Research Institute of Petroleum Processing, SINOPEC, Beijing, 100083, PR China.
Research Institute of Petroleum Processing, SINOPEC, Beijing, 100083, PR China.
Chemosphere. 2021 Jun;273:129675. doi: 10.1016/j.chemosphere.2021.129675. Epub 2021 Jan 18.
Low permeability zones (LPZs) are typically bypassed when remedial reagents are injected into heterogeneous aquifers, which hinders the in situ remediation. Although shear-thinning polymers have emerged as promising tools to meet this challenge, their applicability in complex remedial systems remains unconfirmed. We investigated the sweeping efficiencies of calcium polysulfide (CPS) into Cr(VI)-contaminated LPZs using xanthan gum (XG) as the model shear-thinning polymer. Firstly, the compatibility of XG-CPS fluids and their reduction capacities toward Cr(VI) were demonstrated based on batch experiments. The removal rates of Cr(VI) exceeded 85% in the presence of 250-2000 mg/L of XG. Besides, XG-CPS fluids exhibited a greater impact on the permeability decrease of transmissive zones than that of LPZs as confirmed by sand column experiments. Furthermore, the sweeping efficiencies in LPZs during XG-CPS flooding were investigated by multiple sand tank experiments. The sweeping rate in LPZs (r) in Cr(VI)-contaminated aquifer (1.68 × 10/min) was found to be approximately 11% higher than that of uncontaminated system, and two possible reasons behind this phenomenon were proposed. The spatial distribution profiles of Cr under different XG-CPS flooding conditions were depicted based on 20 representative samples. The results indicated that all Cr(VI) in LPZs can be effectively removed either by displacement or immobilization as Cr(III). The percentages of displaced Cr(VI) and immobilized Cr(III) were calculated to be 65%-75% and 25-35%, respectively. This work demonstrates the applicability of XG-CPS fluids as remedial materials for Cr(VI)-contaminated heterogeneous aquifers and provides novel insights into the role of Cr(VI) in in situ remediation using shear-thinning polymers.
低渗透带 (LPZ) 在向非均质地层注入修复试剂时通常会被绕过，这阻碍了原位修复。尽管剪切变稀聚合物已成为应对这一挑战的有前途的工具，但它们在复杂修复系统中的适用性仍未得到证实。我们研究了使用黄原胶 (XG) 作为模型剪切变稀聚合物将钙多硫化物 (CPS) 扫入 Cr(VI) 污染的 LPZ 的扫洗效率。首先，通过批处理实验证明了 XG-CPS 流体的相容性及其对 Cr(VI) 的还原能力。在 250-2000mg/L 的 XG 存在下，Cr(VI) 的去除率超过 85%。此外，通过砂柱实验证实，XG-CPS 流体对传输带渗透率降低的影响大于 LPZ。此外，通过多次砂槽实验研究了 XG-CPS 驱替过程中 LPZ 中的扫洗效率。在 Cr(VI) 污染含水层中，LPZ 中的扫洗速率（r）为 1.68×10-4/min，发现比无污染系统高约 11%，并提出了这种现象背后的两个可能原因。根据 20 个代表性样本描绘了不同 XG-CPS 驱替条件下 Cr 的空间分布曲线。结果表明，LPZ 中的所有 Cr(VI) 都可以通过置换或固定化为 Cr(III) 而被有效去除。计算出的被置换的 Cr(VI) 和固定化的 Cr(III) 的百分比分别为 65%-75%和 25-35%。这项工作证明了 XG-CPS 流体作为 Cr(VI) 污染非均质含水层修复材料的适用性，并为使用剪切变稀聚合物进行原位修复中 Cr(VI) 的作用提供了新的见解。
