【作者】 黄界颍；

【导师】 徐晓春；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2013， 博士

【摘要】 土壤镉污染对生态系统、粮食安全及人体健康具有巨大的潜在危害,已成为当今全球共同关注的重大环境问题。我国秸秆资源丰富,通过秸秆还田降低污染土壤Cd危害,既可以消除Cd污染影响,又解决了秸秆难以无害化处置的普遍难题,符合农业可持续发展的规律。在对铜陵地区地质背景和地理及生态环境特征全面了解的基础上,本研究选取铜陵有色金属矿区的农田土壤,开展了静态吸附、动力学吸附、土壤培养和盆栽模拟试验研究,研究结果不仅对寻求有效的控制土壤中Cd的环境行为的对策措施具有重要意义,而且对于实现秸秆循环利用以及农产品安全生产等方面具有实际应用价值。动力学吸附及静态吸附试验结果表明,粉碎处理的水稻、油菜秸秆对Cd2+的吸附过程符合准一级动力学方程,其等温吸附曲线符合Langmuir方程,其吸附过程可能以化学吸附为主。随着秸秆投加量的增加,2种秸秆对Cd2+的去除率逐渐增加,单位质量吸附剂吸附量逐渐减小,本次试验的秸秆最佳投加量为10g/L;2种秸秆在初始pH2.0-7.0的范围内,吸附量随pH值的升高而升高,在pH值为6.0时,水稻和油菜秸秆吸附量达到最高,分别为13.30mg/g和13.64mg/g;秸秆对Cd2+的吸附试验中,最佳振荡速率为150rmp。因此,把秸秆用作吸附材料处理废水重金属Cd2+时,可控制废水pH值为6.0,振荡速率为150rmp,秸秆投加量为10g/L,将获得最佳处理效果,且油菜秸秆对Cd2+的去除效果优于水稻秸秆。利用吸附-解吸试验研究了秸秆还田对镉在土壤中的吸附-解吸特性的影响。研究发现,Langmuir模型拟合土壤上Cd2+的吸附特征效果最佳,而添加秸秆后,水稻土的Cd2+吸附特征以Temkin模型拟合效果更佳。秸秆还田促进土壤Cd2+的吸附,降低了土壤Cd2+的解吸量,水稻秸秆处理对土壤解吸Cd2+的影响大于油菜秸秆处理。因此,在高浓度Cd污染的土壤上施用秸秆可以有效地降低Cd的生态风险性。采用土壤培养试验研究了施用未腐熟秸秆对土壤性质及镉形态的动态影响。结果表明,淹水培养与旱作培养模式下,秸秆还田均提高了红壤和水稻土的土壤pH值、降低了土壤Eh值、提高了土壤DOC浓度。内源Cd污染土壤中,土壤Cd主要以残渣态Cd形式存在,当土壤添加外源Cd时,土壤Cd形态以交换态Cd最高,残渣态Cd的比例随外源加入Cd的增加而显著降低。与对照相比,添加秸秆处理显著提高了土壤水溶态Cd、EDTA结合态Cd含量及残渣态Cd含量,而降低了交换态Cd含量,且在前30d内变化比较剧烈。秸秆提取的DOM富含羧基、醛基、酮基等不饱和度高的物质,经过土壤腐解后,提取的DOM脂族性降低,芳香性趋于升高和增强。应是导致土壤EDTA结合态Cd及残渣态Cd含量增加的原因。在模拟污染的土壤上,秸秆还田引起土壤pH、Eh和DOC的变化与各形态Cd变化间达到显著相关。利用油菜和水稻进行盆栽试验研究了粉碎的油菜秸秆或水稻秸秆还田后对镉生物有效性的影响和机理。结果表明,随着Cd污染程度的增加,油菜、水稻生长受抑制程度相应增加(P<0.05),秸秆还田在一定程度上缓解了Cd对植物生长的毒害,但是在生物量、经济性状、光合作用、生理性状各指标间并未达到显著差异水平。油菜、水稻各器官Cd浓度亦随着土壤Cd污染程度的增加相应增加(P<0.05),秸秆还田后,显著降低了油菜、水稻各部位中的Cd浓度及其生物富集系数,尤其以高浓度Cd污染的土壤上效果最显著,且全量秸秆还田处理有较好的降低Cd吸收的作用。秸秆还田主要通过改变土壤Cd形态分布情况来影响植株Cd吸收。在外源添加Cd的情况下,植物体内的Cd含量主要与交换态Cd含量有关(P<0.05),秸秆还田促进土壤Cd由活性大的交换态向活性较弱的EDTA结合态及残渣态转化,降低了Cd的生物有效性。综上所述,秸秆还田可有效促进污染土壤Cd2+吸附,降低土壤Cd2+解吸,通过降低土壤交换态Cd含量,显著降低了作物各部位的生物富集系数及Cd浓度,减少了Cd向环境中的迁移和在食物链中的传递。在红壤区水旱轮作体制下,推荐油菜秸秆全量还田,可以较好地钝化土壤Cd,减少水稻吸收,避免镉米的生产。更多还原

