The principle and process of calcining kaolin from fly ash.
I. Introduction. Fly ash is a solid waste from coal-fired power plants, which contains a large amount of active ingredients and has potential resource value. Among them, kaolin is a common mineral component that can be transformed into a more reactive material by calcination under the right conditions. The purpose of this paper is to understand the principle of calcined kaolin in fly ash and its related processes, in order to improve the utilization efficiency and added value of fly ash.
Second, the principle analysis.
Structure and properties of kaolin.
Kaolin is a clay mineral with silicate and aluminate as its main components and has a layered structure. The silicon-oxygen tetrahedron and aluminum-oxygen octahedron in its crystal structure are interconnected by shared oxygen atoms to form stable layered silicate minerals. Kaolin has good plasticity, adsorption and ion exchange, so it is widely used in ceramics, papermaking, rubber, coatings and other industries.
Physicochemical changes during calcination.
During the calcination process, kaolin undergoes physicochemical changes such as dehydroxylation, dehydration, and crystal structure transformation. As the temperature increases, the hydroxyl group (-OH) in the kaolin is gradually removed, forming an amorphous metakaolin. As the temperature continues to rise, metakaolin is gradually dehydrated to form an amorphous aluminosilicate gel. In this process, the crystal structure of kaolin is destroyed and the active ingredients are released, forming a material with higher activity.
Migration and reaction of active ingredients.
During the calcination process, active ingredients such as silica (SiO2) and aluminum oxide (Al2O3) in kaolin migrate and react. These active ingredients can react with water or other chemicals to form silicate and aluminate gels, which increase the strength and durability of the material. In addition, these active ingredients can react with other mineral components to form new mineral phases, further improving the properties of the material.
Third, the process.
Preparation of raw materials. Fly ash containing kaolin is selected as raw material, and pretreatment is carried out through crushing, screening and other processes to remove impurities and obtain raw materials with suitable particle size.
Ingredients and mixing.
According to the product requirements, mix the appropriate amount of fly ash and additives in a certain proportion to obtain a slurry with good fluidity.
Forming and drying.
The slurry is injected into the mold and then dried. Temperature and humidity need to be controlled during the drying process to prevent cracking and deformation.
Calcination and cooling.
The dried products are placed in a calciner for calcination. The calcination temperature and time should be adjusted according to the raw material composition and product requirements. The calcined products are subjected to natural cooling or forced cooling to room temperature.
Crushing and grading.
The cooled product is pulverized to obtain the desired particle size distribution. It is then graded to meet the needs of different application areas.
4. Conclusions and prospects.
Through the in-depth understanding of the principle and process of calcined kaolin in fly ash, we can draw the following conclusions: through reasonable batching and process control, the kaolin resources in fly ash can be effectively used to prepare materials with excellent propertiesThe physicochemical changes during the calcination process are one of the key factors in improving the properties of materials;In the future, new process technologies and equipment can be further researched and developed to improve product quality and reduce production costs, and provide more possibilities for high-value utilization of fly ash.