Mechanisms of solidification of cadmium in municipal solid waste incineration fly ash usinga slag cemented backfill agent
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摘要: 胶结充填采矿协同利用垃圾焚烧飞灰是解决飞灰日益激增的新思路,可大量资源化利用飞灰并固化其中的重金属离子.本文以矿渣-钢渣基胶凝材料(简称冶金渣胶凝材料)分别结合4种城市垃圾焚烧(MSWI)飞灰制备胶凝材料,并以全尾砂作为骨料制成胶结充填料,测定充填料试样的流动度、抗压强度以及Cd2+浸出质量浓度:冶金渣-垃圾焚烧飞灰基充填料试样的流动度为240~265 mm,满足矿山充填的泵送要求;28 d抗压强度均大于8.88 MPa,满足一般矿山充填1~6.5 MPa的强度要求;Cd2+浸出液质量浓度低于饮用水标准5 μg·L-1的限值.通过X射线衍射(XRD)、红外光谱(IR)和热重-差示扫描量热法(TG-DSC)分析表明胶凝材料的主要水化产物组成为钙矾石、Friedel盐和C-S-H凝胶;通过X射线光电子能谱(XPS)发现Cd2+对Al2+的结合能有较大影响,钙矾石、Friedel盐可能对镉离子有固化作用.Abstract: In cement production, the synergistic use of municipal solid waste incineration (MSWI) fly ash provides a novel approach to solve the problem of the increasing productions of fly ash and heavy metal ions. In this study, slag-steel slag based cementitious material (referred to as metallurgical slag cementitious materials) was combined with four types of MSWI fly ash for preparing cementitious materials, all of which use sand as a binder. According to the determination of fluidity, compressive strength and Cd2+ leaching concentration of filler samples, the following are found:(1) the flow rate of filler material prepared from metallurgical slag and fly ash is 240-265 mm, which fulfills the pumping requirement of mine filling; (2) the 28-day compressive strength values are>8.88 MPa, which meets the general mine filling strength requirements (1-6.5 MPa); and (3) the Cd2+ leachate concentration is lower than the drinking water standard of 5 μg·L-1 limit. The results of X-ray diffraction, infrared spectroscopy, and thermogravimetry-differential scanning calorimetry show that the leading hydration products of gelling materials are ettringite, Friedel, and C-S-H. Furthermore, X-ray photoelectron spectroscopy results reveal that Cd2+ has a great effect on the binding energy of Al3+. Ettringite and Friedel salts are found to have a curing effect on cadmium ions.
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Keywords:
- metallurgical slag /
- waste incineration fly ash /
- cementitious materials /
- cadmium
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