Novel bauxite tailings concept a success in full operation

Hydro’s new method for storing bauxite tailings from its mine in Brazil has proven to be a more-sustainable solution. Following 18 months of extensive testing and monitoring, the site is nearing a year of full operation.

The method – called Tailings Dry Backfill – puts the leftovers from extracting bauxite from processing, back in areas that have already been mined.

Hydro Paragominas has two dam systems for bauxite waste storage. Both systems use a tailings disposal methodology based on the alternate operation of their reservoirs, allowing the tailings to dry out in each reservoir by combining drainage and evaporation, which results in tailings with a minimum solid content of 60%.

Now, late in 2021, Tailings Dry Backfill is in full swing at Hydro Paragominas. The methodology that allows for the final disposal of tailings in areas that have already been mined is living proof of more-sustainable mining. Hydro invested around BRL 30 million in the testing phase.

Previously, bauxite mines built so-called tailings ponds where water could be removed, leaving a residue that could be stacked. With Tailings Dry Backfill, this is not necessary, thus eliminating the need to build new permanent tailings dams.

“Hydro is committed to driving sustainability in the aluminum industry, and the pursuit of sustainable mining is an essential element in achieving this goal,” says John Thuestad, executive vice president of Hydro’s Bauxite & Alumina business.

“It is an important advance in terms of sustainability in the industry that brings greater operational safety and economic benefits while responding to the industry’s challenge to reduce its environmental footprint.”

All stages of the project were closely monitored by the company and environmental agencies, and following the technical standards of Conama, the National Environment Council.

TAILINGS DRY BACKFILL TECHNOLOGY

The Tailings Dry Backfill technology allows inert tailings from bauxite mining to be returned to the already open and mined areas, before the rehabilitation process, instead of being deposited in separate, permanent storage areas. After drying in temporary storage for 60 days, the bauxite tailings are put back into the mined areas before the area is rehabilitated and reforested.

This will further reduce the environmental footprint of bauxite mining and increase operational safety. The tailings from bauxite mining are chemically and physically similar to what was removed during the mining process. Therefore, it is returned to nature without any impact on the environment.  

Before testing the method in Paragominas, Hydro carried out technical studies and detailed planning. In July 2019, after obtaining authorization from the environmental agency, Hydro began the field-testing phase. The tests have been carried out in different seasons, continuously monitored by the project’s technical team and detailed reports are regularly forwarded to the environmental authorities. The results are positive in relation to the environment, operational safety and within forecast costs.

REHABILITATION OF MINED AREAS  

Hydro Paragominas is committed to applying the best environmental practices and continuously invests in the rehabilitation of mined areas. In the recovery of these areas, the original form of the soil is reproduced with the addition of organic matter. Then, the land is prepared for the planting of seedlings that will restore the vegetation.  

Since the reforestation program was initiated in 2009, Hydro Paragominas has worked on 2,300 hectares in the recovery process. On average, 200,000 seedlings of native species are produced per year in a Hydro Paragominas nursery.  

To improve the rehabilitation process, Hydro is part of the Brazil-Norway Biodiversity Research Consortium (BRC), which brings together researchers from the Federal University of Pará (UFPA), the Federal Rural University of the Amazon (UFRA), the Emílio Goeldi Museum, the University of Oslo (UIO) and Hydro professionals in Brazil, seeking the best alternatives for reforestation and monitoring of mined areas.