Blog: why dry tailings is important

Posted on Wednesday, 10 August 2022 at 02:42

In this blog, we will share more information about the important reasons for density measurement in the process of dry tailings, and how important it is to maximize the water recovery in that process.

To extract valuable minerals, mining companies have to move large amounts of earth. The waste resulting from this process is usually stored in a large pond, as a semi-liquid known as tailings. It is expected that these ponds are stable enough to withstand the pressure of the stored material, however, unfortunately, history shows that this is not always the case. Some dam failures in 2015 and 2018 resulted in the loss of many lives and environmental destruction on an unprecedented scale.

Dry stacking

Current generation engineering has shown that an alternative process known as dry stacking is a practical solution to semi-liquid tailings. In addition to achieving the dry tailing benefits, it is possible to recover valuable process water while dewatering the tailings sludge utilizing modern separation technology.

With environmental sustainability being seen as a key factor in modern mining, the method of dry stacking tailings is becoming increasingly popular. Dry stacking can eliminate concerns related to potential dam failures. According to CRC Care 2013, every year more than 10 billion tons of tailings are produced by mining activity. Globally, many mining sites struggle due to insufficient amounts of fresh water intake available in their regions; the dewatering process can capture as much as 90 percent of the water for reuse.

Dry tailings are typically achieved through a multi-step process. The sludge is thickened or concentrated through gravity settling in a thickener. The concentrated sludge is withdrawn from the bottom and clarified water exits through the overflow of the thickener. The thickened sludge is then processed through one of several types of mechanical dewatering machines to achieve dry tailings for stacking. Three devices proven to have various degrees of success with dewatering the thickened sludge are: belt presses; plate and frame chamber filter presses and decanter centrifuges.

Main benefits of dry tailings:

  • Optimized footprint of tailings storage and minimized fresh water intake
  • Reduced dam construction with decreased operational costs
  • Lower tailings risks and insurance rates
  • Easier permitting and socio-political acceptance
  • Low environmental impact and savings at the rehabilitation
  • Resistance to high seismic activities

Why density control is important

In the process of dry tailings, which is just one step ahead of the thickening process, the density value can be used to monitor and improve the efficiency of the dewatering process.

In a dewatering plant using a filtering station, a density meter in the inlet of the filter allows control over the %solids being fed to the dewatering process, which must be within a certain range as established by the supplier of the filtering station based on the type of ore and tailings. Keeping density stable means a more efficient dewatering process, resulting also in better water recovery. By measuring density and flow in the inlet of the filtering station and calculating the mass flow, it is possible to then calculate the efficiency of the dewatering process based on the amount of dry solids from the outlet. In theory, the amount of solids being fed to the station should not differ much from the amount of solids in the outlet.

Benefits of density control in the dewatering process

It was mentioned before that there are different modern dewatering technologies, and Rhosonics density meters have been used also in Decanter centrifuges. This type of equipment requires the use of flocculant in the separation process, therefore, a density control on its inlet allows for precise dosage of such polymer, which will result in a highly efficient dewatering process. See the figure below.

Processing plants ideally want to have steady operating conditions, with an efficient and sustainable process. However, process conditions are subject to changes over time. When changes occur, real-time instrumentation and automation can help operators to keep control over the processes.

Main benefits of density measurement in dewatering processes:

  • Maintain steady operations
  • Efficient polymer dosing
  • Improve water recovery
  • Mass calculation

Please contact Rhosonics if you want to know more about the importance of density measurement in the dewatering process.

Source: website Outotec

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