Production of polycrystalline silicon by chlorination from rice husk and purification of chlorine-containing gases by adsorption method

Introduction. In the article we analysed the technology for producing silicon from rice husks. The analysis showed that the production of polycrystalline and amorphous silicon based on rice waste in the form of rice husk solves the simultaneous disposal of rice waste. Rice husk processing produces valuable organic products, and the residual solid waste mainly contains silicon, carbon and other trace metal elements. Therefore, obtaining silicon and silicon-containing materials from rice husk is relevant. Methods and materials. Various methods for obtaining silicon from rice husk are given. Among them, the methods of chlorination and sublimation were chosen, and experimental installations were assembled to conduct the experiment. The object of study was samples obtained from rice husks of Uzgen rice in the Kyrgyz Republic. Results. The composition and structure of rice husks for the production of crystalline silicon were studied. Lime milk was used to purify toxic chlorine-containing gases in the air of the working area and atmospheric air. The condensing system, designed to capture volatile chlorides, has two receivers. In the first receiver at a temperature of 60°C, condensation of iron, aluminum and magnesium chlorides occurs. It has been established that highly volatile silicon (IV) chloride (SiCl4) at a given temperature remains in the gaseous phase and is completely distilled off in the next receiver of the refrigerator. This indicates that the silicon is in the form of SiCl4 (60°C) and condenses only at a lower temperature in the next receiver. The data obtained indicate that when the temperature rises to 200°C, the process of chlorination of metal compounds initiates. The optimal conditions for maximum extraction of metals and silicon tetrachloride from rice husk were identified: temperature 500–550°C and time 120 minutes. Non-volatile chlorides of calcium, sodium, potassium and other elements form a floating mixture at 450°C. During the reaction, metal chlorides harden and settle on the cold walls of the reactor. Therefore, at this temperature there is not enough heat to maintain them in a gaseous state, and they condense to form solid precipitates. Lime milk containing CaO – 130 g/dm2 is a very effective and cheap means for purifying toxic chlorine-containing gases in the air of the working area and atmospheric air. At high temperatures (1050–1100°C), it is possible to activate chemical reactions between the carrier gas (hydrogen) and silicon chloride (SiCl4), which promotes the decomposition of SiCl4 into components, including silicon and hydrogen chloride, and also provides certain conditions for the formation and deposition silicon crystals. Conclusion. A technology for producing polycrystalline silicon by chlorination from rice husks of Uzgen rice of the Kyrgyz Republic has been studied and developed.