【作者】 罗涛；

【导师】 李取生；

【作者基本信息】 暨南大学 ， 环境科学， 2016， 硕士

【摘要】 由于植物根际分泌、微生物合成以及动植物残体分解等作用,低分子有机酸通常以微摩尔浓度广泛存在于各类土壤中,低分子有机酸对土壤重金属的活化已有大量研究,但模拟根际低浓度下低分子有机酸对土壤重金属的解吸及形态变化则鲜有报道。此外,稳定化处理是土壤重金属污染修复的常用措施,研究低分子有机酸对针铁矿、蒙脱石、生物炭三种稳定剂结合态重金属的活化,能够用于评价三种稳定剂的性能同时为土壤修复方案的可行性提供技术参考。本文通过外源添加根际浓度低分子有机酸于重金属污染土壤中,探讨低分子有机酸对土壤中Cd、Pb的解吸及形态变化的影响;然后制备针铁矿及市购蒙脱石、生物炭三种稳定剂对Cd进行吸附,用氯化镁对吸附后的材料进行洗脱,去除表面吸附态Cd,得到具有稳定态Cd的三种修复材料,并着重对针铁矿吸附Cd前后进行XPS表征,以探讨其结合形态;最后探究了柠檬酸、苹果酸、马来酸、酒石酸、草酸和琥珀酸在不同浓度下对三种材料中Cd的活化情况,结果表明:(1)供试浓度下低分子有机酸对污染土壤中的Cd、Pb解吸影响较小,解吸浓度均在μg/kg水平,但其能够促使土壤中碳酸盐结合态的Cd、Pb向可交换态转化。(2)针铁矿、蒙脱石、生物炭对Cd具有很好的吸附性能,1mmol/L吸附浓度下Cd含量分别达到3.58、3.64、4.07 mg/g,其中稳定结合态含量分别为2.52、0.93、1.04 mg/g。其中,针铁矿XPS表明,Cd能够与针铁矿中氧原子形成Cd-O而吸附在其表面。(3)六种低分子有机酸对针铁矿、蒙脱石、生物炭中结合态的Cd均表现出一定的活化效果,其中六种低分子有机酸之间的差异在活化三种结合态Cd中表现出一致的效果:柠檬酸的活化作用最大,其次为草酸,其余四种酸的活化效果差异不显著。其中,柠檬酸对针铁矿、蒙脱石、生物炭三种材料中Cd的活化率及单位摩尔活化量最大值分别为:4.2%、11.0%、5.6%和4.3、4.1、2.3 mg/mmol。故在使用上述土壤稳定化修复剂时,应考虑稳定化修复后土壤中重金属重新被土壤中低分子有机酸活化的风险。此外,可以考虑在植物修复处理中持续添加低分子有机酸于土壤中,以提高修复效率。更多还原

【Abstract】 Low-molecular-weight organic acids are widely present in all types of soil at micromolar concentrations due to plant root secretion,synthesis by microbial and decomposition of animal or plant residues.Effect of low-molecular-weight organic acids on the mobilization of cadmium in soil has been intensively investigated.But the effect of low-molecular-weight organic acids at rhizophere concentrations on desorption and speciation of heavy metals in soil has been rarely reported.In addition,stabilizing is the often applied to remediate heavy-metal contaminated soil.Research on effect of low-molecular-weight organic acids on Cd bound to goethite,montmorillonite and biochar can be used to evaluate the performance of these three kinds of stabilizers and provide technical assessment on their feasibility for soil remediation.The effect of low-molecular-weight organic acids on Cd and Pb desorption and morphological changes of a garden soil was studied in detail.In addition,goethite,montmorillonite and biochar are prepared to adsorb Cd;then three materials contained stabilizing bound cadmium are subject to MgCl₂ elution to removal mobile Cd on the surface of the materials.XPS was conducted to find the way Cd bound in goethite.Finally,six different low-molecular-weight organic acids are selected to study the effect of Cd desorption from the three kinds materials.The results showed that:（1）The impact of low-molecular-weight organic acids toward Cd and Pb desorption wasminor and the desorption concentrations are all inμg/kg level;but portion of carbonate bound Cd and Pb was converted to exchangeable fraction.（2）Goethite,montmorillonite and biochar havegood adsorption capability toward Cd.The adsorption capacity can reach 3.58,3.64,4.07 mg/g for these sorbents respectively.There are 2.52,0.93and1.04 mg/g Cd in goethite after elution by MgCl2.The XPS results show that Cd can be adsorbed on goethite thorough formation of Cd-O-Fe.（3）Six kinds of low-molecular-weight organic acids all have the ability to monilize Cd on goethite,montmorillonite and biochar and show the same effecttoward Cd mobilization sorbed on the three studied sorbents.For each organic acid,the ability to mobilize Cd sorbed on the sorbents follows the order,follow the order:citric acid>oxalic acid>malic acid≈tartaric acid≈maleic acid≈succinic acid.The maximum activation ratio and unit molar ratio of citric to goethite,montmorillonite and biochar were 4.2%,11.0%5.6 and 4.3,4.1,2.3 mg/mmol,respectively.In conclusion,risk of the heavy metals in soil can be enhanced by low-molecular-weight organic acids after remediation by the amendments,which heights the inportant role of low-molecular-weight organic acids in controlling heavy metal mobilization.In addition,it may be useful to add organic acid to soil to mobilize heavy metals in order to enhance heavy metal remvoal in phytoremediation process.更多还原