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首页> 外文期刊>Environmental toxicology and chemistry >Sorption Irreversibility Of 1,4-dichlorobenzene In Two Natural Organic Matter-rich Geosorbents
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Sorption Irreversibility Of 1,4-dichlorobenzene In Two Natural Organic Matter-rich Geosorbents

机译：1，4-二氯苯在两种天然有机物富集吸附剂中的吸附不可逆性

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摘要

Hysteresis, a frequently observed phenomenon in sorption studies, is inconsistent with the key assumption of sorption reversibility in most fate and bioavailability models. Therefore, a study of the underlying causes of hysteresis is essential. Carbon-radiolabeled 1,4-dichlorobenzene (DCB) isotope tracer exchange was carried out at select points along the isotherms of DCB in a brown coal and a peat soil, holding total DCB concentration constant. Tracer exchange was performed both in the forward (sorption) and reverse (desorption) directions at the bulk sorption points and in the desorption direction at the corresponding bulk desorption points. Bulk DCB isotherms showed concentration-dependent hysteresis. However, tracer reequilibration in all cases was consistent with free exchange between sorbed and aqueous-phase molecules. These results rule out common experimental artifacts and demonstrate that sorption of bulk DCB is truly hysteretic (i.e., irreversible). The differences in rates between bulk and tracer sorption and desorption are consistent with the coupling of bulk DCB diffusion to other processes that retard equilibration, which we assign to matrix swelling or shrinking. Hysteresis is attributed to matrix deformation-specifically, to inelastic expansion and creation of voids accommodating sorbate molecules in the matrix, which leads to enhanced affinity in the desorption step. Comparing the results to previous results for naphthalene in the coal, we find that irreversible effects are similar for DCB and naphthalene in the coal but differ for DCB between the two sorbents. An explanation based on the different physical properties of these sorbents is provided. Solid-phase extraction of equilibrated DCB with Tenax~R revealed a highly desorption-resistant fraction. While too small to account for the observed hysteresis, this fraction may represent molecules that become trapped as the matrix collapses and simultaneously stiffens during abrupt desorption.
机译：滞后现象是在吸附研究中经常观察到的现象，与大多数命运和生物利用度模型中的吸附可逆性的关键假设不一致。因此，研究滞后的根本原因至关重要。在褐煤和泥炭土中，沿DCB等温线的选定点进行了碳-放射性标记的1,4-二氯苯（DCB）同位素示踪剂交换，使总DCB浓度保持恒定。示踪剂交换在本体吸附点处在正向（吸附）和反向（解吸）方向上以及在相应的本体解吸点处在解吸方向上进行。大量DCB等温线显示出浓度依赖性的磁滞现象。然而，在所有情况下示踪剂重新平衡与吸附相和水相分子之间的自由交换是一致的。这些结果排除了常见的实验假象，并证明了大块DCB的吸附确实是滞后的（即不可逆的）。本体和示踪剂吸附和解吸速率之间的差异与本体DCB扩散与其他阻碍平衡的过程的耦合一致，我们将其分配给基质溶胀或收缩。迟滞归因于基质变形，特别是由于基质中无弹性的膨胀和容纳山梨酸酯分子的空隙的产生，这导致了解吸步骤中亲和力的提高。将结果与煤中萘的先前结果进行比较，我们发现煤中DCB和萘的不可逆作用相似，但两种吸附剂之间的DCB则具有不可逆作用。提供了基于这些吸附剂不同物理性质的解释。用Tenax〜R固相萃取平衡后的DCB表现出很高的抗脱附率。虽然太小而无法解释所观察到的滞后现象，但该分数可能表示随着基质塌陷并在突然解吸期间同时变硬而被困住的分子。

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