| Abstract
| - Chromate is a widespread contaminant that has deleteriousimpacts on human health, the mobility and toxicity ofwhich are diminished by reduction to Cr(III). While biologicaland chemical reduction reactions of Cr(VI) are wellresolved, reduction within natural sediments, particularlyof arid environments, remains poorly described. Here, weexamine chromate reduction within arid sediments fromthe Hanford, WA site, where Fe(III) (hydr)oxide and carbonatecoatings limit mineral reactivity. Chromium(VI) reductionby Hanford sediments is negligible unless pretreated withacid; acidic pretreatment of packed mineral beds havinga Cr(VI) feed solution results in Cr(III) associating with theminerals antigorite and lizardite in addition to magnetiteand Fe(II)-bearing clay minerals. Highly alkaline conditions(pH > 14), representative of conditions near high-levelnuclear waste tanks, result in Fe(II) dissolution and concurrentCr(VI) reduction. Additionally, Cr(III) and Cr(VI) are foundassociated with portlandite, suggesting a secondarymechanism for chromium retention at high pH. Thus, mineralreactivity is limited within this arid environment andappreciable reduction of Cr(VI) is restricted to highly alkalineconditions resulting near leaking radioactive wastedisposal tanks.
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