水泥硬化体中Cr的形态及分布——改进的Tessier连续浸提法

SPECIATION AND DISTRIBUTION OF Cr IN HARDENED CEMENT PASTE——MODIFIED TESSIER SEQUENTIAL EXTRACTION PROCEDURE

采用改进的Tessier连续浸提法,结合电感耦合等离子体原子发射光谱、X射线衍射、扫描电子显微镜和能谱等测试手段,分析了不同形态Cr在水泥水化产物中的分布。结果表明:硅酸盐水泥硬化体中可交换态和碳酸盐结合态Cr占其总量的7%～35%,主要以吸附和沉淀形式存在于颗粒表面,对pH变化较为敏感,Cr的溶出对应于Ca(OH)2的溶解和部分水化硅酸钙(C-S-H)的溶解。不容易迁移的铁锰氧化态、硫化物结合态和残渣态的Cr约占总Cr含量的65%～93%,为Cr的主要分布形态,其溶出对应于钙矾石(AFt)和C-S-H和未水化熟料相的分解。随龄期延长,Cr逐渐向迁移能力较强的可交换态和碳酸盐结合态转变。

A modified Tessier＇s sequential extraction procedure was used to investigate the speciation of Cr in hardened portland cement.The amount of Cr in extracting solution was determined by inductively coupled plasma atomic emission spectroscopy.The distribution of Cr in portland cement hydrates was analyzed via X-ray diffraction,scanning electron microscopy and energy dispersive X-ray spectroscopy.The results show that：7%-35% of Cr in hydrated cement exists in the exchangeable form or in the form bound to carbonates,which is adsorbed or deposited on the surface of cement hydrate grains and is easy to leach out.The leaching of the two species is sensitive to the variation of pH value and accompanied by the dissolution of Ca（OH）2 and part of calcium silicate hydration（C-S-H）.65%-93% of Cr existed as species bound to Fe-Mn oxides,to sulfide compounds or as insoluble residue,which leached out with the decomposition of hydration products such as ettringite（AFt）,C-S-H and unhydrated cement particles.The presence of Cr as species in the exchangeable form or in the form bound to carbonates increased gradually with curing age.