Mining legal areas in Brazil would emit 2.5 Gt of CO2 – 07/15/2023 – Environment

In the midst of record temperature records in the world and the intensification of discussions on ways to mitigate climate change, researchers from Esalq-USP (Luiz de Queiroz College of Agriculture at the University of São Paulo) released a study showing that, if all active legal mining areas in Brazil are exploited in the coming decades, at least 2.55 gigatons of carbon dioxide equivalent (Gt CO2 eq.) would be emitted.

Part can be caused by loss of vegetation (0.87 Gt CO2 eq.) and the other by soil changes (1.68 Gt CO2 eq.). This total represents about 5% of the world’s annual emission of greenhouse gases from human activities.

According to the research, published in the scientific journal Communications Earth & Environmental, Brazil currently has 5.4 million hectares of legally active mines, which is equivalent to an area slightly smaller than Croatia (with 5.6 million acre). They are scattered throughout the country, however, most are concentrated in subtropical and tropical regions (with the largest stocks, estimated at 1.05 Gt CO2 eq.).

To offset these emissions, the researchers propose a solution based on nature, with the construction of soils from waste from the mines themselves, called Tecnosols. This strategy has the potential to sequester up to 1 Gt of CO2 eq., which corresponds to 60% of the carbon dioxide that could be emitted by soil alterations.

“The first step, when we thought of carbon stock, was to analyze emissions, since most of the existing work evaluates the impacts of mineral processing, with the burning of fuel and the expense of electricity, for example”, he explains to Agência FAPESP doctoral student Francisco Ruiz, from Esalq-USP.

“But we know that most mining in the world, and especially in Brazil, is done in pits, in the open. And soils are the main terrestrial ecosystems for storing carbon. When the soil is removed, this organic matter and the vegetation change, eliminating carbon dioxide. Therefore, we analyzed the potential emissions with the removal of soil and vegetation to reach the number of 2.55 gigatons of CO2 equivalent”, he says.

Ruiz is the first author of the research and has a FAPESP scholarship.

For Professor Tiago Osório Ferreira, from the Department of Soil Science at Esalq-USP, corresponding author of the article and advisor to Ruiz, one of the main points of the study was to show that soils built using tailings can be an alternative for decarbonization .

“This specific work shows a potential that helps to allocate tailings and residues in a new way to build a fundamental resource, that is, the soil that sequesters carbon in a stable way. The research serves as a warning to other countries, mainly large miners, such as China and the United States, that there are alternatives in this urgent race against climate change”, says the professor, who is also coordinator of the Soil Geochemistry Study and Research Group at Esalq.

Soil is one of the four major carbon sinks on the planet, along with the atmosphere, oceans and plants. However, in a state of degradation, it can release CO2, as happens with vegetation.

A MapBiomas survey revealed that, of the total 37 gigatons of soil organic carbon (SOC) existing in Brazil in 2021, almost two thirds (63%) are stored in areas under stable native cover (23.4 Gt SOC), mainly in the Amazon. Only 3.7 Gt COS are stored in soils in regions converted to anthropic use since 1985.

Artificial soils can be created using materials derived from human activities, including industrial, urban and mining waste. In addition to climate regulation, Technosols can restore essential ecosystem services, lost with mining activities, for example, ranging from food and energy production to biodiversity protection, water quality regulation and nutrient cycling. .

According to the research, provided the appropriate properties are employed, Technosols can act as a substrate for the development of plants —native or of agricultural and forestry interest— and sequester carbon through the accumulation of organic matter.

Brazil is among the ten main producers of mineral commodities in the world. Mining is an important area for economic development, but it is also linked to the degradation of ecosystems, with soil and water pollution and loss of biodiversity.

In addition, Brazil has recently recorded two major disasters, the rupture of the Mariana (in 2015) and Brumadinho (in 2019) dams, both in Minas Gerais, with high human, economic and environmental costs.

The process

The elaboration of Technosols is based on the understanding of naturally occurring processes in soil, such as its formation, weathering and stabilization of organic matter.

To test the hypothesis that construction of Technosols could help overcome CO2 emissions from surface mining, the scientists estimated stocks using data available in the literature. To do so, they determined the geolocation and areas of all legal mining sites in the country using the Sigmine online platform of the National Mining Agency.

They found that recovery of carbon dioxide stocks is climate dependent, with tropical Technosols showing the greatest potential. This performance can be attributed to the high input of plant-derived carbon and the potential for CO2 stabilization through mineral-organic interactions.

The researchers point out that some types of mining tailings contain potentially toxic elements, such as arsenic, mercury, cadmium, copper and lead, and that, therefore, their use should be avoided or combined with strategies to prevent pollution and mobilize heavy metals. . In these cases, they suggest the use of remediation techniques (such as phytoremediation) and the application of soil amendments.

“What draws a lot of attention in this work is the amount of carbon obtained from Technosols. In some cases, it exceeds the total of natural soils. The studies that Francisco [Ruiz] been developing show that it is possible to build soils in a very short time with performance even better than the natural ones and helping to mitigate the effects of climate change”, says Ferreira.

Ruiz has been researching Tecnosols since his master’s degree and received, in 2020, the Brazilian Mining and Metallurgical Industry Excellence Award, promoted by Minérios magazine, a publication considered a reference in the sector.

At the time, the researcher carried out a study at a limestone mining company in the city of Saltinho (SP), reusing the waste produced by mining itself to build soils, recomposing the topography and vegetation.

In addition to scientists from Esalq, the work now published had the participation of researchers from international institutions, such as the Sorbonne (France) and Santiago de Compostela (Spain) universities, as well as the Woodwell Climate Research Center (United States). It is linked to CCarbon, the new Center for the Study of Carbon in Tropical Agriculture, a Fapesp Research, Innovation and Dissemination Center coordinated by Professor Carlos Eduardo Pellegrino Cerri, co-author of the article (read more at: agencia.fapesp.br/41018/) .

Headquartered at Esalq, CCarbon aims to produce knowledge and innovation in nature-based solutions aimed at reconciling the growing demand for food and energy with environmental, economic and social sustainability.

_{The article Constructing soils for climate-smart mining can be read at:}