Spectroscopic Investigation of Ni Speciation in Hardened Cement Paste

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• 作者：M. Vespa ; R. D&auml ; hn ; D. Grolimund ; E. Wieland ; and A. M. Scheidegger
• 刊名：Environmental Science & Technology
• 出版年：2006
• 出版时间：April 1, 2006
• 年：2006
• 卷：40
• 期：7
• 页码：2275 - 2282
• 全文大小：516K
• 年卷期：v.40,no.7(April 1, 2006)
• ISSN：1520-5851

文摘

Cement-based materials play an important role in multi-barrier concepts developed worldwide for the safe disposalof hazardous and radioactive wastes. Cement is used tocondition and stabilize the waste materials and to constructthe engineered barrier systems (container, backfill, andliner materials) of repositories for radioactive waste. In thisstudy, Ni uptake by hardened cement paste has beeninvestigated with the aim of improving our understandingof the immobilization process of heavy metals in cement onthe molecular level. X-ray absorption spectroscopy(XAS) coupled with diffuse reflectance spectroscopy(DRS) techniques were used to determine the localenvironment of Ni in cement systems. The Ni-doped sampleswere prepared at two different water/cement ratios (0.4,1.3) and different hydration times (1 hour to 1 year) using asulfate-resisting Portland cement. The metal loadingsand the metal salts added to the system were varied (50up to 5000 mg/kg; NO₃^-, SO₄^2-, Cl^-). The XAS study showedthat for all investigated systems Ni(II) is predominantlyimmobilized in a layered double hydroxide (LDH) phase,which was corroborated by DRS measurements. Only aminor extent of Ni(II) precipitates as Ni-hydroxides(mages/gifchars/alpha.gif" BORDER=0>-Ni(OH)₂ and mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-Ni(OH)₂). This finding suggests thatNi-Al LDH, rather than Ni-hydroxides, is the solubility-limiting phase in the Ni-doped cement system.