改性生物炭材料对稻田原状和外源镉污染土钝化效应

为研究改性处理后的生物炭对镉污染土壤钝化效应,以油菜秸秆制备的生物炭(BC)为原材料,通过不同处理(HNO_3氧化、NaOH碱化、KMnO_4浸渍、FeCl_3浸渍)制备改性炭材料,在室内连续培养试验中,分析了其对原土/外源镉污染土壤的钝化效应.结果表明,原炭及改性生物炭均降低了原状土壤有效态镉含量,其中Na OH和KMnO_4改性的炭材料钝化作用超过50%;在外源污染土壤中,NaOH、KMnO_4、FeCl_3改性炭材料均降低了土壤有效态镉含量,以添加10%的BC-KMnO_4较佳,降低作用超30%,HNO3改性炭却活化了3.8%~24.5%的土壤有效态镉.10%BC-KMnO_4显著降低原状土壤中可交换态镉含量达65.1%,而BC-HNO_3在外源污染土壤中活化可交换态镉含量高达20.2%.原炭及改性生物炭均增加了土壤中有机碳、盐基离子含量;原炭及NaOH、KMnO_4改性生物炭提高了土壤pH,HNO_3改性炭则降低了土壤p H;原状土中有效态镉含量与pH、交换性钠离子含量呈显著负相关,外源镉污染土中有效态镉含量则与pH、有机碳、交换性镁、钾、钠离子含量呈显著负相关.KMnO_4改性生物炭显著提高土壤pH,增加土壤有机碳和盐基离子含量,降低土壤镉活性形态含量,可作为优选的原位钝化修复材料,而HNO_3改性生物炭显著降低了土壤pH,提高了土壤有效态和可交换态镉含量,具有促进土壤镉生物有效性的风险.

Effect of Modified Biochars on Soil Cadmium Stabilization in Paddy Soil Suffered from Original or Exogenous Contamination

To investigate the passivation of different modified biochars on the speciation and availability of cadmium contaminated soil, the modified biochars were treated by different approaches (acid/base treatment, impregnation with manganese oxides, magnetic modification) and biochars(BC) were used as soil passivating agents for soil culture experiments. The result indicated that the content of available cadmium decreased significantly by BC and modified biochars in originally contaminated soil. Compared with CK, the percentage of available cadmium in originally contaminated soil was reduced by more than 50% using impregnable biochars by KMnO₄(BC-KMnO₄) and basic biochars by NaOH(BC-NaOH). And the content of available cadmium decreased significantly by three modified biochars which were BC-KMnO₄, BC-NaOH and FeCl₃ magnetization biochars(BC-FeCl₃) in exogenously contaminated soil. Particularly, the best performance was observed with BC-KMnO₄ that reduced 30% available cadmium in exogenously contaminated soil. However, the passivation of BC was not significant, and the content of available cadmium slightly increased (3.8%-24.5%) by BC-HNO₃ in exogenously contaminated soil. Furthermore, the content of exchangeable cadmium was increased by 20.2% with 2.5% BC-HNO₃ in exogenously contaminated soil, while significantly decreased by other modified biochars and BC, and the 10% BC-KMnO₄ reduced 65.1% exchangeable cadmium in originally contaminated soil. Meanwhile, soil pH was increased significantly by BC, BC-KMnO₄ and BC-NaOH, while was reduced by BC-HNO₃. The contents of organic carbon and exchangeable base cations in soil were improved by all the treatments. The results of regression analysis showed that the content of available cadmium in originally contaminated soil was significantly negatively correlated with soil pH, soil exchangeable Na⁺, while the content of available cadmium in exogenously contaminated soil was significantly negatively correlated with soil pH, soil organic carbon, soil exchangeable Mg²⁺, Na⁺, K⁺. Accordingly, the lower available cadmium in contaminated soil may correlate with the increasing content of organic carbon, exchangeable base cations and pH. In summary, the materials of BC-KMnO₄ could be used as a superior passivating agent for in situ remediation of cadmium pollution, while the materials of BC-HNO₃ could slightly activate cadmium in the soil, leading to some risk in in situ remediation.