Carbon capture and storage (CCS) is an emerging technology which safely captures greenhouse gas emissions from the air and stores them underground for thousands to millions of years, such as in reservoirs or depleted oil and gas fields.
CO2 that has been injected is then permanently isolated; large-scale projects have demonstrated this approach is feasible.
Biological Sequestration
Biological carbon sequestration refers to the natural ability of living organisms and ecosystems to store atmospheric carbon for long-term storage, most visibly demonstrated in forests, peat marshes and coastal wetlands.
Earth has undergone 4.54 billion years of history, during which global carbon cycling was driven by geological and climate factors. Prior to humans arriving, this process had not changed substantially until recently (in the last 12 millennia). With their arrival and subsequent activities, this started changing significantly.
Perennial woody species and agroforestry can increase biological carbon sequestration capacity. Trees are especially effective at this task by fixing CO2 through photosynthesis to form lignified biomass that lasts in landscapes for decades or even longer.
Fungi are highly efficient at sequestering carbon in soil, as they convert atmospheric CO2 into organic matter that feeds soil fungi. Other methods to enhance biological carbon sequestration efficiency include system-based conservation agriculture, agroforestry, biochar production and afforestation/reforestation projects as well as restoring wetlands.
Saline Sequestration
Saline sequestration is an underground method of carbon dioxide storage that uses saline geological formations as storage sites. Although this technology is relatively new and still requires refinement to maximize efficiency. Research must take place to better understand its underlying processes – for instance understanding what impact saline formation characteristics have on CO2 storage capacity or the effects of injection rates have on sequestration efficiency.
CO2 injection into saline aquifers increases pressure and storage capacity by increasing pressure, and can be trapped through structural, residual and solubility mechanisms. Structural sequestration depends on contact angles between CO2 and brine and interfacial tension; storage capacity depends on fractures and reservoir heterogeneity as well as fracture depth; Residual and solubility sequestration involve chemical interactions between caprock and brine as well as dissolving CO2 into brine to increase storage capacity while dissolving CO2 increases storage capacity while salt precipitation prevention can prevents this effect from taking place.
Geological Sequestration
Geological sequestration (GS) is the final stage in carbon capture and storage (CCS), designed to store CO2 for centuries to millennia. CO2 collected from emissions sources is compressed and chilled until liquid-like before being pumped underground into porous rock layers via impermeable seal rocks and monitored using monitoring technologies that detect CO2 movement underground to ensure it stays within the storage formation.
CO2 injection into deep underground geological formations such as depleted oil and gas reservoirs, saline aquifers and coal seams provides secure long-term storage options when combined with proper site selection, monitoring and management practices. CO2 can remain trapped underground using various trapping mechanisms – structural trapping (under caprock layer), dissolution trapping or mineralization trapping whereby CO2 reacts with minerals in rocks to crystallize into solid form – providing secure long term storage when site selection, monitoring and management practices are in place.
Mineral Sequestration
Carbon mineralization is an innovative form of CCS that accelerates reactions between carbon dioxide and certain minerals to form carbonates, solid substances that effectively and permanently store CO2. It can be completed either underground or above ground using chemical reactors.
This approach not only reduces carbon dioxide emissions but may also lower costs by capitalizing on existing mining infrastructure. The technology relies on mining iron-rich waste rocks containing magnetite, wollastonite and anorthite minerals before reacting them with CO2 under controlled conditions to form mineral carbonates that form mineral carbonates.
This approach also has the potential to provide significant co-benefits, such as mitigating local ocean acidification and protecting coral reefs and commercially valuable aquaculture. However, more research and testing needs to be conducted in order to fully comprehend its effects and optimize this process – in particular by developing a reliable method for estimating wastes’ mineral carbonation capacity which optimizes this process and considers aspects such as pH condition and particle size fraction on reaction stoichiometry stoichiometry calculations.