Southwest Florida Research and Education Center, University of Florida, 2685 State Rd. 29 N, Immokalee, FL 34142, USA.
Jacobs Engineering, 5701 Cleveland Street, Suite 200, Virginia Beach, VA 23462, USA.
Sci Total Environ. 2022 Oct 1;841:156596. doi: 10.1016/j.scitotenv.2022.156596. Epub 2022 Jun 9.
Field lysimeters tests examined leaching of technetium-99 (Tc) from two types of cementitious waste forms and found that the presence of blast furnace slag reduced the overall leaching of Tc from the waste form. The two cementitious waste forms were a slag-grout 45%/45%/10% mixture of fly ash, blast furnace slag, and cement, respectively, referred to as slag-grout or a 55%/45% mixture of cement and fly ash, respectively, referred to here simply as cement. Duplicate sources of each composition were buried in four lysimeters for approximately 10 months to evaluate leaching characteristics under natural meteorological conditions in South Carolina, USA. Effluent samples were collected four times during the experiment, and the distribution of Tc in the sediment was determined by destructively segmenting the lysimeters at the end of the experiment. The transport of Tc within the lysimeter was simulated by assuming advection, dispersion, and sorption in partially saturated porous media, and by using a shrinking-core type approximation for the release of Tc from the source. The shrinking-core model predicted that the oxidation front created by the oxygenated infiltrating groundwater moved into the cementitious source at a rate of 14 μm/day. As this front moved through the source, Tc(IV) was oxidized to the highly mobile Tc(VII) (as TcO) species, which then was transported through the sediment primarily via advection due to a small partitioning coefficient (C/C; K = 0.14 mL/g). The simulations predicted a cycle of accumulation of Tc in sediment at the source between rainfall events, followed by downward advection due to infiltration during rainfall events. The anomalous upward movement of Tc peak was predicted to be due to upward flux caused by evaporation after the experiment was terminated by capping the lysimeter. These experiments demonstrate that Tc leaching from cementitious waste forms under simulated vadose zone oxidizing conditions can be reasonably approximated by the shrinking core model, and the migration of Tc through the sediment is profoundly influenced by the presence of slag in the grout formulation and hydraulic conditions due to the low sorption affinity of TcO.
田间淋溶试验研究了锝-99（Tc）从两种水泥基废物形式中的浸出情况，发现高炉矿渣的存在降低了废物形式中 Tc 的整体浸出率。这两种水泥基废物形式分别是一种炉渣-泥浆 45%/45%/10%的粉煤灰、高炉矿渣和水泥混合物，分别称为炉渣-泥浆或水泥和粉煤灰的 55%/45%混合物，这里简单地称为水泥。每种成分的两个来源分别埋在四个淋溶器中，大约 10 个月，以评估美国南卡罗来纳州自然气象条件下的浸出特性。在实验过程中收集了四次流出物样品，并在实验结束时通过破坏性地分段淋溶器来确定 Tc 在沉积物中的分布。Tc 在淋溶器中的迁移通过假设在部分饱和多孔介质中的对流、弥散和吸附来模拟，并使用从源中释放 Tc 的收缩核类型近似值。收缩核模型预测，含氧渗入地下水形成的氧化前沿以 14 μm/天的速度移动到水泥基源中。随着这个前沿通过源，Tc(IV)被氧化成高迁移性的 Tc(VII)（作为 TcO 物种），然后主要通过对流穿过沉积物，因为分配系数（C/C；K = 0.14 mL/g）很小。模拟预测了在降雨事件之间，在源处的 Tc 在沉积物中的积累循环，随后在降雨事件期间由于渗透而向下对流。异常的 Tc 峰值向上移动预计是由于实验结束时通过覆盖淋溶器导致蒸发后向上通量引起的。这些实验表明，在模拟的非饱和带氧化条件下，水泥基废物形式中的 Tc 浸出可以通过收缩核模型合理地近似，而 Tc 通过沉积物的迁移受到炉渣在灌浆配方中的存在和水力条件的深刻影响，因为 TcO 的吸附亲和力很低。
