Fe(Ⅲ)水解过程中的Fe同位素分馏研究  

Equilibrium fractionation of Fe isotopes during Fe(Ⅲ) hydrolysis

作　　者：李津[1] 朱祥坤[1] 唐索寒[1] 

机构地区：[1]中国地质科学院地质研究所,国土资源部同位素重点实验室,大陆构造与动力学国家重点实验室,北京100037

出　　处：《岩石矿物学杂志》2012年第6期891-896,共6页Acta Petrologica et Mineralogica

基　　金：国土资源公益性行业专项经费资助项目(201011027);国家自然科学基金资助项目(40973037,40921001)

摘　　要：三价铁水解是铁地球化学循环中的一个重要过程,在一定程度上控制了铁在水体中的运移和再分配。实验研究了Fe(Ⅲ)在20℃和46℃水解生成沉淀过程中,上清液的存在形态以及该过程导致的Fe同位素分馏。20℃水解实验有两个时间长度,分别是95天和130天,水解实验结束时上清液中的Fe(Ⅲ)主要以胶体形式存在。不同的水解时间导致的Fe同位素分馏在误差范围内是一致的。20℃水解实验结束时上清液和沉淀之间56Fe/54Fe的同位素组成之间的差异Δ56FeFe(Ⅲ)sup-Fe(Ⅲ)pre为1.15‰;46℃水解实验的时间长度为95天,结束时上清液中的Fe(Ⅲ)主要以离子形式存在,46℃水解实验结束时Δ56FeFe(Ⅲ)sup-Fe(Ⅲ)pre为1.37‰。通过瑞利分馏的公式计算出20℃和46℃时Fe(Ⅲ)水解过程中沉淀和上清液间的瞬时平衡分馏系数分别为0.999 121和0.999 260。Fe （Ⅲ） hydrolysis is an important process during geochemical circulation of iron, and controls the mi- gration and redistribution of iron in water to some extent. The existing form of Fe （ Ⅲ） in supernatant and the difference of Fe isotopic composition between the supernatant and the precipitate caused by Fe （Ⅲ） hydrolysis at 20℃ and 46℃ were studied in this paper. The experimental time lasted 95 days and 130 days at 20℃. At the end of this experiment, the existing form of Fe （Ⅲ） was colloid, Fe isotopic composition in different experimental periods were the same, and the difference of Fe isotopic composition between the supernatant and the precipitate （A 56Ffe（Ⅲ）sup Fe（Ⅲ）pre） was 1.15%o. The experimental time lasted 95 days at 46℃. At the end of this ex- periment, the existing form of Fe（Ⅲ） was aqueous, and the difference of Fe isotopic composition between the supernatant and the precipitate （A 56FeFe（ Ⅲ）sup- Fe（Ⅲ）pre） was 1.37‰. The instantaneous equilibrium fractionation factor （a） of Fe（Ⅲ） hydrolysis could be calculated by Rayleigh fractionation formula, and the a of 20℃ and 46℃; were 0. 999 121 and 0. 999 260 respectively.

关 键 词：三价铁 水解 铁同位素 瑞利分馏 瞬时平衡分馏系数 

分 类 号：P597.2[天文地球—地球化学]