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Chemical state analysis of trace heavy metals in concrete and recycling of waste

混凝土中微量重金属化学态分析及废物回收利用

基本信息

批准号：
15560396
负责人：
UCHIKAWA Hiroshi
金额：
$ 2.05万
依托单位：
Kanazawa Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15560396/
关键词：
cement X-ray absorption fine structure chromium zinc chemical state analysis speciation

项目摘要

It is essential to clarify chemical behavior of harmful heavy metals in cement because of the rise of the tendency that uses waste for raw materials of the cement. The aim of this study is to clarify how a chemical state of a small amount of chromium (58.4ppm) and zinc (205.1ppm) originally contained in the ordinary portland cement changed with hydration.The following findings were obtained by applying XAFS (X-ray absorption fine structure) analysis by the synchrotron radiation to the cement system for the first time.As for the chromium, the reduction reaction from hexavalent to trivalent proceeded with hydration because the peak intensity of hexavalent chromium appearing at the absorption edge of the XANES region was decreased with hydration. This reduction reaction was presumed to be due to the trace divalent iron ion contained in cement. As for zinc, XAFS spectra indicated that in unhydrated cement the intrinsic trace zinc exists at the same local structure as the wurtzite ZnO, in which Zn atoms are surrounded by four O atoms in the first-coordination shell. As the hydration of cement proceeds, only the coordination number of the second shell decreases from 15.4 (unhydrated) to 7.5 (294 day) whereas that of the first shell and the interatomic distances of the both shells remain 4, 0.20nm, and 0.32 nm, respectively. Our results elucidate that zinc exists as a solid solution in unhydrated cement having the same local structure as the wurtzite ZnO, and that this trace zinc hydrolyzes to tetrahydroxozincate (II) ion [Zn(OH)_4]^<2-> with the hydration of cement keeping their fundamental structure of ZnO_4 tetrahedra.

由于利用废弃物作为水泥原料的趋势日益明显，有必要对有害重金属在水泥中的化学行为进行研究。本研究的目的是阐明少量铬的化学状态（58.4ppm）和锌普通波特兰水泥中原来含有的205.1ppm的硅酸盐矿物随水化作用发生了变化本文首次用同步辐射X射线吸收精细结构分析技术对水泥体系进行了分析。从六价到三价的还原反应随着水合作用而进行，因为在XANES区域的吸收边缘处出现的六价铬的峰强度随着水合作用而降低。这种还原反应被认为是由于水泥中含有微量的二价铁离子。对于锌，XAFS谱表明，在未水化的水泥中，本征微量锌存在于与纤锌矿ZnO相同的局部结构中，其中锌原子在第一配位壳层中被四个O原子包围。随着水泥水化过程的进行，只有第二壳层的配位数从15.4（未水化）下降到7.5（294天），而第一壳层的配位数和两个壳层的原子间距分别保持在4、0.20 nm和0.32 nm。结果表明，锌在未水化水泥中以固溶体的形式存在，具有与纤锌矿ZnO相同的局部结构，并且在水泥水化过程中，微量锌水解为四羟基锌酸根离子[Zn（OH）_4]~（2+），<2->保持了ZnO_4四面体的基本结构。