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生物炭的添加对紫色土中草甘膦吸附与解吸行为影响的研究
Alternative TitleThe Effect of Biochar on the Adsorption-Desorption of Gglyphosate in Purple Soil
Language中文
王茜
Thesis Advisor唐翔宇
2015
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name硕士
Degree Discipline土壤学
Keyword紫色土 生物炭 草甘膦 吸附-解吸 理化性质
Abstract草甘膦是一种广泛应用于全国乃至全世界的除草剂,也是使用量最大的除草剂之一,由于其低毒性,有关草甘膦在土壤中残留危害的研究较少。生物炭对有机污染物环境行为的影响及其机理是当前热门的研究领域,关于生物炭对土壤中有机污染物吸附-解吸行为影响的研究已经很多,如阿特拉津、敌草隆、西玛津、啶虫脒等。然而,目前有关生物炭对紫色土中草甘膦吸附-解吸行为影响的研究较少。本研究选取典型的紫色土代表区域忠县(中性紫色土)和盐亭(石灰性紫色土)作为采样点,分别采集果园、菜地、农田三种不同土地利用类型下的紫色土,采样深度为0~20 cm,分析其pH值、有机质、土壤阳离子交换量(CEC)等基本理化性质。将土壤和秸秆基生物炭按照不同的比例(0%、0.5%、1%、2%、3% w/w)充分混均,在室内干湿交替老化3个月后作为人工吸附剂用于实验。首先,通过草甘膦在紫色土中的吸附动力学实验,确定达到吸附-平衡所需的时间以及草甘膦吸附的机理;采用批量平衡方法,通过草甘膦的等温吸附-解吸实验,研究紫色土中草甘膦的吸附-解吸特征参数和生物炭的添加对紫色土中草甘膦吸附-解吸的影响,同时研究添加生物炭对紫色土基本理化性质的影响,探讨生物炭对紫色土中草甘膦影响的机理。主要研究结果如下: 1.添加生物炭的紫色土中草甘膦的吸附-解吸动力学特征 草甘膦在添加生物炭的中性紫色土(忠县)和石灰性紫色土(盐亭)中的吸附过程在8 h左右达到平衡,解吸过程在5 h左右达到平衡。吸附和解吸过程均包括快速和慢速两个阶段。伪二级吸附动力学模型能够较为准确的描述草甘膦在添加生物炭的紫色土中的吸附动力学特征( >0.99,P<0.01),推断草甘膦的吸附过程包括快速的外部液膜扩散、表面吸附过程及慢速的颗粒内部扩散等过程。 2.紫色土中草甘膦的等温吸附-解吸特征参数 (1)草甘膦在紫色土上的等温吸附实验结果表明:草甘膦在六种不同紫色土中的吸附等温线属于“S”型等温线,根据Freundlich模型的吸附强度常数( )得出,草甘膦在6个供试紫色土中的吸附强度大小顺序为:中性紫色土(忠县):果园土壤(57.98)>菜地土壤(37.56)>农田土壤(33.49);石灰性(盐亭):果园土壤(71.89)>菜地土壤(53.00)>农田土壤(47.99),这与忠县紫色土和盐亭紫色土中有机质含量大小的变化一致,紫色土中草甘膦的吸附量和吸附强度的大小与土壤有机质含量呈正相关,有机质含量越高越有利于紫色土中草甘膦的吸附,而与pH值、CEC含量和粘粒含量没有表现出相关性。说明草甘膦的吸附过程可能是有机质表面吸附与有机质相-水相分配作用的综合结果,其微观机理仍需进行深入的研究。吸附过程均可以用Freundlich模型( >0.9069,p<0.01)和Langmuir模型( >0.9998,p<0.01)较好地拟合。 (2)草甘膦在6个供试紫色土中的解吸过程均可以用Freundlich模型( >0.9069,p<0.01)和Langmuir模型( >0.9998,p<0.01)拟合。解吸过程均不是吸附的可逆过程,表现出解吸迟滞效应。解吸滞后系数(HI)大小顺序为:中性紫色土(忠县):农田土壤(1.31)>菜地土壤>果园土壤;石灰性紫色土(盐亭):菜地土壤(1.35)>农田土壤(1.13)≌果园土壤。根据滞后系数(HI)的分类依据可知,草甘膦在忠县果园紫色土上基本不存在解吸滞后效应。 3.生物炭的添加对紫色土中草甘膦吸附-解吸行为的影响及机理 (1)生物炭的添加对紫色土基本理化性质的影响: a) 使土壤有机质含量显著增加,忠县:果园土壤、农田土壤、菜地土壤的有机质含量分别由2.05%、1.71%、1.96%增大到4.72%、3.69%、3.81%;盐亭:果园土壤、农田土壤、菜地土壤有机质含量分别由2.52%、1.72%、2.33%增大到3.92%、2.43%、4.01%; b) 生物炭的添加使中性紫色土(忠县)的pH值显著提高,忠县土壤中,果园土壤、菜地土壤和农田土壤的pH值分别增大了0.45、0.44和0.47;而对于石灰性紫色土(盐亭)的影响不显著; c) 生物炭的添加,显著提高了紫色土的阳离子交换量CEC。以添加2%的生物炭为例,中性紫色土(忠县):农田土壤、菜地土壤和果园土壤分别增大了6.31、3.84和3.82 cmol/kg;石灰性紫色土(盐亭):果园土壤、农田土壤和菜地土壤分别增大了6.13、5.77和5.16 cmol/kg。 (2)草甘膦在添加生物炭的紫色土中的等温吸附实验结果表明:生物炭添加增强了6种紫色土对草甘膦的吸附量,吸附量随生物炭添加比例的增加而增大。在3种中性紫色土(忠县)中,生物炭添加对果园土壤中草甘膦吸附的影响较大,其次为菜地土壤,对农田土壤的影响最小;在3种石灰性紫色土(盐亭)中,对农田土壤中草甘膦吸附的影响最大,其次为果园土壤,对盐亭菜地土壤的影响较小。当生物炭添加比例为3%时,吸附强度( )的大小顺序为:中性紫色土(忠县):果园土壤(209.88)>菜地土壤(87.03)>农田土壤(71.57);石灰性紫色土(盐亭):农田土壤(99.94)>果园土壤(99.07)>盐亭菜地(69.54)。 (3)数据拟合的结果表明:采用Freundlich模型( =0.9284~0.9984)和Langmuir模型( =0.9812~0.998)能很好地拟合添加了生物炭的紫色土中草甘膦的等温吸附特征,相关系数达到极显著水平(p<0.01)。 (4)草甘膦的投加浓度为250 mg/L时,单点吸附常数( )随着生物炭添加比例的增加而增大。当生物炭添加比例为3%时,生物炭对草甘膦吸附量的贡献率的大小顺序为:中性紫色土(忠县):菜地土壤(10.11%)>农田土壤(1.95)>果园土壤(1.43%);石灰性紫色土(盐亭):农田土壤(9.61%)>菜地土壤(8.35%)>果园土壤(5.92%) (5)草甘膦在添加生物炭的紫色土上的等温解吸实验结果表明:与对照土壤相比,添加生物炭使供试紫色土(除忠县果园紫色土)中草甘膦的解吸滞后系数(HI)增大,滞后效应增强。当生物炭添加比例为3%时,滞后系数(HI)的大小顺序为:中性紫色土(忠县):农田土壤(1.42)>菜地土壤(1.24)>果园土壤(0.82);石灰性紫色土(盐亭):菜地土壤(1.52)>果园土壤(1.33)>农田土壤(1.27)。根据解吸滞后系数可知,草甘膦在添加了生物炭的忠县果园土壤中基本没有解吸滞后效应。
Other AbstractGlyphosate is a widely used herbicide in China and even in the whole world. It is also one of the most used herbicides in the world. However, few studies have been carried out with respect to the risk effects of residual glyphosates in soils. The impacts of biochar on the fates of organic contaminants are currently extensively studied. Mechanisms regarding the influence of biochar on the adsorption-desorption behavior of organic contaminants e.g. atrazine, diuron, simazine, acetamiprid, etc. have been presented. Nevertheless, much less attentions have been paid to the influence of biochar on the adsorption-desorption behavior of glyphosate in