What is Enhanced Rock Weathering, the technique to reduce CO2 emissions from agricultural land

In recent years there has been a growing interest in new approaches and technologies aimed at accelerate CO sequestration₂ from the atmosphere. Among these, the technique ofEnhanced Rock Weathering (ERW) applied to agricultural land is emerging as an economically and ecologically advantageous solution capable of guaranteeing negative emissionsIn this article, we will explore in detail what ERW represents, its potential, and the main challenges and limitations related to its adoption.

What is Enhanced Rock Weathering for CO2 Emissions?₂

Enhanced Rock Weathering (ERW) is a technique aimed at accelerate the natural process of chemical degradation of silicates. To achieve this goal, the predominant approach involves the shattering And dispersion of fine particles of rocks rich in silicate minerals, especially those of calcium and magnesium, within agricultural soils. basaltic rocks They are among the most used as they contain minerals with an ideal chemical composition, such as augites ((Ca, Na) (Mg, Fe, Al) (Al, Si)₂OR₆) And olivine ((Mg,Fe)₂YesO₄), degrade rapidly and are widely available globally, thus ensuring greater large-scale applicability of the approach. Theoretical estimates suggest that weathering of approximately a ton of basaltic rocks or ultrabasic rocks can sequester between 0.3 and 0.8 tons of CO₂.

In essence, the ERW aims to amplify the contact surface between minerals and the atmosphere, thus increasing the number of interactions and allowing the absorption of greater quantities of carbon dioxide in shorter times. The ions generated by the degradation of silicates are then conveyed by runoff and infiltration waters, and subsequently transferred to the seas and oceans.

Use in agricultural land brings a number of additional benefits. The specific chemical composition of soilsplant activities and those microbiotics These are all factors that could accelerate degradation reactions of silicates. In addition to promoting the removal of CO₂ from the atmosphere, the dispersion of silicates in agricultural soils improves soil qualityraising its pH and increasing the presence of essential nutrients, such as calcium, magnesium and potassium, which are released during chemical degradation, thus increasing plant productivity

Advantages and disadvantages of this technique

Theoretical estimates suggest that by applying ERW to approximately 50% of global agricultural land it might be possible to remove over 2 billion tons of carbon dioxide per year. It is important to note, however, that ERW is a recently conceived approach. There are pilot projects and feasibility studies underway, especially in Brazil, India, China, England and the United States. Consequently, we do not yet have sufficient data from real ERW operations to confirm or deny the theoretical predictions.

As an emerging and developing technology, ERW still has many challenges. unanswered questionsnot only on its actual potential, but also on its long-term impacts on the atmosphere, soils and oceans. There are also many questions regarding the factors that influence its effectiveness. A study recently published in ‘Nature Scientific Report’ highlights how factors such as structurethe chemical composition and the soil porositythe degree of saturation, the size and arrangement of crushed rock particles within soils, play a key role in the kinetics of degradation reactions. No less important is the chemical composition of the rocks used: not all basaltic rocks, for example, are suitable for ERW.

Other uncertainties concern the scalability of ERW. Variables such as precipitation, temperature and soil characteristics determine the most suitable areas for the application of this technique. For example, to ensure optimal effectiveness using basalt powders, it is necessary to annual precipitation that exceed the 1200 mm and of average annual temperatures of soils that exceed the 15 °C. The availability and findability of raw materials are also central to the feasibility of the process. In fact, most of the costs related to ERW are associated with the extraction, crushing and transportation of rocks, and these increase proportionally to the distance from the extraction site.

In conclusion, although numerous theoretical studies indicate ERW as a solution to accelerate carbon dioxide capture, the road to its large-scale application is still long. Only in the coming years will we be able to truly evaluate the effectiveness and actual feasibility of this technology.

What is chemical degradation of silicates?

The rocks that make up the Earth’s crust are made up of over 90% silicates. These minerals are made up of silicon (Si) and oxygen (O) associated with other elements of the periodic table such as aluminum (Al), potassium (K), sodium (Na), manganese (Mn), magnesium (Mg), iron (Fe), calcium (Ca). Most silicate minerals originate within the Earth’s crust through the slow cooling of magma on the way up and metamorphism processes.

Silicates are stable at the high temperature and pressure conditions at which they formed inside the Earth. However, once brought to the surface, the chemical stability of many silicates is reduced. This is due, among other things, to exposure to environmental conditions different from those of formation and tointeraction with surface waterswhich, over time, cause a slow but irreversible alteration and dissolution. The process of chemical degradation of silicates is known as “chemical weathering”, or even “silica weathering” (silicate degradation). Weathering is a long natural process that helps shape the face of our planet. But not only that. In fact, the chemical degradation of silicates plays an essential role in the carbon cycle, regulating the concentrations of CO₂ into the atmosphere, with long-term effects on global temperatures.

Carbon dioxide in the atmosphere dissolves in rainwater, forming a light carbonic acid (H₂CO₃) which, in contact with the rocks on the surface, gradually dissolves the silicate components less stable. This reaction transforms carbonic acid into bicarbonate (HCO₃^–) and at the same time releases other metal ions that were original components of the mineral. In this way, the carbon is removed from the atmosphere and does not contribute further to the greenhouse effect. Subsequently, the weathering products are transported by rivers to the seas and oceans. Here, by interacting with the metals present in the water, compounds such as calcium carbonate (CaCO₃), which will then be deposited on the ocean floor trapping carbon within sediments.

The natural process of removing CO₂ from the atmosphere through the weathering of silicates and its subsequent trapping in marine sediments may require several hundreds of thousands of years to over a million years. The duration is influenced by the atmospheric concentration of carbon dioxide present and the presence of alterable rocks on the surface. These, in turn, are conditioned by thevolcanic activitythe tectonics local, the precipitation rates and those of erosion of rocks. Despite this, silicate weathering is thought to have played a major role in accelerating climate recovery and stabilizing global temperatures after some of the major environmental crises documented in Earth’s geologic history.