轉爐石（basic oxygen furnace slag，BOFS）為一貫作業煉鋼廠中轉爐煉鋼過程所產生之副產物，其原料內含豐富之鈣離子，具有成為吸收二氧化碳（carbon dioxide，CO2）作為碳捕捉之原料潛力，透過間接碳酸化之方式，利用氯化銨溶液（ammonium chloride，NH4Cl）對BOFS進行前置溶出，將BOFS中鈣離子有效地萃取出，後續進行碳酸化之程序生成碳酸鈣，以此評估其碳捕捉之能力及成核之晶相。
本研究透過改變相關參數，如：氯化銨濃度、液固比、溫度及粒徑等，探討其對鈣離子萃取效率之影響，初始實驗先以試藥級氧化鈣（calcium oxide，CaO）作為原料進行探討，後續將其置換為BOFS，實驗系統配置以1 M NH4Cl溶液、液固比30 mL/g、溫度30℃ 與原料粒徑0.075~0.600 mm作為基礎。
當溶液種類以外其他參數為基礎值時，以0.5 M氯化銨溶液取代去離子水對CaO進行萃取，其溶出效率由40.08% 提升至63.12%，其相對於去離子水具有良好萃取鈣離子之效率，當氯化銨溶液濃度提高時，其溶出效率也隨之上升；當液固比以外其他參數為基礎值時，液固比30 mL/g時，其為最佳之配比，而粒徑與溫度的部分，由於CaO為純物質，因此在溶出結果上並無顯著之影響，於初始階段時，溶出速率較快。
 
將原料替換為BOFS後，氯化銨濃度及液固比結果與CaO作為原料結果相似，皆與鈣離子溶出濃度呈正相關；而溫度的部分，當溶出環境溫度越高時，其溶出率也隨溫度則有些許之上升；粒徑的部分則受到顯著影響，當粒徑越小時，BOFS與萃取液接觸之表面積越大，而萃取液也易擴散至BOFS顆粒內部中，使得鈣離子較易溶出而濃度隨之提升。
碳酸化時間受流速及通入CO2之比例所影響，流速越快及通入CO2之比例越高時，碳酸化反應時間則越短，在高流速與高CO2氣體比例之混合氣下進行碳酸化反應時，其反應時間並無顯著之差異，隨著通入混合氣中CO2比例下降時，其碳酸化反應時間則隨之越長。
當溶出液中通入固定流速45 mL/min及CO2氣體比例15%之混合氣於不同溫度時，溫度對碳酸化反應時間並無影響，而在最終鈣離子濃度上則有些許變高，由於[CO32-]/[Ca2+]值會隨著溫度越高而降低，於高溫時，碳酸根較難存於溶液中，使得其值變小。
碳酸化後所形成之碳酸鈣晶相，大多為穩定態之菱方晶體結構，在通入固定流速45 mL/min對溶出液進行碳酸化時，隨著混合氣中CO2之比例減少，可發現其菱方晶體結構之晶相邊與稜角則逐漸圓潤，當CO2氣體比例15%時，則可以於菱方晶體之碳酸鈣表面發現結晶性較差的碳酸鈣依附或團聚於其結構上，隨著溫度的提高，其結果更加顯著。
二氧化碳捕捉效率之結果，於CaO溶出液中通入最低流速45 mL/min及15% CO2其可獲得最大捕捉效率，其值為73.02%，而當溶出液替換為F_BOFS溶出液時，其最大捕捉效率為37.59%，由此得知，BOFS溶出液作為碳捕捉之溶液時，再受到其他離子影響下，其捕捉仍可以維持約4成之效率。

In this era of limited global resources, urban mining has emerged as a critical strategy for nations to attain sustainable resources and enable continuous economic development. This study employs an indirect carbonation method using ammonium chloride (NH4Cl) for the extraction of BOFS. Subsequently, various proportions of carbon dioxide (CO2) are introduced to investigate the distinctions in calcium carbonate formation and the efficiency of CO2 capture. The NH4Cl solution possesses effective capabilities for extracting calcium ions from the raw material. As the concentration of the NH4Cl solution increases, its ability to extract calcium ions also rises. At a constant flow rate, a decrease in the proportion of CO2 results in a gradual increase in CO2 capture efficiency. During the carbonation of the leachate at a constant flow rate of 45 mL/min, it can be observed that as the proportion of CO2 in the mixed gas decreases, the edges and angles of the rhombic crystal structure gradually become more rounded.

