Progress on Hydraulic Dewatered Stacking (HDS)

Mineral processing operations commonly use large amounts of water for the recovery of valuable minerals. This ultimately results in the production of large volumes of wet tailings which are routinely disposed in conventional tailings storage facilities. If not safely constructed and maintained, they pose a major risk to communities and the environment. Eliminating these facilities is a key objective for a safe and sustainable mining industry.

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What is Hydraulic Dewatered Stacking?

Hydraulic Dewatered Stacking (HDS) is an innovative concept for tailings management developed after the successful implementation of Coarse Particle Recovery (CPR). It is desaturated storage technology that delivers a new way to safely dispose of mining by-products and accelerates our progress towards the end of wet tailings storage. Ultimately, it allows us to reclaim and reuse water, our most precious and undervalued resource, and create stable, dry, economically viable land, long after mining ends.

Three main advantages of HDS

Safety

By dewatering the tailings and eliminating the surface pond, HDS improves the stability and safety of tailings storage, a key element of the Global Industry Standard on Tailings Management (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.

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 the demand for fresh water (or desalinated), 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.

Legacy

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, accelerating the stabilisation of the facility. 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 realised quickly at the end of mining operations.

Work at El Soldado, Chile

A bespoke 150,000m³ capacity HDS tailings facility has been built at the El Soldado copper mine. The sand transportation and placement system was commissioned in August 2022 and tailings placement commenced at the start of November 2022.

Early results measured water recovery at more than 80 percent, and the extensive instrumentation is confirming that the tailings remain unsaturated.

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