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Chemical Aspect of Ocean Liming for CO2 Removal: Dissolution Kinetics of Calcium Hydroxide in Seawater
Full text linkOcean liming is attracting ever-increasing attention as one of the most suitable and convenient ways of removing carbon dioxide from the atmosphere and combating global warming and the acidification of the oceans at the same time. However, the short-term consequences of Ca(OH)2 [slaked lime] dissolution in seawater have been scarcely studied. In this work, we investigate in detail what happens in the initial stages after the dissolution of slaked lime, analyzing the kinetics of the process and the effects on the physicochemical parameters of seawater. A series of experiments, carried out by varying the seawater conditions (like temperature and salinity) or the liming conditions (like the dispersion in the form of slurry or powder and the concentration) allow us to draw conclusions on the ideal conditions for a more efficient and environmentally friendly liming process
Assessing the limits for Ocean Alkalinity Enhancement and CO2 removal: from laboratory to modelling approaches
No full textDOTTORATOLa ricerca sui processi di carbon dioxide removal (CDR) ha suscitato un crescente interesse nella comunità scientifica. Un promettente approccio per rimuovere la CO2 dall’atmosfera e stoccarla, è l’Ocean Alkalinity Enhancement (OAE), un insieme di processi ideati per sequestrare la CO2 atmosferica aumentando contemporaneamente l’alcalinità marina, contrastando l’acidificazione degli oceani. L’OAE ha il potenziale per rimuovere tra 1 e 100 GtCO2 all’anno e immagazzinarlo per un periodo di circa 10.000 anni, garantendo uno stoccaggio con stabilità a lungo termine.
Questa tesi indaga i limitazioni e fattibilità dell’OAE, concentrandosi su due processi principali: Ocean Liming (OL) e Buffered Accelerated Weathering of Limestone (BAWL).
La ricerca esplora sia limiti applicabili a tutte le tecniche OAE, che aspetti specifici associati ai singoli processi.
OL prevede l’aggiunta diretta di calce idrata [Ca(OH)2, slaked lime, SL] nell’acqua di mare, aumentando il pH e facilitando l’assorbimento di CO2 atmosferica, che viene quindi
convertita in ioni bicarbonato, la forma ionica di carbonio stabile al pH marino. Al contrario, il BAWL è una tecnologia di stoccaggio della CO2 che utilizza una fonte esterna
di CO2 combinata con minerali alcalini [CaCO3 o Ca(OH)2] per produrre una soluzione ad alta alcalinità, poi rilasciata in mare.
Questo lavoro presenta i risultati di quattro studi di ricerca, due dei quali pubblicati, che esaminano sia gli aspetti sperimentali che quelli modellistici dell’OL e BAWL. Gli obiettivi principali includono la determinazione del dosaggio ottimale di Ca(OH)2 nell’OL per studiare i processi innescati nel breve termine a seguito dell’aumento di pH e alcalinità, e la valutare la stabilità dello stoccaggio di CO2 nel lungo termine, per il BAWL.
Gli studi sperimentali sull’OL hanno dimostrato l’efficacia del processo nell’aumentare l’alcalinità dell’acqua di mare e sequestrare CO2 atmosferica. La rapida dissoluzione
della calce idrata, seguita dall’assorbimento della CO2, ha confermato l’efficienza del processo. Tuttavia, l’aumento del pH associato potrebbe essere potenzialmente dannoso per
gli ecosistemi marini e favorire la precipitazione di minerali di CaCO3, come l’aragonite, riducendo l’efficienza del processo. La nostra ricerca ha identificato un intervallo di dosaggio sicuro compreso tra 120 e 135 μmol/L di TA per l’acqua di mare del Mediterraneo, minimizzando efficacemente i picchi di pH e prevenendo precipitazioni minerali significative. Inoltre, è stato sviluppato un modello cinetico per la precipitazione dell’aragonite, fornendo un primo approccio per lo sviluppo di uno strumento utile nella gestione dei livelli di alcalinità e nel controllo della precipitazione minerale.
La ricerca sul BAWL ha confermato la sua capacità di immagazzinare permanentemente la CO2, con esperimenti condotti su un impianto pilota che hanno validato la stabilità chimica delle soluzioni alcaline nell’acqua di mare. I risultati hanno dimostrato un rischio minimo di precipitazione o degassamento della CO2 in condizioni ottimali con un’aggiunta di alcalinità pari a 1000 μmol/L.
Oltre a questi lavori principali, vengono presentati studi che contribuiscono ad uno sviluppo più ampio delle tecnologie OAE. La tesi contiene una valutazione tecno-economica del BAWL, insieme ad un contributo a una conferenza dedicato all’integrazione degli impatti dell’acidificazione oceanica nelle metodologie di Life Cycle Assessment (LCA).
