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

• 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
• Project Status: Completed (Fiscal Year 2021)
• Budget Amount: ¥2,860,000 (Direct Cost: ¥2,200,000、Indirect Cost: ¥660,000); Fiscal Year 2020: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2019: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
• 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 / 六価クロム / クロム同位体 / 安定同位体 / 岩石風化 / ニッケルラテライト鉱床 / TIMS / クロム / ニッケル / 環境動態

Outline of Research at the Start

かんらん岩や蛇紋岩などの超苦鉄質岩の化学風化により形成されたラテライト鉱床は，インドネシアやミャンマーなどの東南アジア諸国を含む熱帯・亜熱帯地域に広く分布しており，レアメタルの新たな供給源として注目されている．しかしながら，鉱床の開発においては人体に有害な6価クロムの溶出による周辺土壌および河川の汚染が問題となっている．本研究では，酸化・還元反応によって大きな変動を示すクロムの安定同位体比（53Cr/52Cr）に着目し、6価クロムの生成機構および逐次抽出法による溶出挙動を明らかにすることで風化岩石・土壌中のクロムの環境動態を定量的に理解し，6価クロムの有効な汚染防止策や浄化策の提案に繋げる.

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).

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。

Research Products

• [Journal Article] Geochemical constraints on the mobilization of Ni and critical metals in laterite deposits, Sulawesi, Indonesia: A mass‐balance approach (2021)
  • Author(s): Ito Akane、Otake Tsubasa、Maulana Adi、Sanematsu Kenzo、Sufriadin、Sato Tsutomu
  • Journal Title: Resource Geology Volume: 71 Issue: 3 Pages: 255-282
  • DOI: 10.1111/rge.12266
  • NAID: 120007089509
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] The formation of Fe colloids and layered double hydroxides as sequestration agents in the natural remediation of mine drainage (2021)
  • Author(s): Chikanda Frances、Otake Tsubasa、Koide Aoi、Ito Akane、Sato Tsutomu
  • Journal Title: Science of The Total Environment Volume: 774 Pages: 145183-145183
  • DOI: 10.1016/j.scitotenv.2021.145183
  • NAID: 120007044500
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Large Fe isotope fractionations in sulfide ores and ferruginous sedimentary rocks from the Kuroko volcanogenic massive sulfide deposits in the Hokuroku district, northeast Japan (2021)
  • Author(s): Otake Tsubasa、Yamada Ryoichi、Suzuki Ryohei、Nakamura Shunsuke、Ito Akane、Shin Ki-Cheol、Sato Tsutomu
  • Journal Title: Geochimica et Cosmochimica Acta Volume: 295 Pages: 49-64
  • DOI: 10.1016/j.gca.2020.12.009
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Chromium occurrence in a nickel laterite profile and its implications to surrounding surface waters (2020)
  • Author(s): Delina Ruth Esther、Arcilla Carlo、Otake Tsubasa、Garcia Jhonard John、Tan Mark、Ito Akane
  • Journal Title: Chemical Geology Volume: 558 Pages: 119863-119863
  • DOI: 10.1016/j.chemgeo.2020.119863
  • Peer Reviewed / Int'l Joint Research
• [Presentation] Mobilization and isotope fractionation of chromium in Ni laterites, Indonesia (2021)
  • Author(s): Ito A., Otake T., Yamashita T., Maulana A., Sanematsu K., Sufriadin, Sato T., Tanimizu M
  • Organizer: Goldschmidt Conference 2021
  • Int'l Joint Research
• [Presentation] IC-ICP-MSを用いたCr(III)およびCr(VI)の同時定量法の確立と環境試料への応用 (2020)
  • Author(s): 伊藤茜、森下雄平、谷水雅治
  • Organizer: 2020年度質量分析学会総合討論会
• [Presentation] Ni enrichment associated with Fe isotope fractionation in Ni laterite deposits, Sulawesi Island, Indonesia (2020)
  • Author(s): Ito, A., Otake, T., Maulana, A., Sanematsu, K., Sufriadin, and Sato, T.
  • Organizer: Mineral Deposits Studies Group Annual Meeting 2020
  • Int'l Joint Research
• [Presentation] 超苦鉄質岩の化学風化におけるCr同位体分別と移動・溶出挙動の理解 (2019)
  • Author(s): 伊藤茜、大竹翼、山下勝行、申基澈
  • Organizer: 第9回同位体環境学シンポジウム