A new study reveals that olivine, the mineral responsible for the shiny green in the gemstone peridot, can drastically reduce the carbon footprint of the construction industry, which alone contributes to 37 percent of the global CO2 emissions. The study authors showed that olivine can be used to make strong, durable, and carbon-negative cement.
Moreover, products derived from this mineral can replace clay-fired bricks and gypsum boards, two commonly used but also highly carbon-intensive construction materials. By replacing bricks and cement with olivine-based alternatives, we could potentially reduce global emissions by nearly 11 percent (cement and bricks are responsible for eight and 2.7 percent of emissions, respectively).
The best part is that our planet has loads of olivine. The igneous rocks that form Earth’s upper mantle (the layer between Earth’s core and crust) and most of the oceanic floor are primarily made of olivine.
The problem with traditional cement and bricks
Cement is manufactured using clay, water, and limestone. These ingredients are blended, crushed, and heated at high temperatures, resulting in the formation of numerous tiny lumps collectively known as clinker. In the next stage, materials like gypsum and fly ash are added to the clinker. This mix is then ground until it turns into cement powder.
Clinker serves as the main binding agent in cement. It contains various compounds that contribute to the cement’s strength and hydraulic properties when mixed with water. However, it also happens to be the main source of industry emissions. This is because the blending, crushing, heating, and grinding of clinker is powered by fossil fuels.
Bricks are also produced using clay and water. To make bricks hard and durable, they are baked at high temperatures ranging from 1,000 to 1,200 °C (1,832 to 2,192 °F). This process also involves the use of fossil fuels, resulting in the release of high amounts of CO2 into the atmosphere.
The production of both cement and bricks also requires large volumes of water. A study suggests that producing just one ton of ordinary Portland cement requires up to 680 liters of water. The manufacturing process also contributes to large-scale clay mining, resulting in land degradation, soil erosion, and loss of biodiversity.
This is why these latest findings are exciting. The study authors claim that two olivine-derived products, amorphous silica and nesquehonite, can be used to make carbon-negative cement and bricks respectively.
Making olivine-based cement and bricks
Chemically olivine is magnesium silicate [(Mg, Fe)2·SiO4]. It produces magnesium carbonate upon coming in contact with the CO2 in the air. The researchers knew that hydrous magnesium carbonate (MgCO3·3H2O), also called nesquehonite can be used to make construction materials. However, the naturally occurring reaction between olivine and CO2 is very slow and cannot be utilized for commercial purposes.
The study authors devised a new way to produce magnesium carbonate. They dissolved crushed olivine samples in sulfuric acid (H2SO4). The reaction resulted in the breakdown of olivine into silica and magnesium sulfate, the latter of which was flushed with carbon dioxide gas forming magnesium carbonate. This multi-step reaction essentially sequesters the greenhouse gas carbon dioxide, which is offered a new life as a construction material.
“The silica product from acid dissolution of olivine has an amorphous structure, and this makes it highly reactive and valuable as a supplementary cementitious material (SCM) that can be used to form carbon-negative cement and low-carbon concrete. The nesquehonite has the potential to be transformed into low-carbon blocks, bricks, and boards,” the study authors from Imperial College London, note.
They suggest that if you replace 35 percent of Portland cement in a concrete sample with silica, the cement will become carbon-neutral. Increasing the silica percentage to 75 percent will make the cement carbon-negative. Although the study authors need to test the material in real-world settings, they assume that, as per the current construction standards, their olivine-derived silica has the potential to replace 55 percent of the cement used to make concrete.
Moreover, turning olivine into silica and nesquehonite doesn’t require large amounts of energy and can easily be achieved using electricity derived from renewable sources.
“This is a low-cost chemical-based carbon capture process that generates two end products with commercial value as low-carbon construction materials. No other carbon capture and utilization systems processes currently provide these unique benefits,” the study authors added.
The authors have already patented this process and have launched a company named Seratch that will manufacture olivine-derived cement and other construction materials.
The study is published in the journal Royal Society Open Science.
