Abstract:

The reservoir subsidence zone is affected by alternate inundation and exposure, so the release, migration and transformation of As in the sediment are affected. In addition, the mechanism of the effect of action of humic acid (HA), as the main organic component of sediment, on As is still controversial. Therefore, it is of great significance to stabilize As in sediment by passivating agent for the utilization of sediment resources. In this paper, FeMnMg-LDH was prepared by a modified co-precipitation method to simulate flooding and drop-dry tests on artificially cultured As(V) contaminated sediment, while considering the effect of HA, and FeMnMg-LDH was used as a passivating agent to stabilize the sediment in the abatement zone area to study the morphological transformation characteristics and leaching toxicity changes of As, and to analyze the correlation between them. The results showed that HA promoted the release of As to the overlying water under flooding conditions, and the higher the HA level, the more the release amount. The maximum mass concentrations of As released from 60 mg·kg^-1 and 250 mg·kg^-1 contaminated sediment to the overlying water were 4.81×10³ μg·L^-1 and 1.22×10⁴ μg·L^-1, respectively, and the addition of FeMnMg-LDH effectively inhibited the release of As from the sediment to the overlying water. With the increase of FeMnMg-LDH addition level, the percentage of mild acido-soluble fraction arsenic (MASF-As) in 60 mg·kg^-1 contaminated sediment decreased to 0.06% and 0.07% under flooding and drying conditions; the percentage of MASF-As in 250 mg·kg^-1 contaminated sediment decreased to 0.13%; and MASF-As changed to a more stable form. With the increase of FeMnMg-LDH addition level, the leaching mass concentration of As in sediment decreased gradually, and the stabilization efficiency increased gradually. The stabilization efficiency of 60 mg·kg^-1 and 250 mg·kg^-1 contaminated sediment reached 76.0% and 74.1% in the flooding period, and 75.9% and 73.3% in the drying period. The leaching toxicity risk of As in the sediment during the drying period was higher than that during the flooding period. The addition of HA under flooding and drying conditions positively influenced the stabilization effect on As in contaminated sediment from FeMnMg-LDH. The results of correlation analysis showed that the leaching toxicity of As in some sediments was not significantly correlated with MASF-As and reducible fraction arsenic (RF-As) due to the release of As from sediments to overlying water during flooding. The leaching toxicity of As in sediment under dry conditions was positively correlated with MASF-As and negatively correlated with RF-As. In conclusion, FeMnMg-LDH materials are of practical significance in the passivation remediation of As-contaminated sediment in the abatement zone.

Key words: arsenic, sediment, FeMnMg-LDH, flooding-drying, stabilization

摘要：

水库消落带因受到交替淹没与暴露的问题，其底泥As释放、迁移和转化受到影响，此外，腐殖酸（HA）作为底泥的主要有机成分，其对As的作用机制尚存在争议，因此通过钝化剂来稳定底泥中的As，对底泥资源化利用具有重要意义。采用改进的共沉淀法制备FeMnMg-LDH，在人工培养的As(Ⅴ)污染底泥上模拟淹水和落干试验，同时考虑HA的影响，以FeMnMg-LDH作为钝化剂对消落带地区的底泥进行稳定化处理，研究As的形态转化特征及浸出毒性变化，并分析两者的相关性。结果表明：淹水条件下HA促进As向上覆水体释放且HA水平越高释放量越多，60 mg·kg^-1和250 mg·kg^-1污染底泥向上覆水体释放的As质量浓度最高分别可达4.81×10³ μg·L^-1和1.22×10⁴ μg·L^-1，添加FeMnMg-LDH后有效抑制As由底泥向上覆水体释放；随FeMnMg-LDH添加水平的增加，淹水和落干条件下60 mg·kg^-1污染底泥中弱酸提取态砷（MASF-As）百分比降至0.06%和0.07%，250 mg·kg^-1污染底泥中MASF-As百分比均降至0.13%，MASF-As向更稳定的形态转变；随FeMnMg-LDH添加水平的增加，底泥中As的浸出质量浓度逐渐降低，稳定化效率逐渐升高，60 mg·kg^-1和250 mg·kg^-1污染底泥在淹水期稳定化效率高达到76.0%和74.1%，在落干期高达75.9%和73.3%；落干期底泥中As的浸出毒性风险高于淹水期；淹水及落干条件下HA的添加影响FeMnMg-LDH对污染底泥中As的稳定化作用，表现为正效应。相关性分析结果表明，由于淹水过程中底泥向上覆水体释放As，部分底泥As的浸出毒性与MASF-As和可还原态砷（RF-As）的相关性不显著；落干条件下底泥As的浸出毒性与MASF-As呈正相关，与RF-As呈负相关。综上所述，FeMnMg-LDH材料在消落带As污染底泥钝化修复工作中，具有一定的实践意义。

关键词: 砷, 底泥, FeMnMg-LDH, 淹水-落干, 稳定化