不同天然矿物对铊污染土壤中铊生物有效性的影响

Effects of different natural minerals on Thallium bioavailability in Thallium contaminated soil

以贵州黔西南铊(Tl)污染土壤作为试验对象,对3种铁系材料(氧化铁、高铁酸钾和硫化亚铁)、3种磷系材料(磷酸二氢钾、聚磷酸钾和磷酸钙)、3种硅系材料(硅酸钠、蒙脱石和海泡石)及2种有机质(腐殖酸和黄腐酸)材料进行15 d室内初筛试验,最终选择能有效降低TCLP提取态Tl的3种典型天然矿物氧化铁(Fe_(2)O_(3))、蒙脱石(Al_(4)Si_(8)O_(2)(OH)_(4)nH_(2)O)和磷酸钙(Ca_(3)(PO_(4))_(2))进行30d土培试验的深入研究,采用TCLP毒性浸提和BCR连续形态提取试验评价不同矿物材料对高铊土壤Tl生物有效性的影响.结果表明,不同类型材料对高铊土壤TCLP-Tl含量影响差异显著,与对照相比,高铁酸钾、硅酸钠、磷酸二氢钾、聚磷酸钾和黄腐酸的添加均可显著增加土壤TCLP-Tl含量(p<0.05)而具有活化土壤中Tl的风险;而氧化铁、硫化亚铁、海泡石、蒙脱石、磷酸钙和腐殖酸等材料的处理则可显著降低高铊土壤TCLP-Tl含量(p<0.05)而具有明显的钝化土壤中Tl的作用,降低效果总体表现为磷酸钙>蒙脱石>氧化铁>腐殖酸>硫化亚铁>海泡石;对3种天然矿物进行进一步的土培试验表明,施加量为1.5%时高铊土壤中TCLP-Tl含量显著降低(p<0.05);与对照相比,培养30d后磷酸钙处理组高铊土壤中TCLP-Tl含量降幅最大(40.64%),其次是蒙脱石(39.10%)和氧化铁(32.38%).施加上述天然矿物均可使Tl的酸可交换态、易还原态和可氧化态向残渣态转化而显著降低高铊土壤中Tl的生物有效性.X-射线衍射分析结果表明,土壤中赤铁矿特征峰强度增强和新矿物(黄钾铁矾)生成与高铊土壤中Tl生物有效性的降低密切相关.相关性分析结果表明,土壤CEC、Fe_(o)和OM含量是影响高铊土壤中Tl生物有效性的关键因素.上述结果可为典型汞铊矿区周边污染农用地土壤的安全利用及铊污染土壤的原位钝化修复提供理论依据.

In this study,soil contaminated with thallium in southwest Guizhou Province was selected as the test subject.A preliminary screening test was conducted over 15 days,focusing on three types of ferric materials(ferric oxide,potassium ferrate and ferrous sulfide),three phosphorous materials(potassium dihydrogen phosphate,potassium polyphosphate and calcium phosphate),three siliceous materials(sodium silicate,montmorillonite and sepiolite) and two organic(humic acid and fulvic acid) materials.Subsequently,three natural mineral materials such as iron oxide(Fe_(2)O_(3)),montmorillonite(Al_(4)Si_8O_(2)(OH)_(4)nH_(2)O) and calcium phosphate(Ca_(3)(PO_(4))_(2)),demonstrating efficacy in reducing the TCLP extracted T1 were selected for a 30-day soil culture experiment.The evaluation of the impact of different mineral materials on soil T1 bioavailability was conducted through TCLP toxicity extraction and BCR continuous form extraction tests.The results showed that different materials used had significant effects on the content of TCLP extracted Tl in thallium-contaminated soil.Compared with the control treatment,the addition of potassium ferrate,sodium silicate,potassium dihydrogen phosphate,potassium polyphosphate,and fulvic acid significantly increase the content of TCLP extracted Tl in soil(p <0.05),posing a risk of activating soil Tl.Conversely,treatments involving ferric oxide,ferrous sulfide,sepiolite,montmorillonite,calcium phosphate and humic acid significantly reduced the content of TCLP extracted Tl in soil(p <0.05),and effectively deactivating Tl in the soil.The overall reduction effect ranked as follows:calcium phosphate> montmorillonite> iron oxide> humic acid> ferrous sulfide> sepiolite.Further tests on three natural mineral materials indicated that a significant decrease in the content of TCLP extracted Tl in soil when different types of natural minerals were applied at 1.5%(p <0.05).Compared with the control treatment,the content of TCLP extracted Tl in the calcium phosphate treatment exhibited the most substantial decrease(40.64%) after 30 days of passivation,followed by montmorillonite(39.10%) and iron oxide(32.38%).The application of these natural minerals transformed acid exchangeable,easily reducible,and oxidizable Tl states into residue states,thereby significantly reducing the bioavailability of Tl in contaminated soil.XRD results demonstrated an increase in the characteristic peak intensity of hematite and the formation of a new mineral(jarosite) in soil,closely associated with the decrease in Tl bioavailability.Correlation analysis showed that the contents of CEC,Fe_(o) and OM as key factors affecting the bioavailability of Tl in soil.These results can provide a theoretical basis for the safe utilization of contaminated agricultural soil around typical mercury-thallium mining areas and the in-situ passivation restoration of thallium-contaminated soil.