Two methods for purifying high-purity quartz stone

High temperature roasting

This process means that when the temperature is above 1000°C and the vacuum state is 0.01Mpa, a huge pressure difference is formed between the inside and outside of the gas-liquid inclusion, causing it to burst. At the same time, the high-temperature vacuum state is conducive to the removal of hydroxyl groups in the quartz sand.

During the high-temperature roasting process, the quartz crystal lattice will undergo transformation, from a-quartz to β-quartz at low temperatures, and will transform again to cristobalite as the reaction temperature further increases. Quartz lattice transformation occurs through changes in the Si-O bond angles in the quartz lattice. When the quartz lattice deforms, its lattice volume changes, causing the structural balance inside the original quartz crystal to be destroyed. The impurity metal elements no longer maintain a stable state and undergo a series of thermal movements, eventually diffusing to the quartz lattice surface and vaporizing and diffusing to the quartz surface.

At the same time, under high-temperature vacuum roasting conditions, the gas-liquid inclusions in the quartz sand expand due to heat. When the quartz lattice deforms, it breaks as the lattice volume changes, exposing the impurities inside the inclusions and being affected by the concentration difference between the inside and outside. The influence eventually vaporizes and diffuses out, thereby achieving the purpose of quartz purification.

Chlorinated roasting

Chlorination roasting, also known as chloride degassing, uses the chemical potential gradient generated on the surface and inside of the particles under the action of high-concentration chlorine to promote the diffusion of gas-liquid inclusions. Impurities such as alkali metals, alkaline earth metals and residual inclusions on the surface of quartz particles react with chlorine at high temperatures to form gaseous chlorides. Compared with other metal ions, Al and B have lower reactivity, and the high-temperature airflow removes these impurity elements. The chloride is taken away to achieve the purpose of deep purification.

Chlorination roasting is a deep purification process with high cost, limited processing capacity and certain risks.

This process has high requirements for feed materials. Generally, after purification by traditional processes, the SiO2 purity reaches 99.99% and the total impurity content is less than 100×10-6. Only quartz sand can meet the feed requirements. Chlorination roasting equipment is mostly self-designed. There is no unified standard equipment and it is still in the process of continuous development and improvement.

According to the type of chlorinating agent, chlorination roasting can be divided into solid chlorination roasting and gaseous chlorination roasting. Among them: the chlorinating agents used in solid-state chlorination roasting are generally NaCl, CaCl2, and NH4Cl; the chlorinating agents used in gaseous chlorination roasting are generally Cl2 and HCl.