Thickeners in mineral processing can be monitored and improved by measuring density in the feed of the system, in the feedwell and in the underflow. Combined with a flow meter, the mass flow can be calculated, giving real-time insights into the efficiency of the thickener operation.

In mineral processing operations, water is very important and therefore water recovery plants have an important position. According to CRC Care 2013, mining activities are producing more than 10 billion tonnes of tailings. Also, they use thickeners as a water recovery system, to meet requirements in the recovery and reprocessing of water. A growth of 1 or 2% in underflow density can return large amounts of water to the operating installations. The increasing of density is also important to avoid accidents in tailings dams, which can collapse when there is too much liquid pumping to the dams.

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Measuring density in thickening process

Compared to other technologies, you can process high volumes of slurry at a quite low cost by sedimentation using thickeners in mineral processing. The two outputs, underflow and overflow, are not often prioritized at the same time. In tailings applications where water recovery is a requirement, underflow is a target. But in concentrate applications, the overflow measurement is essential. Otherwise, the important material will return to the concentrator and will lose recovery.

With a thickener, the solid-liquid separation is mainly done by sedimentation. A thickener has several layers, the upper layer being clarified water. Below the clarified water is the interface, this is solids and water. Under this layer is mud and the lowest layer is heavy mud. Companies use sedimentation to produce two phases by thickening the incoming feed stream. In the ideal situation, the overflow contains minimal solids, and the underflow contains minimal liquid. That is why it is very important to measure the density.

Thickener optimization

Thickeners are very important to the processing plant, because if the material fed into the thickener is not getting out of its underflow, it will lead to less overall metal recovery.

In concentrate thickeners, the feed usually comes from the flotation circuit. The concept of the flotation process is that desired particles attach to air bubbles and are carried to the surface and removed from the cell, while the particles that aren’t attached to air bubbles remain in the liquid phase. If the same event occurs in the thickener tank, the foam could carry valuable materials into the overflow. When these valuable materials aren’t recovered, this will lead to a lower overall recovery of concentrator metal at the processing plant. This event can also lead to extra reagent costs, damage to pumps and valves and costs for cleaning process water tanks where the solids could eventually deposit.

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