purplr soil. Typical shallow (0-20 cm) purple soils from Zhongxian (neutral purple soil) and Yanting (alkaline purple soil) were sampled in different land uses including orchard, vegetable field and farmland. pH, organic matter content and cation exchange capacity (CEC) were analyzed for these soil samples. Soil and biochar was mixed in different proportions (0%, 0.5%, 1%, 2%, and 3%, w/w). The mixtures were aged for three months with wetting and drying cycles applied before the start of the experiment. Firstly, the equilibrium time and adsorption mechanisms were determined based on the adsorption kinetics of glyphosate in biochar-soil mixtures. Then, batch equilibrium methods and isothermal adsorption desorption experiments were carried out to study the impacts of biochar addition on the adsorption-desorption behavior of glyphosate as well as the physicochemical properties of purple soil. The results are as follows: 1. The adsorption-desorption kinetics of glyphosate in biochar added purple soil The equilibrium time for the adsorption and desorption of glyphosate by biochar in both neutral (Zhongxian) and alkaline (Yanting) purple soil was 8 h and 5 h, respectively. The adsorption and desorption process could be separated into a fast phase and a slow phase. The pseudo-second-order kinetics equation could accurately describe the sorption kinetics of glyphosate in biochar added purple soil (r^2>0.99,P<0.01). It could be concluded that fast external liquid membrane diffusion or surface adsorption process and a slow internal diffusion process would occur for the adsorption of glyphosate by biochar. 2. The isothermal adsorption–desorption parameters of glyphosate in purple soil (1) “S” type adsorption isotherm was found for glyphosate in six different purple soils. According to Freundlich model, the adsorption constant of glyphosate in the neutral purple soil (Zhongxian) follows the trend: orchard soil (57.98) > vegetable field soil (37.56) > farmland soil (33.49). While in alkaline purple soil (Yanting), the trend was: orchard soil (71.89) > vegetable field soil (53.00) > farmland soil (47.99). Both trends were consistent with the organic matter contents in the soil, indicating the adsorption of glyphosate in purple soil is positively correlated with soil organic matter content. However, the adsorption amount showed little correlations with soil pH, CEC or clay fractions. Therefore, glyphosate may be absorbed by organic matters as surface adsorption in purple soil or as a result of partitions between organic phases and aqueous phase. The adsorption process could be fitted both by Freundlich model (r^2 ? 0.9069,p < 0.01) and Langmuir model (r^2 ? 0.9998, p < 0.01). (2) Similarly, desorption process could be fitted both by Freundlich model and Langmuir model. However, the desorption process was not the reversible process of adsorption process but showed an obvious desorption hysteresis. The desorption hysteresis coefficients (HI) in the neutral purple soil (Zhongxian) followed the trend: farmland soil (1.31) ? vegetable field soil (1.09) > orchard soil (0.99). While alkaline purple soil (Yanting) showed a different trend: vegetable soil (1.35) ? farmland soil (1.13) ≈ field orchard soil. Therefore desorption hysteresis does not occur for glyphosate during its adsorption in orchard soil in the neutral purple soil (Zhongxian), while it occurs in other five purple soils under different land uses. 3. Mechanisms of biochar on the adsorption-desorption behavior of glyphosate in purple soil (1) Impacts of biochar on soil physicochemical properties a) After biochar addition, organic matter content increased significantly. In soil