Under the current conditions of mineral processing technology, high-purity quartz sand processing is inseparable from pickling . Pickling has the effect and effect of washing, flotation, magnetic separation and other methods, which can effectively remove quartz sand particles in the form of inclusions. Surface or impurities embedded in the particles are important high-purity quartz processing tools.
In the actual production process, acidity, time, temperature, acid washing, process and equipment are the main factors affecting the pickling effect.
1
acidity
The pickling process actually makes the chemical reaction between the impurities and the acid. Under certain conditions, the concentration and composition of the various acids are different, and the effects of the impurities are different, so the degree of influence on the quality of the high-purity quartz is also different.
Quartz ore raw materials are accompanied by a large number of impurity minerals such as attapulgite, rutile, mica, etc. Most of them contain metal oxides and salts attached to the surface of quartz ore. Hydrochloric acid can react with various metal oxides and salts to form soluble chlorine. But the hydrochloric acid does not dissolve most of the silicate.
Many of the associated minerals of quartz are silicon-containing minerals, so a certain proportion of hydrofluoric acid is needed to effectively dissolve the silicon-containing minerals in the quartz.
Practice has shown that at a certain temperature, the acidity is appropriately increased, and the total number of reactant molecules per unit volume is increased. The more activated molecules, the faster the reaction rate and the higher the pickling effect.
2
temperature
The quality of quartz pickling, the temperature plays a decisive role . The effect of associated minerals such as epidote and rutile on acid at room temperature is negligible. If heated during acid soaking, the effect will increase with increasing temperature. There is a clear difference between the winter and summer treatments in a year, the main reason is that the external temperature is different.
The higher the temperature, the faster the molecular motion, the more collisions between molecules, and the faster the reaction. On the other hand, heating can convert non-activated molecules in the solution into activated molecules, which speeds up the reaction and improves the treatment effect.
However, the temperature is not as high as possible. At 60 ° C, the acidity is also accelerated due to the increase in temperature, so the pickling temperature is preferably about 50 ° C. Of course, if the pickling equipment is sealed quite well, the high temperature treatment will be better.
3
time
When the acidity and temperature are the same, the length of the acid immersion time of the quartz directly affects the quality of the impurity removal effect. In winter, the outside temperature is low, and the reaction speed of acid and mineral impurities in quartz is slow, and it is necessary to extend the appropriate time to achieve the desired effect.
In addition, the acid leaching time is also related to the size of the quartz particles. The quartz particles are small, have a large contact area with acid, and have a fast reaction speed. When the quartz powder particles are large, the impurity elements contained in the particles cannot be quickly contacted with the acid, and the pickling effect is poor when the time is short.
4
Washing acid
Impurity minerals in quartz react with acids to form various soluble or insoluble salts. If the acid washing process is not properly operated, the quality of the acid washed products will be seriously affected.
For example, when the acid-treated quartz sand is washed with high-purity water, the acidity is lowered, and the impurity element Ca reacts with the HF acid to form a CaF 2 precipitate which is adsorbed on the surface of the quartz particle, and the CaF 2 is drawn in the quartz glass tube. When the color is blue .
Studies have shown that in the process of acid washing of quartz, the principle of equilibrium movement of chemical reaction can be used to eliminate the precipitation of CaF 2 . , that is, the pH value is used to control the production and dissolution of CaF 2 precipitation, and the mechanism is as follows:
CaF 2 ionizes a small amount of Ca 2+ and F − in the solution , while Ca 2+ and F − collide with each other to form CaF 2 , which constitutes a reversible equilibrium. If the H + concentration is increased so that H + and F - generate HF, the F - concentration can be reduced , which causes the CaF 2 to undergo a dissolution reaction.
Therefore, when washing the acid, it is necessary to control the pH value of 0.5-1, stir for 3-5 minutes, and then remove the cleaning solution for 3-5 times to separate the Ca 2+ , Mg 2+ , Fe 2+ in the quartz powder cleaning solution . Al 3+ , Na + , K + plasma, then washed with a large amount of deionized water to neutral. Thus, even if a small amount of CaF 2 remains on the surface of the particles, precipitation does not occur as long as it does not exceed its solubility product. When the high-purity quartz sand thus treated is drawn, the blue discoloration caused by CaF 2 is not generated when the quartz glass tube is drawn .
Of course other mineral elements can also cause discoloration. Therefore, high-purity quartz sand is required to be strictly operated during acid washing.
5
Pickling process and equipment
Some manufacturers said that the pickled quartz sand will be yellowed again for a period of time, mainly for the following three aspects:
(1) There is no magnetic separation process before pickling of quartz sand. After pickling, some mechanical iron remains in the quartz sand, and the mechanical iron is rapidly oxidized, which causes the quartz sand to turn yellow directly;
(2) The acid washing is not complete, and the surface acid remains on the surface of the quartz particles, which may cause yellowing;
(3) Quartz sand does not dry before contact with the handling tool to cause secondary pollution (oxidation with iron) and yellowing.
Therefore, in order to prevent the yellowing of quartz sand, a magnetic separation process must be set before pickling; acid pickling equipment should use plastic containers resistant to acid and alkali; quartz sand should be dehydrated and dried immediately after cleaning; all processing equipment should be protected To avoid contact between quartz sand and iron materials.
In addition, the external environment will also affect the effect of pickling. In order to prevent dust pollution in the air, it is necessary to strictly control the air environment such as production, packaging and storage .
The main factors affecting the acid treatment quality of high-purity quartz powder, author:: Some sources Fong was
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