Pregrinding

Pregrinding is a stage in a grinding circuit where the material is ground to a relatively coarse product prior to the final, finer grinding step. The approach is used to reduce the energy and equipment requirements of the subsequent grinding stage and to improve particle size distribution and liberation of valuable minerals or components.

In mineral processing, pregrinding is implemented with equipment such as high-pressure grinding rolls (HPGR), roller presses, or rod mills located ahead of a ball mill or vertical roller mill. The goal is to create a product with a higher proportion of fines before the main grinding stage, which can lower specific energy consumption and increase throughput. It is common in two-stage grinding circuits and in operations focused on liberation of ore minerals.

In cement production, pregrinding refers to the use of a roller press or a similar device to pregrind clinker and additives before final grinding in a ball mill or vertical roller mill. This arrangement reduces the work performed by the finish mill and can yield substantial energy savings, often reported in the range of 20 to 40 percent depending on plant design and materials.

Benefits include lower energy use per ton of finished product, increased production capacity, and better control of particle size distribution. Drawbacks include higher capital and maintenance costs, more complex process control, and potential for increased circulating loads or overgrinding if not properly managed.

Design considerations include feed characteristics, desired fineness, equipment choice, and integration with classifiers and downstream mills. Pregrinding is a widely used strategy to improve energy efficiency in grinding-focused industries but requires careful optimization to balance gains against costs.