Iron is a key element that affects bioactivity in the global environment as a nutrient and also as an adsorbent that controls the circulation of other elements in the hydrosphere. This element is abundant in sea ice and is released into the aquatic environment during the thawing process. Due to the low solubility of iron compounds, they exist as solid materials, such as oxides and oxyhydroxides, which effectively adsorb transition metal ions and affect their circulation in the hydrosphere. This process occurs not only in the hydrosphere but also in the cryosphere. In this study, adsorption of first-row transition metal cations on ferric oxyhydroxide (FeOxH) under frozen conditions is evaluated by ex-situ measurements with sample thawing and also by in situ X-ray fluorescence (XRF) measurements without thawing. The adsorption and desorption characteristics of transition metal cations on FeOxH are discussed from the difference in the adsorption ratio between these two measurements. For in situ XRF measurements, linear regression analysis assuming two states of analytes, i.e., adsorbed on FeOxH and dissolved in the freeze-concentrated solution (FCS) is efficient in estimating adsorption ratios. While complete adsorption is found for all metal cations studied here (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺) at pH > 8, the adsorption ratio determined by in situ XRF is larger than the corresponding value obtained with the ex situ method with thawing at lower pH. This strongly suggests that metal cations are well adsorbed on FeOxH when concentrated in the FCS under frozen conditions but are desorbed upon thawing. The comparison of the adsorption ratios obtained by in situ and ex situ methods reveals specific adsorption of Mn²⁺ and Co²⁺. Interestingly, the specific adsorption of Mn²⁺ is irreversible, and desorption does not occur upon thawing. In contrast, thawing causes the desorption of specifically adsorbed Co²⁺, suggesting that different mechanisms are responsible for the specific adsorption.

中文翻译：

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冻融循环过程中氢氧化铁上金属离子的吸附/解吸特性

铁是影响全球环境生物活性的关键元素，作为营养物质，也是控制水圈中其他元素循环的吸附剂。这种元素在海冰中含量丰富，并在融化过程中释放到水生环境中。由于铁化合物的溶解度较低，它们以氧化物和羟基氧化物等固体物质存在，可有效吸附过渡金属离子并影响其在水圈中的循环。这个过程不仅发生在水圈中，也发生在冰冻圈中。在本研究中，通过样品解冻时的异位测量以及不解冻时的原位 X 射线荧光 (XRF) 测量来评估冷冻条件下第一排过渡金属阳离子在羟基氧化铁 (FeOxH) 上的吸附。从这两次测量之间的吸附比差异讨论过渡金属阳离子在 FeOxH 上的吸附和解吸特性。对于原位 XRF 测量，假设分析物的两种状态（即吸附在 FeOxH 上和溶解在冷冻浓缩溶液 (FCS) 中）的线性回归分析可有效估计吸附率。^{虽然本文研究的所有金属阳离子（Mn 2+}、Co ²⁺、Ni ²⁺、Cu ²⁺和 Zn ²⁺ ）在 pH > 8 时均发现完全吸附，但原位 XRF 测定的吸附率大于相应的值是通过异位法在较低pH值下解冻获得的。这强烈表明，当在冷冻条件下浓缩在FCS中时，金属阳离子在FeOxH上被很好地吸附，但在解冻时被解吸。通过原位和非原位方法获得的吸附率的比较揭示了Mn ²⁺和Co ²⁺的特异性吸附。^{有趣的是，Mn 2+}的特异性吸附是不可逆的，解冻时不会发生解吸。相反，解冻导致特异性吸附的Co ²⁺解吸，表明不同的机制导致特异性吸附。