【作者】 王丽；

【导师】 任珺；

【作者基本信息】 兰州交通大学 ， 环境科学， 2022， 硕士

【摘要】 坡缕石由于其特殊的晶体结构及大比表面积,对重金属具有优异的吸附性能而被广泛应用于修复重金属污染的土壤。甘肃坡缕石储量丰富,但天然坡缕石中含有许多杂质,因此为了更好地发挥坡缕石的作用,需要对其进行改性。聚合硫酸铁是一种羟基聚合物,生产简便且廉价环保,具有较强的吸附、架桥性能。目前,将聚合硫酸铁改性坡缕石的材料用于重金属污染土壤修复的研究尚未有报道。因此,开展此类研究对于新型环境友好型钝化材料的开发具有重要意义。本研究以甘肃临泽的坡缕石为原料,依据协同增效的原理将聚合硫酸铁与坡缕石按不同质量比混合,其中聚合硫酸铁在混合体系中所占质量分数分别为5%,10%,15%,20%,25%,采用浸渍法制备出两种不同类型的聚合硫酸铁改性坡缕石钝化材料(PFS、APFS)。通过表征实验分析坡缕石经聚合硫酸铁改性前后的表面形貌、晶体结构及特征官能团的变化。将制备的两种钝化材料,以4%的添加量分别加入人工模拟Cd污染土壤和白银矿区重金属污染土壤中,通过室内钝化实验研究钝化材料对重金属污染土壤的理化性质、重金属的生物有效性及化学形态分布的影响;通过盆栽实验及种子萌发实验研究钝化材料对土壤中重金属生态毒性效应的影响。通过以上实验综合评估钝化材料对重金属污染土壤的修复效果。主要研究结果如下:(1)通过表征分析发现,经聚合硫酸铁改性后坡缕石材料表面变得粗糙、接触面积增大。聚合硫酸铁改性并未破坏坡缕石的晶体结构,而且红外光谱图中出现Fe-O和Fe-OH吸收峰,证明聚合硫酸铁改性成功。(2)钝化材料的添加能够改善土壤的理化性质。聚合硫酸铁改性坡缕石钝化材料较未改性的坡缕石相比,土壤的p H值、电导率(EC)和阳离子交换量(CEC)升高。与钝化Cd污染土壤理化性质相比,钝化矿区重金属污染土壤的p H、EC、CEC变化趋势基本一致但增幅减小。(3)钝化材料的添加能降低土壤中重金属的生物有效性。改性坡缕石材料对土壤中重金属的生物有效态(DTPA、TCLP萃取态)含量降低效果优于未改性坡缕石材料,不同的钝化材料对不同的重金属含量降低效果有差异。在人工模拟Cd污染土壤修复研究中,聚合硫酸铁在混合体系中所占质量分数为25%(PFS25)时DTPA、TCLP萃取态Cd含量均达到最小值,较对照组分别降低34.84%、25.03%。在白银矿区重金属污染土壤修复研究中,聚合硫酸铁在混合体系中所占质量分数为5%(APFS5)时土壤中DTPA、TCLP萃取态的Cd、Ni、Zn含量均达到最小值。聚合硫酸铁在混合体系中所占质量分数为25%(APFS25)时土壤中DTPA、TCLP萃取态的Cu、Pb含量均达到最小值。(4)钝化材料的添加对土壤中重金属的化学形态变化影响显著,钝化土壤中重金属均呈现由活性较高的酸溶态向更加稳定的残渣态转变。人工模拟Cd污染土壤修复研究表明,PFS25处理时Cd的形态转化最明显。白银矿区重金属污染土壤修复研究表明,APFS5钝化材料对Cd、Ni、Zn的形态转化影响较大,APFS25钝化材料对Cu、Pb的形态转化影响较大。APFS25处理时Cu的酸溶态、残渣态组分占比分别为0.66%、69.49%,实现由酸溶态向残渣态的最大转化。(5)钝化材料的添加能有效降低土壤中重金属的生态毒性。盆栽实验结果表明,钝化材料能促进玉米生长并显著降低玉米体内的Cd含量,其中PFS25处理效果最好。玉米种子萌发实验结果表明,钝化材料能显著提高玉米种子的萌发率和根伸长率,其中APFS5、APFS25处理效果较好。(6)聚合硫酸铁改性坡缕石钝化材料对土壤中重金属的钝化效果较好。人工模拟Cd污染土壤修复研究表明,PFS25处理对Cd的钝化效果最好。白银矿区重金属污染土壤修复研究表明,APFS5处理时Cd、Ni、Zn的钝化效率达到最高,APFS25处理时Cu、Pb的钝化效率最高。(7)钝化材料的添加能够降低土壤中重金属的环境风险。人工模拟Cd污染土壤修复研究表明,施加钝化材料后土壤中Cd的环境风险由高风险水平降到中等风险,PFS25钝化土壤中Cd的环境风险指数、生态风险指数均降至最小。白银矿区重金属污染土壤修复研究表明,APFS5钝化土壤中Cd、Ni的环境风险等级均下降。APFS25钝化土壤中Cu的环境风险由低风险变为无环境风险。添加钝化材料后,Zn、Pb的环境风险指数虽显著下降,但环境风险等级并未降低。聚合硫酸铁改性坡缕石的钝化材料可有效降低土壤中重金属的生态毒性效应,对重金属有较好的钝化效果,且原料易得、制作简便、廉价环保,具有开发应用的前景。更多还原

