CALL FOR PROPOSALS:

ORGANIZERS

  • Harvey Thorleifson, Chair
    Minnesota Geological Survey
  • Carrie Jennings, Vice Chair
    Minnesota Geological Survey
  • David Bush, Technical Program Chair
    University of West Georgia
  • Jim Miller, Field Trip Chair
    University of Minnesota Duluth
  • Curtis M. Hudak, Sponsorship Chair
    Foth Infrastructure & Environment, LLC

 

Paper No. 10
Presentation Time: 11:15 AM

FORMATION OF CR(VI) RELATED TO CR(III)-MUSCOVITE IN SOIL AND GROUNDWATER SYSTEMS


RAJAPAKSHA, Anushka Upamali, Korea Biochar Research Center & Department of Biological Environment, Kangwon National University, Chuncheon, Korea, 200-701, South Korea, VITHANAGE, Meththika, Chemical and Environmental Systems Modeling Research Group, National Institute of Fundamental Studies, Hantana Road, Kandy, 20000, Sri Lanka, OZE, Christopher, Department of Geological Sciences, University of Canterbury, Private bag 4800, Christchurch, 4800, New Zealand, WEERASOORIYA, R., Institute of Fundamental Studies, Hantana Road, Kandy, 20000, Sri Lanka and BANDARA, W.M.A.T., Department of Chemistry, University of Peradeniya, Peradeniya, 20400, Sri Lanka, anushkaupamali@gmail.com

Chromium release and oxidation from Cr(III)-bearing minerals is an environmental hazard in sediments, soils and groundwater related to ultramafic rocks and their metamorphic derivatives. Birnessite has been shown to promote Cr(III) oxidation from Cr(III)-enriched oxides (i.e., chromite). However, Cr(III)-bearing silicates with overall less total Cr(III) are hypothesized to result in faster rates of Cr(VI) production due to lower mineral solubilities. Here, we investigate Cr(III) release and oxidation related to geochemical interactions between Cr(III)-muscovite (i.e., fuchsite) and birnessite in subsurface aqueous environments with and without humic matter (HM). The initial rates of Cr(VI) production are fast (1.52 to 3.39 × 10-4 mg kg-1 h-1 at pH values of 6 and 3, respectively, without HM) and thereafter rates are decreasing, where 20 µg of Cr(VI) per kilogram of fuchsite can be achieved in 45 days. Rates of Cr(VI) formation are dependent on both birnessite and Cr-muscovite suspension densities (m2 L-1) and on solution pH where higher Cr(VI) production rates are achieved with higher suspension densitites and at lower pH values, agreeing with past studies. When HM is added to the system, Cr(VI) production decreases significantly, supported by observations made on serpentine soils in Sri Lanka. Overall, Cr-muscovite and potentially other Cr(III)-bearing silicates (e.g., chlorite and clays) are major inputs of Cr(VI) to soils, sediments and groundwater capable of being moderated by the abundance and availability of HM.
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