Thesis
Assessing the dissolution of various crushed rocks and minerals for ocean alkalinity enhancement
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2023
DOI:
https://doi.org/10.25918/thesis.332
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Abstract
Anthropogenic activities, such as the burning of fossil fuels, cement production and land-use change have released huge quantities of carbon dioxide (CO2) into the atmosphere, leading to climate change. To avoid major threats to natural ecosystems and human societies, a global warming limit of 1.5-2.0 degrees Celsius above pre-industrial levels is necessary. To achieve such goals, active CO2 removal strategies are required, among which ocean alkalinity enhancement (OAE) is a prime candidate. This PhD project has been developed to gain insights into the changes in seawater chemistry during the dissolution of various crushed minerals for OAE, and to identify and tackle potential pitfalls and shortcomings. The first chapter describes the preparation of secondary reference materials for ocean carbonate chemistry measurements since certified reference materials were in short supply during the COVID-19 pandemic. The second chapter provides the first laboratory data for OAE, covering the dissolution of two alkaline minerals, quick and hydrated lime in natural seawater. It also identified the issue of runaway calcium carbonate (CaCO3) precipitation, eventually removing more alkalinity than had been added. The third chapter focuses on the use of magnesium hydroxide (Mg(OH)2) for OAE, addressing the importance of seawater salinity, alkaline mineral grain size, and dissolved organic carbon concentrations on Mg(OH)2 dissolution and CaCO3 precipitation kinetics. Finally, the fourth chapter explores the potential of other alkaline materials for OAE, such as iron and steel slag, by-products of respective industries. While using by-products for OAE could be very cost-effective, the potential release of toxic elements needs to be addressed. Across four data chapters, this thesis explores the potential of OAE as a mean to actively remove CO2 from the atmosphere by studying the dissolution of various alkaline minerals in seawater. One of the highlights of the thesis is the discovery of runaway CaCO3 precipitation, where eventually more alkalinity can be removed than had been added. This appears to occur if specific CaCO3 saturation state thresholds are exceeded which must be avoided as it would eventually turn the ocean from a sink of atmospheric CO2 to a source. Another highlight is the finding that there is an optimum grain size to avoid secondary CaCO3 formation, balancing higher pH levels around larger particles with increasing surface area for precipitation for smaller particles. Finally, the observation that hardly any of the toxic elements that can be present in slag is actually being leached out in seawater, is promising news for slag-based OAE.
Details
- Title
- Assessing the dissolution of various crushed rocks and minerals for ocean alkalinity enhancement
- Creators
- Charly Andre Moras
- Contributors
- Kai G Schulz (Supervisor) - Southern Cross UniversityRenaud Joannes-Boyau (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- xxvi, 152
- Identifiers
- 991013161713702368
- Copyright
- © CA Moras 2023
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis