膨润土和海泡石复配对农田土壤Cd、Pb的钝化潜力

The Potential of Deactivation and Remediation of Cadmium and Lead Co-contaminated Agricultural Soil by Combination of Bentonite and Sepiolite

黏土矿物被广泛应用于农田土壤重金属污染修复研究和实践。为探究膨润土和海泡石复配用于重金属Cd、Pb复合污染土壤修复的钝化效果和钝化机理,采用小麦根箱试验研究2种黏土矿物以不同比例(1∶1、1∶2、2∶1)复配,在1%施用量的情况下对根际和非根际土壤理化性质、重金属有效性和赋存形态、小麦各部位(根茎叶籽实)重金属富集的影响。结果表明:(1)膨润土和海泡石复配施加,除对根际和非根际土壤的pH(升高)和水解性氮(降低)有轻微影响外,对其他指标(速效磷、速效钾、总有机碳、总硫)的影响可以忽略。(2)膨润土和海泡石按照质量比1∶1复配施用(1%)对根际土壤中Cd、Pb的有效态含量降低幅度分别为37.2%、66.6%,对非根际土壤中Cd、Pb的有效态含量降低幅度分别为33.0%、38.6%,对小麦籽实部位的Cd、Pb含量降低幅度分别为41.9%、75.0%。(3)膨润土和海泡石复配施用使根际土壤中的离子交换态Cd和铁锰氧化态Cd转化为残渣态Cd为主的非活性形式,使根际土壤中碳酸盐结合态Pb、腐殖酸结合态Pb主要转化为残渣态Pb。综合而言,膨润土和海泡石复配施加对土壤的环境扰动较小,二者按照1∶1的比例复配对Cd、Pb的钝化效果更佳,钝化机制上主要是将土壤中的Cd、Pb活性态转化为残渣态为主的非活性态。尽管施用1%的膨润土和海泡石1∶1复配钝化材料后,小麦籽实中的Cd仍然高于国家的限量指标,但采用此种钝化材料,适当增加施用量(1%~3%)或者联合其他手段,有望实现Cd、Pb复合污染农田的安全利用。

Clay minerals are widely used as a kind of passivation material in research and practice for the remediation of heavy metal-contaminated agricultural soils.To explore the passivation effects and mechanisms of bentonite and sepiolite when used in combination for the remediation of Cd and Pb co-contaminated soils,wheat cultivation rhizobox experiments were conducted with the two clay minerals at different mass ratios(1∶1,1∶2,2∶1)applied at a rate of 1%.The impact on the physicochemical properties of rhizosphere and non-rhizosphere soils,the availability and speciation of heavy metals,and the accumulation of heavy metals in various parts of wheat(roots,stems,leaves,grains)were studied.The results indicate that the co-application of bentonite and sepiolite had slight effects on pH(increased)and hydrolyzable nitrogen(decreased)in both rhizosphere and non-rhizosphere soils,had negligible effects on other indicators(available phosphorus,available potassium,total organic carbon,and total sulfur).The application of bentonite and sepiolite at a 1∶1 mass ratio(1%)reduced the available concentrations of Cd and Pb in rhizosphere soil by 37.2%and 66.6%,respectively,and in non-rhizosphere soil by 33.0%and 38.6%,respectively.The concentration of Cd and Pb in wheat grains were reduced by 41.9%and 75.0%,respectively.The co-application of bentonite and sepiolite converted exchangeable Cd and Fe-Mn oxide Cd in rhizosphere soil into residual Cd,a less bioavailable form,and converted carbonate-bound Pb and humic acid-bound Pb in rhizosphere soil mainly into residual Pb.In summary,the co-application of bentonite and sepiolite has minimal environmental disturbance on soil.The 1∶1 ratio is more effective for the passivation of Cd and Pb,primarily by transforming the bioavailable forms of Cd and Pb in the soil into less bioactive residual forms.Although Cd content in wheat grains remained higher than the national limit after apply⁃ing 1%bentonite and sepiolite at 1∶1 mass ratio as passivation materials,it is expected that with proper increase in application rate(1%~3%)or combined with other measures,the safe utilization of Cd and Pb co-contaminated farmland could be achieved.