| Abstract
| - Mineralogical examination, using scanning electronmicroscopy (SEM), X-ray diffractometry (XRD), and opticalmicroscopy, was conducted on the Fe0-bearing reactivematerials derived from long-term column experimentsundertaken to assess the treatment capacity of Fe0 underdifferent geochemical conditions. The columns receivedeither deionized water or solutions of differing dissolvedcalcium carbonate concentrations, together either withtrichloroethene (TCE) or hexavalent chromium (Cr(VI)). Themajor reaction product in the columns receiving deionizedwater was magnetite−maghemite, and for the columnsreceiving dissolved calcium carbonate, the main productswere iron hydroxy carbonate and aragonite. Replacementof Fe0 by reaction products occurred mainly at the edges ofthe Fe0 particles, and penetrative replacement wasfocused along cracks and along and around graphiticinclusions. Fibrous or flake-shaped iron hydroxy carbonatemostly replaced the edges of the Fe0 particles. Aragonitehad needle-shaped morphology, and some occurred asclusters of crystals. Aragonite was deposited on iron hydroxycarbonate, thus providing at least a partial armoringeffect. The mineral was also observed to cement groupsof Fe0 particles into compact aggregates. The Cr was presentmostly as Cr(III) in Cr(III)-Fe(III) (oxy)hydroxides and intrace amounts in iron hydroxy carbonate.
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