澎湖鹼性玄武岩二氧化碳礦化封存岩水試驗

Abstract

自工業革命以來，大氣中二氧化碳濃度急遽上升，進而導致大氣平均溫度上升，促使極端氣候事件及生物滅絕事件頻傳，因此減少大氣中二氧化碳濃度勢在必行；除此之外，臺灣國發會也於 2022 年發布了 2050 年淨零排放政策策略，其中也提及了需要發展碳封存等負排放技術。地質碳封存被認為是一門具有龐大發展潛力的一種封存技術，而礦化封存是地質封存中永久且最安全的封存反應機制，其原理利用材料中的鹼性物質中與二氧化碳反應，產生碳酸鹽材料達成負碳的效果，但在傳統的砂頁岩系統中的礦化封存需要千年至萬年的反應時間，在過程中有極大的二氧化碳洩漏風險。而玄武岩在近幾年來被認為是一種極具快速達成礦化封存的地質材料之一，冰島於 2014 年進行了現地玄武岩碳封存試驗當中，將大量二氧化碳氣體混和水溶液後注入到玄武岩地層中，經歷兩年的地下水井監測，據其計算有注入之 95%的二氧化碳氣體在兩年之年完成礦化封存反應。因此，在本研究中應用此概念，設計一套在實驗室模擬玄武岩的礦化封存反應系統，並以澎湖玄武岩作為研究材料，嘗試於實驗室中模擬玄武岩礦化封存反應。因此，在本研究實驗過程中，我們連續監測了反應中水溶液的 pH 值變化，並定期取樣分析水中離子濃度，希望透過 pH 值與水中陽離子濃度的變化得知礦化封存反應的機制。通過 ICP-OES分析水溶液中有利於礦化反應之陽離子，如鈣 (Ca)、鐵 (Fe)、鎂 (Mg) 等元素；並搭配化學計量分析濃度作圖、水化學沉澱相圖等水化學分析技術探討不同水岩比例下玄武岩溶解及二次礦物沉澱反應，自結果中可以得知水岩比例 D2 有最佳的反應條件及環境；而為了更進一步分析整體礦化封存反應的結果，以電子顯微鏡搭 配能量色散光譜儀分析反應後的玄武岩表面特徵，其在水岩比例 D2 的組別中能在玄武岩的表面上發現微量的碳酸鹽訊號，由此證實本研究框下的反應已有初步的礦化反應出現；除此之外，在本研究中也嘗試探討反應完畢之水溶液中所含之二氧化碳，因此將水溶液蒸乾並收集其沉澱固體進行熱重分析，其中分析可以得知水溶液中能在短時間內將注入之二氧化碳以電荷平衡方式將其初步封存於水溶液之中，在水岩比例二比一組合反應 70 天的組別中可以達到 43%的封存效率。由常壓系統及固體表面特徵分析可以得知水岩比例 D2 為最佳的反應分別，因此在本研究中也以此水岩比例模擬高壓地下封存之環境進行實驗，自結果中可以得知增加二氧化碳之分壓有助於玄武岩的溶解且使其沉澱環境更快速的達成相較於常壓有更佳的碳酸鹽沉澱條件。因此綜合以上研究及討論結果可以得知在澎湖鹼性玄武岩極具二氧化碳礦化封存之潛力。

Since the industrial revolution, the concentration of carbon dioxide in the atmosphere has increased dramatically, which has led to an increase in the average temperature of the atmosphere and contributed to the frequent occurrence of extreme climate events and biocide. therefore, it is imperative to reduce the concentration of carbon dioxide in the atmosphere; in addition, the National Development Council of Taiwan has released the policy strategy of net-zero emissions by 2050 in 2022, which also mentions the need to develop negative emission technologies such as carbon sequestration. Geological carbon sequestration is regarded as a sequestration technology with great development potential, and mineralization sequestration is the permanent and safest sequestration reaction mechanism in geological sequestration. which uses the alkaline substances in materials to react with carbon dioxide to produce carbonate materials to achieve the effect of negative carbon emissions, But mineralization sequestration in the traditional sandstone system requires a reaction time of one thousand to ten thousand years, and there is a great risk of carbon dioxide leakage during the process. In recent years, basalt has been regarded as one of the geological materials that can achieve mineralization and sequestration very quickly compared with traditional sandstione system. In 2014, Iceland conducted an in-situ basalt carbon sequestration test, in which a large amount of carbon dioxide gas was injected into the basalt layer by mixing it with an aqueous solution, and after two years of monitoring underground water wells, In CarbFix they calculated that 95% of the carbon dioxide gas injected into the basalt layer has been mineralized the mineralization and sequestration reaction within two years. Therefore, this concept was applied in this study to design an in-house system to simulate the mineralization sequestration reaction of basalt in the laboratory. Penghu basalt was used as the research material to simulate the mineralization sequestration reaction of basalt in the laboratory. During the experimental process of this study, we continuously monitored the pH changes of the aqueous solution in the reaction, and regularly sampled and analyzed the ion concentration in the water, aiming to understand the mechanism of the mineralization sequestration reaction through the changes of pH and cation concentration in the water. Through Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) analysis, we analyzed the cations in the aqueous solution that are beneficial to the mineralization reaction, such as calcium (Ca), iron (Fe), magnesium (Mg) and other elements. With the chemical metrology analysis, concentration mapping, hydrochemical precipitation phase diagram and other hydrochemical analysis techniques , We explored the dissolution of basalt and the secondary mineral precipitation reaction under different water and rock ratios. We find that there are optimal conditions and environments for the reaction under the water-rock ratio of 2. For further analysis, we can also analyse the overall mineralization and sequestration reaction mechanism through the changes in pH and cation concentrations in the water. To further analyze we find trace carbonate signals could be find on the surface of the basalt in the D2 water-rock ratio group, which confirms that the reaction under the present study has already had a preliminary mineralization reaction. In addition, in this study, we also tried to investigate the carbon dioxide contained in the aqueous solution at the end of the reaction. The aqueous solution was evaporated and the precipitated solid was collected for thermogravimetric analysis. We found that the carbon dioxide injected into the aqueous solution could be initially sequestered into the aqueous solution by charge equilibrium in a short period of time, and a sequestration efficiency of 43% could be achieved in the 70 days reaction group with water-rock ratio D2. From the analysis of atmospheric pressure system and solid surface characteristics, we find that the water-rock ratio D2 is more better in our reaction group. Therefore, in this study, this water-rock ratio is also used to simulate the environment of high-pressure underground storage for the experiment. Our results showed that increasing the partial pressure of carbon dioxide promotes the dissolution of basalt and expedites the precipitation environment faster to achieve better carbonate precipitation conditions compared to atmospheric pressure. Finally we conclud that the basalt in Penghu has great potential for carbon dioxide mineralization and storage.