Chlorination roasting purification of high purity quartz sand

The purification methods of high-purity quartz are mainly divided into physical methods and chemical methods. Different co-associated minerals use different sorting technologies. Physical purification methods mainly include scrubbing, gravity separation, magnetic separation, color separation and flotation. They can remove almost all mineral impurities that exist in monomers. After impurity removal, the impurity elements content is at a low level.

At this time, gas-liquid inclusions and homogeneous impurities inside the crystal lattice are the main sources of impurities, and these impurities are the key factors restricting the preparation of high-purity quartz products. For example, alkali metal element impurities K and Na will reduce the service temperature and mechanical strength of quartz glass, and catalyze the crystallization of quartz glass at high temperatures, leading to devitrification, high-temperature deformation and other phenomena in quartz glass.

Physical purification cannot remove these impurities and requires deep chemical purification. Chemical depth purification mainly includes acid (alkali, salt) treatment and heat treatment. Acid (alkali, salt) treatment mainly removes impurities that exist in the form of inclusions on the surface of quartz sand particles or embedded in the particles. The heat treatment method mainly uses high temperature to remove impurities. Isomorphic impurities in inclusions or crystal lattices. Compared with physical purification methods, chemical purification operations are complex and costly, but when preparing high-purity quartz, chemical treatment is the most effective and essential.

Among them, chlorination roasting is the most important method to remove interstitial atom impurities such as quartz lattice impurities and alkali metals. Chlorination roasting converts the ions of impurity components into low-boiling chlorides under certain temperature and atmosphere conditions, and then The process of separating impurity components.

The chloride roasting method is not a new mineral smelting method. It has been successfully used in precious and refractory metal minerals and mineral recycling a long time ago. With the deepening of research on mineral processing technology, the application of chlorine roasting has begun to develop towards the processing of non-metallic minerals.

In the chlorination roasting purification process, commonly used chlorination agents include chlorine, hydrogen chloride, ammonium chloride, sodium chloride, potassium chloride, calcium chloride, etc. Chlorination roasting can be divided into high-temperature roasting (chlorination volatilization method) according to the product form. ), medium temperature roasting (chlorination roasting-leaching method), chlorination-isolation. There are great differences in the ways and effects of different chlorinating agents and roasting temperatures on lattice impurities.

In traditional chlorination roasting purification technology, quartz sand is usually heated to 1000-1200°C in a Cl2 or HCl gas atmosphere. Main trace metal elements (such as Al3+, Fe3+ and Ti4+ combined in the quartz lattice) diffuse to the surface/interface of the quartz grains, and then react with the ionized Cl- to form low-boiling point chlorides, which can be quickly removed.