Iodine dynamics in soils
Iodine dynamics in soils
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DOI：
10.1016/j.gca.2011.10.034
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发表时间：
2012-01-15
影响因子：
5
通讯作者：
Bailey, E. H.
中科院分区：
文献类型：
--
作者：
Shetaya, W. H.;Young, S. D.;Bailey, E. H.
在10℃和20℃条件下培养9个月，研究了具有不同性质（pH值、Fe/Mn氧化物、有机碳和碘含量）的9种土壤中碘（I-129）的溶解度和形态的变化。有机碳含量高、pH值低、温度高的土壤中I-129的吸附速率更快。碘化物（I-）从溶液中损失非常快，显然在几分钟至几小时内完成；碘酸盐（IO3-）从溶液中损失较慢，通常发生在数小时-数天内。在所有的土壤中，明显的瞬时吸附反应之后是对IO3-较慢的吸附过程。对于碘化物来说，更快的整体反应意味着两个过程之间的区别不太清楚。铁锰氧化物含量高、pH值低、有机碳含量低的土壤对IO3-的瞬时吸附速率较大，而有机碳含量高的土壤对IO3-的瞬时吸附速率最大。土壤的磷酸盐提取（0.15 M KH2PO4），与添加I-129后100 h相似，表明所有土壤中吸收的无机碘（I-129）浓度都很低，这表明无机碘在氧化相上的吸附对碘同化到腐殖质的速度影响很小。利用一系列基于反应和扩散的方法模拟了溶解的无机(IO3-)-I-129和I-129（-）向吸附的有机形式的转变。不可逆和可逆一级动力学模型以及球形扩散模型充分描述了土壤溶液中IO3-和I-损失的动力学，但需要包含分配系数（k(d)）以允许瞬时吸附。通过使用pH、土壤有机碳浓度和铁锰氧化物组合含量作为模型参数(k（d)和d /r(2)）的决定因素，对所有土壤进行了球形扩散模型的集体参数化。动力学模型参数与单一土壤参数没有直接关系；pH， SOC，氧化物含量和温度是描述观察到的行为所必需的。根据吸附数据的温度依赖性，估计(IO3-)- i -129转化为有机形式的活化能（E-a）近似于43 kJ mol（-1）。E-a值与%SOC无关，符合反应机理，比孔隙扩散或物理吸附慢，但比大多数表面反应快。(C) 2011 Elsevier Ltd.版权所有。
We investigated changes in iodine (I-129) solubility and speciation in nine soils with contrasting properties (pH, Fe/Mn oxides, organic carbon and iodine contents), incubated for nine months at 10 and 20 degrees C. The rate of I-129 sorption was greater in soils with large organic carbon contents (%SOC), low pH and at higher temperatures. Loss of iodide (I-) from solution was extremely rapid, apparently reaching completion over minutes-hours; iodate (IO3-) loss from solution was slower, typically occurring over hours-days. In all soils an apparently instantaneous sorption reaction was followed by a slower sorption process for IO3-. For iodide a faster overall reaction meant that discrimination between the two processes was less clear. Instantaneous sorption of IO3- was greater in soils with high Fe/Mn oxide content, low pH and low SOC content, whereas the rate of time-dependent sorption was greatest in soils with higher SOC contents. Phosphate extraction (0.15 M KH2PO4) of soils, similar to 100 h after I-129 spike addition, indicated that concentrations of sorbed inorganic iodine (I-129) were very low in all soils suggesting that inorganic iodine adsorption onto oxide phases has little impact on the rate of iodine assimilation into humus. Transformation of dissolved inorganic (IO3-)-I-129 and I-129(-) to sorbed organic forms was modelled using a range of reaction- and diffusion-based approaches. Irreversible and reversible first order kinetic models, and a spherical diffusion model, adequately described the kinetics of both IO3- and I- loss from the soil solution but required inclusion of a distribution coefficient (k(d)) to allow for instantaneous adsorption. A spherical diffusion model was also collectively parameterised for all the soils studied by using pH, soil organic carbon concentration and combined Fe + Mn oxide content as determinants of the model parameters (k(d) and D/r(2)). The kinetic model parameters were not directly related to a single soil parameter; inclusion of pH, SOC, oxide content and temperature was necessary to describe the observed behaviour. From the temperature-dependence of the sorption data the activation energy (E-a) for (IO3-)-I-129 transformation to organic forms was estimated to be similar to 43 kJ mol(-1). The E-a value was independent of %SOC and was consistent with a reaction mechanism slower than pore diffusion or physical adsorption, but faster than most surface reactions. (C) 2011 Elsevier Ltd. All rights reserved.