1. 行政院環境保護署，中華民國國家溫室氣體清冊報告，2021.
2. Feron, P. H. M.; Hendriks, C. A. CO2 Capture Process Principles and Costs. Oil & Gas Science and Technology - Rev. IFP 2005, 60 (3), 451-459.
3. Metz, B.; Davidson, O.; Coninck, H. D.; Loos, M.; Meyer, L. Carbon Dioxide Capture and Storage.; Group III of the Intergovernment Panel on Climate Change, Intergovernment Panel on Climate Change, 2005.
4. Robin Irons; Gnanapandithan Sekkappan; Raghbir Pansear; Jon Gibbins; Lucquiaud, M. CO2 capture ready plants; IEA Greenhouse Gas R&D Programme, Orchard Business Centre, Stoke Orchard, Cheltenham, Glos., GL52 7RZ, UK, IEA Greenhouse Gas R&D Programme 2007.
5. Olajire, A. A. CO2 capture and separation technologies for end-of-pipe applications – A review. Energy 2010, 35 (6), 2610-2628.
6. Songolzadeh, M.; Soleimani, M.; Takht Ravanchi, M.; Songolzadeh, R. Carbon Dioxide Separation from Flue Gases: A Technological Review Emphasizing Reduction in Greenhouse Gas Emissions. The Scientific World Journal 2014, 2014, 828131.
7. Zhu, X.; Hoang, T.; Lobban, L. L.; Mallinson, R. G. Low CO content hydrogen production from bio-ethanol using a combined plasma reforming–catalytic water gas shift reactor. Applied Catalysis B: Environmental 2010, 94 (3), 311-317.
8. Thiruvenkatachari, R.; Su, S.; An, H.; Yu, X. X. Post combustion CO2 capture by carbon fibre monolithic adsorbents. Progress in Energy and Combustion Science 2009, 35 (5), 438-455.
9. Menard, D.; Py, X.; Mazet, N. Activated carbon monolith of high thermal conductivity for adsorption processes improvement: Part A: Adsorption step. Chemical Engineering and Processing: Process Intensification 2005, 44 (9), 1029-1038.
10. Timmerhaus, K. D.; Reed, R. P. Cryogenic engineering: fifty years of progress. 2007.
11. Brouwers, J.; van Kemenade, H. Condensed Rotational Separation for CO2 capture in coal gasification processes. In 4th International Freiberg Conference on IGCC & XtL Technologies, Germany, Dresden, 2010; pp 1-18.
12. Tsang, C. Y.; Street, W. B. Phase equilibria in the H2/CO2 system at temperatures from 220 to 290 K and pressures to 172 MPa. Chemical Engineering Science 1981, 36 (6), 993-1000.
13. Zhao, L.; Riensche, E.; Menzer, R.; Blum, L.; Stolten, D. A parametric study of CO2/N2 gas separation membrane processes for post-combustion capture. Journal of Membrane Science 2008, 325 (1), 284-294.
14. Corti, A.; Fiaschi, D.; Lombardi, L. Carbon dioxide removal in power generation using membrane technology. Energy 2004, 29 (12), 2025-2043.
15. Adams, E. E.; Caldeira, K. Ocean storage of CO2. Elements 2008, 4 (5), 319-324.
16. Harrison, B.; Falcone, G. Carbon capture and sequestration versus carbon capture utilisation and storage for enhanced oil recovery. Acta Geotechnica 2014, 9 (1), 29-38.
17. Lin, Q.; Zhang, X.; Wang, T.; Zheng, C.; Gao, X. Technical Perspective of Carbon Capture, Utilization, and Storage. Engineering 2022, 14, 27-32.
18. Lee, M.-G.; Kang, D.; Yoo, Y.; Jo, H.; Song, H.-J.; Park, J. Continuous and Simultaneous CO2 Absorption, Calcium Extraction, and Production of Calcium Carbonate Using Ammonium Nitrate. Industrial & Engineering Chemistry Research 2016, 55 (45), 11795-11800.
