Silicon concentration and pH controls over competitive or simultaneous incorporation of iodate and chromate into calcium carbonate phases

Journal Article · Sat May 01 00:00:00 EDT 2021 · Applied Geochemistry

DOI:https://doi.org/10.1016/j.apgeochem.2021.104941· OSTI ID:1797421

Katsenovich, Yelena ^[1]; Gort, Rocio Trimino ^[1]; Gudavalli, Ravi ^[1]; Szecsody, James E. ^[2]; Freedman, Vicky L. ^[2]; Qafoku, Nikolla  ^[2]

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1. Florida International University
2. BATTELLE (PACIFIC NW LAB)

Iodate and chromate coprecipitation with CaCO3 minerals is a potential approach that can significantly decrease their mobility in the subsurface. Identifying the pH and Si concentration controls on these in situ processes is needed to assess the feasibility of the in situ strategy in the field. Batch experiments combined with solid phase characterization studies examined the co-precipitation/incorporation of iodate and chromate into CaCO3 minerals and measured the release of contaminants during dissolution. Experiments conducted at variable pH (e.g., 6.5, 8 and 9) and Si concentrations (e.g., 0 mM, 0.5 mM and 20 mM) showed that the incorporation of iodate is pH dependent and it is favored at a lower pH and higher Si concentration within 7 days. The presence of chromate had little effect on the removal of iodate except at pH 6.5 where iodate uptake increased 6-10% due to the formation of dietzeite, Ca2H2O(IO3)2(CrO4). More aqueous iodate was removed in all experiments compared to chromate. The removal of chromate was slightly higher in samples where vaterite was formed. The presence of aqueous Si is a factor that influences iodate and chromate removal during CaCO3crystalization. The release of iodate and chromate from dissolving CaCO3 is pH and Si concentration dependent. The I released fraction from CaCO3 doped with IO3- was 1.5-2.3% and leveling off after 24h; however, 2.6-4.6% of I was released from CaCO3 doped with IO3- and CrO42- for all tested conditions. More chromate than iodate was released during dissolution up to 36.5±4.6% at pH 6.5 and 20 mM Si. The results provide new insights on the role of pH and Si concentrations on the coprecipitation of IO3- and CrO42- with calcite and their release during the dissolution of doped calcite.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1797421
• Report Number(s): PNNL-SA-153342
• Journal Information: Applied Geochemistry, Vol. 128
• Country of Publication: United States
• Language: English