Quantification of iron minerals formed during aging of iron-containing colloids


Quantification of iron minerals formed during aging of iron-containing colloids

Reuther, H.; Ulrich, K.-U.

Due to their large specific surface area and high sorption affinity, iron-containing colloids are capable to remove dissolved contaminants from solution and to retard their migration by the water path. In a pH range near to the point of zero charge, the low electrostatic stability favors agglomeration and sedimentation of such colloids, enabling their retention (e.g., by the formation of crusts). Freshly formed iron-rich colloids mainly consist of metastable iron phases such as schwertmannite or ferrihydrite. X-ray diffraction is not sensitive enough to quantify these phases because of small particle size (< 50 nm) and/or poor structural order. Aging of these metastable phases to more crystalline Fe minerals such as goethite or hematite may have consequences on the fate of the adsorbed contaminants. The modification of surface binding sites and of steric mineral properties by the recrystallization process may cause either desorption of the contaminants from the surface, or allow their incorporation into the lattice.

Our research focuses on the mobility of uranium during the flooding process of abandoned uranium mines in East Germany. The aim is to study the behavior of uranium during the aging process of iron-rich colloids which have scavenged uranium. Information on the speciation of uranium and its migration in the vicinity of such mines is crucial for hazard prognosis.
It is thus necessary to identify and to quantify precisely the transformation of iron phases into more crystalline Fe minerals by chemical analysis. Mössbauer spectroscopy is a powerful tool to discriminate the expected minerals goethite, hematite and ferrihydrite. In mixtures, fractions < 5 % can be separated without difficulties. We used Mössbauer spectroscopy at room temperature to identify the aging products. Transmission spectra of calibration standards of ferrihydrite, goethite, hematite and mixtures of defined ratios were compared with spectra of the iron-containing colloids. This enabled us to characterize the aging process.

  • Contribution to proceedings
    International Conference on Applications of Mössbauer Effect, 05.-09.09.2005, Montpellier, France
  • Poster
    International Conference on Applications of Mössbauer Effect, 05.-09.09.2005, Montpellier, France

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Publ.-Id: 7269