Sia BAWL che OL si sono dimostrate soluzioni adattabili e scalabili per la rimozione della CO2 in ambienti marini. La loro dipendenza da materie prime abbondanti e infrastrutture modulari le rende alternative praticabili in contesti in cui lo stoccaggio geologico è impraticabile o troppo costoso. Questi risultati rafforzano il potenziale delle tecnologie OAE all’interno dei portfoli di strategie globali per la mitigazione del cambiamento climatico.Research on carbon dioxide removal (CDR) technology has risen in interest within the scientific community. One promising approach for removing CO2 from the atmosphere and store it is Ocean Alkalinity Enhancement (OAE), a set of processes designed to sequester atmospheric CO2 while increasing ocean alkalinity to counteract ocean acidification. OAE has the potential to remove between 1 and 100 GtCO2 per year and store it on the order of 10,000 years, providing long-term stability.
This thesis investigates the limitations and feasibility of OAE applications, focusing on two primary processes: Ocean Liming (OL) and Buffered Accelerated Weathering of Limestone (BAWL). The research explores general constraints applicable to all OAE techniques, as well as specific challenges associated with each process.
OL involves the direct addition of slaked lime [Ca(OH)2, SL] into seawater, increasing pH and facilitating the absorption of atmospheric CO2, ultimately converting it into stable bicarbonate ions, the stable form of inorganic carbon at seawater pH. BAWL, in contrast, is a CO2 storage technology that utilizes an external CO2 source combined with alkaline materials [CaCO3 or Ca(OH)2] to produce a solution with high alkalinity, which is then discharged in sea.
This work presents findings from four research studies—two of which are published—examining both experimental and modeling aspects of OL and BAWL. The primary objectives include identifying the optimal Ca(OH)2 dosage in OL to investigate the short-term chemical processes following pH and alkalinity increases, as well as assessing the long-term stability of CO2 storage in BAWL.
Experimental OL studies demonstrated its effectiveness in enhancing seawater alkalinity and sequestering atmospheric CO2. The rapid dissolution of slaked lime, followed by CO2 absorption, confirmed the efficiency of the process. However, the associated pH increase could be potentially harmful to marine ecosystems and may also trigger the precipitation of CaCO3 minerals, such as aragonite, which could reduce the process efficiency. Our research identified a safe dosage range of 120 to 135 μmol/L of TA for Mediterranean seawater, effectively minimizing harmful pH spikes and preventing significant mineral precipitation. Additionally, a kinetic model for aragonite precipitation was developed, providing an initial framework for a predictive tool to manage total alkalinity levels and control mineral formation.
The research on BAWL confirmed its capability to permanently store CO2, with experiments on a pilot plant validating the chemical stability of alkaline solutions in seawater. The results demonstrated minimal risk of precipitation or CO2 degassing under optimal conditions with an alkalinity addition of 1000 μmol/L.
Beyond this core work, additional studies are presented that contribute to the broader development of OAE. This includes a techno-economic evaluation of BAWL, as well as a conference contribution discussing the integration of ocean acidification impacts into Life Cycle Assessment (LCA) methodologies.
Both BAWL and OL emerged as adaptable and scalable solutions for carbon removal in marine environments. Their reliance on abundant raw materials and modular infrastructure makes them viable alternatives to geological storage, when this impractical or too expensive. These findings reinforce the potential for OAE technologies within the portfolio of climate change mitigation strategies.DIPARTIMENTO DI CHIMICA, MATERIALI E INGEGNERIA CHIMICA "GIULIO NATTA"37DOTELLI, GIOVANNIBERTARELLI, CHIAR
Analysis of slaked lime spreading methodologies for ocean alkalinity enhancement
Full text linkLAUREA MAGISTRALEPer limitare il riscaldamento globale entro i limiti definiti dall’Accordo di Parigi è necessario rimuovere ingenti quantità di CO2 dall'atmosfera grazie all’adozione di tecnologie per le emissioni negative; fra queste l’alcalinizzazione artificiale degli oceani permette contemporaneamente il sequestro chimico della CO2 e il contrasto dell’acidificazione degli oceani, mediante lo spargimento di materiali alcalini, come l’idrossido di calcio (slaked lime, SL).
La prima parte della tesi è incentrata sulla valutazione di diverse configurazioni di spargimento di SL, considerando diversi scenari di scarico nelle scie delle navi, tramite “rainbowing” e per mezzo di aerei. La fattibilità di queste diverse configurazioni dipende da
molte variabili, come il numero di aerei o di navi e le loro caratteristiche (i.e.: capacità di carico, rateo di scarico). Sono stati valutati il potenziale di mitigazione, i costi, la logistica dello
spargimento, nonché le concentrazioni di SL nell’acqua di mare o l'aumento temporaneo del pH che potrebbe avere effetti nocivi sull’ecosistema marino. Le analisi effettuate hanno mostrato una maggiore efficienza sia in termini di rimozione di CO2 sia economici negli scenari di scarico nella scia delle navi e con il rainbowing. Queste metodologie hanno una penalità (CO2 emessa nello spargimento/CO2 rimossa) variabile tra l’1-4 % e costi variabili tra 6-9 € per ton di CO2 rimossa; gli aerei, in funzione degli scenari,
hanno una penalità variabile tra il 28-77% e costi tra € 30-€ 1846 per ton di CO2 rimossa. Lo scarico tramite aerei mostra quindi molte limitazioni, soprattutto a causa dell’ingente consumo di carburante che ha notevoli riflessi anche sui costi.
