How might we make the most effective use of the calcium carbonates and magnesium hydroxides/ carbonates formed through the capture of carbon dioxide (CO₂) in seawater in the most beneficial and economically viable way?

Technology Department – Technology Development Division

In line with Singapore public sector’s target, PUB aims to achieve net zero emissions around 2045. PUB’s decarbonisation strategies are to:

• Replace carbon-emitting fuels with renewables,
• Reduce carbon emissions by improving efficiency and reducing water demand, and
• Remove carbon from the environment through technologies that can be integrated with PUB’s operations.

Under the strategy to remove carbon, PUB is exploring with partners on technologies to capture CO2 in seawater and locking it in calcium carbonate and magnesium hydroxide/magnesium carbonate precipitates that form as by-products. Besides permanently storing carbon dioxide, these carbonate and hydroxide precipitates could potentially have valuable industrial applications such as base materials for cement and concrete production, cosmetics, paints and many others.

Seawater contains about 0.4kg of calcium and 1.3kg of magnesium per cubic meter. Hence 1kg of calcium carbonate and 3.2kg of magnesium hydroxide or 4.6kg of magnesium carbonate per m³ of seawater could potentially be produced from such mineralisation processes. Large quantities of calcium carbonates and magnesium hydroxides/carbonates will potentially be available if technologies for CO₂ capture with seawater are successfully employed with desalination. These materials are valuable resources that can be recovered for industrial and commercial use. 

We are interested in seeking partners to work with who can identify and demonstrate how the calcium carbonates and magnesium hydroxides/carbonates can be used either directly or repurposed for applications in industry that offer the most economical and environment-friendly utilisation, especially in Singapore’s context. We are seeking to support solutions that will be able to demonstrate through lab scale or pilot trials, the utilisation of these by-products.

• The calcium carbonates and magnesium hydroxides/carbonates from the CO2 capture and removal technologies that PUB is currently exploring are recovered from the process by sedimentation and are in the form of slurry, which may have anywhere from 50 to 99% saline water content.
• The slurry may contain other minerals and precipitates that occur naturally in seawater or are formed during the CO2 capture and removal process. This needs to be verified as part of the proposed solution for this challenge. Additional treatment processes may be required to achieve the necessary purity for the proposed application.
• Treatment of the slurry may be required to facilitate transportation of the resource to the point of use.
• Regulatory requirements and standards related to the proposed application shall be complied with​.
• Applications for magnesium hydroxide shall enable the magnesium hydroxide to capture CO2 permanently while it is used.
• The proposed application shall not compromise the permanence of the CO2 captured in the calcium and magnesium carbonates.
  

Some of the known potential applications identified for calcium and magnesium carbonates are in building construction, land reclamation and re-mineralisation in the desalination process. We welcome solutions in these areas as well as any others.

After selection

• From PUB, slurries containing approximately 15-25 kg of calcium carbonate and 50-80 kg of magnesium hydroxide per day could be available for the study of the proposed application in this challenge
• PUB facilities as test sites
  

Total project period – less than 18 months

A proof-of-concept in the form of a lab-scale or pilot trial to apply the recovered materials in the proposed application and demonstrate its feasibility and techno-economics. In addition, innovators in their applications should provide details on

• Technical merits of the proposed application,
• How the calcium carbonate and magnesium hydroxide slurries might be utilised either directly or repurposed before they could be used.
• An assessment of the quantity and purity of calcium carbonates and magnesium hydroxides/carbonates
• Total system techno-economics should be inclusive of transportation to point of use, additional treatment processes and other considerations should be included.

If the proof-of-concept is successful, the solution will be developed further and considered for implementation with the partner.

Q: What method is used for carbon capture in the SeaChange (Pilot with UCLA) process?

A: Electrolysis is used in the SeaChange process to generate hydroxides and increase alkalinity for CO₂ capture to take place.

Q: What happens to the CO₂ from the SeaChange (Pilot with UCLA) process?

A: In the SeaChange process, CO₂ is captured by calcium in seawater to produce calcium carbonate and magnesium in seawater is transformed into magnesium hydroxide, which would remove CO₂ by alkalinity enhancement to form magnesium carbonate.

Q: What are the components inside the slurry of the by-products?

A: The slurry is expected to contain elements typically found in seawater and compounds that could be formed during the electrolysis and CO2 capture process. We are currently unable to determine the detailed composition of the slurry of by-products as the pilot trial with UCLA is still ongoing and has yet to produce its first batch of product or by-products. The slurry is expected to ready by the end of our GIC3 evaluations. As part of your pilot proposal, your team should be prepared to perform an analysis of the resulting slurry and propose potential additional treatment processes that may be required to achieve the necessary purity for the proposed application