Geochemical behavior of chromium and its isotope fractionation during the weathering of ultramafic rocks

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K24388
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 1101:Environmental analyses and evaluation, environmental conservation measure and related fields
• Research Institution: Kwansei Gakuin University
• Principal Investigator: Ito Akane 関西学院大学, 生命環境学部, 助教 (30844659)
• Project Period (FY): 2019-08-30 – 2022-03-31
• Keywords: 6価クロム / 超苦鉄質岩 / 風化 / ラテライト / 逐次抽出 / 同位体

Outline of Final Research Achievements

Leaching of hexavalent chromium (Cr(VI)) during the development of the laterite deposits has become a problem. This study aims to clarify the formation mechanism and leaching behavior of Cr(VI) in lateritic deposits. The Cr isotopic composition of weathered and bedrock samples collected from laterite deposits in Indonesia indicates that the oxidation from Cr(III) to Cr(VI) is occurring near the surface. The sequential extraction showed that in the limonite horizons, Cr(VI) was most abundant in the adsorption fraction, which is the fraction with relatively high leachability. In contrast, Cr in the highly leachable fraction of the saprolite sample was less than 0.1%, suggesting that Cr(VI) is mainly produced in the limonite horizons. The correlation between Cr isotopic composition of the whole rock and depth variation of Cr concentration in the adsorptive fraction suggests that isotopic composition may reflect the mobility of Cr(VI).

Free Research Field

地球化学

Academic Significance and Societal Importance of the Research Achievements

ラテライト鉱床における6価クロムの溶出問題は、レアメタルの供給をこのタイプの鉱床に頼っている日本においては重要な課題である。また、超苦鉄質岩の風化による6価クロムの自然起源汚染はいくつかの国で確認されており、本研究成果はこれらの研究について同位体分析および存在形態分析が有効であることを示した。