A trial that aimed to remove carbon dioxide from the atmosphere using seawater off the coast of Cornwall in the south-west of the UK has been shelved. It is not because the science did not work, but due to associated commercial and logistical challenges. But it is the latest in a string of carbon capture projects to falter under the weight of public concerns, complex permitting and supply chain hurdles.
Planetary Technologies, a Canadian start-up, had proposed an ocean-based carbon capture project in the bay of St Ives in Cornwall. The core idea was to enhance the ocean’s natural ability to absorb carbon dioxide by adding alkalinity to seawater.
In practice, this meant dosing treated wastewater released into the bay with a diluted slurry of magnesium hydroxide, which is a compound often used as an antacid. The magnesium hydroxide would dissolve and raise the water’s pH, counteracting acidity.
Because less acidic water can hold more dissolved CO2, the treated seawater would draw in additional CO2 from the atmosphere, converting it to stable bicarbonate ions and locking it away in the ocean for thousands of years.
For the Cornwall pilot, Planetary Technologies worked with local utility South West Water to launch a small-scale trial in September 2022. This saw about four tonnes of magnesium hydroxide added over three days to the effluent stream at a nearby wastewater treatment plant.
The bay of seaside town St Ives was identified as an ideal location for the trials
The mixture was then discharged through an existing pipe 2.4 kilometres offshore into St Ives Bay. Scientists from Plymouth Marine Laboratory and other independent experts monitored the experiment, measuring water chemistry around the outfall in real time.
Initial results were encouraging. Even at a 1:5,000 dilution, magnesium hydroxide increased seawater alkalinity, confirming CO2-neutralising reactions were taking place. A later analysis reported enhanced alkalinity and reduced CO2 near the discharge point, with no short-term harm observed.
Planetary Technologies effectively demonstrated that adding a dose of antacid to the ocean could remove measurable CO2, marking a world-first for this method.
Buoyed by this, the company proposed a larger 2023 trial, dispersing up to 450 tonnes of brucite, a natural form of magnesium hydroxide, over three to four months. Modelling estimated a net removal of 200 tonnes of CO2, comparable to the annual emissions of around 40 cars.
Long term, Planetary Technologies wants to scale up to dispersing 40 tonnes of magnesium hydroxide per day, forming part of a global CO2 removal network, pending safety validation.
A promising start in Cornwall
Planetary Technologies, founded in 2019 and fresh off winning a $1m carbon removal XPrize award, received a £250,000 UK government grant to explore its ocean alkalinity method. The company identified conditions in St Ives Bay, including shallow waters with good mixing, as ideal for a trial and began liaising with regulators and South West Water. The 2022 experiment took place with limited public awareness.
Once word of the experiment spread in spring 2023, public concern escalated. Community groups questioned the environmental impact and raised concerns about a lack of transparency.
In response, Planetary Technologies held consultations, published FAQs, and brought in scientists from Plymouth Marine Laboratory to present their findings. The company also pledged not to monetise the Cornwall trial and sought a UK-based source of magnesium hydroxide.
By late 2024, the project had stalled. An independent audit commissioned by the Environment Agency concluded the trial posed a low environmental risk, but momentum was lost.
In April 2025, Planetary Technologies confirmed it would no longer pursue the St Ives Bay project. The high-purity magnesium hydroxide required was difficult to source locally and expensive to ship from overseas. Delays in permitting, supply chain hurdles and a lack of clear public support also contributed to the decision.
The company maintains that the Cornwall trial yielded valuable data and says its focus is now on other sites. In Canada, similar trials in Halifax Harbour have proceeded with less public resistance. A future trial in Vancouver remains on the roadmap.
Wider challenges
The cancellation of the St Ives Bay project is not an isolated case. In April 2025, another UK-based carbon capture initiative, a direct air capture tower project in Suffolk, was also shelved due to similar concerns over commercial viability and logistics.
Several other international projects have faced similar outcomes, often driven by strong public opposition. In the US, Navigator CO2 Ventures cancelled its 1,300-mile Heartland Greenway CO2 pipeline across the Midwest in late 2023 after encountering intense regulatory resistance and community pushback, particularly in South Dakota and Iowa. Summit Carbon Solutions, another US pipeline project, has faced over 150 lawsuits from landowners and legislative backlash over the use of eminent domain.
In the Netherlands, Shell’s Barendrecht CCS project was scrapped after residents raised safety concerns and questioned the lack of public consultation. In a similar way, mining company Glencore’s proposal to store CO2 in Australia’s Great Artesian Basin was halted following opposition from local councils and agricultural groups over potential groundwater contamination.
These setbacks highlight a broader issue. While CCS technologies are recognised as essential tools in the fight against climate change, their implementation is fraught with challenges.
A white, odourless powder, magnesium hydroxide is also sold as milk of magnesia – used as an antacid and laxative
The St Ives Bay trial became a textbook example of the communication challenges around geoengineering and climate experiments. On one side were scientists and the company, insisting the method was safe – backed by data. On the other side were concerned residents, faced with unsettling unknowns and in some cases amplified by misinformation.
Early on, Planetary Technologies provided evidence that the plan would not damage the bay. Magnesium hydroxide is a common, FDA-approved substance (often taken as milk-of-magnesia for indigestion) and has a track record of safe use in water treatment.
The quantities proposed were also tiny relative to the volume of the ocean. The dilution ratio of about 2.5 kg per 10 tonnes of water (or around 0.025%) meant the pH change would be minuscule – of the order of 0.01 or less, according to the EIA.
In Nova Scotia, where the company was conducting a parallel trial, researchers noted the highest concentration of the alkalinity lasted less than two minutes in the ocean before dissipating.
Financial constraints, supply chain dependencies, regulatory complexities, and public perception all play major roles in determining the feasibility of such projects, even when backed by scientific research and funding.
The UK government has pledged up to £22bn ($29bn) towards carbon reduction and green technology initiatives. However, the recent cancellations suggest that funding alone may not be sufficient. There is a pressing need for companies involved to prioritise community engagement.
In addition, any perceived secrecy or top-down decision-making can trigger backlash that might otherwise be avoidable with early transparency and inclusive dialogue.
