In this blog, Dr Junyao Kang, Data Analysis and Modeling Lead, and Dr. Matthew Clarkson, Head of Carbon at InPlanet share about Rock Powder Dissolution and Carbon Capture processes, CO₂ capture quantification, and the challenges posed by fertilizers.
The dissolution process and cation release
At the core of Enhanced Rock Weathering (ERW) is the dissolution of rock powder, which releases essential cations into the soil system. As Dr. Junyao Kang explains:
“You can see all these dark particles as our rock powder spreads onto the surface of the soil. We see dissolution happening, releasing important cations for our enhanced rock weathering process. This allows us to track how the cations are released and estimate how much CO₂ can be potentially captured.”
The dissolution process is not solely CO₂-driven; other acids, such as those from fertilizers, contribute significantly, and we have to understand these competing reactions to accurately determine the carbon sequestration potential and how they affect rock powder dissolution and carbon capture.
So how do we know how much CO₂ is actually captured?
Quantifying CO₂ capture is a complex challenge, Dr. Kang explains:
“Losses due to soil adsorption, acid dissolution, and plant uptake must be factored in before reaching a verified CDR number. Additionally, once cations exit the soil system, whether into the river or the marine environment, additional chemical processes can impact final CO₂ sequestration figures.”
The InPlanet team employs conservative estimates to ensure credibility. This avoids overestimation and ensures reported CDR figures remain robust in the context of rock powder dissolution and carbon capture.
“We take a conservative approach: in the long run, 84% of the time, we are underestimating our true CDR value. This provides confidence in our estimates when selling credits to customers.”
Final verified numbers show that out of an initial potential of 755 tons of CO₂ capture, accounting for losses resulted in 235.53 tons of verified CDR credits. These losses might sound large, but this reflects the conservative nature of the calculation. They are also project specific and likely smaller for other crop systems.
Fertilizers introduce an added layer of complexity
While rock powder dissolution is expected to be CO₂-driven, fertilizers contribute strong acids, which can artificially inflate dissolution figures. Some dissolution occurs due to these strong acids, particularly those from fertilizers. The key to success is to isolate CO₂-driven reactions. The team estimates the impact of strong acids by measuring non-carbonic anions, a proxy for strong acid presence. These measurements help them determine what portion of the dissolution was acid-induced rather than CO₂-induced. This careful analysis further helps in understanding the multifaceted process of rock powder dissolution and carbon capture.
To track the dissolution process, InPlanet uses immobile tracers
What are immobile tracers? These are elements that remain in the soil after rock powder application.
“We focus on tracers like neodymium because, even after dissolution, it remains in the soil. This allows us to estimate how much rock powder was applied and how much has dissolved over time.”
By isolating reliable tracers, the team improves the accuracy of their dissolution assessments, crucial for understanding rock powder dissolution and carbon capture.
