Study on Beneficiation and Purification Process of Ultra-Pure Quartz Sand

With the rapid development of high-tech technologies such as the electronics industry, the demand for ultra-pure quartz is increasing. Quartz powders having a SiO2 content of more than 99.99% are generally referred to as ultrapure quartz sand. The earliest production raw material of ultra-pure quartz is natural crystal , but its reserves are limited, and it has gradually dried up with the increase of mining intensity. Quartz sand is cheap and has abundant reserves. It can replace natural crystal to produce ultra-pure quartz sand.

1

Experimental part

The experimental raw material is a quartz sandstone mine. The chemical composition of the multi-element analysis results are: SiO2 99.02, Fe 178.2, A1 152.6, Na 56.4, K 66.6, Li 2.0, Ca 44.4, Mg 3.5, Ti 22.5 (SiO 2 unit is 5%, The other is μg/g). The main impurity elements of the sample were Fe, Al, Na, K, Ca and Ti, and the total content exceeded 500 ug/g. According to the mineral phase analysis, the sample is mainly blocky, light white translucent, fine grain structure, particle size less than 0.6mm, and the surface has obvious yellow-brown dyeing. Phlogopite impurity minerals are sheet-like, a small amount of muscovite, feldspar, and clay minerals containing iron.

The original ore X-ray diffraction pattern, see Figure 1, was found to be a quartz peak by comparison with the standard map JCPDS No. 33-1161. This indicates that the content of quartz in the original is high, which is consistent with the results of chemical composition analysis.

Since the hardness of the quartz sand is large and the gap contains impurities, the raw material is placed in a muffle furnace and calcined at 900 ° C for 2 h, and the direct water quenching is taken out, so that the hardness of the sample is greatly reduced, and the crack is opened, and the impurity mineral Fully exposed to facilitate subsequent processes. After drying, the product is crushed by a roller crusher to obtain a product having a particle diameter of less than 0.3 mm, and the material having a particle diameter of +0.105-0.3 mm is sieved to be a sample to be treated. The test principle process is shown in Figure 2.

2

magnetic separation

The purpose of magnetic separation is to remove magnetic impurity minerals dissociated from quartz sand and particles with magnetic mineral inclusions.

It can be seen from Fig. 3 that as the magnetic induction intensity increases, the concentrate yield gradually decreases, and the removal rate of iron-containing impurity minerals in the quartz sand gradually increases, that is, the SiO2 grade gradually increases. The contents of Fe and Ti were significantly reduced after magnetic separation, from 178.2 μg/g and 22.5 μg/g to 61.3 μg/g and 1.4 μg/g, respectively. Through microscopic observation, the magnetic separation concentrate is basically white or yellowish brown quartz sand particles and a small amount of mica. The tailings are mainly mica and iron-bearing minerals. The SiO2 content in the concentrate is not less than 99.95%, and the magnetic separation effect is good.

3

Flotation

The content of Fe and Al after magnetic separation is still very high, mainly feldspar and residual mica. They are similar in nature to quartz, but have different crystal structure and surface properties. Therefore, flotation is the best way to remove them. The cationic reverse flotation method is adopted in an acidic environment, and the flotation process is shown in Fig. 4.

200 g of magnetic separation concentrate was added to a 1 L XFD type flotation machine with sulfuric acid as a regulator, water glass as an inhibitor, and dodecylamine as a collector and a foaming agent. The effects of solution pH, inhibitor dosage, and collector dosage on the test were studied.

(1) pH value

The effect of pH on the test was investigated under the conditions of 600 g/t of inhibitor and 1200 g/t of collector. The results are shown in Fig. 5.

The flotation tailings are mainly mica and feldspar. As can be seen from Fig. 5, when the pH value is 1.5-3.5, the flotation effect is basically the same, because the electrical properties of various minerals are not substantially changed within the pH range set by the test, and the flotation effect is not greatly changed. As the pH value increases, the Al content decreases all the time. When the pH value is 2.5, the Fe content is the lowest. Therefore, the pH is kept at 2.5-3.

(2) Collector dosage

The pH value was controlled to 2.5-3, the inhibitor dosage was 600g/t, and the effect of the amount of collector on the test results is shown in Fig. 6.

