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Experimental determination of Ni isotope fractionation during Ni adsorption from an aqueous fluid onto calcite surfaces
Geochimica et Cosmochimica Acta ( IF 5 ) Pub Date : 2020-03-01 , DOI: 10.1016/j.gca.2020.01.010
Cristina Castillo Alvarez , Ghylaine Quitté , Jacques Schott , Eric H. Oelkers

Abstract The fractionation of Ni isotopes during Ni adsorption from aqueous fluids onto calcite surfaces was measured at 25 °C and as a function of pH from 7.7 to 8.9. Experiments showed that the percent Ni adsorbed and the degree of Ni isotope fractionation attained constant values in less than 30 hours after the calcite was exposed to the Ni bearing, calcite saturated aqueous solution. The percentage of Ni adsorbed from the fluid onto the calcite surfaces increased from 9 to 67% as the pH increased over this range. Calcite preferentially adsorbs light Ni isotopes during adsorption, resulting in a fractionation between adsorbed and aqueous, Δ60Nicalcite-fluid, of −0.52 ± 0.16‰. This value is pH independent, within uncertainty, over the experimental pH range. The preferential adsorption of light Ni isotopes into calcite likely results from the change in coordination environment between adsorbed and aqueous nickel; the Ni O length in the Ni CO3 bond formed at the calcite surface is greater than that in the Ni2+ aquo ion.

中文翻译:

方解石表面从水性流体吸附 Ni 过程中 Ni 同位素分馏的实验测定

摘要 在 25 °C 和 7.7 至 8.9 的 pH 值函数中测量了 Ni 同位素从水性流体吸附到方解石表面期间的分馏。实验表明,在方解石暴露于含 Ni 的方解石饱和水溶液后不到 30 小时内,吸附的 Ni 百分比和 Ni 同位素分馏度达到恒定值。随着 pH 在此范围内增加,从流体吸附到方解石表面的 Ni 百分比从 9% 增加到 67%。方解石在吸附过程中优先吸附轻 Ni 同位素,导致吸附和水相之间的分馏,Δ60 方解石-流体,-0.52 ± 0.16‰。该值在整个实验 pH 范围内在不确定性内与 pH 无关。轻镍同位素优先吸附到方解石中可能是由于吸附镍和含水镍之间的配位环境发生了变化;在方解石表面形成的 Ni CO3 键中的 Ni O 长度大于 Ni2+ 水离子中的长度。
更新日期:2020-03-01
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