【Abstract】 Palygorskite has been widely used in remediation of heavy metal contaminated soil due to its special crystal structure,large specific surface area and excellent adsorption capacity for heavy metals.Palygorskite is abundant in Gansu province,but there are many impurities in natural palygorskite,so in order to better play the role of palygorskite,it needs to be modified.Polyferric sulfate is a kind of hydroxyl polymer,which is easy to produce,cheap and environmentally friendly,and has strong adsorption and bridging properties.At present,the application of polyferric sulfate modified palygorskite to remediation of heavy metal contaminated soil has not been reported.Therefore,this kind of research is of great significance for the development of new environmentally friendly stabilization materials.In this study,palygorskite from Linze,Gansu province was used as raw material,and polyferric sulfate and palygorskite were mixed according to different mass ratios according to the principle of synergism.The mass fraction of polyferric sulfate in the mixing system was5%,10%,15%,20%,25%,respectively.Two different types of polyferric sulfate modified palygorskite stabilization materials(PFS and APFS)were prepared by impregnation method.The changes of surface morphology,crystal structure and characteristic functional groups of palygorskite before and after modification by polyferric sulfate were analyzed by characterization experiments.Two kinds of stabilized materials were added to artificially simulated Cd contaminated soil and heavy metal contaminated soil in silver mining area with the addition amount of 4% respectively.The effects of stabilized materials on the physical and chemical properties,bioavailability and chemical morphology distribution of heavy metal contaminated soil were studied through indoor stabilizing experiments.Pot experiment and seed germination experiment were conducted to study the effects of stabilized materials on ecotoxicity of heavy metals in soil.Through the above experiments,the remediation effect of the stabilized materials on heavy metal contaminated soil was comprehensively evaluated.The main results are as follows:(1)Characterization analysis showed that the surface of palygorskite modified by polyferric sulfate became rough and the contact area increased.The modification of polyferric sulfate did not damage the crystal structure of palygorskite.The absorption peaks of Fe-O and Fe-OH appeared in the ir spectrum,which proved that the modification of polyferric sulfate was successful.(2)The addition of stabilizing materials can improve the physical and chemical properties of soil.The soil p H value,conductivity(EC)and cation exchange capacity(CEC)of polyferric sulfate modified palygorskite stabilized materials were higher than those of unmodified palygorskite.Compared with the physical and chemical properties of the soils contaminated by Cd,the p H,EC and CEC of the soils contaminated by Cd in the stabilized mining area showed the same trend but the increase rate decreased.(3)The addition of stabilized materials can reduce the bioavailability of heavy metals in soil.The effect of modified palygorskite on the reduction of bioavailable state(DTPA,TCLP extraction state)of heavy metals in soil is better than that of unmodified palygorskite,and the effect of different stabilization materials on the reduction of different heavy metals content is different.In the remediation of artificially simulated Cd contaminated soil,the extraction Cd content of DTPA and TCLP reached the minimum when the mass fraction of polyferric sulfate in the mixed system was 25%(PFS25),which was 34.84% and 25.03% lower than that of the control group,respectively.In the remediation of heavy metal contaminated soil in Baiyin mining area,when the mass fraction of polyferric sulfate in the mixed system is 5%(APFS5),the contents of Cd,Ni and Zn in DTPA and TCLP extracted soil reach the minimum values.When the mass fraction of polyferric sulfate in the mixed system was 25%(APFS25),the content of Cu and Pb in DTPA and TCLP extraction reached the minimum.(4)The addition of stabilized materials had a significant effect on the chemical morphology of heavy metals in soil,and all the heavy metals in stabilized soil were transformed from highly active acid-soluble state to more stable residual state.Remediation of simulated Cd contaminated soil showed that the morphology transformation of Cd was the most obvious under PFS25 treatment.Remediation of heavy metal contaminated soil in Baiyin mining area showed that APFS5 stabilized material had a great influence on the morphological transformation of Cd,Ni and Zn,while APFS25 stabilized material had a great influence on the morphological transformation of Cu and Pb.In APFS25 treatment,the ratio of acid soluble and residue of Cu is 0.66% and 69.49%,respectively,achieving the maximum transformation from acid soluble to residue.(5)The addition of stabilized materials can effectively reduce the ecological toxicity of heavy metals in soil.Pot experiment results showed that the stabilized materials could promote the growth of corn and significantly reduce the content of Cd in corn,and PFS25 treatment had the best effect.The results of maize seed germination experiment showed that the stabilized materials could significantly improve the germination rate and root elongation rate of maize seeds,and the effect of APFS5 and APFS25 was better.(6)Polyferric sulfate modified palygorskite stabilization material has a better stabilization effect on heavy metals in soil.Remediation of simulated Cd contaminated soil showed that PFS25 treatment had the best effect on Cd stabilization.Remediation of heavy metal contaminated soil in Baiyin mining area showed that Cd,Ni,Zn stabilization efficiency reached the highest in APFS5 treatment,while Cu,Pb stabilization efficiency reached the highest in APFS25 treatment.(7)The addition of stabilized materials can reduce the environmental risk of heavy metals in soil.Remediation of artificially simulated Cd contaminated soil showed that the environmental risk of Cd in soil decreased from high risk to medium risk after the application of stabilized materials,and the environmental risk index and ecological risk index of Cd in PFS25 stabilized soil decreased to the minimum.Remediation of heavy metal contaminated soil in Baiyin Mining area showed that the environmental risk levels of Cd and Ni in APFS5 stabilized soil decreased.The environmental risk of Cu in APFS25 stabilized soil changed from low risk to no environmental risk.After the addition of stabilized materials,the environmental risk index of Zn and Pb decreased significantly,but the environmental risk grade did not decrease.The stabilization material of polyferric sulfate modified palygorskite can effectively reduce the ecological toxicity effect of heavy metals in soil,and has a good stabilization effect on heavy metals.Besides,it is easy to obtain raw materials,simple to manufacture,cheap and environmentally friendly,and has a prospect of development and application.更多还原