19. Sanna, A.; Dri, M.; Maroto-Valer, M. Carbon dioxide capture and storage by pH swing aqueous mineralisation using a mixture of ammonium salts and antigorite source. Fuel 2013, 114, 153-161.
20. Hargis, C. W.; Chen, I. A.; Devenney, M.; Fernandez, M. J.; Gilliam, R. J.; Thatcher, R. P. Calcium Carbonate Cement: A Carbon Capture, Utilization, and Storage (CCUS) Technique. Materials 2021, 14 (11), 2709.
21. Owais, M. Enhanced Calcium Extraction From Steel Converter Slag Using Wet Extractive Grinding And Comparison With Traditional Mechanical Mixing-Selective extraction of Ca, V, Si and Mg. 2021.
22. Lee, S.; Kim, J.-W.; Chae, S.; Bang, J.-H.; Lee, S.-W. CO2 sequestration technology through mineral carbonation: An extraction and carbonation of blast slag. Journal of CO2 Utilization 2016, 16, 336-345.
23. Udrea, I.; Capat, C.; Olaru, E. A.; Isopescu, R.; Mihai, M.; Mateescu, C. D.; Bradu, C. Vaterite Synthesis via Gas–Liquid Route under Controlled pH Conditions. Industrial & Engineering Chemistry Research 2012, 51 (24), 8185-8193.
24. Pan, S.-Y.; Chang, E.; Chiang, P.-C. CO2 capture by accelerated carbonation of alkaline wastes: a review on its principles and applications. Aerosol and Air Quality Research 2012, 12 (5), 770-791.
25. Kunzler, C.; Alves, N.; Pereira, E.; Nienczewski, J.; Ligabue, R.; Einloft, S.; Dullius, J. CO2 storage with indirect carbonation using industrial waste. Energy Procedia 2011, 4, 1010-1017.
26. Maries, A. The activation of Portland cement by carbon dioxide. In Proceedings of Conference in Cement and Concrete Science, Oxford, UK, 1985.
27. Fernández Bertos, M.; Simons, S. J. R.; Hills, C. D.; Carey, P. J. A review of accelerated carbonation technology in the treatment of cement-based materials and sequestration of CO2. Journal of Hazardous Materials 2004, 112 (3), 193-205.
28. Szekely, J. Gas-solid reactions. Elsevier, 2012.
29. Shafique, M. S. B.; Walton, J. C.; Gutierrez, N.; Smith, R. W.; Tarquin, A. J. Influence of Carbonation on Leaching of Cementitious Wasteforms. Journal of Environmental Engineering 1998, 124 (5), 463-467.
30. Saito, T.; Sakai, E.; Morioka, M.; Otsuki, N. Carbonation of & gamma;-Ca2SiO4 and the Mechanism of Vaterite Formation. Journal of Advanced Concrete Technology 2010, 8 (3), 273-280.
31. Katsuyama, Y.; Yamasaki, A.; Iizuka, A.; Fujii, M.; Kumagai, K.; Yanagisawa, Y. Development of a process for producing high-purity calcium carbonate (CaCO3) from waste cement using pressurized CO2. Environmental Progress 2005, 24 (2), 162-170.
32. Azdarpour, A.; Asadullah, M.; Junin, R.; Manan, M.; Hamidi, H.; Daud, A. R. M. Carbon Dioxide Mineral Carbonation Through pH-swing Process: A Review. Energy Procedia 2014, 61, 2783-2786.
33. Jaschik, J.; Jaschik, M.; Warmuzinski, K. The utilisation of fly ash in CO2 mineral carbonation. Chemical and Process Engineering 2016, 37.
34. 許伯良、林平全、徐登科，轉爐石產製與工程應用，2011年轉爐石應用於瀝青混凝土鋪面研討會，2011.
35. 中國鋼鐵股份有限公司、中龍鋼鐵股份有限公司，轉爐石應用於水泥生料使用手冊，2020.
36. Backes, J. G.; Suer, J.; Pauliks, N.; Neugebauer, S.; Traverso, M. Life Cycle Assessment of an Integrated Steel Mill Using Primary Manufacturing Data: Actual Environmental Profile. Sustainability 2021, 13 (6), 3443.
37. 中國鋼鐵股份有限公司、中龍鋼鐵股份有限公司，轉爐石道路基底層使用手冊，2020.
