摘要
通过X射线衍射仪、傅里叶变换红外光谱仪和热重分析仪表征了钢渣、硅酸三钙(C3S)和电石渣3种富钙材料的固碳能力;分析了其碳化体系的pH值变化;通过扫描电子显微镜和纳米压痕仪测试了3种材料碳化前后的微观形貌和力学性能.结果表明:富钙材料的固碳能力与其化学组成,尤其是其可溶解钙有直接的关系,可溶解钙含量最高的电石渣具有最高的固碳能力;而碳化后的力学性能则取决于碳化产物的微观力学性能以及原材料与碳化产物的堆积形态,微观形貌粗糙的钢渣和C3S更易与碳化产物紧密堆积,碳化后微观力学性能增强;但碳化产物难以填充在片状的电石渣空隙中,碳化后电石渣的微观力学性能减弱.
目前,中国水泥生产过程中的碳排放量占全国总碳排放量的8%~9
有研
本文以钢渣、硅酸三钙(C3S)和电石渣3种富钙材料为代表,在有/无液态水的情况下对3种材料进行碳化处理,探究3种材料碳化行为的差异,分析其固碳能力及碳化增强性能的影响因素与作用机理,有望为选择具有高固碳能力和优异碳化增强性能的富钙材料提供依据.
钢渣(SS)由山西省某钢铁厂提供;C3S为参照文献[
Raw material | CaO | SiO2 | Fe2O3 | MgO | Al2O3 | MnO | P2O5 | Other | IL |
---|---|---|---|---|---|---|---|---|---|
Steel slag | 37.35 | 17.92 | 24.66 | 6.25 | 4.25 | 4.82 | 1.71 | 1.03 | 2.01 |
C3S | 66.51 | 18.63 | 3.34 | 2.25 | 4.28 | 0.15 | 0.13 | 3.96 | 0.75 |
Carbide slag | 68.34 | 3.07 | 0.50 | 0.16 | 1.74 | 0.01 | 1.49 | 24.69 |
将约2 g原材料分别放入直径4 cm、高2 cm的聚四氟乙烯盒中,设置液固比(mL/mS)分别为0、0.15,使用去离子水拌和并制备样品,随后将其放入CO2质量分数为40%、相对湿度(RH)为60%、25 ℃的碳化箱中碳化处理1 d;取出样品并放入真空干燥箱中干燥3 d,之后研磨成粒径小于0.075 mm的粉末,密封保存,用于后续测试.每组试验重复3次.具体的试验分组及样品编号如
Sample | Raw material | Carbonation time/d | mL/mS |
---|---|---|---|
SS | Steel slag | 0 | |
SS‑0 | Steel slag | 1 | 0 |
SS‑0.15 | Steel slag | 1 | 0.15 |
C3S | C3S | 0 | |
C3S‑0 | C3S | 1 | 0 |
C3S‑0.15 | C3S | 1 | 0.15 |
CS | Carbide slag | 0 | |
CS‑0 | Carbide slag | 1 | 0 |
CS‑0.15 | Carbide slag | 1 | 0.15 |
利用Bruker D8 Discover 型X 射线衍射仪(XRD)、Nicolet iS10型傅里叶红外光谱仪(FTIR)和TA TGA 550型热分析仪(TG/DTG)测定碳化前后样品的物相组成.在XRD测试中,样品中掺入质量分数为20 %的α‑Al2O3作为内标物质,与适量异丙醇湿磨并混合均匀后真空干燥2 d再进行测试,并使用Tomas软件定量分析物相含量.
参考标准ISO 10390: 2005(E) Soil Quality—Determination of pH测定碳化前后样品粉末的pH值.取适量样品粉末浸入去离子水中,液固比为5∶1,搅拌5 min使粉末均匀分布,静置3 h后取上清液测pH值.
利用Nova Nano SEM450型扫描电子显微镜(SEM)表征样品碳化前后的微观形貌.
利用纳米力学性能测试系统测试碳化前后样品的硬度和弹性模量,其过程为:取适量样品粉末压制成直径8 mm的圆片并放入直径25 mm的硅胶模具中,在真空环境下浇筑环氧树脂以消除气泡;环氧树脂固化后,依次使用粒度为38.0、13.0、6.5 μm的SiC砂纸研磨样品的底部,再依次使用粒度为9、3、1 μm的金刚石抛光至表面光滑;随后测试样品的硬度和弹性模量,选择16(平面布局为4×4)个点作为压痕测试点,压痕间隔4 μm,加载速率为0.2 mN/s,加载至2 mN并持荷60 s,卸载时间为10 s.
钢渣、C3S和电石渣碳化前后的XRD图谱如