samples from Zhongxian, organic matter content increased from 2.05%, 1.71%, 1.96% to 4.72%, 3.69%, 3.81% for orchard soil, farmland soil and vegetable field soil, respectively. While in soil samples from Yanting, organic matter content increased from 2.52%, 1.72%, 2.33% to 3.92%, 2.43%, 4.01% for orchard soil, farmland soil and vegetable field soil, respectively. b) After biochar addition, pH of neutral purple soil (Zhongxian) showed an obvious increase with the increment being 0.45, 0.44 and 0.47 for orchard soil, vegetable field soil and farmland soil, respectively. However, the addition of biochar did not affect soil pH in alkaline purple soil (Yanting). c) After biochar addition, CEC increased significantly in purple soil. For the purple soil with biochar addition of 2%, CEC increment in neutral purple soil samples from Zhongxian was 6.31, 3.84 and 3.82 cmol/kg for farmland soil, vegetable field soil and orchard soil, respectively. While CEC increment in alkaline purple soil samples from Yanting was 6.13, 5.77 and 5.16 cmol/kg, respectively. (2) The addition of biochar in purple soil enhanced the adsorption capacity of glyphosate in purple soil and the adsorption capacity increased with the increase of biochar addition proportion. For the neutral purple soil (Zhongxian) from three land uses, the addition of biochar showed the largest effect on the adsorption of glyphosate in orchard soil, followed by in vegetable field soil and farmland soil. For the alkaline purple soil (Yanting) from three land uses, the addition of biochar showed the largest effect on the adsorption of glyphosate in farmland soil, followed by in orchard soil and vegetable field soil. When the addition proportion of biochar was 3%, adsorption constant (K_f) in the neutral purple soil (Zhongxian) under different land uses followed the trend: orchard soil (209.88) ? vegetable soil (87.03) ? farmland soil (71.57). While in the alkaline purple soil (Yanting) under different land uses, adsorption constant (K_f) showed the trend: farmland soil (99.94) ? orchard soil (99.07) > vegetable field soil (69.54). (3) Freundlich model (r^2=0.9284~0.9984) and Langmuir model (r^2=0.9812~0.998) could both fit well the isotherm adsorption kinetics of glyphosate in biochar added purplr soil with the correlation coefficient being very significant (p < 0.01). (4) When the dose of glyphosate was 250 mg/L, the single-point adsorption constant (Kd) increased with the increasing addition proportion of biochar. When the biochar addition proportion was 3%, the contribution of biochar to glyphosate adsorption in the neutral purple soil (Zhongxian) followed the trend: vegetable field soil (10.11%) > farmland soil (1.95%) > orchard soil (1.43%). While the contribution trend was: farmland soil (9.61%) > orchard soil (8.35%) > vegetable field soil (5.92%) in the alkaline purple soil (Yanting). (5) The addition of biochar led to the increase of desorption hysteresis coefficients of glyphosate in purple soil (except orchard soil in Zhongxian). When the biochar addition proportion was 3%, desorption hysteresis coefficient (HI) of glyphosate showed the following trend in neutral purple soil (Zhongxian): farmland soil (1.42) > vegetable field soil (1.24) > orchard soil (0.82). While HI presented the following trend in alkaline purple soil (Yanting): vegetable field soil (1.52) > orchard soil (1.33) > farmland soil (1.27).
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/13958
Collection山地表生过程与生态调控重点实验室
Affiliation中国科学院成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
王茜. 生物炭的添加对紫色土中草甘膦吸附与解吸行为影响的研究[D]. 北京. 中国科学院大学,2015.
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