![]() Magnesium-rich silicate minerals, such as olivine ((Mg,Fe) 2SiO 4), in ultramafic and mafic rocks have the potential to produce reactive Mg(OH) 2 with zero CO 2 emissions. The high-temperature pyrohydrolysis process of using MgCl 2♶H 2O to form MgO and HCl 14 could potentially provide a low-carbon Mg(OH) 2 alternative however, concentrations of Mg-chloride in seawater are relatively low which limits the efficiency of the process unless highly concentrated brines are used. Recovery of Mg(OH) 2 from seawater has the potential to provide virtually limitless supplies of the material however, it’s commercial production typically requires the use of lime, which itself has significant embodied CO 2, resulting in little overall environmental benefit. MgO and Mg(OH) 2 are usually sourced from either the calcination of magnesite or precipitated from Mg-rich brines and seawater 13. One of the benefits of Mg(OH) 2 with regard to overall conversion rates and transportation is that it does not contain significant quantities of unreactive material, such as silica or iron which are typically found in olivine or serpentine. Seeding Mg(OH) 2 slurries with magnesite at elevated pressures and temperatures has been shown to produce a stable anhydrous magnesite 12. The formation of magnesite (MgCO 3) is also possible but this typically requires higher temperatures (>100 ☌) and pressures above 100 bar. Aqueous carbonation of Mg(OH) 2 can result in the formation of a hydrated Mg-carbonate such as nesquehonite (MgCO 3♳H 20), dypingite (Mg 5(CO 3) 4(OH) 2.5H 2O), and hydromagnesite (Mg 5(CO 3) 4(OH) 2♴H 2O) under atmospheric or near-atmospheric conditions 11. Of the various materials which may be suited for transport to the emissions source, Mg(OH) 2 is one of the most reactive for carbonization 5. Ocean storage has also been proposed as a potential means of CO 2 sequestration but comes with a number of environmental consequences 4.Ī number of materials have been proposed for carbon mineralization, including serpentine, olivine, wollastonite, magnesium oxide, and magnesium hydroxide 6, 7, 8, 9, 10. Carbon mineralization can be further divided into three approaches: (1) ex situ, where the material is transport to the site and reacted with CO 2 typically at elevated temperatures and pressures, (2) surficial, using dilute or concentrated CO 2, and (3) in situ, where the CO 2 is transported to site with suitable geological formations, typically containing serpentine or olivine-bearing basalts 5. Methods for long-term storage of CO 2 can be classified as either underground sequestration or carbon mineralization, of which underground sequestration in sedimentary formation is considered the most mature technology 5. ![]() Point source emissions such as power generation and industrial production account for ~60% of the total CO 2, but this is expected to decrease to 50% by 2050 4. In 2018, ~37 billion tonnes of CO 2 was released into the atmosphere 3. ![]() Urgent action is needed to limit future emissions and sequester existing atmospheric CO 2 in order to circumvent issues related to global warming 2. Examples of issues include increased land and sea temperatures, glacier and sea ice loss, and sea-level rise 1. The effects of unchecked CO 2 emissions on global climate change are being increasingly seen and felt across the world.
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