Study on pilot production process of quartz doping and high temperature purification

Taking Donghai ordinary quartz powder as raw material, the process parameters such as calcination temperature, doping substance type and concentration, high temperature constant temperature time of quartz powder are optimized, and pilot test is carried out.

1 quartz doping, high temperature purification process optimization

(1) Effect of calcination temperature on the purification effect of quartz powder

The quartz powder is calcined at different temperatures, and directly mixed with acid leaching after calcination. The test results show that:

At 500-550 ° C, the impurity content of quartz powder did not decrease;

At 600 ° C, the impurity content decreased significantly;

At 650-850 ° C, the impurity content is basically the same as 600 ° C;

At 900 °C, the impurity content decreased significantly, and the purification effect on quartz powder was better;

At 950-1400 ° C, the impurity content does not change much compared to 900 ° C;

At 1450 ° C, compared with 900 ° C, the impurity content is significantly reduced, the purification effect on quartz powder is very good, but there is vitrification.

Analysis of the cause: at 600 ° C, 900 ° C and 1450 ° C is the silica crystal transition temperature, quartz undergoes a large volume expansion during the crystal transformation, and produces cracks due to rapid cooling, due to impurity enrichment points and two The expansion coefficient of silicon oxide is quite different, especially for the heterogeneous minerals in quartz. Large cracks often occur at the interface between the inclusions and the quartz matrix. According to the crystal transformation process of quartz, the change in temperature difference is used in the quartz. The impurities can be fully exposed, and the quartz particles after the crystal transformation are loose, and the edges are smashed along the edges of the impurities, which is favorable for the exposure and fracture of the impurities. The impurities in the quartz powder form a crystal nucleus when heated at a high temperature, and then quenched to cause cracking of the powder, and the mixture is immersed and washed with a mixed acid. The mixed acid of the powder is easily immersed in the crack, and the surface and internal impurities can be dissolved.

(2) Effect of doping substance type and concentration on the purification effect of quartz powder

In the process of quartz roasting, the impurity content of quartz powder can be significantly reduced by adding some doping substances. The test results show that the impurity content of quartz powder doped with NaNO3 and Al(NO3)3·9H2O is significantly reduced.

Analysis: NaNO3 and Al (NO3) 3 · 9H2O decompose at high temperatures into Na2O and A12O3, Na2O promote surface cristobalite quartz powder, quartz powder enhanced cracking effect; with an alkali metal aluminum affinity and ability than silicon A12O3 can react with alkali metal impurities to form an acid-soluble compound, which is easy to clean and remove.

The content of impurities in the quartz powder purified by high-temperature calcination with alkali metal chloride is obviously decreased. It may be due to the volatilization or sublimation of the incorporated chloride at high temperature, and the quartz powder mixed with potassium nitrate and potassium chloride, K There is also a slight increase in the content, and the content of Ca and Mg in the quartz powder doped with calcium, magnesium nitrate and chloride also has some increase.

(3) The best pilot process parameters for quartz doping and high temperature purification

Doping substance: NaNO3, Al(NO3)3·9H2O

Doping amount: 100kg quartz powder is mixed with NaNO3 10g, Al(NO3)3·9H2O 80g

Constant temperature: 900 ° C

Constant temperature time: 2h when NaNO3 is added, 2.5h when Al(NO3)3·9H2O is added

Doping material sequence: first doped with NaNO3, then doped with Al(NO3)3·9H2O

2 quartz doping, high temperature purification pilot production test

(1) crushing and screening

The 20-50mm quartz block to be crushed is placed on the flat material selection table, and manually selected, the side skin, the stain and the inclusion-containing material block are selected, and the qualified block material is subjected to water quenching and water quenching. The block material is crushed into 5-15mm particles by the jaw crusher and then manually sorted, and the debris mixed with the excellent spots, inclusions and crushing process is selected.

The fine crushing is carried out by the roller machine, and the finely crushed particles are added to the vibrating screen through the sliding channel for screening, and the particles meeting the particle size specification enter the next process, and the large particles on the sieve are returned to the roller machine and the quartz block together. Re-crushing is carried out until all the crushing screens are separated into particles meeting the particle size specifications.

