Grinding concentration refers to the concentration of the slurry within the grinding mill. Grinding fineness refers to the content of a specified grade in the mill discharge. Grinding concentration and grinding fineness are interconnected and mutually influential, and are mainly controlled by adjusting the grinding feed water (post-grind water) during production operations.

In open-circuit grinding, factors affecting grinding concentration include the properties of the raw ore (mainly particle size distribution), feed rate, and feed water. Factors affecting grinding fineness, besides the particle size distribution of the raw ore, include grinding concentration and balling regime. When the properties of the raw ore change, if coarse particles increase, the feed rate should remain constant, and the post-grind water should be reduced to increase the grinding concentration to ensure grinding fineness; if fine particles increase, the post-grind water should be increased, and the feed rate should be appropriately increased to reduce over-grinding. Under the condition of keeping the ore properties and media conditions constant, within a certain range, grinding fineness generally increases with increasing grinding concentration, and vice versa. In summary, the grinding concentration is adjusted by regulating the feed water flow, thereby controlling the grinding fineness.

In closed-circuit grinding, the situation becomes more complex, as the amount of returned sand becomes a factor. With a fixed feed water, increasing both the original feed and returned sand will increase the grinding concentration, and vice versa. Grinding fineness is affected not only by the amount of returned sand but also by the classification efficiency. When the amount of returned sand is large, the overall feed particle size distribution changes, increasing the amount of fine particles and resulting in a faster grinding speed. In this case, the grinding concentration should be appropriately reduced, and the discharge speed increased to reduce over-grinding. Conversely, when the amount of returned sand is reduced but the original ore is coarser, the amount of water supplied should be reduced to increase the grinding concentration.