以碳酸化煉鋼爐渣進行固碳及其再利用於混合水泥

Abstract

鋼鐵與水泥業是國家經濟發展之重要產業，如何兼顧產業經濟發展與環境保護儼然已成為最重要的問題。本研究探討將鹼性固體廢棄物透過碳酸化程序轉換成「永續營建材料」之可行性；同時，應用超重力旋轉填充床以提升碳酸化程序之效率。實驗材料為中鋼轉爐渣細粒料。本研究目標包括:(一) 鑑定爐渣碳酸化前後之物化性質；（二）評估不同操作因子對於轉爐渣之固碳效率與容量之影響；（三）研析碳酸化後轉爐渣對於再利用於混合水泥之效益，探討項目包括：物理性質、強度發展、體積穩定性與耐久性。 研究結果顯示，在超重力旋轉填充床中，二氧化碳可於常溫環境下有效轉換為穩定之碳酸鈣沉澱。於溫度30 oC與60 oC時，每公斤爐渣之固碳容量分別可達0.202 與 0.221 公斤CO2。此外，將碳酸化實驗數據以表面覆蓋模式進行分析，模擬其碳酸化反應之動力學特性，表面覆蓋模式迴歸之R2介於0.97至0.98。此外，碳酸化後之爐渣進行事業廢棄物毒性特性溶出程序，檢出值符合台灣建築中心之綠建材標章標準，且碳酸化可有效去除爐渣之free-CaO與Ca(OH)2，加強其再利用於混合水泥之健度與耐久性。另一方面，將碳酸化爐渣應用於混合水泥之工程材料初探，混合水泥配比為以碳酸化前後之爐渣分別取代10%重量比之水泥。碳酸化爐渣藉沉澱碳酸鈣產生之高比表面積特性，提供水泥水化產物額外之成核點，提升混合水泥水化速率、縮短凝結時間，並提升混合水泥早期之抗壓與抗彎強度發展；此結果亦藉由水化熱與水化產物微觀分析佐證。此外，爐渣經過碳酸化後於混合水泥之抗硫酸鹽侵蝕能力與乾縮行為亦明顯改善。據此，本研究結果顯示爐渣透過碳酸化程序可有效固定二氧化碳，並提升產物應用於混合水泥之潛力，早期強度發展、物理性質、抗硫酸鹽侵蝕能力與乾縮行為較未反應前爐渣優異。

This study explores the feasibility of developing sustainable construction materials via mineral carbonation of steelmaking slag, i.e., basic oxygen furnace slag (BOFS). The carbon fixation capacity of BOFS was quantified by thermo-gravimetric analysis. Various engineering properties and hydration characteristics of blended cement with 10 % of both fresh BOFS and carbonated BOFS by weight as cement replacement was investigated. The results indicate mineral carbonations accompanied by significant reduction in basicity and fixing 0.202 and 0.221 kg CO2/kg BOFS at 30 oC and 60 oC within the rotating packed bed (RPB) reactor. The reaction kinetics of carbonation experiments could be well expressed by the surface coverage model, with R2 values ranged from 0.97 to 0.98. Cement blended with 10 wt% of carbonated BOFS resulted in reduced setting times and accelerated early strength development, which was consistent with the results of hydration heat and XRD observations. The SEM observations suggest that the carbonated BOFS could serve as nuclei for the precipitation of hydration products, while also accelerating the hydration. In addition, blended cement with 10 % of carbonated BOFS improved sulfate resistance ability and drying shrinkage property compared to 10 % of fresh BOFS at ambient temperature (23oC). The mineralogical composition changes after carbonation have beneficial effects on the hydraulic property in concrete. It was thus concluded that the carbonation of steelmaking slag should be considered as a feasible and attractive process for carbon fixation and waste valorization.