CASE STUDY

Dry Tailings Storage using Geotextile Tubes

ABOUT ZEBRATUBE®

ZebraTube® has its origins in the manufacturing of large dewatering bags for the deepest mines in the world. We have more than two decades of experience in retaining solids and percolating liquids through our woven geotextile bags.

ZebraTube® products are designed and manufactured in South Africa. Our geotextiles are produced and woven locally by experienced weavers and thereafter converted to dewatering bags. Our complete control over the manufacturing process allows for design flexibility and speed of delivery. We cater for both large and small projects and our ease of deployment means ZebraTube® is ideal for emergency dewatering projects.

Each roll of geotextile goes through a comprehensive set of tests at our factory to ensure absolute quality and traceability. Extruded strands are tested before weaving for tensile strength and, once woven, each roll of geotextile is tested for tensile strength and permeability.

 

Background

Dry tailings storage has received increased interest in the past few years as recent tailings dam failures shed the light on the risks associated with wet tailings management.

ZebraTube® conducted a trial at gold processing plant in South Africa in order to establish dewatering efficiency using ZebraTube® geotextile dewatering tubes on gold tailings.

ZebraTube® ran two separate trials. The first utilised a low flow geotextile 5 m circumference x 10 m length dewatering tube and allowed for 4 weeks of standing time after pumping was complete. The second trial used two off 5 m circumference x 5 m length dewatering tubes and allowed for two weeks of standing time after pumping was complete

Figure 1: Bags laid out before trial commencement
Figure 2: Contained material after 1 month standing time

 

Feed Material

The apparent opening size (AOS) of the ZebraTube®’s Low Flow geotextile is 207 µm. The feed slurry had a solids concentration of 34%. The particle size distribution of the feed slurry, shown in Figure 3, indicate that 4.35% of the material is below 10 µm in size, whilst the majority of the material is above 100 µm. Whilst the AOS is 207 µm, the blinding of the geotextile and the related formation of a filter cake on the surface of the geotextile results in the efficient retention of fines below 10 µm.

For this specific PSD, no flocculant addition is required to act as filter aid for the retention of fines.

Figure 3: Feed material particle size distribution

 

Filling of the tubes

The dewatering of sludge by means of geotextile tubes is a cyclical process. A schematic illustrating this concept is show in Figure 4.

During the initial filling cycle the dewatering tube is filled to the maximum design height and pumping is terminated. Static drainage then commences. After sufficient dewatering the tube can then be refilled. This process is repeated until the tube is completely filled. Thereafter further consolidation occurs and the dewatering process allows for the solids concentration of the dewatered material to increase, as illustrated by the red line shown in Figure 4 below.

Figure 4: Dewatering cycle using geotextile tubes (Lawson, 2008*)

 

Dewatering efficiency

The solids concentration of the feed slurry was analysed as 34% solids. For each trial the moisture content of the dewatered and contained material were analysed following varying periods of standing time, as shown in Table 1.

Dewatering efficiency is a measure of the capacity of a geotextile to allow permeation of water without the loss of solids and is calculated as follows:

where PSfinal is the percentage solids in the contained material and PSinitial is the percentage solid in the slurry feeding the tube.

 

Benefits of utilising geotextile tubes for dry tailings storage

The following summarises the primary benefits of utilising geotextile tubes for dry storage of tailings:

  • Risk of tailings dam failure is eliminated.
  • Rapid dewatering of large sludge volumes within a short period.
  • The ability to easily scale the dewatering process in-line with production requirements.
  • Minimal skilled labour required, with low labour requirements overall.
  • Simple auxiliary equipment required, with minimal maintenance requirements and low energy usage.
  • The stackability of tubes enable efficient usage of the laydown area, reducing the overall footprint required.
  • Improved water recovery as the filtrate can be captured, allowing for ease of monitoring and containment for recycling, re-use or disposal.
  • Lower up-front capital expense.
  • Improved access to dewatered tailing for secondary processing or salvage value.
  • Lower rehabilitation costs.
Figure 5: Filled tube (Trial 1)

* Lawson, C.R. (2008) Geotextile containment for hydraulic and environmental engineering, Geosynthetics International, 15 No. 6: pp. 384-427, IGS.