【Abstract】 Cadmium contamination has a huge potential threat to the ecosystem, food safety and human health, which has become a major environmental problem widely concerned. There are abundant straw resources in China. By using straw returning to reduce mobility of cadmium not only solves environmental problems caused by agricultural waste, but also realizes resource utilization of straw, which accords with the requirements of sustainable agriculture. Based on the studies on geological background and geochemical characteristics of Tongling mine area, this study selected farmland soil from Tongling nonferrous metal mining area, carried out static adsorption, adsorption kinetics, soil incubation and pot experiments, in order to determine the impact mechanism of straws returning on Cadmium speciation and bioavailability in polluted soils. All the results of the study could not only seek effective countermeasures to control soil Cd environmental behavior, but also have practical application value to the realization of straw recycle and agricultural production safety.The dynamic adsorption experiment and static adsorption experiment were carried out to study the adsorption characteristics of straw power on cadmium. The results showed that the dynamics adsorption process conformed to the pseudo first order kinetics equation. The isotherms adsorption of cadmium was described well by the Langmuir model, chemisorption maybe dominated the adsorption process. With increased dosage of straw, the removal rate of Cd2+increased gradually, and unit mass adsorbent adsorption amount decreased. The best dosage of the straw in the study is lOg/L; In the initial pH range of2.0-7.0, the adsorption capacity increased with the pH value increasing; at pH value6, rice and rape straw reached highest adsorption capacity,13.30mg/g and13.64mg/g, respectively. In the research, the best oscillation rate was150rmp. Therefore, the straw used as adsorption material in wastewater treatment of heavy metal Cd2+could keep the wastewater pH value at6, the oscillation velocity at150rmp, straw dosage at10g/L, which are the best treatment effects. Rape straw on the removal effect of Cd2+is better than that of rice straw.Adsorption and desorption experiments were conducted to study the effect of straw returning on the adsorption and desorption characteristics of cadmium in soil. It was found that the isotherms adsorption of soil were described well by Langmuir model, while on paddy soil with straw returning Temkin model fitted the best according to the statistical analysis of the data. Straw returning promoted soil absorption of Cd2+, also reduced the amount of soil Cd2+desorption. In general, rice straw treatment on soil desorption of Cd2+was greater than that by rape straw treatment. In soil seriously contaminated by cadmium, straw returning can effectively reduce the ecological risk of cadmium.A soil incubation experiment was conducted to study the effect of non-decomposed straw returning on soil properties and dynamic changes of cadmium fractions in soils. The results showed that, in submerged incubation mode and dry cultivation mode, straw returning significantly increased soil pH in both red soil and paddy soil, the Eh value of soil was reduced, but soil DOC concentration increased. In native cadmium contaminated soil, soil cadmium existed in residual cadmium form; while in added cadmium contaminated soil, most of the added cadmium existed in exchangeable form, and residual cadmium ratio decreased significantly with added cadmium. Compared with the control, added straw treatment significantly increased soil water soluble cadmium, EDTA bound cadmium and residual cadmium content, while reduced the exchangeable cadmium content, and the changes were more violent within the former30days. The DOM extracted from straw is rich in carboxyl, aldehyde and ketone groups, which are high unsaturation material. Through the decomposition of soil, DOM’s aliphatic properties decreased, and aromatic properties rose, which should be the cause of the increase of soil EDTA bound cadmium and residual cadmium content. In the simulated contaminated soil, different forms of cadmium correlated with soil pH, Eh and DOC in straw returning treatments, and all reached a significant level.Rape and rice pot experiments were conducted to study the effect of non-decomposed rape straw power or rice straw power returning on bioavailability of cadmium in cadmium contaminated soils and the mechanisms. Results showed that, with the increase of cadmium concentration, rape and rice growth inhibition increased (P<0.05); straw returning alleviated the toxicity of cadmium on plant growth in a certain extent, but did not reach the significant difference level in biomass, economic characters, photosynthesis, and physiological traits. Cadmium concentration in different parts of rape and rice increased with the degree of cadmium pollution in soil (P<0.05), straw returning significantly reduced cadmium concentration and BCF, the effect was more significant in high concentration of cadmium contaminated soil, and the full amount of straw returning treatment had better effect to reduce the absorption of cadmium. Straw returning influenced plant cadmium uptaking mainly through changing soil cadmium fractions. Under the condition of added cadmium, cadmium content in plants was mainly related to the exchangeable cadmium contents (P<0.05), straw returning promoted soil cadmium transformation from active exchangeable cadmium to low activity state of EDTA combination state and residual cadmium, which reduced the bioavailability of cadmium.In summary, straw returning effectively promoted polluted soil absorption of Cd2+, decreased the amount of soil Cd2+desorption. And through reduced the exchangeable cadmium content, significantly reduced cadmium concentration and BCF in each tissues of crops. That reduced cadmium migration to the environment and avoided transfer in the food chain. In the red soil region of paddy-upland rotation system, recommended the rape straw total returning, can better decreased soil Cd uptake of rice, avoided cadmium rice production.更多还原