| 摘要: | 氣候變遷儼然已經成為全球迫切的議題，有許多證據顯示工業發展和人類活動的增加，導致溫室氣體排放量迅速上升，尤其是二氧化碳的增加，會對環境造成負面影響，因此，減緩溫室氣體排放，以避免氣候變遷狀況加劇是必要的。台灣日前正式發布《台灣2050淨零排放路徑藍圖》，旨在實現2050年淨零排放目標和行動計畫。碳捕獲、利用和儲存(Carbon capture, utilization, and storage, CCUS, CCUS)技術被認為是最有前景的碳減排策略，將二氧化碳捕捉和儲存到礦物、地層或海洋中是最有效和可行的方法。本研究利用電爐石作為萃取Ca之原料，電爐石的鈣含量相當豐富，可以與二氧化碳反應形成碳酸鈣沉澱，沉澱後的碳酸鈣還可應用在建築材料等其他再利用方式，達成循環經濟和環境永續的概念，利用氯化銨對Ca高選擇性之特性作為萃取劑，來提升Ca的萃取效果，此外，本研究創新將微波技術運用在Ca的萃取，微波技術可以在反應過程中增強Ca的溶出，以及加快反應速率，對於整體實驗的效能大幅度增加。萃取實驗探討不同反應時間、粒徑大小、氯化銨濃度及液固比四項參數，對鈣、鎂及Si萃取濃度之影響。結果顯示，隨著反應時間增加，鈣與Mg的萃取濃度上升，但Si在反應過程不斷受熱形成矽膠，使Si萃取濃度降低。電爐石粒徑越小，比表面積越大，萃取效果越好。氯化銨濃度越高，可以促進鈣與Mg的溶出，由於使用氯化銨作為萃取劑，針對Ca的選擇性較良好，因此，相同條件下，Mg的萃取濃度小於Ca，但Si卻得到相反的結果，由於高濃度的氯化銨會優先和電爐石中Ca結合，抑制Si的溶出。液固比越小，有助於提高鈣、鎂及Si的萃取濃度。最佳萃取條件為反應10分鐘、電爐石粒徑≤74 µm、氯化銨濃度 2 M、液固比5:1，可得到萃取液 Ca: 52000 ± 563 mg/L、Mg: 1100 ± 4.3 mg/L、Si:64.8 ± 8.4 mg/L。在碳酸化反應試驗中，主要探討反應時間、反應溫度及pH值對碳酸化效率的影響，結果顯示，隨著反應時間和溫度的增加，碳酸化效率僅有些微的提升，而pH值才是影響碳酸化效率的關鍵，在高pH值的作用下，輕質碳酸鈣(Precipitated Calcium Carbonate, PCC)沉澱量大幅提升，可以成功碳酸化84.1 ± 0.59 g CO2/kg slag，為了證實沉澱碳酸鈣的性質，本研究利用XRD及SEM進行分析，發現在25℃下沉澱的碳酸鈣為球霰石結晶型態，在60℃下沉澱的碳酸鈣則為方解石結晶型態。使用微波加熱設備，碳排放量僅有0.066 kg CO2e，證實微波加熱不僅可以縮短反應時間，並提高萃取濃度，節省更多能源。;Climate change has clearly become an urgent global issue. There is substantial evidence showing that the rapid rise in greenhouse gas emissions, especially carbon dioxide, is primarily caused by industrial development and increased human activities, leading to negative environmental impacts. Therefore, reducing greenhouse gas emissions is essential to prevent the worsening of climate change. Recently, Taiwan officially released the "Taiwan 2050 Net-Zero Emissions Pathway Blueprint," aiming to achieve the goal of net-zero emissions by 2050. Carbon capture, utilization, and storage (CCUS) technology is considered the most promising carbon reduction strategy. Capturing and storing carbon dioxide in minerals, geological formations, or oceans is seen as the most effective and feasible method.
In this study, electric arc furnace slag was used as the material for calcium ion extraction, as it contains a high amount of calcium, which can react with carbon dioxide to form carbonate precipitates. These carbonates can be reused in construction materials, promoting the concepts of circular economy and environmental sustainability. Ammonium chloride was employed as the extracting agent due to its high selectivity for calcium ions, enhancing the extraction efficiency. Moreover, microwave technology was used to accelerate the dissolution of calcium ions and speed up the reaction, significantly improving the overall experiment′s efficiency.
The extraction experiments examined the effects of four parameters—reaction time, particle size, ammonium chloride concentration, and liquid-to-solid ratio—on the extraction of calcium, magnesium, and silicon ions. The results showed that as the reaction time increased, the extraction concentrations of calcium and magnesium ions rose, while silicon ions formed silica gel due to prolonged heating, resulting in a decrease in their concentration. Smaller particle sizes with larger surface areas improved the extraction efficiency. Higher ammonium chloride concentrations promoted the dissolution of calcium and magnesium ions. Since ammonium chloride is more selective for calcium ions, the magnesium ion concentration was lower under the same conditions. However, silicon ions exhibited the opposite trend because high concentrations of ammonium chloride prioritized the binding with calcium ions in the slag, inhibiting the dissolution of silicon ions. A lower liquid-to-solid ratio also helped increase the extraction concentrations of calcium, magnesium, and silicon ions. The optimal extraction conditions were a reaction time of 10 minutes, particle size ≤ 74 µm, ammonium chloride concentration of 2 M, and a liquid-to-solid ratio of 5:1 (calcium ions: 52,000 ± 563 mg/L; magnesium ions: 1,100 ± 4.3 mg/L; silicon ions: 64.8 ± 8.4 mg/L).
In the carbonation reaction tests, the effects of reaction time, temperature, and pH on carbonation efficiency were examined. The results indicated that increasing reaction time and temperature only slightly improved carbonation efficiency, whereas pH was the critical factor. At higher pH levels, the amount of calcium carbonate precipitated increased significantly, successfully carbonating 84.1 ± 0.59 g CO2 per kg of slag. To confirm the properties of the precipitated calcium carbonate, XRD and SEM analyses were conducted, showing that the calcium carbonate precipitated at 25°C formed as vaterite crystals, while at 60°C, it formed as calcite crystals. Using microwave heating equipment results in carbon emissions of only 0.066 kg CO2e, demonstrating that microwave heating not only shortens reaction time and increases extraction concentration but also saves more energy. |
