The use of steel slag as a sintering flux is a relatively mature method for the secondary utilization of metallurgical slag. It is widely adopted by steel plants both in China and around the world, generating significant economic and social benefits.
Common issues that arise during its application include:
1. Inconsistent particle size and unstable composition of steel slag, which cause significant fluctuations and create numerous challenges for sintering ingredient control and process management.
2. Reduction in vertical sintering speed, prolonging sintering time and adversely affecting the sintering utilization coefficient.
3. Decrease in the iron grade of the sintered ore. When the iron content of the sintering raw materials is high, adding steel slag reduces the iron grade of the sintered ore, negatively impacting blast furnace smelting.
4. Phosphorus enrichment resulting from the addition of steel slag in the sintering process. Phosphorus removed during steelmaking enters the steel slag; when this slag is used in sintering, phosphorus re-enters the hot metal. Repeated recycling leads to phosphorus accumulation, increasing the phosphorus content in the sintered ore.
Treatment methods include:
1. Controlling the amount of steel slag added during sintering can resolve most of these issues.
2. After crushing and screening converter steel slag, establishing an appropriate mixing yard to achieve homogenization, ensuring the composition and particle size of the steel slag meet sintering requirements.
3. Magnetic separation of steel slag can improve its iron grade. However, this method has a narrow scope of application and is only effective for steel slag with high iron content.
4. Measures such as optimizing the raw material structure, reducing fuel consumption, adding coarse ore powder, reasonably controlling the basicity of the sintered ore, increasing effective air volume, and implementing negative pressure operation can be employed to enhance sintering speed.
5. Under certain conditions, adding specific substances to modify the steel slag can help aggregate dispersed phosphorus into a single phase or convert it into gas, thereby achieving dephosphorization. Current main methods for steel slag dephosphorization include reduction, flotation, magnetic separation, and other treatment techniques.