38. 林志棟; 蔡瑋倫; 郭孟鑫. 轉爐石在道路工程應用的相關國家標準及綱要規範，2012年轉爐石瀝青混凝土研討會，2012.
39. Wang, G.; Wang, Y.; Gao, Z. Use of steel slag as a granular material: Volume expansion prediction and usability criteria. Journal of Hazardous Materials 2010, 184 (1), 555-560.
40. Yildirim, I. Z.; Prezzi, M. Chemical, Mineralogical, and Morphological Properties of Steel Slag. Advances in Civil Engineering 2011, 2011, 463638.
41. 中國鋼鐵股份有限公司、中龍鋼鐵股份有限公司，轉爐石瀝青混凝土使用手冊，2017.
42. Liu, X.; Feng, P.; Cai, Y.; Yu, X.; Yu, C.; Ran, Q. Carbonation behavior of calcium silicate hydrate (C-S-H): Its potential for CO2 capture. Chemical Engineering Journal 2022, 431, 134243.
43. Ma, M.; Mehdizadeh, H.; Guo, M.-Z.; Ling, T.-C. Effect of direct carbonation routes of basic oxygen furnace slag (BOFS) on strength and hydration of blended cement paste. Construction and Building Materials 2021, 304, 124628.
44. He, T.; Li, Z.; Zhao, S.; Zhao, Z.; Zhao, X. Effect of reductive component-conditioning materials on the composition, structure, and properties of reconstructed BOF slag. Construction and Building Materials 2020, 255, 119269.
45. Jennings, H. M. Refinements to colloid model of C-S-H in cement: CM-II. Cement and Concrete Research 2008, 38 (3), 275-289.
46. Shi, C. Characteristics and cementitious properties of ladle slag fines from steel production. Cement and Concrete Research 2002, 32 (3), 459-462.
47. Chan, C. J.; Kriven, W. M.; Young, J. F. Physical Stabilization of the β→γ Transformation in Dicalcium Silicate. Journal of the American Ceramic Society 1992, 75 (6), 1621-1627.
48. 曾耀弘、李育成. 改質轉爐石在工程材料與循環經濟之應用，工程期刊，2021，39~50.
49. 行政院環境保護署，110年事業廢棄物申報量統計報告，2022.
50. Tong, Z.; Ma, G.; Zhang, X.; Zhang, B.; Xue, Z. Thermodynamic analysis on calcium dissolution in the system of Ca(II)-NH3-NH4Cl-H2O. Separation Science and Technology 2016, 51 (13), 2225-2231.
51. Olofsson, G. Thermodynamic quantities for the dissociation of the ammonium ion and for the ionization of aqueous ammonia over a wide temperature range. The Journal of Chemical Thermodynamics 1975, 7 (6), 507-514.
52. Chaïrat, C.; Schott, J.; Oelkers, E. H.; Lartigue, J.-E.; Harouiya, N. Kinetics and mechanism of natural fluorapatite dissolution at 25°C and pH from 3 to 12. Geochimica et Cosmochimica Acta 2007, 71 (24), 5901-5912.
53. Oelkers, E. H.; Schott, J.; Devidal, J.-L. The effect of aluminum, pH, and chemical affinity on the rates of aluminosilicate dissolution reactions. Geochimica et Cosmochimica Acta 1994, 58 (9), 2011-2024.
54. Sun, Y.; Zhang, J. P.; Zhang, L. NH4Cl selective leaching of basic oxygen furnace slag: Optimization study using response surface methodology. Environmental Progress & Sustainable Energy 2016, 35 (5), 1387-1394.
55. Chen, J.; Xiang, L. Controllable synthesis of calcium carbonate polymorphs at different temperatures. Powder Technology 2009, 189 (1), 64-69.
56. Wang, L.; Chen, L.; Provis, J. L.; Tsang, D. C. W.; Poon, C. S. Accelerated carbonation of reactive MgO and Portland cement blends under flowing CO2 gas. Cement and Concrete Composites 2020, 106, 103489.
57. Hills, C. D.; Sweeney, R. E. H.; Buenfeld, N. R. Microstructural study of carbonated cement-solidified synthetic heavy metal waste. Waste Management 1999, 19 (5), 325-331.