Planetary Technologies (Planetary), a Canadian company founded in 2019, focuses on ocean-based carbon removal technology which works by producing magnesium hydroxide (Mg(OH)₂) from MgSiO₃ rocks through electrolysis technology and adding Mg(OH)₂ to seawater to speeds up the ocean's natural carbon sequestration process and lowers ocean acidity. This process converts the dissolved carbon dioxide (CO₂) into a mineral salt, which will remain in that state for 100,000 years. Planetary aims to remove 1 billion tons of CO₂ from the atmosphere by 2045.
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Challenges: Ocean-based carbon removal
CO₂ emissions
Since the early 1900s, carbon dioxide (CO₂) levels in the atmosphere have increased by 50% due to human activities. When fossil fuels (such as coal, oil, and natural gas) are burned for energy production, transportation, and industrial processes, CO₂ is released into the atmosphere. This excess CO₂ acts as a greenhouse gas, trapping heat and causing the air and ocean temperatures to rise. CO₂ emissions play a crucial role in driving climate change.
This warming effect has caused the global average temperature to rise by about 1.1 ºC since the pre-industrial period. This has led to rising in the frequency and intensity of extreme weather events, melting of polar ice caps and glaciers and rising sea levels, shifts in species ranges and increased risk of species extinction, agriculture and food security, and ocean acidification.
To mitigate these impacts, the Paris Agreement aims to limit global warming to well below 2 ºC above pre-industrial levels. The Intergovernmental Panel on Climate Change (IPCC) estimates that a “carbon budget” of about 500 GtCO₂, which corresponds to about ten years at current emission rates, provides a 66% chance of limiting global warming to 1.5 ºC.
Ocean carbon sequestration
The oceans cover more than 70% of the earth's surface. They store a lot of CO₂. They are the largest carbon sink on the planet, absorbing about 40% of the CO₂ emitted by human activities. They are an important buffer in climate change.
At its current average pH of 8.1, seawater contains 150 times more CO₂ than an equal volume of the air. The seawater locks the atmospheric CO₂ in the form of ions (HCO₃⁻ and CO₃²⁻) and solid precipitates (CaCO₃ and MgCO₃) according to the following reversible chemical reactions:
CO₂ + H₂O ⇆ H₂CO₃
H₂CO₃ ⇆ H⁺ + HCO₃⁻
HCO₃⁻ ⇆ H⁺ + CO₃²⁻
CO₃²⁻ + Ca²⁺ ⇆ CaCO₃↓
CO₃²⁻ + Mg²⁺ ⇆ MgCO₃↓
As CO₂ emissions increase, the ocean absorbs more CO₂, forming more carbonic acid and lowering the ocean's pH, making it more acidic. As the oceans absorb more CO₂ than they can handle, it could lead to several potential consequences, such as ocean acidification. Ocean acidification can have negative effects on marine life, particularly organisms with calcium carbonate shells or skeletons, such as corals, mollusks, and some plankton species.
Ocean Alkalinity Enhancement
Ocean Alkalinity Enhancement (OAE) is a technical carbon removal approach that involves adding alkaline substances to seawater to enhance the ocean's natural carbon sink. It is one of the important Negative emissions technologies (NETs). NETs are important because they can help companies, sectors, or countries remove more CO₂ from the atmosphere than they emit. According to climate models, a significant deployment of NETs will be needed to prevent catastrophic ocean acidification and global warming beyond 1.5 ºC.
By increasing the alkalinity of seawater, the above chemical reactions shift towards right, resulting in more dissolved CO₂ and converting more CO₂ to bicarbonates (HCO₃⁻), and carbonates (CO₃²⁻), according to the following chemical reactions:
CO₂ + OH⁻ → HCO₃⁻
HCO₃⁻ + OH⁻ → CO₃²⁻ + H₂O
Bicarbonates and carbonates are stable forms of carbon in the ocean. Therefore, the Ocean Alkalinity Enhancement process accelerates the ocean's natural ability to sequester CO₂ from the atmosphere, helping to mitigate climate change and ocean acidification.
While OAE has the potential to remove significant amounts of CO₂ from the atmosphere, there are concerns about its environmental impacts, such as the effects on marine organisms and ecosystems. Further research is needed to fully understand the potential risks and benefits of OAE, as well as the feasibility, cost, and scalability of this approach.
Planetary Technology
How does Planetary technology work?
Planetary has developed an approach of Ocean Alkalinity Enhancement by electrochemically producing magnesium hydroxide (Mg(OH)₂) substance via an electrolyzer and safely adding Mg(OH)₂ to seawater by using a floating platform.
Planetary’s electrolyzer system electrolyzes sodium sulfate (Na₂SO₄) electrolyte to produce sulfuric acid (H₂SO₄) and sodium hydroxide (NaOH) base in order to convert MgSO₃ minerals into Mg(OH)₂. Due to its low toxicity to aquatic organisms and humans, Mg(OH)₂ is commonly used in wastewater treatment. Important aspect of Mg(OH)₂ is its sluggish dissolution, which limits its environmental impact. This prevents rapid pH rises at the outfall location, after which rapid dilution in the seawater maintains a pH well within safe limits.
Planetary has also developed a floating platform for safely dispersing Mg(OH)₂ in the ocean for carbon dioxide sequestering. The platform has a vessel for holding solid Mg(OH)₂ pellets and exposes them to a flow of seawater to create a Mg(OH)₂ solution with a safe pH level. The solution is released into the seawater, producing HCO₃⁻ or MgCO₃ solid, thus sequestering CO₂ present in seawater through chemical reactions:
Mg²⁺ + 2OH⁻ + 2CO₂ → Mg²⁺ + 2HCO₃⁻
Mg²⁺ + OH⁻ + HCO₃⁻ → MgCO₃↓ + H₂O
How does Planetary produce magnesium hydroxide?
The diagram below depicts Planetary’s electrolyzer system for producing Mg(OH)₂ from MgSiO₃ minerals and generating green hydrogen gas ( H₂) as a by-product, which could be used as a zero-carbon fuel.
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