The external circulation steel slag vertical mill process transforms steel slag into high-value-added building material raw materials through efficient grinding, graded magnetic separation and energy-saving design, achieving a win-win situation of waste resource utilization and economic benefits.

Abstract: The external-circulation steel slag vertical mill process is a key technology for resource utilization of steel industry waste. Through efficient grinding, graded magnetic separation, and energy-saving and environmentally friendly design, it achieves high-value-added conversion of steel slag. This article systematically explains the core principles and engineering value of this process from the perspectives of process flow, technical advantages, application cases, and benefit analysis, providing a reference for the steel and building materials industries.

1. The external circulation of steel slag is mainly used in the construction and building materials industry, and there are several ways to use it:

1. Making cement raw material: The sum of CaO, MgO, FeO and Fe2O3 in steel slag can reach 70%. These components are useful for cement. The main function of steel slag as cement raw material is to serve as an iron corrector for cement. The current addition amount in the raw material is 3% to 5%, and the process is relatively mature.

2. As raw material for steel slag cement and admixture of composite silicate cement: The current varieties of steel slag cement include clinker-free steel slag slag cement, low-clinker steel slag slag cement, steel slag zeolite cement, steel slag slag silicate cement and steel slag silicate cement, all of which have corresponding national standards and industry standards, and the addition amount is between 20% and 50%.

3. Steel slag powder as concrete admixture: The development and utilization of steel slag powder has become a hot topic in recent years following the large-scale application of slag powder. The production of steel slag powder or composite powder can eliminate the problem of difference in grindability in the production of steel slag cement. When the steel slag is ground to a certain fineness and the specific surface area is greater than 400m2Kg, the metallic iron can be removed to the greatest extent. The ultrafine grinding can reorganize the crystal structure of the material, change the surface condition of the particles, increase the surface energy, mechanically stimulate the activity of the steel slag, and give full play to the characteristics of hydraulic cementitious materials.

2. External circulation steel slag vertical mill process flow

1. Preprocessing stage

The steel slag raw materials are crushed to a particle size of ≤5mm to remove large impurities, and metallic iron is initially separated through magnetic separation to reduce the risk of subsequent equipment wear.

2. Vertical mill grinding and classification

● Feeding and rolling: The material enters the center of the vertical mill grinding disc through the discharge pipe. The grinding disc rotates at a constant speed with the help of centrifugal force to evenly spread the material into a material bed, and multiple grinding rollers use high-pressure rolling to achieve crushing.

● Hot air drying: Introduce high-temperature gas (200-300℃), dry while grinding, evaporate the moisture of the material (to <0.5%), and avoid agglomeration.

● Dynamic classification: The airflow carries the fine powder into the high-efficiency powder classifier, and the fineness of the finished product (specific surface area ≥450m²/kg) is controlled by adjusting the speed, and the coarse powder is recycled to the grinding disc for re-grinding.

3. External circulation iron removal system

● Multi-stage magnetic separation: The slag and iron mixture enters the elevator through the conveying equipment, and the iron grade classification magnetic separation is achieved through the step-by-step enhancement of the magnetic field strength (a multi-stage iron removal device is installed on the second conveying equipment), giving priority to selecting high-grade iron and reducing grinding roller wear.

● RO phase separation: remove RO phase (magnesium oxide, calcium oxide and other enriched phases) in steel slag to improve grinding stability.

4. Finished product collection and recycling optimization

Qualified steel slag powder enters the finished product bin, and the external circulation system reduces metal enrichment in the mill, reducing energy consumption and equipment loss.

The external circulation steel slag vertical mill process focuses on efficient grinding, graded magnetic separation, and energy conservation and environmental protection, providing a mature solution for the resource utilization of steel slag. Through technological integration and innovation, this process not only solves the environmental problems of steel slag disposal, but also creates significant economic benefits.