钙系磷酸盐化学键合材料的制备及其固化重金属研究

Preparation of Calcium Based Chemically Bonded Phosphate Ceramics Using Ferrochrome Slag and Its Utilization on Immobilization of Pb^(2+),Cd^(2+) and Cu^(2+)

利用富含氧化钙的铬铁渣(FS)和磷酸二氢钾(P)反应制备钙系磷酸盐化学键合材料,并用其作为固化重金属离子(Pb^(2+)、Cd^(2+)、Cu^(2+))基体材料。研究了原料配比、缓凝剂及重金属掺量对胶凝材料初凝时间和抗压强度的影响。结果表明:当P/FS(质量比,下同)为1/4及硼砂掺量为2%时,材料性能最好,自然养护28d和常压蒸汽养护24h抗压强度分别可达25.65 MPa和36.86 MPa。随着重金属掺量的增加,材料抗压强度逐渐降低,掺量为3%时,自然养护28d和蒸汽养护24h试块抗压强度均大于10 MPa,满足建筑材料要求。固化体重金属毒性浸出试验表明:磷酸盐化学键合材料对重金属离子(Pb^(2+)、Cd^(2+)、Cu^(2+))均具有很好的固化效果,浸出浓度远低于相应的鉴别标准。通过XRD、SEM和FTIR分析,钙系磷酸盐化学键合材料固化重金属的机理是通过水化产物的化学键合、吸附以及物理包裹作用将Pb^(2+)、Cd^(2+)、Cu^(2+)固化在材料中。

Calcium based chemically bonded phosphate ceramics （CBPCs） were prepared through the reaction between calcium oxide-rich ferrochrome slag （FS） and potassium dihydrogen phosphate （P）, and the prepared CBPCs was used to solidify/stabilize the heavy metal ions such as Pb^2＋ ,Cd^2＋ , Cu^2＋. The influences of the potassium dihydrogen phosphate-to-ferrochrome slag （P/FS） molar ratio, the dosage of the retarders （borax） and the addition of heavy metals on the initial setting time and compressive strength of cementing material were investigated. It was showed that the CBPCs with best performance could be prepared when P/FS was 1/4 and the dosage of borax is 2%, and the compressive strength of the CBPCs reached 25. 65 MPa and 36.86 MPa by curing at room temperature for 28 d and curing at hydrothermal condition for 24 h, respectively. The compressive strength of the CBPCs decreased with the addition of heavy metals, and when the dosage of the heavy metal was up to 3-, the compressive strength of the samples were greater than 10 MPa by curing at room temperature for 28 d and hydrothermal condition for 24 h, which could all meet the standard of the building materials. The leachability of heavy metals including Pb^2＋ ,Cd^2＋ ,Cu^2＋ was determined by toxicity characte- ristic leaching procedure. The results showed that the CBPCs could efficiently solidify/stabilize the heavy metals, and the concentra- tions of heavy metals in the leachate were all far lower than the national standard （5 mg/L, 1 mg/L and 100 mg/L）. The solidified forms were characterized by means of X-ray diffraction （XRD）, Fourier transform infrared （FTIR） and scanning electron microscopy （SEM） to reveal the mechanism of heavy metal immobilization by CBPCs, which included the chemically incorporation, physical ad- sorption and inclusion.