There are different points for measuring density in the grinding circuit. One of the applications is to monitor the dilution of material in the ball mill discharge, to improve the efficiency of the process. Another important application is to monitor changes of density in the cyclone underflow. This is to check the process stability and increases or decreases of circulating load.
Water impacts the grinding process, therefore the efficiency of the ball mill can be greatly improved by better water dosage. This alone could improve the efficiency by 5-15% according to “911 metallurgist”. When combined with a control strategy, the improvement rate could be even higher.
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measuring density in grinding circuits
In general lines, the grinding circuit is composed of a powdering or pulverizing process and a classification process. In most sites a ball mill is used for grinding, to produce fine particles, and a (hydro) cyclone for classification, to separate the fine particles from larger particles. The main goals when controlling the grinding circuit are to maximize the throughput and to decrease the variability of product size and % solids. Material that meets the product size requirements gets removed from the circuit and oversized material gets recycled back to the grinding mill for further comminution. To achieve these objectives the slurry needs to be continuously monitored and controlled, allowing process stabilization and ensuring optimal grinding conditions.
Measuring technologies, such as density meters, helps operators to monitor and control the grinding circuit. It also optimizes it and prevents process failures. When used together with an advanced control system, density readings allow automatic control valves, pumps and have an efficient water addition. This results in the improvement of the process that can lead to higher recovery.
In the grinding circuit, possible installation points are in the ball mill discharge and feed (recirculation), (hydro) cyclone feed, overflow and underflow.
The grinding circuit is mostly considered as the first step of a processing plant. Therefore, operators need to have good control over it. One way to follow changes in the circuit is by measuring slurry density, which is manually done in many sites. The manually taken density sample can be used as a parameter to indicate if the grinding process is operating steadily.
However, manual sampling does not allow to have a trend for real-time control. It is recommended to use an in-line measuring device. This allows to detect changes online (real-time) as it happens. As an example, a recommended application to efficiently dose grinding media (balls) and water into the ball mill is measuring density changes in the ball mill discharge.
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