#limescience

Scientific researches

Limenet has been working with scientists from different research centres from Politecnico di Milano, Milano-Bicocca University and CMCC to study all BOAE (Buffered Ocean Alkalinity Enhancement) uncertainties. In particular, Limenet is researching:

Abiotic precipitation & Biotic precipitation

Marine storage of CO in the form or hydrogen carbonate and carbonate ions appears to be a viable option for the long‐terms storage of CO, in view of the following:

CO₂ is known to be stable in water in the form of hydrogen carbonate or carbonate ions (the relative quantities depend on the pH, temperature, pressure, etc.). In aqueous CO₃²‐ or HCO₃‐, the CO is chemically bonded exactly like in the solid form of these two ions, which are stabilized also in solution. Therefore, the transformation into pure solid form of carbonate/hydrogen carbonate salt of Ca (or other metal ions) is not the only way to store CO in the form of carbonate/hydrogen carbonate (Source Politecnico di Milano).

Adding alkalinity to seawater shifts the pH and carbonate ion concentration and could cause abiotic precipitation of calcium carbonate (CaCO₃) or brucite (Mg(OH)₂). This is important to characterize as this precipitation results in CO₂ outgassing. It remains to be determined what specific combination of suitable nucleation conditions and supersaturation of CaCO₃ is needed to cause significant precipitation. Abiotic precipitation can be minimized by controlling the particle dissolution rate and the dilution and dispersal of equilibrated alkalinity-enhanced water. (Source Carbon Plan¹)

During 2022-2023, Limenet developed two experimental analyses with Politecnico di Milano to study the chemical stability of equilibrated alkalinity added into the ocean.

This was done by simulating different calcium bicarbonate concentrations in different seawater samples.
This helped us to reach a specific Omega Aragonite critical for abiotic precipitation.

The experiments were divided into two parts:

  • Laboratory experiments
  • Field experiments
Preliminary experiments 
Initial sampling
Field experiments 
Weekly sampling
Sampling in La Spezia
Transport in Milan
Analysis of TIC, alkalinity and pH
Preliminary experiments 
Initial sampling
Field experiments 
Weekly sampling
Sampling in La Spezia
Transport in Milan
Analysis of TIC, alkalinity and pH
For three months, we analyzed weekly pH, TIC, alkalinity and conductivity to understand, at different bicarbonate concentrations, the chemical stability. For three months, we were able to test chemical stability and understand the feasibility of BOAE respectively to classical OAE. The results were in accordance with the work on: Moras et al (2021)² and Hartmann et al (2023)³. With an Omega aragonite of 7 and Omega calcite of 11 was possible to have a chemical stability of calcium bicarbonates produced by Limenet TRL 6 at La Spezia (Italy).

With this test we were able to set up the method to study abiotic precipitation and understanding its efficiency compared to theoretical one.
More tests will be done in the next future.

Chemical stability tests in Milan

From left to right, Guido Raos (Politecnico di Milano, full professor), Selene Varliero (Politecnico di Milano, PhD), Federico Comazzi (Ex Politecnico di Milano – now in Limenet, researcher), Piero Macchi (Politecnico di Milano, full professor)

Chemical stability tests in Milan

The work is intended as an illustration to understand the chemichal stability and kinetics of calcium bicarbonates though time in order to guarantee the permanence of the storage though time.

Thanks are due to Professors Macchi Piero and Raos Guido of the Politecnico di Milano chemical department, Professors Caserini Stefano of the Politecnico di Milano Environmental department, who contributed to this project, as well as to PhD student Selene Varlerio and Federico Comazzi.

 

Since calcification releases CO₂ as a by-product, any changes to the rate of biotic calcification in response to alkalinity additions to the surface ocean must be considered. Changes in biotic calcification rates could occur in both coastal and open ocean waters, and at the level of individual calcifiers or calcifier populations.

With this research we try to quantify the biotic calcification response to alkalinity addition.

Mesocosm utilized for CO₂ storage experiments in seawater⁴

Marine bicarbonate monitoring

In order to avoid abiotic and biotic precipitation, is important to study the Omega Aragonite and Calcite saturation across the injection site of Limenet facility.

The aim of this work is to collect and illustrate the simulation and distribution of calcium bicarbonates in an oceanic environment at depth, with the aim of storing the carbon dioxide absorbed from the atmosphere through the BOAE (Buffered Ocean Alkalinity Enhancement) novel techniques.

The aim of the simulations will be to evaluate the distribution of the saturation state of the water Ω during a discharge cycle, in order to assess the probability of carbon dioxide leakages, thus studying a suitable discharge method to minimize the risk.

To handle the complexity of these simulations, we’re developing a FORTRAN code for Large Eddy Simulation (LES). This, after the validation of the code itself, will provide the necessary high resolution on quasi-meso scale domains for longer inspection periods, typically around 24 hours of simulation. 

Thanks are due to Diego Bindoni, Professors Abba’ Antonella, Caserini Stefano, Macchi Piero and Raos Guido of the Politecnico di Milano, who contributed to this project, as well as to PhD student Selene Varlerio than to CMCC and in particular to Giovanni Coppini, Simona Masina and Thomas Lovato.

With this novel techniques is possible to study and monitoring where calcium bicarbonates produced by Limenet facility are dispersed into the ocean with an high confidence. 

For further informations discover more on our report. 

Effect on marine biota of calcium bicarbonates

Limenet did a qualitative test in mesocosm during 2022-2023 at La Spezia Facility.  

We saw in mesocosm a qualitative enhancement of calcified organism in higher alkalinity mesocosm in 2023 and we started testing it in 2023 Q4 and 2024 Q1 to assess the beneficial impact of BOAE on Marine biota. 

This work is be done by Professor Daniela Basso and Arianna Azzellino. The same as they did here: https://meetingorganizer.copernicus.org/EGU23/EGU23-10342.html but with BOAE approach. 

At the La Spezia experimental plant, we are conducting a multidisciplinary study on Limenet technology, evaluating its chemical and biological aspects. Chemically, we focus on the evaluation of the stability of dissolved calcium bicarbonates and the effectiveness of carbon dioxide storage in relation to the ratio of natural sea water treated from the Limenet pilot plant. From a biological point of view, we are investigating the potential effects of Limenet treatment on marine organisms, with particular attention to planktonic and benthic organisms. The study is scheduled to last three months. 

Sources

¹ https://carbonplan.org/research/cdr-verification/ocean-alkalinity-enhancement-mineral
² Ocean Alkalinity Enhancement – Avoiding runaway CaCO3 precipitation during quick and hydrated lime dissolution. https://doi.org/10.5194/bg-2021-330
³ Stability of alkalinity in ocean alkalinity enhancement (OAE) approaches – consequences for durability of CO2 storage https://doi.org/10.5194/bg-20-781-2023
 https://www.frontiere.polimi.it/co2-capture-and-storage-a-promising-technology-to-fight-climate-change/?lang=en

Limenet