柱载水铁矿对重度砷污染水稻土砷的提取研究

Arsenic extraction from heavily arsenic contaminated paddy soils with ferrihydrite-loaded columns

为了降低重度污染土壤砷(As)含量,设计出柱状水铁矿(Fh)提取装置,并利用根箱模拟实验检验其提取污染土壤As的效果.通过定期测量土壤孔隙水和淹水提取结束后土壤样品与装置核心层Fh的相关指标,并运用黑麦草种子发芽率及根芽长评估柱载Fh装置提取后土壤的安全性.结果表明:在As含量为220.9 mg·kg^(-1)的Ⅲ类严格管控污染土壤中使用Fh柱后,3 cm处孔隙水As含量呈现出显著下降的趋势,单次提取使孔隙水As含量较Ⅲ类污染对照土降低了20.3%~88.4%;柱载Fh能够有效提取土壤中无定型Fe结合态As(AAO-As),距柱3 cm和6 cm土壤AAO-As含量较Ⅲ类污染对照土分别降低了23%和8%,与土壤总As含量减少趋势一致;距柱3 cm与6 cm处无定型铁氧化物结合态和结晶水合铁氧化物结合态As含量较Ⅲ类污染对照土分别下降15.6%和6.9%;黑麦草根长和芽长与Ⅲ类污染对照土相比已有明显改善,处理后3 cm处土壤的种子毒性水平和根芽长均与As含量为54.4 mg·kg^(-1)的Ⅱ类安全利用类土相当,表明柱载Fh对Ⅲ类严格管控类重度As污染水稻工具有较好的提取效能与应用潜力.

In order to reduce the concentration of arsenic(As)in heavily contaminated soil,a porous column pre-loaded with ferrihydrite(Fh)was designed,and its extraction effect was tested by root box simulation experiment.The relevant indicators of soil pore water and soil samples after extraction and Fh were regularly measured.The germination rate of ryegrass seeds and the root and shoot length of ryegrass were used to evaluate the safety of the soil after extraction with porous columns pre-loaded with Fh.The results showed that the porous columns pre-loaded with Fh was used in Class Ⅲ soil defined as strictly controlled with a soil As content of 220.9 mg·kg^(-1),resulting in a significant decrease in As content in the pore water at a distance of 3 cm from the column,which was 20.3%~88.4%lower than that in Class Ⅲ contaminated control soil after a single extraction.The content of amorphous Fe bound As(AAO-As)in soil was decreased by 23%and 8%in soil 3 cm and 6 cm away from the column,respectively,compared with the control soil of Class Ⅲ contaminated.This change was consistent with the change trend of soil total As content.The As of amorphous Fe oxide binding fraction and crystalline hydrated Fe oxide binding fraction at 3 cm and 6 cm away from the column decreased by 15.6%and 6.9%,respectively,compared with the control soil of ClassⅢcontaminated.The root length and shoot length of ryegrass were significantly improved compared with that of classⅢpolluted control soil.The seed toxicity level and root-shoot length of ryegrass in 3cm treated soil were equivalent to that of ClassⅡsafe use soil with As content of 54.4 mg·kg^(-1),indicating that Fh loaded in column had better extraction efficiency and application potential for classⅢheavily contaminated As soil.