Solidification behavior and mechanism of K and Na in converter dust-based coolant

Converter dust is a metallurgical secondary resource rich in iron oxides. It is prepared as a coolant and returned to the converter for recycling,which can efficiently recover the iron resources. However,the content of alkali metals such as potassium and sodium in converter dust is high. In the process of preparing coolant by grate-kiln process,alkali metals are prone to volatilize in the preheating section of the grate,causing equipment bonding and affecting stable operation. To address this issue,converter dust and iron concentrate powder were used as raw materials. The raw material ratio of converter coolant produced on site was taken as the benchmark, and a single-factor variable method was adopted to design the control and experimental groups. By adjusting the proportions of limestone and bentonite in the raw materials,the solidification mechanism of K and Na was investigated through briquetting. The drying-preheating process of the coolant briquette samples was strictly simulated according to the thermal regime of the on-site grate. A BFD-1200 blast-exhaust drying high-temperature box furnace was used to simulate the drying section of the grate,and a CVD three-stage high-temperature tube furnace was employed to simulate the working conditions of the first and second preheating sections of the on-site grate. The phase composition,microstructure and chemical composition of the coolant briquettes were systematically characterized by means of X-ray diffraction,FactSage thermodynamic calculation, SEM-EDS and chemical analysis. The optimum raw material ratio was determined, and the alkali metal solidification mechanism was clarified. The results show that the main components SiO₂ and Al₂O₃ in bentonite can react with K₂O and Na₂O to form KAlSiO₄ and NaAlSiO₄,which can effectively solidify K and Na elements,inhibit their high temperature volatilization,and reduce the adverse effects on field production. With the increase of bentonite addition,the K and Na elements in the system were significantly solidified. When the bentonite addition reached 4%,the curing of K and Na basically tended to be stable, and the curing rates of K and Na elements were 85.8% and 74.6%,respectively. The high temperature curing law of alkali metal revealed in this study also provides an important theoretical reference for the harmless disposal and resource utilization of other alkali-rich metal metallurgical secondary resources.