Nella seconda parte è stata effettuata un’analisi modellistica chimico-fluidodinamica finalizzata a valutare la velocità di dissoluzione di SL in acqua di mare, parametro chiave per
la diffusione di SL nella scia di una nave. Dalle valutazioni condotte emerge come l’accoppiamento dello scarico nella scia di una nave e dell’uso di sistemi di rainbowing può permettere di ampliare l’area di mare interessata dallo scarico, riducendo il carico per unità
di superficie e quindi i potenziali impatti.To limit global warming within the limit defined in the Paris Agreement, there is the need to remove huge quantity of CO2 from the atmosphere by the implementation of the Negative Emission Technologies to remain below 1.5 °C from the Preindustrial Level. Among the various strategies, there is a solution that prevents both global warming and ocean acidification: the so-called Ocean Alkalinity Enhancement. This technology is based on atmospheric CO2 sequestration by the addition of alkaline materials into seawater (slaked lime, SL).
The first part of the thesis is focused on the assessment of the discharging’s configurations with the implementation of different discharging scenarios in ships’ wake, through "rainbowing" and by aircraft. However, their viability depends on many variables, such as
fleet size and characteristics needed (i.e.: load capacity, discharge rate). These assessments address the mitigation potential, costs, logistics, as well as the concentrations of SL in seawater or the temporary increase in pH that could have harmful effects on the marine ecosystem.
The various analyses examining each OAE discharging option show a higher CO2 removal efficiency in the scenarios with SL discharge from ships and rainbowing. They have a penalty
(CO2 emitted during spreading / CO2 removed) varying between 1-4 % and costs between € 6-9 per ton of CO2 removed; aircraft, depending on the scenario, have a penalty varying between
28-77 % and costs between € 30-1846 per ton of CO2 removed. It is clear that aircraft have huge limitations due to significant fuel consumption, which implies large economic drawbacks.
In the second part of the thesis, a chemical-fluid dynamic modelling analysis is carried out to evaluate the dissolution rate of SL in seawater, a key parameter for its diffusion in ship’s wake.
The evaluation shows how the coupling of the unloading in the ships’ wake and the use of rainbowing systems can allow widening the sea area affected by the unloading, reducing the
SL load per surface unit and therefore the potential impacts
Assessing the Limit of CO2 Storage in Seawater as Bicarbonate-Enriched Solutions
No full textThe dissolution of CO2 in seawater in the form of bicarbonate ions is an attractive alternative to storage in geological formations, on the condition that the storage is stable over long periods and does not harm the marine environment. In this work, we focus on the long-term chemical stability of CO2 absorbed in seawater as bicarbonate by monitoring the physico-chemical properties of the solutions (pH, dissolved inorganic carbon and alkalinity) in six different sets of experiments on both natural and artificial seawater lasting up to three months. The bicarbonate treatment of natural seawater consists of mixing it with pre-equilibrated solutions obtained from the reaction of CO2 and Ca(OH)2, with the same pH as natural seawater. This was achieved with a pilot plant working with tons of seawater, while small-scale laboratory experiments were carried out by adding sodium bicarbonate to artificial seawater solutions. If the increase in the overall carbon concentration in the final mixture does not exceed a critical threshold (about 1000–1500 μmol/L), the resulting bicarbonate-rich solutions are found to be stable for over three months
Modelling of calcite and dolomite dissolution in the buffered accelerated weathering of limestone technology for CO2 storage
Full text linkLAUREA MAGISTRALELa tesi si incentra sull’analisi della tecnologia per il processo di Buffered Accelerated Weathering of Limestone (BAWL) per lo stoccaggio della CO2, una tecnologia basata sui processi di Enhanced Weathering of Limestone (EWL) per accelerare i naturali cicli geochimici terrestri. Il BAWL si basa sull’utilizzo di acqua marina, che miscelata con CO2 e minerale carbonato polverizzato (come calcite o dolomite) può stoccare la CO2 nel mare sotto forma di ioni carbonati. Dopo la miscelazione di questi tre elementi, la soluzione è convogliata in una tubatura e rilasciata al di sotto della superfice marina: la profondità è fondamentale per evitare che l’anidride carbonica possa tornare in atmosfera.
