干湿交替下生物炭对复合污染土壤中镉砷有效性的影响

为了明确活性炭工业的副产品——杏壳生物炭和水分管理模式对石灰性土壤重金属有效性的钝化效果,采用重度Cd、As复合污染的农田土壤,通过土壤培养方法探索了干湿交替水分管理模式下,添加不同用量生物炭对土壤中Cd、As有效性的影响。结果表明:从土壤溶液中Cd、As浓度的变化来看,干湿交替培养条件下,添加2%~10%生物炭处理的土壤溶液中Cd浓度均显著低于对照(P<0.05),降幅为33.1%~62.2%,说明干湿交替模式下添加生物炭显著促进了Cd由土壤液相向土壤固相的转移,而添加生物炭对土壤溶液中砷浓度的影响不稳定,其主要受土壤水分管理模式的影响;从土壤固相Cd、As提取态的变化来看,添加生物炭(6%,8%,10%)处理与CK相比,可显著降低土壤中DTPA提取态Cd和NH4H2PO4提取态As的含量(P<0.05),降幅分别为8.7%~16.8%,5.1%~7.9%,表明干湿交替下添加生物炭显著降低了土壤Cd、As有效性;土壤连续分级提取的结果显示,施用生物炭促进了土壤Cd由酸可提取态和可氧化态向残渣态转化,土壤As由专性吸附态和无定形—弱结晶铁铝或铁锰水化氧化物结合态向残渣态转化,显著降低了污染土壤Cd、As活性。因此,在重度Cd、As复合污染的石灰性土壤区,施用6%生物炭并保持干湿交替的水分管理模式能显著降低土壤镉砷的有效性。

Effects of Biochar Application on the Availability of Cadmium and Arsenic in Cd/As-contaminated Soil Under the Alternate Unflooded-flooded Condition

In order to verify the effects of biochar application and water management on the availability of heavy metals in contaminated soil,a soil incubation experiment was conducted to explore the effects of biochar application on the availability of cadmium(Cd)and arsenic(As)in the heavily Cd/As contaminated farmland soil under the alternate unflood-flooded condition.The results showed that under the alternate unflood-flooded condition,the application of biochar at the rates of 2%~10%significantly reduced the concentrations of Cd in soil solution by 33.1%~62.2%,indicating biochar promoted the immobilization of Cd from porewater to soil solid phase.However,the impacts of biochar application on the concentrations of As in soil solution was not stable,which mainly depended on the water management.For the variation of extractable Cd and As,the biochar application at the rates of 6%,8%,10%significantly decreased the levels of DTPA—Cd and NH4H2PO4—As in soil by 8.7%~16.8%and 5.1%~7.9%compared with the control(CK)(P<0.05),respectively.This indicated that the addition of biochar could significantly reduce the concentrations of DTPA—Cd and NH4H2PO4—As in the Cd/As-contaminated soil.Moreover,the soil sequential extraction experiment illustrated that the application of biochar promoted the transfer of soil Cd from the fractions of acid-soluble and oxidative to the residues,and the transfer of soil As from the fractions of specifically sorbed,and amorphous and poor-crystalline hydrous oxides of iron-aluminum or iron-manganese to the residues,which suggested that biochar inhibited the availability of Cd and As in contaminated soil significantly.Therefore,the application of biochar at the rate of 6%combined with alternate unflooded-flooded water regimes might reduce the availability of soil Cd and As in the Cd/As contaminated calcareous soil.