Open-Circuit Grinding VS Closed Circuit Grinding: What Are the Differences? Which One Is Better?

Grinding process is a vital part of the mineral processing plant. There are two types of grinding process: open-circuit grinding and closed-circuit grinding. What are the differences of these two grinding process? Which grinding process are more effective? These questions will be answered below.

Open-circuit grinding means that the material passes directly to the next mill or the next process after the primary grinding.

The advantage of open-circuit grinding is that the production process is relatively simple and the investment cost is low. And its disadvantage is that open-circuit grinding has lower production efficiency and generates greater energy consumption during operation.

Closed-circuit grinding means that the material passes through primary grinding and classification, then the ore with unqualified particle size is returned to the mill for regrind, and finally the ore with qualified particle size is sent to the next process.

Closed-circuit grinding has high-efficiency crushing rate, so the product quality obtained is higher, and at the same time, the output of closed-circuit production is larger. But the main disadvantage is that the closed-circuit production process is more complicated and the investment cost is relatively larger.

In closed-circuit grinding, more minerals can be fed into the grinding equipment, so that the energy of the ball mill can be fully utilized, and the use and production efficiency of the grinding mill can be improved.

Ball mill is not suitable for open-circuit process. Because ball mill itself does not have the ability to control grinding particle size, there are both qualified fine particles and unqualified coarse particles in the discharge.

On the contrary, rod mill is suitable for open-circuit process. The coarse ore existing between the steel rods will be crushed preferentially, and the upwardly moving steel rods are similar to several grid bar screens, and fine-grained materials can pass through the gaps between the steel rods. Therefore, the rod mill has the ability to control the particle size and can be used as a grinding equipment for open-circuit grinding.

The ball mill can control the particle size with the aid of the classifying equipment. The mill discharges the ore into the classifying equipment. The qualified fine-grained materials enter the next process through the grinding and classification cycle, and the unqualified coarse-grained materials are returned to the mill for regrinding. 

Therefore, the unqualified coarse-grained materials for closed-circuit grinding may pass through the mill several times and must be ground to a qualified particle size before being discharged by the classification equipment. There are almost no restrictions on the grinding equipment that can be selected in the closed-circuit grinding stage.

Depending on the nature of the ore and the separation process, the requirements for the fineness of grinding are different. The appropriate degree of dissociation for different materials is different. Before operation, you should determine the nature of the mineral based on the test firstly, and then decide which grinding process to use.

In closed-circuit grinding, most of the materials returned to the mill are relatively close to the qualified particle size, and only need to be re-grinded slightly to become qualified products. In addition, When the material in the mill increases, the speed of the material passing through the mill will increase and the grinding time will be shortened. 

Therefore, closed-circuit grinding has the following advantages: high productivity, avoiding over-crushing, finer and uniform product size. Generally speaking, flotation plants and magnetic separation plants mostly use closed-circuit grinding processes.

Open-circuit grinding is generally used in two-stage grinding as the first stage of grinding process. The material discharged from the rod mill enters second grinding equipment for fine grinding. In this way, the first-stage rod mill has a smaller crushing ratio and higher production capacity, and open-circuit grinding process is simple.

The above mainly introduces the characteristics of open-circuit grinding and closed-circuit grinding, the use of related grinding equipment and practical applications. But the choice of grinding process is more complicated and requires comprehensive consideration of material properties, investment costs, technological processes and many other aspects. It is recommended that mine owners consult with mining equipment manufacturers with mine design qualifications to avoid economic losses.

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