{"title":"Chromium Isotope Geochemistry","authors":"L. Qin, Xiangli Wang","doi":"10.2138/RMG.2017.82.10","DOIUrl":null,"url":null,"abstract":"Chromium consists of four stable isotopes (50Cr, 52Cr, 53Cr and 54Cr) with natural abundances of 4.35%, 83.79%, 9.50% and 2.36%, respectively (Rossman and Taylor 1998). Among these four isotopes, 50Cr, 52Cr and 54Cr are non-radiogenic, whereas 53Cr is a radiogenic product of the extinct nuclide 53Mn, which has a half-life of 3.7 Myr (Honda and Imamura 1971). Chromium isotope systems have a wide range of applications in geochemistry and cosmochemistry. They have been used to study early solar system processes (e.g., Rotaru et al. 1992); the oxidation/reduction (redox) potential of underground systems, which governs the transport and fate of many contaminants (e.g., Ellis et al. 2002); and more recently, the redox evolution of Earth’s early ocean-atmosphere system, which is intimately linked to the evolution of life (Frei et al. 2009; Crowe et al. 2013; Planavsky et al. 2014; Cole et al. 2016). ### Chemical properties of Cr Chromium is redox-sensitive. In Earth’s near-surface environments, Cr has two main valence states, +3 and + 6, which are expressed as Cr(III) and Cr(VI), respectively. The valence state of Cr is controlled by the prevailing redox potential (Eh) and pH conditions (Fig. 1). Cr(VI) is always bound with O2− to form the oxyanion species CrO42− (chromate), HCrO4− (bichromate), and Cr2O72−(dichromate), all of which are water-soluble. In contrast, Cr3+ usually forms oxyhydroxides or oxides, which are insoluble and immobile in the natural pH range. During oxidative weathering, Cr(III) in minerals can be oxidized by O2 to Cr(VI), a process that is catalyzed by manganese oxides (Fendorf and Zasoski 1992; Economou-Eliopoulos et al. 2014). The Cr(VI) migrates to rivers and eventually to the ocean. In the modern ocean, Cr occurs as both Cr(VI) and …","PeriodicalId":49624,"journal":{"name":"Reviews in Mineralogy & Geochemistry","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2017-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"79","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Reviews in Mineralogy & Geochemistry","FirstCategoryId":"89","ListUrlMain":"https://doi.org/10.2138/RMG.2017.82.10","RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"Earth and Planetary Sciences","Score":null,"Total":0}
引用次数: 79
Abstract
Chromium consists of four stable isotopes (50Cr, 52Cr, 53Cr and 54Cr) with natural abundances of 4.35%, 83.79%, 9.50% and 2.36%, respectively (Rossman and Taylor 1998). Among these four isotopes, 50Cr, 52Cr and 54Cr are non-radiogenic, whereas 53Cr is a radiogenic product of the extinct nuclide 53Mn, which has a half-life of 3.7 Myr (Honda and Imamura 1971). Chromium isotope systems have a wide range of applications in geochemistry and cosmochemistry. They have been used to study early solar system processes (e.g., Rotaru et al. 1992); the oxidation/reduction (redox) potential of underground systems, which governs the transport and fate of many contaminants (e.g., Ellis et al. 2002); and more recently, the redox evolution of Earth’s early ocean-atmosphere system, which is intimately linked to the evolution of life (Frei et al. 2009; Crowe et al. 2013; Planavsky et al. 2014; Cole et al. 2016). ### Chemical properties of Cr Chromium is redox-sensitive. In Earth’s near-surface environments, Cr has two main valence states, +3 and + 6, which are expressed as Cr(III) and Cr(VI), respectively. The valence state of Cr is controlled by the prevailing redox potential (Eh) and pH conditions (Fig. 1). Cr(VI) is always bound with O2− to form the oxyanion species CrO42− (chromate), HCrO4− (bichromate), and Cr2O72−(dichromate), all of which are water-soluble. In contrast, Cr3+ usually forms oxyhydroxides or oxides, which are insoluble and immobile in the natural pH range. During oxidative weathering, Cr(III) in minerals can be oxidized by O2 to Cr(VI), a process that is catalyzed by manganese oxides (Fendorf and Zasoski 1992; Economou-Eliopoulos et al. 2014). The Cr(VI) migrates to rivers and eventually to the ocean. In the modern ocean, Cr occurs as both Cr(VI) and …
铬由四种稳定同位素(50Cr、52Cr、53Cr和54Cr)组成,自然丰度分别为4.35%、83.79%、9.50%和2.36% (Rossman and Taylor 1998)。在这四种同位素中,50Cr、52Cr和54Cr是非放射性成因的,而53Cr是已灭绝核素53Mn的放射性成因产物,其半衰期为3.7 Myr (Honda and Imamura 1971)。铬同位素系统在地球化学和宇宙化学中有着广泛的应用。它们已被用于研究早期的太阳系过程(例如,Rotaru et al. 1992);地下系统的氧化/还原(氧化还原)电位,它控制着许多污染物的运输和归宿(例如,Ellis et al. 2002);最近,地球早期海洋-大气系统的氧化还原演化与生命的演化密切相关(Frei et al. 2009;Crowe et al. 2013;Planavsky et al. 2014;Cole et al. 2016)。CrChromium的化学性质对氧化还原敏感。在地球近地表环境中,Cr主要有+3和+ 6两种价态,分别表示为Cr(III)和Cr(VI)。Cr的价态受当前氧化还原电位(Eh)和pH条件的控制(图1)。Cr(VI)总是与O2 -结合形成氧化离子CrO42−(铬酸盐)、HCrO4−(重铬酸盐)和Cr2O72−(重铬酸盐),它们都是水溶性的。相反,Cr3+通常形成氢氧化物或氧化物,在自然pH范围内不溶且不移动。在氧化风化过程中,矿物中的Cr(III)可被O2氧化为Cr(VI),这一过程由锰氧化物催化(Fendorf and Zasoski 1992;Economou-Eliopoulos et al. 2014)。Cr(VI)迁移到河流,最终进入海洋。在现代海洋中,Cr以Cr(VI)和…
期刊介绍:
RiMG is a series of multi-authored, soft-bound volumes containing concise reviews of the literature and advances in theoretical and/or applied mineralogy, crystallography, petrology, and geochemistry. The content of each volume consists of fully developed text which can be used for self-study, research, or as a text-book for graduate-level courses. RiMG volumes are typically produced in conjunction with a short course but can also be published without a short course. The series is jointly published by the Mineralogical Society of America (MSA) and the Geochemical Society.