Blog: Improve thickener operations by measuring density 2/3
Posted on Friday, 24 January 2020 at 16:06
In a series of blogs we highlight ways to improve the thickening process. Last week we described the importance of water recovery for the mineral processing plant and this week we will focus on investments that help to improve the recovery of valuable minerals.
Mineral recovery is done using the so-called product thickeners. Thickeners are very important to the processing plant, because if the material fed into the thickener is not getting out of its underflow, this leads to less overall metal recovery. First we will explain how product thickeners, in this case concentrate thickeners, operate and then we will highlight the advantages of density measurement for process control.
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 are not attached to air bubbles remain in the liquid phase. If the same event occurs in the thickener tank, foam could carry valuable materials into the overflow. When these valuable materials are not 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.
Example of foam issues at a concentrate thickener in a phosphate plant
Once solids are lost into the overflow of concentrate thickeners, almost 90% will be regained in later stages of the process, such as tanks and dams according to Outotec. However, not all valuable material will be recovered in the process. The other 10% will be lost and represents a high economic value. Therefore, reducing the amount of solids lost in the overflow should be prioritized. Investments in process control equipment can lead to higher recovery rates and this will eventually generate easy returns.
The density value (or mass flow) can be used to monitor and improve the thickening efficiency. A density meter together with a flow meter in the underflow can help to check the productivity of the thickener, while solids can be detected real-time using a density or solids meter in the overflow. The 4-20mA signal of the instruments can be used for direct process control, such as dosing flocculants, controlling the underflow pump speed, the energy of feedwell mixing and more.
Please contact Rhosonics if you want to learn more about the importance of density measurement in the thickening process. Also, you can click here to read the first blog about water recovery in the thickening process.
Example of different measurement points at a thickener tank