Classification work in the grinding and classification process

Grinding and classification is a subsequent process after crushing and screening within the scope of ore preparation. The position and role of this classification operation in the process are divided into five categories.

1. Pre-grading

Pre-classification is generally not used before the first stage of grinding. It is only considered when the feed size is less than 6-8mm and the qualified product content in the feed is greater than 15%. The main function of pre-classification in the process is to pre-separate qualified products of the feed ore in order to increase the processing capacity of the mill, or to separate secondary ore slime for the next step of processing.

2. Fully closed circuit grinding inspection and grading

The function of closed-circuit grinding inspection and classification is to control the particle size of the grinding products. The classified sand is returned to the mill to increase the ore throughput per unit time and improve the production capacity of the mill. However, the circulating load of the returned sand will affect the production capacity of the mill.

Inspection and classification in the first and second stages of grinding can make the mill work effectively, avoid over-grinding and meet the grinding fineness requirements of the next stage of separation. Therefore, inspection and classification operations are always necessary.

3. Overflow control classification

Overflow controlled classification is used when a very fine final product must be obtained in the first stage of grinding, when stage separation is to be carried out in the first stage of grinding, or when hydrocyclone classification is to be used and the coarse particles must be removed in the mechanical classifier first.

4. Return sand control and classification

返砂控制分级的目的是降低返砂中合格产物的含量，效果虽不甚显著，且需增设分级机，增加配置的复杂性，但在实践中仍有采用。

5. Inspection and classification of local closed circuit grinding

The inspection and classification of local closed-circuit grinding is both the inspection and classification of the first stage of grinding and the pre-classification of the second stage of grinding. The main feature of this classification process is that the change of the load of the second stage mill is not through overflow, but through sand settling, so the load between the two stages of grinding mills is easy to distribute and adjust. However, this classification process also has disadvantages. A large amount of ore mud is removed in the first stage of classification, which greatly reduces the amount of ore mud in the second stage of classification, reduces the viscosity of the ore pulp, and makes the classifier unstable.