L’altra caratteristica che evita il degassamento della CO2 è l’uso di idrossido di calcio, il quale serve a neutralizzare l’anidride carbonica rimanente e garantire che la soluzione abbia un pH simile a quello marino.
La modellizzazione della tecnologia è stata svolta con il software PHREEQC. Con esso la tecnologia è stata esaminata per determinare le caratteristiche di funzionamento del BAWL in termini di: lunghezza e profondità della tubatura, e dosaggio e caratteristiche del minerale.
La tesi valuta quale minerale carbonato, tra calcite e dolomite, sia più idoneo per l’utilizzo nel BAWL.
L’analisi viene svolta definendo dei valori iniziali per i parametri operativi (lunghezza e profondità della tubatura, dimensione dei grani di minerale...), i quali vengono variati e combinati per definirne l’impatto sulla dissoluzione del minerale. Sono quindi definiti diverse condizioni operative che garantiscono una completa dissoluzione del minerale e ottimizzano i parametri. Sui punti di funzionamento viene poi fatta un’analisi dei costi per determinare quali siano le condizioni operative che rendono la tecnologia più conveniente.
La calcite risulta più efficiente della dolomite in quanto permette un corretto funzionamento del BAWL, con condizioni operative più convenienti sia per fattibilità tecnologia che per costi correlati.The thesis analyses the technology of Buffered Accelerated Weathering of Limestone (BAWL) for CO2 storage. This process is based on the Enhanced Weathering of Limestone (EWL), which aim to speed up the processes that speed up the natural geochemical reactions.
The functioning of BAWL is based on the usage of seawater, which by mixing with carbon dioxide and a powdered carbonate mineral (e.g. calcite or dolomite), can store CO2 in the ocean in the form of carbonate ions. After that these three components are mixed, the solution is channelled into a pipeline, where the reaction takes place, and discharged under the ocean's surface layers. The discharge in deep water is fundamental to avoid the release of carbon dioxide into the atmosphere.
The other characteristic that avoids carbon dioxide degassing is the usage of calcium hydroxide, which is required to neutralise the unreacted CO2 and guarantee that the solution released has a pH comparable with the seawater.
The technology model is implemented within the software PHREEQC. The functioning of BAWL has been examined to assess feasible operative points of the technology, and evaluate its working parameters as the time required for the reaction, length and deep of the pipeline, and dosage and characteristics of the carbonate minerals.
The thesis focuses on assessing which carbonate minerals, between calcite and dolomite, are most suitable for its usage in BAWL.
The analysis is performed by defining initial values for the different operative parameters, which are then changed one at a time, to define their impact on the carbonate mineral dissolution. Once identified the most influential parameters, different operative points that guarantee a complete dissolution of the carbonate minerals are defined (e.g. length and deep of the pipeline).
Once defined the optimal operating points for BAWL, these are compared from an economic point of view by a costs analysis.
The usage of calcite results more efficient than the utilisation of dolomite in the functioning of BAWL because the working conditions results more advantageous, both for the feasibility of that technology and from an economic point of view
The effect of ocean alkalinity enhancement on zooplankton standing stock and community composition in the Eastern Mediterranean Sea: a mesocosm study
No full textOcean acidification (OA) due to anthropogenic CO2 emissions has significantly altered ocean chemistry since the industrial era. Ocean alkalinity enhancement (OAE) is an innovative strategy to mitigate excess CO2, with ocean liming (OL) serving as a potential carbon dioxide removal (CDR) method, through the spreading of Ca(OH)2 (slaked lime) at the ocean surface. This study examined the ecological effects of OL on a natural zooplankton community from the ultraoligotrophic Eastern Mediterranean Sea during a 14-day mesocosm experiment conducted in spring-summer. We investigated how varying concentrations of slaked lime (low: 0.00074 g L- 1, high: 0.0067 g L- 1) affected zooplankton community structure, abundance, composition and species diversity The experiment revealed complex temporal dynamics in the zooplankton community across all treatments. Tintinnina and Copepoda dominated the community (80-100 %), with nauplii significantly outnumbering copepodites and adults by an order of magnitude. Redundancy Analysis and correlations showed that pH, temperature and nutrient availability were crucial factors shaping the zooplankton community structure. These environmental variables explained more of the community variation than the lime treatments themselves, highlighting the importance of considering multiple ecological factors when assessing OAE impacts. The overall community response to OL treatments was subtle, suggesting potential resilience of the zooplankton community to shortterm alkalinity enhancement. This research provides insights into the ecological implications of OL as a potential OA mitigation strategy. It emphasizes the need for longer-term studies to fully understand the cascading effects on marine food webs and ecosystem functioning. Future research should focus on the interplay between OL, nutrient dynamics, and trophic interactions to better predict the ecological consequences of large-scale OAE implementation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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