Grinding and grading of ore are necessary preparations before ore dressing.
Grinding operation
The main task of the grinding operation is to realize the dissociation of useful mineral monomers and provide the appropriate size for separation operation, which is the key process of mineral processing. The mill is a hollow cylinder with a hollow shaft neck at both ends. The material enters from one end of the cylinder and the product is discharged from the other end. Grinding medium (steel ball, steel rod, or gravel) is installed in the barrel. According to the different grinding media, mills are divided into ball mills, rod mills, and autogenous mills, etc. When the cylinder rotates, the medium is brought to a certain height and falls, which impacts and grinds the material, so that the material is crushed.
Ball mill and rod mill machine are widely used grinding equipment in ore dressing plant. At the same time, some special fine grinding equipment is also used in grinding operations, such as vertical mill, centrifugal mill, Raymond mill, etc. In the grinding process, the principle of "replacement of grinding with the crushing" should be followed. It is recommended that users use ultra-fine crushing and more crushing and less grinding process to optimize and shorten the beneficiation process flow. According to the properties of different ores, the discharge particle size of the crushing process and grinding process is scientifically regulated, which increases the operating rate of crushing equipment by nearly 20% and the utilization factor of ball mills by nearly 10%, thereby reducing the total energy consumption of crushing and grinding by15%-30%.
Grading operation
The useful minerals of most ores are embedded very finely with the disseminated grain size can reach 0.1-0.01mm, or even finer. In order to separate these fine useful minerals from gangue, the ore must be ground to a certain fineness. However, if it is too fine, it will become slimy, which will affect the product quality and increase the grinding cost. Therefore, the finished product after grinding must be classified in time. According to the different sedimentation speed of the ore particles in the medium, the materials are divided into several granularity levels. The commonly used media are air and water, the use of air as the medium is called dry classification, and the use of water as the classification medium is called wet classification. In wet classification, it can be divided into hydraulic classification and mechanical classification according to the purpose of the operation and different equipment used. Spiral classifier is conventional classification equipment, which forms a closed circuit with a wet ball mill to complete grinding and classification together. The hydrocyclone is often used in the second stage grinding and grading operation, and can also be used in the first stage grinding and grading operation, and may even replace the spiral classifier.
In order to remove the gangue of ore and separate various useful minerals from each other to achieve the required particle size of separation operation. On the one hand, it depends on the separation method, on the other hand, it also depends on the disseminated particle size of useful minerals in the ore. The finer the disseminated particle size of useful minerals is, the finer the crushing grain size is. Therefore, grinding and grading is a preparatory work that must be carried out before ore beneficiation.
