Experimental study on purification process of metamorphic quartzite in Yunnan
Silica is a general term for various quartz raw materials, including quartz sand, quartz sandstone , quartzite , vein quartz , and siliceous rock. The purification of silica to produce electronic grade quartz products is a high-tech high-tech, which is currently the world's leading level in the United States. In some developed countries such as the United States, high-quality silica resources have been listed as strategic resources to protect. It is understood that there are currently three ways to produce high-purity quartz (silica micropowder) and high-quality crystal : one is artificial crystal; the other is sol-gel method, namely silicon tetrachloride vapor deposition method for synthesizing quartz glass; Natural silica is replaced by high-quality crystal raw materials after beneficiation . China's crystal mineral resources are extremely scarce, and the application of silica to produce high-tech silicon can solve the problem of natural crystal substitutes. The use of natural silica instead of high-quality crystal raw materials is characterized by abundant resources and low production cost, and is an effective way to develop and utilize silica.
First, the type and nature of silica
Silica deposits in Yunnan Province have many genetic types and wide distribution. According to the geological survey of key mining areas (mountain), combined with the ore-forming geological conditions, metallogenesis and ore body output form, the Yunnan Silice Mine can be divided into four types of deposits: sedimentary type, metamorphic type, post-magmatic period. Hydrothermal type and medium and low temperature hydrothermal type.
This experimental study focuses on mineral technology research and purification research focusing on the metamorphic type of quartz in Yunnan.
(1) Metamorphic type quartzite composition
The quartzite is milky white, grayish white, partially flesh-colored, and occasionally a small amount of yellow-brown iron . The quartzite essentially of quartz, a small amount of white mica, pyrite occasionally, limonite. The muscovite is enriched in the quartzite wall, and the muscovite contained in the quartz is extremely fine and the distribution is also very common, which is difficult to dissociate from the quartz. This will affect the purity of the quartz. There are pyrite and limonite particles in the interior and between the grains. There are iron stains in the quartzite fissures, and there are very few limonite and pyrite.
(II) Structural structure and embedding characteristics of metamorphic quartzite
Quartzite is a granular structure with a massive structure. There is also some clay powder on the quartz wall, there are fine veins of muscovite in the quartz crack, and there is yellow-brown iron dye. Quartz in quartzite is distributed in the ore in its granular shape. The quartz grain size is mainly 0.1 to 1.0 mm. Quartz grains are often embedded in needle-like, flaky, long strips of muscovite, and there are often finer muscovite inclusions inside the quartz. On the wall of quartzite, see also the collection of muscovite. Limonite and pyrite inclusions are occasionally seen in quartz. The silicon in the quartzite is basically present in the quartz, and a small amount is present in the muscovite. The impurities in the ore are mainly aluminum , potassium and a small amount of iron, of which aluminum and potassium are mainly distributed in muscovite, and the particle size is fine. Iron is mainly found in ores in the form of iron, and is rarely found in limonite and pyrite. The analysis of the main 13 impurity elements in quartzite is shown in Table 1.
(III) Preparation of metamorphic quartzite samples
Quartzite has a Mohs hardness of about 7, and it is difficult to crush it into a test sample under normal pollution-free conditions. It is calcined at a high temperature of about 1000 ° C and then water quenched. The sample was further crushed to -5 mm, and the sample was sieved by an international standard Taylor sieve. The main chemical elements of each of 5 mm, 0.2 mm, 0.1 mm, and 0.063 mm were analyzed in Table 2.
It can be seen from the sieve analysis test that the finer the grain size of the quartz, the higher the impurity Al 2 O 3 content, and the -0.063 mm grain-level quartz fine powder contains more fine-grained muscovite by microscopic observation.
2. Experimental design of metamorphic quartzite purification
From the characteristics of quartzite inlay and multi-element chemical analysis, the main elements affecting quartz purification are aluminum, calcium, magnesium and iron. The impurity minerals are mainly muscovite, limonite and pyrite. Due to the low content of aluminum, calcium, magnesium and iron impurities, quartzite can be purified by direct acid leaching test.
(I) Determination of the purification process of metamorphic quartzite
The test sample is firstly calcined at a high temperature, and crystal transformation occurs when quartz is calcined at a high temperature (α quartz→β quartz→β-scale quartz) to increase the volume, and then water quenching. The crystal ruptures at the original defect when water quenching. The broken silica is then subjected to an artificial hand selection to pick up the silica with the accompanying organism. Finally, the remaining piece of quartz is further finely pulverized ( agate grinder), and divided into different fractions as chemical purification test materials for chemical purification (acid leaching) test. After acid leaching, the residual liquid is only contaminated on the surface. It can be washed with ordinary clean water. When it is washed to neutral, it can be washed with deionized water to obtain a high-purity product. The quartzite purification test process is shown in Figure 1.
