine feldspar minerals were used for simulating the flotation concentrates to carry out deeply deslime investigation. Ultrasonic treating combined surface active agent eliminated the adsorption of fine feldspar on the mimical quartz concentrate and this novel flow sheet can guide purification for the actual low-grade ore.Quartz ores from Jilin, Inner Mongolia, Liaoning three different origins were purified using the new reagent system and flow sheet. Jilin quartz ore was easy to purify, with the flow sheet of rod mill scrub-grinding-flotation-deep deslime, SiO2 grade of final concentrate reached 99.9%; Chaoyang quartz ore involved in finer dissemination, with the flow sheet of grinding-classification-flotation-deep deslime the SiO2 grade of final concentrate reached 99.9%; Inner Mogolia quartz ore, with the flow sheet of grinding-flotation-deep deslime, the SiO2 grade of final concentrate reached 99.76%. There maybe still a part of impurities can not be removed by this flow sheet, it could be infered that fine grained feldspar included in quartz particles not fully dissociated at this grinding fineness, it is more difficult to further a higher grade of SiO2.The leaching of quartz purification was explored making use of high boiling point properties of concentrated sulfuric acid. For the first time, high-temperature sulfuric acid leaching at atmospheric pressure was introduced into quartz purification, the following results were achieved: result of conventional leaching for-0.5mm+0.1 mm size fraction of quartz ore was not satisfactory, Al2O3 grade of ore leached was over 1%; the result of flotation concentrate leaching under conventional condition was also not satisfactory, the final concentrate with SiO2 grade 99.6%, Al2O3 grade 0.3%; the leaching experiment using 98.3% concentrated sulfuric acid under the boiling point of 338℃for quartz flotation concentrate with SiO2 grade 99.4% was carried out and SiO2 grade of 99.8% quartz sand products was obtained after deep washing, so was the 80% concentrated sulfuric acid leaching, and more than 99.8% SiO2 grade quartz products were obtained. Pure feldspar mineral leaching experiment showed that the atmospheric temperature sulfuric acid leaching can not leach completely Al2O3 from feldspar and the reason may be that after the Al on the surface of feldspar particles were leached, the internal Al did not turn out because of frame structure remained, Therefore, leaching was not complete, but the absorption ability of fine feldspar was destroyed during leaching. They can be ultimately wiped out from quartz particles by repeated washing.Finally, by means of crystal chemistry, flotation solution chemical theory and modern surface testing technology (X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy andξpotential measurement, etc.), surface characteristics of feldspar and quartz after dissociation was investigated thoroughly. The main dissociation surface of feldspar was (010), its zero-power point was calculated to be 1.2, the second dissociation surface surface was (001), and the fracture surface was (100). The surface characteristics of main dissociation surface are quite different from the other two surfaces. The main dissociation involved in strong electronegative and strongest function with dodecylamine; different surface properties of feldspar and quartz resulted in the interactive effects between feldspar and quartz flotation separation. (010) surface of feldspar charged strongest negative, at pH2.5, the fine feldspar and quartz can adsorb with each other by electrostatic force, so that the quartz surface turned out activation point, which activated the quartz flotation, resulting in reduced recovery of quartz; oxalic acid functioned mainly on (001) and (100) of feldspar forming complex and functioned very limitedly on (010) of feldspar, after added oxalic acid, dodecylamine can still adsorb on (010) surface of feldspar to float it; and oxalic acid can adsorb on all locations quartz surface forming complex, preventing the adsorption of dodecylamine. Another role of oxalic acid was to buffer solution pH value to maintain the inhibition range of quartz, which could improve the recovery rate of quartz. The different functions of ultrasonic between coarse and fine particles was the main reason for the deep deslime of quartz concentrate, moreover, the addition of surfactant made a more negative surface potential of quartz and formed steric effects, more conducive to electrostatic repulsion between micro-fine particles slime and quartz.The results of this investigation enriched the framework of flotation principles on silicate minerals, set up a series novle method on the research of interactive effect between complicated mineral flotation systems, and can guide the purification of low-grade quartz ore.