Correctly placing sampling systems in strategic locations makes all the difference in determining ore grade. The right location for a sampling system depends on the characteristics of each process, as well as what results are expected from the sample.
Generally, to determine the entrance mineral grade (or the mine grade) at concentrator plants, the sampling system is located after the grinding process and before the cyclone batteries. This has important advantages, but mainly that the particle size is 80 percent under 150 µm. The material to be processed here is pulp, with solid percentages between 25 and 35 percent and densities of +/-1.3.
Another advantage of placing the sampling system in the right location is that less equipment is required when compared to a system installed upstream, prior to grinding. This is possible as long as there are no process changes in the grinding, such as the addition of reagents that modify the conditions of the minerals. If these changes occur, the installation should be evaluated in the stages prior to grinding.
The installation of a pre-grinding sampling system also has some restrictions and the viability of developing a project in that area will depend on the particle size. For example, if it is necessary to install a system in the SAG mill, particle sizes tend to be too large, which makes it difficult to design the primary cutter and crushing stages, where large equipment is required and there is limited space. Some options have been evaluated but due to the high investment needed, these have been discarded by customers.
In post-crushing applications, sampling becomes technically and economically viable and accessible.
A fundamental and recommended application is when an operation does not have its own mine or the ore it extracts is not sufficient to meet the demands of its clients. In such cases, the operation is forced to acquire ore from third parties. Just like any other product that is commercialized, the value will depend on the quality. For that reason, it is necessary to know the grade.
For the most part, there are several suppliers that provide ore to the same company and the need to quantify the quality of the ore from each will result in clear conditions for both parties.
It is also critical to control the product. In many operations, each stage of the sampling process is carried out under strict, automated management to avoid human intervention, leaving out the possibility of sample contamination and fraud, which has occurred to the benefit of some of the parties.
A sampling system for particulate material, like any other type of sampler, is subject to a series of regulatory requirements so that the sample can meet its main objective: to be representative and manageable for the operator. It is also important that, depending on the process, the sample be divided into two different lines to obtain a chemical sample and a particle sample.
The systems are designed according to the process conditions and the available space if the operation is already underway.
A sampling system for this application usually has a straight path cutter, which is located at the discharge of a conveyor belt to obtain the increments from the main flow. Each of these increments is discharged to a conveyor belt that is part of the sampling system and doses the material to the secondary straight path cutter that divides the sample into chemical and granulometric lines.
In the case of the chemical line, a reduction in the size of the ore is realized by installing one or two crushing stages (crushers) to better control sampling errors. The rejects produced by the system must be returned to the downstream process and according to the configuration, they can be handled by gravity, conveyor belts or elevators.
Promi-Mex was founded in 2014 in Saltillo, Coahuila, and is specialized in the development of technologies and equipment used in the area of mineral processing and related industries.