(2) Magnetic separation, pickling

The sieved quartz powder is added to the electromagnetic separator for magnetic separation. The magnetic field strength is above 15000 gauss, and the iron and other magnetic or weak magnetic minerals brought by the fracture are selected. The magnetically selected quartz powder is placed in a plastic box and immersed in a mixture of 15% HCl, 10% HNO3 and 5% HF for about 7-10 days.

(3) flotation, cleaning, drying

The quartz powder after the mixed acid immersion is deacidified and washed, and then floated. At the time of flotation, about 500 kg of quartz powder is put into each time. Deionized water is added in a ratio of quartz powder to water of 1:2. The temperature of the slurry is 40-45 ° C, and the adjusting agent NH4F is added for 1 g, and the mixture is stirred for 1-2 min. 1NH4OH adjust the pH value of the slurry to 8-9, add 10 mL of collector oleic acid, stir for 1-2 min, add 12 mL of isooctyl alcohol flotation for 30 min, repeat once. The floated quartz powder is washed with deionized water to neutrality, discharged and dehydrated, and dried in a vertical drying oven.

(4) Primary doping, high temperature roasting, mixed acid soaking

Each time weighed 100kg of dried quartz powder, placed in a blender, weighed 10% of NaNO3 in a 1000-liter beaker with a tray balance, dissolved in 800mL of deionized water, poured into quartz powder in the blender, stirred and mixed. After 30 minutes, take it out and dry it in a vertical drying oven.

The dried doped powder is added to a fluidized bed type quartz high temperature furnace by a screw feeder, and is subjected to high temperature baking, and the furnace temperature is set to 900±5 ° C, and the temperature is kept for 2 hours. The quartz powder after the constant temperature is directly poured through the quartz feeding tube. Into a plastic bucket containing HCl 15%, HNO3 10% and HF 5% mixed acid, cover the lid and soak it.

(5) Secondary doping, high temperature roasting, mixed acid soaking

After the mixed acid soaked for one week, the quartz powder is filtered through an acid-resistant filter tank to remove the mixed acid, and then added to a washing machine, washed with deionized water until the conductivity is consistent with deionized water, and then dried and dried by an electric heating quartz drying oven. Weigh 100kg of quartz powder after purification and drying, put it in the mixer, weigh Al(NO3)3·9H2O 80g with a tray balance and put it in a 1000mL beaker. Add 800mL of deionized water to dissolve it, then pour it into the mixer. In the quartz powder, stir and mix for 30 minutes, take it out, and dry it in a vertical drying oven.

The dried doped powder is added to a fluidized bed type quartz high temperature furnace by a screw feeder, and is subjected to high temperature roasting, and the furnace temperature is set to 900±5° C., the constant temperature is 2.5 h, and the quartz powder after constant temperature is directly passed through the quartz discharge tube. Pour into a plastic bucket containing HCl 15%, HNO3 10% and HF5% mixed acid. Cover the lid and soak it when it is full.

(6) Cleaning, drying, inspection, packaging

After the mixed acid soaked for one week, the quartz powder is filtered through an acid-resistant filter tank to remove the mixed acid, and then added to a washing machine, washed with deionized water until the conductivity is consistent with deionized water, and then dried and dried by an electric heating quartz drying oven. The dried quartz powder is sampled for sample processing and impurity content analysis, and the products are packaged and stored after passing the test.

(7) Pilot product analysis results

Table 1 Analysis results of pilot products and quality standards of Juniper standard sand (1×10-6)

3 conclusions

(1) After high temperature cooling and mixed acid immersion, the purification effect of quartz powder is not good, and the impurity content of purified quartz powder is not significantly decreased.

(2) The high-temperature direct mixed acid immersion has a better purification effect on the quartz powder, and the impurity content of the purified quartz powder is significantly decreased.

(3) The doping-high temperature direct mixed acid immersion has a good effect on the purification of quartz powder, and the impurity content of the purified quartz powder is greatly reduced.

(4) The doping substance, concentration and doping sequence have certain influence on the purification of quartz powder. The appropriate doping substance, the appropriate concentration and the appropriate incorporation sequence can be selected to achieve the best purification purpose.

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