Full definition
SAG mills, or Semi-Autogenous Grinding mills, are crucial in the mineral processing industry, specifically for copper (Cu) and gold (Au) extraction. These mills utilize the ore itself as the primary grinding medium in combination with a reduced charge of steel balls, typically constituting 6–12% of the total mill volume. This unique design allows for a more efficient grinding process by using the ore's own hardness to aid in the comminution, effectively combining the processes of secondary crushing and primary grinding into a single unit. SAG mills typically have diameters ranging from 6 to 12 meters and can operate with power ratings between 5 and 25 megawatts (MW), depending on the specific application and throughput required.
Operationally, SAG mills are designed to handle large volumes of material, and their efficiency is influenced by factors such as the size of the grinding media, the speed of the mill, and the ore characteristics. The use of a smaller steel ball charge not only reduces wear on the mill components but also minimizes energy consumption, making SAG mills a more economical choice for many operations. The grinding action in a SAG mill is a combination of impact and abrasion, which leads to a more uniform particle size distribution in the output.
SAG mills are typically used in conjunction with ball mills to further grind the materials after initial reduction. In a typical grinding circuit, the output from the SAG mill is sent to a ball mill for fine grinding, enabling a two-stage comminution process that optimizes recovery rates of valuable minerals. This process is essential in modern mining operations and is a significant contributor to the overall efficiency of mineral processing plants.