(II) Test on purification conditions of metamorphic quartzite by acid leaching
Before the test, the test samples of different grades of -100 mesh, -200 mesh, and -500 mesh were respectively pulverized with +300 mesh samples, and subjected to a chemical purification test. The acid leaching test was carried out by using quartz raw materials finely crushed to -100 mesh, and the acid leaching conditions were 1, 2, respectively, and acid leaching purification was carried out under stirring conditions for 24 hours, and the results are shown in Table 3. 1m (mine): m(H2O): m(H2SO4): m(HCl)=100:50:20:4; 2m(mine):m(H2O):m(HCl):m(HF)=100: 50:15:1.4.
It can be seen from Table 3 that when the two acids are combined with acid leaching, the leaching effect of Al 2 O 3 and Fe 2 O 3 is obvious, but the leaching effect of MgO and CaO is not obvious.
(3) Acid leaching time condition test
Considering the acid leaching purification time and the acid type will directly affect the quartz purification effect, use -200 mesh quartz raw material in m (mine): m (H 2 O): m (H 2 SO 4 ): m (HCl): m (HNO 3 ): When m(HF)=100:50:25:12.5:7.5:5, four kinds of acid immersion time conditions were tested, and the results of acid leaching conditions test are shown in Table 4.
It can be seen from Table 4 that the longer the acid leaching time is, the better the leaching effect is when the appropriate amount of hydrofluoric acid is added. Since hydrofluoric acid has a certain dissolution effect on quartz, the concentration of hydrofluoric acid used should not be too high.
(4) -500 mesh infusion test
Under the same acid leaching conditions as in Table 4, a quartz material having a particle size of -500 mesh was selected, and a 24 h leaching test was conducted. The test results are shown in Table 5.
Comparing the test results of Tables 4 and 5, it can be seen that, in the acid leaching purification, the finer the immersion particle size, the better the leaching effect. This is because the impurity monomer is substantially dissociated in the case of a fine particle size, so that the purification effect is greatly improved.
(5) Contents of various impurities in high-purity quartz concentrate
When the quartz powder is chemically purified at -500 mesh, the contents of the main 13 impurities in the quartz concentrate are shown in Table 6.
It can be seen from Table 6 that after the -500 mesh quartz powder is chemically purified, the total content of 13 impurities is 93.7 g/t, and the content of Fe 2 O 3 is only 5 g/t, and the indexes satisfy the requirements of high-purity quartz.
(6) Comparative test of metamorphic quartzite and sedimentary type quartz sandstone
The metamorphic type quartzite does not belong to the same type as the sedimentary type quartz sandstone. The quartz sandstone has a whiteness of only 64.6% and a high impurity content. Quartz sandstone is embedded in its granular and round granular phase. The clay minerals such as muscovite are often filled with cement and filled with tourmaline and zircon . A small amount of zircon is seen under the microscope. Some of the zircon is cemented together with the tourmaline by the muscovite, and occasionally the zircon is encapsulated in the quartz. Muscovite is more common, it is mainly in the form of flakes, scales, fine veins, branches, and film-like filled quartz particles, and a small amount of vein-like aggregates are filled in quartzite fissures. According to the characteristics of impurity minerals, we use the grinding scrub-magnetic separation-flotation-acid leaching purification process to compare with quartzite. The content of impurities in the quartz sand concentrate after purification is reduced, but after purification, Al 2 O 3 , 0.1%; Fe 2 O 3 , 0.0064%; CaO, 0.016%; MgO, 0.010%, the impurity content is still high, and Compared with quartzite, the purification effect of quartz sandstone is not obvious and difficult.
Third, the conclusion
(A) found that mineral impurities have good removal of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, the quartz metal. The dissolution of hydrofluoric acid on quartz helps to destroy the inclusions of impurities, which can achieve further purification, but the concentration should not be too high.
(2) Metamorphic type Quartz acid leaching and purifying process can meet the requirements of high-purity quartz, but the cost is high and the time is long.
(3) According to the comparative test, although the sedimentary quartz sandstone is purified by magnetic separation-flotation-acid leaching, the main impurity content is reduced, but the purification effect is not obvious.
(4) After preliminary purification, the total amount of metamorphic quartz concentrate is 93.7g/t, the product quality fully meets the quality requirements of high-purity quartz (high-purity silicon micropowder), and is close to the quality of ultra-high-purity quartz fine silicon micropowder) Claim.
references
[1] Li Wei, et al. New technology of quartz sand beneficiation and deep processing [J]. Mineral Protection and Utilization, 1995 (5): 23-26.
[2] Liu Ligen, et al. Study on high-purity quartz sand beneficiation process [J]. Non-metallic minerals, 1996 (4): 39-41.
[3] Han Xianjing. Deep processing of ultra-high purity quartz sand [J]. Foreign metal ore dressing, 1998 (7): 31-32.
[4] Niu Fusheng, et al. Study on purification process of quartz sand beneficiation[J].Yunnan Metallurgy,2001(2):18-21.
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