褐煤基改良剂对石灰性土壤复合体镉赋存形态的影响

Effects of lignite-based amendments on cadmium chemical speciation in calcareous soil complexes

为筛选和评估褐煤基材料对镉污染的修复效果,降低通过垂直入渗进入地下水或通过地面径流污染更大面积水土的镉通量,通过将3%各种材料均匀混入污染土壤并培养120 d,提取其胶散分组复合体并测定镉化学形态变化。结果表明：1）各改良剂处理的离子交换态、碳酸盐结合态、铁锰氧化物结合态镉质量分数在复合体中分布均为G0〉G1〉G2,而弱有机态、强有机态质量分数分布的顺序相反。残渣态镉质量分数具有G0组复合体低于G1组和G2组复合体内镉质量分数的趋势,除钙化处理,其他处理3组复合体中残渣态之间均无显著差异。2）施用褐煤基材料普遍提高土壤中弱有机结合态镉质量分数,主要提高水稳性复合体中弱有机态镉,G0、G1和G2中施用材料的比对照分别提高5.27%、20.74%和17.82%。褐煤、硝化褐煤、腐植酸显著提高水稳性复合体强有机态镉质量分数,平均分别提高27.26%、23.90%和40.05%,显著降低交换态镉质量分数和水稳性复合体碳酸盐态镉质量分数,平均降低幅度分别为14.63%～22.79%和14.31%～34.56%。硝化褐煤和腐植酸显著降低G1和G2中铁锰氧化物结合态镉的质量分数。3）褐煤改性后多数提高了交换态镉和碳酸盐态镉质量分数,以碱化、钙化、去矿化和活性炭在改性后提高交换态镉质量分数的幅度较大,较褐煤提高幅度最大值分别是29.41%、34.03%、33.82%和43.32%。改性后所有材料普遍降低土壤弱有机结合态镉的质量分数,除腐植酸外,强有机态镉质量分数均比改性前降低。残渣态镉质量分数有向易利用态转化的趋势。总之,非水稳性复合体主要由离子交换态和碳酸盐结合态等易效性镉赋存,水稳性复合体中主要由有机态和残渣态等难效性镉赋存。褐煤、硝化、腐植酸处理显著降低污染土复合体中离子交换态、碳酸盐态、铁锰氧化物态镉质量分数,显著提高水稳性G1和G2复合体强有机态镉质量分数,腐植酸还提高残渣态镉质量分数,起到对镉的钝化作用,但改性后多数是削弱了钝化效果。

[ Background] This work is for screening and evaluating the remediation effect of lignite- based materials on cadmium pollution, and for reducing cadmium flux into the ground water through vertical infiltration or to large water and soil area by surface runoff pollution. [ Methods ] The soil samples were from 200 m surroundings of a lead metallurgical factory at 0 - 20 cm depth contaminated with heavy metals. The lignite from Zhaotong city of Yunnan was modified to be alkalization, calcium- loaded, nitrified, humic acid, demineralization, activated carbon, and sulphonated ones, and the 3% of each of them was evenly mixed with contaminated soil and incubated for 120 days. The organo-mineralcomplexes （Go： water-dispersing complex, G1： NaCl-dispersing complex, and G2： NaCl-grinding- dispersing complex） were extracted, and the determination of cadmium content was conducted by Tessier sequential extraction method, flame atomic absorption spectrophotometer determination; soil physical and chemical properties were determined by Lu Rukun method. Microsoft Excel 2007, SPSS 20.0 and Graphpad Prism 5.0 were used to process and analyze the acquired data and Duncan＇s method for ANOVA. [ Results] 1 ） The content distribution of ion exchange, carbonate-bound, Fe-Mn-oxide-bound cadmium in the complexes was as GO 〉 Gl 〉 G2 in all ameliorator treatments, however, the content distributions of organics-weakly-bound and organics-strongly-bound cadmium were in opposite order. Residual Cd in GO complex had no significant differences with that in Gl and G2 complex except for calcification lignite. 2 ） The application of lignite-based materials generally increased the organics- weakly-bound cadmium content of soil, compared with raw polluted soil. And mainly the organics- weakly-bound Cd in the water-stable complexes increased, i. e. , in the complex Go, Gl and G2 by 5.27%, 20.74% and 17.82% compared to the control, respectively. The use of lignite, nitrified lignite, and hmnic acid significantly resulted in the increase of organics-strongly-bound Cd content in water-stable complex by the average value of 27.26%, 23.90% and 40.05% respectively, and significantly reducing the content of exchangeable and carbonate fractions content in water-stable complex in the range of 14.63% -22.79% and 14. 31% -34.56%. Residual fraction was slightly improved by lignite, nitrified lignite and humic acid than other treatments. The nitrified lignite and humic acid remarkably decreased the content of Fe-Mn-oxide-bound Cd, and alkalization, calcium-loaded, lignite, demineralization, sulphonated and activated carbon increased the content of Fe-Mn-oxide-bound fraction. Alkalization, calcification, demineralization and activated carbon presented no obvious effect on the exchangeable Cd. 3） Modified lignite mainly improved the content of exchangeable and carbonate-bound Cd. In addition to the humic acid, modified lignite generally reduced the soil organics-weakly-bound and organics-strongly-bound Cd content compared with that before modification, and residual fraction content showed a trend of transformation to the available form. [ Conclusions ] In short, non-water-stable complexes contain mainly ion exchangeable and carbonate-bound fraction, water-stable complex is mainly composed of organics-bound and residual form. Some lignite-based materials could change Cd availability to unavailable speciation by inactivation or immobilization. In general, modified lignite mostly weakened the passivation or immobilization effect.