图1 钢渣、C3S和电石渣碳化前后的XRD图谱
Fig.1 XRD patterns of steel slag, C3S and carbide slag before and after carbonation
对碳化前钢渣、C3S和电石渣的XRD图谱中含钙矿物相进行定量相分析,结果见
Raw material | C3S | C2S | Calcite | Ca(OH)2 | Amorphous |
---|---|---|---|---|---|
Steel slag | 22.54±0.89 | 44.98±2.35 | 4.81±0.46 | 24.82±2.11 | |
C3S | 88.97±3.41 | 1.11±0.28 | 9.92±1.06 | ||
Carbide slag | 19.39±1.32 | 78.97±4.21 | 0.33±0.09 |
Raw material | mL/mS=0 | mL/mS=0.15 |
---|---|---|
Steel slag | 8.15±0.81 | 12.72±0.94 |
C3S | 8.02±0.53 | 20.48±1.36 |
Carbide slag | 55.44±2.79 | 72.85±3.98 |
无论是否存在液态水,电石渣生成的CaCO3都最多,其次是C3S和钢渣,说明电石渣更容易发生碳化反应.根据
由
钢渣、C3S和电石渣碳化前后的FTIR光谱如

图2 钢渣、C3S和电石渣碳化前后的FTIR光谱
Fig.2 FTIR spectra of steel slag, C3S and carbide slag before and after carbonation
钢渣、C3S和电石渣碳化前后的TG/DTG曲线如

图3 钢渣、C3S和电石渣碳化前后的TG/DTG曲线
Fig.3 TG/DTG curves of steel slag, C3S and carbide slag before and after carbonation

图4 去离子水、钢渣、C3S和电石渣碳化前后的pH值
Fig.4 pH values of deionized water, steel slag, C3S and carbide slag before and after carbonation
钢渣、C3S和电石渣碳化前后的SEM图像如
Before carbonation | After carbonation mL/mS=0 | After carbonation mL/mS=0.15 | |
---|---|---|---|
SS |
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C3S |
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CS |
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图5 碳化前后的纳米压痕测试结果
Fig.5 Nanoindentation test results before and after carbonation
由2.1可知,3种材料的最主要碳化产物是方解石.据报道,方解石的弹性模量和硬度分别为35~60 GPa和2~4 GP
(1)当液固比为0和0.15时,钢渣、C3S和电石渣的主要碳化产物为方解石和少量无定形碳酸钙.3种材料中电石渣的固碳能力最高,因为其含钙物相(Ca(OH)2)的含量最多且易溶解和碳化.
(2)钢渣、C3S和电石渣的初始pH值在12.5左右,均属于强碱性材料,有利于碳化反应;碳化后,3种材料的pH值均有所降低,但电石渣中尚未碳化的Ca(OH)2对pH的降低起到了缓冲作用.
(3)钢渣、C3S和电石渣碳化后均生成了尺寸不足1 μm的块状方解石;当液固比为0.15时,相较于未碳化样品,碳化后钢渣的弹性模量提高了84.48%,碳化后C3S的弹性模量提高了105.96%,但电石渣碳化后弹性模量和显微硬度均有所降低.碳化后的微观力学性能与原材料和碳化产物的微观力学性能以及堆积状态有关.
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