残留药剂对土壤As、Hg、Cd、Pb浸出测试干扰及消除方法

Interference of residual stabilization agents with leaching test of As,Hg,Cd,Pb contaminated soil and a solution

固化/稳定化是应用最广泛的重金属污染土壤修复技术,但残留药剂在浸出测试过程对土壤二次修复导致的验收假达标风险未引起充分重视.本研究分别采用Fe_(2)(SO_(4))_(3)、Na_(2)S和KH_(2)PO_(4)修复As、Hg、Cd-Pb污染土壤,探究不同养护反应时间、药剂混合均匀度和投加量等工艺条件下土壤重金属浸出浓度差异,验证液相二次修复干扰效应的发生,并考察Cu^(2+)和Al^(3+)等竞争剂对土壤残留KH_(2)PO_(4)药剂干扰的消除效果,提出最佳的残留药剂消除方法.结果表明,分别投加6.7%的Fe_(2)(SO_(4))_(3)、6.7%的Na_(2)S和3.3%的KH_(2)PO_(4)修复含As、Cd和Pb土壤时,土壤中各重金属浸出浓度从第0 d起分别持续小于0.05、0.5和1.6 mg·L^(-1),稳定化效率分别保持在99%、83%~99%和97%~98%.投加0.0008%的Na_(2)S修复土壤Hg时,Hg浸出浓度自第0 d起随养护反应时间显著下降,稳定化效率维持在78%~88%.虽然修复后土壤中Hg浸出浓度随药剂混合均匀度增加而显著下降,As、Cd、Pb浸出浓度在混合均匀度为67%和33%时相较混合均匀度为100%时均无显著变化(1.7%Fe_(2)(SO_(4))_(3)修复组除外),但均小于无二次反应理论值.此外,Cu^(2+)能与Pb^(2+)竞争浸出液中的残留PO_(4)^(3-)减弱干扰效应,当Cu^(2+)优化投加量为5.7%、11.3%、14.2%时,混合均匀度67%处理组Pb浸出浓度分别升至理论值的51%、72%、84%,混合均匀度33%处理组Pb浸出浓度则分别升至理论值的38%、71%、81%.而Al^(3+)无法与Pb^(2+)竞争PO_(4)^(3-),甚至对土壤Pb具有显著活化效果.Cu^(2+)对Pb也具有一定的活化效果,因此,需控制Cu^(2+)投加量以寻求活化效果与优化作用的最佳平衡点.

The ongoing reactions between stabilization agents and pollutants during the leaching test have not got enough attention,which could result in false negative prediction for heavy metal in the treated soil.In this study,Fe_(2)(SO_(4))_(3),Na_(2)S and KH_(2)PO_(4) were amended to remediate As,Hg and Cd-Pb contaminated soils.Effects of curing time,degree of mixing and dosage on the heavy metal leaching concentration were investigated.Cu^(2+) and Al3+ions were examined as competing agents to reduce interference of residual KH_(2)PO_(4) with the leaching test.The results showed that after 6.7%Fe_(2)(SO_(4))3,6.7%Na_(2)S and 3.3%KH_(2)PO_(4) treatment,As,Cd and Pb leaching concentrations were consistently lower than 0.05,0.5 and 1.6 mg·L^(-1),respectively,with stabilization efficiency of 99%,83%~99%and 97%~98%.After 0.0008%Na_(2)S treatment,the Hg leaching concentration decreased significantly over curing time,with stabilization efficiency of 78%~88%.There were no significant differences in heavy metal(As,Cd and Pb)concentrations between treatments of mixing degree of 67%and 100%or 33%and 100%(except 1.7%Fe_(2)(SO_(4))_(3) treatment),but the Hg leaching concentration decreased significantly as degree of mixing increased.Hg,As,Cd and Pb leaching concentrations were all lower than corresponding theoretical values with no ongoing reactions during the test.After optimization of 5.7%,11.3%and 14.2%Cu^(2+) addition,Pb leaching concentrations were increased to 51%,72%and 84%of the theoretical value(mixing degree of 67%),to 38%,71%and 81%(mixing degree of 33%),respectively,due to competitive coprecipitation between Cu^(2+) and Pb^(2+) with PO_(4)^(3-),.Al^(3+) ion could not compete with Pb^(2+) for PO_(4)^(3-) and would mobilize Pb in soil.The balance between optimization effect and mobilization side effect should be kept by controlling Cu^(2+) dosage because of the potential of Cu^(2+) to activate Pb to a certain extent.