Journal
CEMENT AND CONCRETE RESEARCH
Volume 38, Issue 5, Pages 681-688Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.cemconres.2008.01.006
Keywords
geopolymer; waste management; chromium; fly ash; immobilization
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The use of fly ash-based geopolymer binders to immobilize chromium is investigated in detail, with particular regard to the role of the sulfide ion as a reductant for Cr(VI) treatment. In the absence of sulfide, Cr added as Cr(VI) is highly leachable. However, addition of a small quantity of Na(2)S reduces the Cr to Cr(III), and enables leaching efficiencies in excess of 99.9% to be reached after 90 days' exposure to deionized water, Na(2)CO(3) or MgSO(4) solutions. Leaching in H(2)SO(4) is somewhat greater than this, due most probably to the oxidation of the Cr(III) present. Addition of the Cr(VI) as a highly soluble salt is preferable to its addition as a sparingly soluble salt, because a higher salt solubility means the Cr(VI) is more available for reduction prior to geopolymeric setting. The potential value of geopolymer technology as an immobilization process for problematic heavy metal waste streams is highlighted by these results, and the need for a full understanding of binder chemistry in any immobilization system outlined. (C) 2008 Elsevier Ltd. All rights reserved.
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