Microwaving rocks could help mining operations pull CO2 out of the air

Mining operations worldwide produce massive amounts of waste rock annually. The unused rock piles have the potential to react with carbon dioxide, aiding in the removal of significant quantities of this greenhouse gas from the atmosphere. Traditional methods involve high-temperature heating of the rocks, which necessitates the burning of fossil fuels. However, a carbon removal start-up, Arca based in Canada, has introduced a more energy-efficient approach by utilizing microwaves to facilitate the reaction between rocks and CO2.

Sean Lowrie from Arca compares the process to making microwave popcorn, where only specific molecules within the rock are heated, similar to how water inside a kernel is heated in a kitchen microwave to pop corn. This innovative technique offers a promising solution to reduce energy consumption compared to conventional methods.

Various companies are exploring the use of rocks to sequester CO2 as a means to offset emissions from fossil fuel combustion. Arca, among others, focuses on utilizing mine tailings, the byproducts of metal extraction processes such as nickel and chromium mining. These tailings contain serpentine minerals rich in magnesium, which react with CO2. Arca’s analysis suggests that the existing global stockpile of tailings could potentially store up to 8.7 billion tonnes of CO2, equivalent to approximately two years of US emissions.

While serpentine rocks exhibit slow reactivity at ambient conditions, heating them to high temperatures enhances their ability to mineralize CO2 rapidly. By employing microwaves for rock heating, Arca aims to achieve several advantages over conventional heating methods. Peter Scheuermann from Arca highlights that the microwave-based approach can be powered by clean electricity, consume less energy, and accelerate the rock treatment process. This technology could be seamlessly integrated into mining operations for processing tailings or implemented as a standalone system.

Arca’s patent filing reveals that microwaving serpentine rocks enhances their reactivity towards CO2, leading to more efficient CO2 mineralization at lower temperatures and energy inputs compared to thermal treatments. The treated rocks exhibit significantly increased CO2 sequestration capacity, indicating a substantial improvement in the process.

Although the technology is currently at the laboratory testing stage, Arca envisions a scaled-up version involving the integration of microwaving units into the tailings processing workflow. This innovative approach not only enhances CO2 storage potential but also offers prospects for extracting valuable metals like nickel from the rocks. Quin Miller from the Pacific Northwest National Laboratory applauds the development, emphasizing its dual benefits in carbon sequestration and metal extraction.