以超重力技術碳酸化後煉鋼廢棄物作為水泥添加材料之表現評估

Abstract

雖然鋼鐵業作為國家經濟發展之重要產業，但其生產過程中不僅產生有害廢棄物還會排放大量之二氧化碳。本研究旨在利用超重力碳酸化技術將不同煉鋼廢棄物進行碳酸化，同時吸收二氧化碳並探討各材料對碳捕捉的能力，而後再將碳酸化後煉鋼廢棄物作為礦粉摻料添加於水泥材料中，探究其對水泥材料的工作性、強度及耐久性的影響。在本研究中預先將磨細的轉爐石、精煉鋼渣、電弧爐碴與 水混合形成泥漿，泵送進超重力旋轉床（RPB）中與二氧化碳反應60 分鐘，透過改變轉速（700-1300rpm）、液固比（10-50 mL / g）和粒徑（32-160μm）求出不同反應條件下之碳酸化轉換率，並找出碳酸化程序的最佳工況點。據本研究顯示，1100rpm、20 mL / g、32μm 之電弧爐還原碴具有高達19.29±0.05 克-二氧化碳/100 克-爐碴的捕碳容量。同時也透過TGA、SEM、XRD 分析可看出碳酸化過程成功將原料中游離氧化鈣、氫氧化鈣及矽氧化鈣轉換為碳酸鈣附著於反應後材料表面。反應後將材料以5-15%添加於水泥漿體和砂漿中，發現水泥雖然流動性稍微下降，但黏性提高可以防止拌和混凝土發生析離，而凝結部分透過碳酸化可打斷電弧爐氧化碴的緩凝機理並使其順利凝結。碳酸鈣過程消除了游離氧化鈣和鹼金屬離子可以防止水泥晚期吸水後發生膨脹，提高水泥的晚期強度和耐久性。另外碳酸化過程形成的碳酸鈣可以和水泥中的鋁酸三鈣進行反應，形成產物填補孔隙，提高水泥早期強度和抗硫性。最後透過強度動力學模式分析添加材料對水泥強度發展的影響。故本研究之碳酸化過程不僅能做到處理二氧化碳，煉鋼廢棄物，同時將其資源化後還能提高水泥性能，極具發展前景。

Steelmaking industry plays an important role in economical development. However, steelmaking slags and carbon dioxide are generated simultaneously during production which are harmful for the environment. This research focused on carbonation of four kinds of steelmaking slags via High-Gravity Carbonation Process and also investigated the workability, strength and durability of cement with partial replacement of slags. In this study, slags after pretreatment were added in tap water and blended into slurry. Next, the slurry would be pumped into the rotating packed bed reactor, react with carbon dioxide for 60 minutes with different operating parameters. The results indicate that the EAFRS under 1100 rpm, 20 mL/g and 32 μm had the best carbonation conversion yield, which could fixed 19.29±0.05 g-CO2/100 g-slag. The difference of slags between carbonation can be analyzed by thermo-gravavimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray diffraction (XRD). During the carbonation process, free lime, calcium hydroxide and calcium silicates would be leached out, react with CO2 and yield calcium carbonate attached on the slags’surface. After that, carbonated slags were used as supplementary materials, blended in cement with 5 to 15% replacement. With slags added, although the fluidity of cement declined, the viscosity of the mortar got increased, which might prevent the cement segregated from aggregates. The carbonation process could wash out the organic compounds in the EAFOS, break off the retarding mechanism and make the cement specimens set normally. Besides, the carbonation process could also eliminate free lime, calcium hydroxide and alkali ions, which prevented the specimens expanding from hydration process and alkali-aggregate reaction. Furthermore, calcium carbonated generated form the carbonation process could react with tricalcium aluminate in clinker, which produced C-A-C̅ -H gel and filled up the porosity between hydration products. Thus, the compressive strength at early age, later age and the durability of mortars could be improved. Consequently, this study can not only deal with carbon dioxide and alkaline wastes from steelmaking, but also produced products which can promote the properties of cement.