Experimental studies on the stability of bicarbonate-enriched seawater solutions

The deployment of carbon dioxide storage is a challenge that must be overcome in order to reach the net zero emissions objective. Ocean alkalinity enhancement (OEA) is a promising method for removing carbon dioxide from the atmosphere and storing it pemanently in seawater as bicarbonates, with the co-benefit of counteracting ocean acidification. The challenge for future applications is ensuring a stable storage, avoiding adverse side effects on the environment or phenomena that can reduce efficiency, such as degassing of carbon dioxide and precipitation of alkaline minerals.

The work presented in this study investigates the stability of the carbonate system of seawater, after adding alkalinity by two different pathways. One is the simple addition of NaHCO₃ to artificial seawater, on a laboratory scale. The other is a test on a more complex system, consisting of a pilot plant that uses natural seawater, CO₂ and calcium hydroxide and produces a carbon-enriched solution at the same pH of natural seawater. We suggest safe levels for the increase of alkalinity and considering the dilution of the solution with seawater in natural environments. The results represent important steps towards the achievement of safe and efficient ocean-based carbon storage and OAE.