Tailings is an area of mining where the industry is constantly seeking new approaches and ideas. They are an inevitable byproduct of the mining process but require extensive management to protect people and the environment. Recent catastrophic failures have rightly resulted in enhanced oversight and calls for change. Through the Global Industry Standard for Tailings Management (GISTM), mining companies are now actively adopting new levels of governance to increase the safety of tailings storage facilities (TSFs).

Governance alone is not the solution, however. Identifying new methods and technologies for managing tailings is imperative. Those methods must be robust, practical, and economical at scale; ideally, they should also minimize any increase in operational complexity at the facility. An innovative tailings management concept, hydraulic dewatered stacking (HDS), appears to tick all these boxes. It is being developed by global mining major, Anglo American, who partnered with WSP to conceptualize and design the new approach. 
  

Innovation breeds innovation

The idea for HDS was born out of the adoption of coarse particle recovery (CPR) at Anglo American’s El Soldado copper mine in Chile. CPR results in a free-draining sand byproduct, which the mine believed could be put to beneficial use. Reaching out to WSP, Anglo American’s question was a simple one: could this waste be turned into a resource? The answer quickly became a resounding yes.

The concept devised by the combined Anglo American-WSP team uses CPR sand as a filter, co-disposing it with tailings to deliver passive drainage and gravitational dewatering of the tailings. The water is then managed separately for re-use in the mining process.
  

The key benefits

The HDS concept thus delivers benefits well beyond just finding a use for CPR sand. The three main advantages studied relate to water, stability, and closure.
 

Water

Conventionally deposited tailings contain a large amount of entrained water with supernatant water typically managed on the surface. This results in large amounts of water being lost through entrainment and evaporation: water losses from tailings are in fact the most significant water loss at the majority of mining operations.

In contrast, HDS liberates the water entrained in the tailings and allows it to be recycled. This reduces demand for fresh water (or desalination), and therefore the overall water sustainability of the mine. In water-stressed regions, this is a significant benefit, not only for the environment, but also to the mine’s bottom line, as the financial cost of water is expected to increase substantially over time. 

Stability

By dewatering the tailings and eliminating the surface pond, HDS improves the stability and safety of tailings storage, a key element of the GISTM. Meanwhile, in the event an HDS facility does fail, the lower interstitial water content and surface pond volume reduces the potential for flow, and thus the potential area of inundation. The dewatered tailings simply do not flow well, making the large-scale mudslides associated with previous tailings dam failures a thing of the past.

HDS technology delivers this without the need to build capital-intensive plant, as in other thickened and filtered tailings solutions. It is therefore able to offer similar benefits, at a fraction of the cost. The free-draining nature of HDS may also make the process suitable for tailings dewatering in tropical climates, which aren’t well suited to the operational complexity of filtered tailings.
 

Closure

The interbedding of sands or installation of vertical sand drains within the tailings mass results in much more rapid consolidation than in traditional wet tailings impoundments, reducing the potential for large-scale subsidence over time. Tailings can also be deposited in cells, which facilitates progressive closure and reclamation over the life of the mine. Finally, because the HDS facility remains free draining after closure, the risk of re-saturation and long-term seepage of contaminated water is significantly reduced, even in areas of high precipitation, with reduced potential for groundwater contamination. 

As a result, closure planning is simplified; there should also be less need for long-term monitoring campaigns. Repurposing of the land can be realized quickly and handover should thus be possible much more quickly at the end of mining operations. 
 

Moving from idea to reality

Drawing on WSP expertise in mine waste, hydrogeology, advanced labs, pumping and pipes - to name just a few - the initial idea has been developed through a series of concept studies and lab trials and is now being tested in the field at Anglo American’s El Soldado mine in Chile. Here the technology is being tested at large scale, with further research underway on the performance of the tailings, as well as closure trials. The early results are extremely promising, with excellent dewatering, consolidation, and water recycling rates already achieved. Read more about the trial.

There is more to be done before HDS becomes a common feature at mines around the world. Data collected at El Soldado is now informing a second planned trial at a mine in South Africa, where the potential for conversion of an existing TSF to HDS is to be studied. There is also potential for benefits beyond those mentioned here, with the team studying whether the HDS facility could be used for carbon storage at closure, and other exciting potential post-closure land uses. 

The development of this innovative new tailings technology marks a step forward in the mining industry’s commitment to improved safety and environmental sustainability.