Mechanisms of Sr sorption in peaty-podzolic-gleyic and alluvial soddy-gleyic soils

Radiostrontium (90Sr), a highly mobile radionuclide of environmental concern, can be strongly retained by soils via interactions with organic and mineral components. This study investigated sorption patterns and mechanisms of 90Sr in two contrasting soil types—peaty-podzolic-gleyic (PPG) and alluvial soddy-gleyic (ASG)—through batch experiments with varying experimental conditions and sequential extraction. Despite differences in pH, organic carbon, and clay content, all soil horizons showed high Sr sorption (85–96%) at near-native pH. In organic-rich horizons, Sr was predominantly bound to organic matter via complexation, while in mineral and organo-mineral horizons, ion exchange with clay minerals was the dominant retention mechanism. pH-dependent sorption revealed that Ca2+ competition significantly reduces Sr retention at low pH. Sequential extraction confirmed that Sr is mostly exchangeable in mineral horizons but more strongly retained in organic layers. These findings highlight the contrasting sorption mechanisms in different soil compartments and provide key insights for predicting Sr mobility in contaminated environments.

放射性锶（90Sr）是一种迁移性极强且受环境关注的放射性核素，可通过与土壤有机质、矿物组分的相互作用被土壤强烈固持。本研究通过设置不同实验条件的批量吸附实验与连续提取法，探究了两种性质迥异的土壤——泥炭潜育灰化土（peaty-podzolic-gleyic, PPG）与冲积草甸潜育土（alluvial soddy-gleyic, ASG）中90Sr的吸附规律与固持机制。尽管各土壤发生层的pH值、有机碳含量与黏粒占比存在差异，但在接近自然pH的条件下，所有土层对锶的吸附率均可达85%~96%。在富含有机质的土层中，锶主要通过络合作用与有机质结合；而在矿物层及有机-矿物复合层中，与黏土矿物发生离子交换则是主要的固持机制。pH依赖型吸附实验表明，在低pH条件下，钙离子（Ca²+）的竞争作用会显著降低锶的固持效率。连续提取实验证实，矿物层中的锶大多以可交换态存在，而有机土层中的锶则被更牢固地固持。本研究结果凸显了不同土壤组分间吸附机制的差异性，同时为预测污染环境中锶的迁移性提供了关键理论依据。