Hydro has developed and implemented a new method for the final disposal of bauxite residue (also known as red mud), which the company has been testing at its Mineração Paragominas bauxite mine in the northern state of Pará, Brazil. This pioneering technology, called Tailings Dry Backfill, replaces the need for raising and building new dams used in traditional methods, improving safety and environmental performance.
“Hydro is committed to driving sustainability in the aluminum industry. This challenge has driven our efforts to pursue practices that can eliminate the need for new permanent tailings storage dams in bauxite mining,” says John Thuestad, executive vice president for the Hydro’s Bauxite & Alumina business.
Tailings Dry Backfill Technology
With the Tailings Dry Backfill technology, the red mud is placed in temporary storage and dried for 60 days. Following the drying process, the material becomes similar to the original ore, making it possible for the tailings to be put back into previously mined areas, which can then be rehabilitated and reforested. This eliminates the need for continuous construction of new permanent tailings dams, or even the need to add layers to existing structures — and thus significantly improves the environmental impact of the tailings.
The Mineração Paragominas bauxite mine 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%.
Following technical studies and detailed planning, Hydro obtained authorization from SEMAS, The Pará State Secretariat for the Environment and Sustainability, to begin the initial field testing stage. The aluminum company launched it’s testing program at Mineração Paragominas in July 2019, with a $5.5 million (R$ 30 million) investment in the study.
Following the technical standards of Conama, Brazil’s National Environmental Council, the tests were carried out in different seasons and continuously monitored by the project’s technical team, with detailed reports are regularly forwarded to the environmental authorities. After one year of testing, the results generated positive results in relation to the environment, operational safety, and forecast costs.
The testing was completed in late 2020 and the project received operational licensing approval from SEMAS on December 30, 2020. According to Hydro, the application of this methodology in Brazil is an important step not only for Hydro’s environmental footprint, but for the sustainability of the primary aluminum industry as a whole.
Rehabilitation and Reforestation
Mineração 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 to receive the seedlings that will restore the vegetation coverage.
Since the reforestation program was initiated in 2009, Mineração Paragominas has already accounted for an area of 2,300 hectares in the recovery process. On average, 200,000 seedlings of native species are produced per year in the Mineração 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.