It can be seen from Fig. 6 that the content of Fe and A1 decreases with the increase of the amount of the collector. When the amount of the collector exceeds 1200 g/t, the increase of the amount of the collector does not significantly reduce the impurity content. Taken together, the optimum collector dosage is 1200g/t.

(3) Inhibitor dosage

The pH value was controlled to 2.5-3, the amount of collector was 1200g/t, and the effect of the inhibitor dosage on the test results is shown in Fig. 7.

It can be seen from Fig. 7 that as the amount of the inhibitor increases, both the Fe and A1 contents decrease first and then increase. This is due to the insufficient amount of pre-inhibitors, which did not effectively inhibit the formation of quartz. The amount of inhibitors in the late stage was too large, and impurity minerals such as mica and feldspar were also inhibited. Considering the total amount of inhibitors, the optimum dosage was 600 g/t.

Under the optimal conditions of pH 2.5-3, inhibitor dosage of 600g / t and collector dosage of 1200g / t, the obtained concentrate detection results (μg / g) are: Na 48.3, K 50.9, Fe 33.3 Ca 35.6, Mg 2.0, Li 1.4, A1 131.3, Ti 1.3, total 304.1. It can be seen that the flotation has a significant effect on the removal of Fe and A1, but the total impurity mineral content is still as high as 300 μg / g.

4

Acid leaching

Physical beneficiation methods such as magnetic separation and flotation can only remove mineral structure impurities, and the removal of impurities on the surface of quartz sand is limited. Acid leaching is a chemical treatment that removes impurities from the quartz sand surface and in the gap. Different acids can produce a synergistic effect, so the mixed acid is used, and the mass ratio of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, and purified water is 10:5:3:2:20. The acid leaching test is to add 20 g of the flotation concentrate to a tetrafluoroethylene bottle, add the mixed acid solution, place it in a water bath, and assist with mechanical stirring. The factors affecting acid leaching are acid immersion time, temperature and liquid-solid ratio.

(1) Acid immersion time

The acid immersion temperature was controlled at 70 ° C and the liquid-solid ratio was 2:1. The influence of acid leaching time on the test was discussed. The results are shown in Table 1.

It can be seen from Table 1 that as the acid leaching time is prolonged, the contents of K, Na, and Ca are decreased, and the total impurity content is lowered. When the time reached 2h, the total impurity content was 37.2μg/g. Continued increase of acid leaching time had little effect on impurity removal, so the acid leaching time was determined to be 2h.

(2) liquid to solid ratio

The acid immersion temperature was controlled at 70 ° C, and the acid leaching time was kept at 2 h. The influence of the liquid-solid ratio on the test was studied. The results are shown in Table 2.

It can be seen from Table 2 that as the liquid-solid ratio increases, the total impurity content decreases first and then increases, and the lowest value occurs at 2:1. This is because when the liquid-solid is relatively small, the diffusion resistance is increased, which is disadvantageous for acid leaching of impurities. When the liquid-solid is relatively large, the amount of acid consumed is increased. Considering the comprehensive consideration, the liquid-solid ratio is selected to be 2:1.

(3) Acid immersion temperature

The fixed liquid-solid ratio was 2:1, and the acid leaching time was 2 h. The effect of acid immersion temperature on the test was investigated. The results are shown in Table 3.

It can be seen from Table 3 that as the acid leaching temperature increases, the total impurity content decreases. When the temperature reaches 70 ° C, the temperature increase continues to have little effect on the removal of impurities, and the temperature is preferably 70 ° C. Acid leaching has a significant effect on the removal of all impurities. The total impurity content of the obtained quartz sand is less than 50 μg / g, which has reached the requirements of high-purity quartz sand raw materials.

5

in conclusion

(1) Calcination-water quenching can significantly reduce the hardness of quartz sand, and can open cracks to expose impurities;

(2) Relative to flotation, the magnetic separation effect is obviously better, which is related to the iron-containing impurities and phlogopite content in the quartz sand ore;

(3) Acid leaching can significantly improve the purity of quartz sand, the content of Fe decreases from 178.2μg/g to less than 5.0μg/g, the content of Al decreases from 152.6μg/g to less than 14.0μg/g, and the total impurity content of the final product is less than 50μg/ g;

(4) The roasting-water quenching-magnetic separation-flotation-acid leaching combined process can obtain high-purity quartz sand with SiO2 content exceeding 99.99%, which can meet the requirements of high-purity quartz sand raw materials.