| 溶液介质条件和腐殖影响下REE在水/粘土界面分配和分馏的实验研究 | |
| Alternative Title | The effect of aqueous chemistry and humic acid on ree distribution and fractionation in the water/clay interface -experimental study |
| 万鹰昕 | |
| 2003 | |
| Degree Grantor | 中国科学院地球化学研究所 |
| Place of Conferral | 中国科学院地球化学研究所 |
| Degree Name | 博士 |
| Degree Discipline | 地球化学（环境） |
| Abstract | 过去几十年，由于REE具有重要的物源和过程示踪的地球化学意义，又与核放射性元素（钢系元素）的地球化学结构类似，因此，稀土元素的表生地球化学分配和行为研究便成为微量元素地球化学研究的一个重要部分。目前"通过水体悬浮物吸附态REE组成变化分析研究水／微粒界面作用REE分异现象．的工作不少，但至今进行的胶体或其他微粒吸附REE的实验研究不多，且已有的实验未能对溶液介质条件（如pH、离子强度、阴离子、固／液比），尤其是天然有机物的控制机理进行系统研究，对所观察到的水体中REE及其他微量元素分布变化多样性的解释仍缺乏实验依据。本文用结晶良好且粘土矿物含量高的苏州高岭土、美国粘土协会高岭土（Kga-1b）和蒙脱土（Wwy-2）作为吸附剂，采用系列吸附实验定量研究了不同理化条件（如pH值、离子强度、固／液比）下，受溶液阴离子（Cl-、C1O4-、SO42-、HCO3-）和Fluka胡敏酸（HA）影响，REE在粘土／水界面的分配和分馏，并讨论了HA和粘土的相互作用及胡敏酸存在与不存在时的REE形态分布。得到以下几点重要认识，为合理解释地表水体中既E和其他微量元素分布变化的多样性提供了实验依据：1、REE在苏州高岭土／水界面的重现性实验结果为：稀土配分系数D的相对标准偏差最大值为Eu8.4％，其他大多介于5．0％和6．6％间。而稀土吸附率Rd的相对标准偏差最大值为D2.2％，其他大多＜2％。较小误差表明本次研究所用实验方法是可行的。2、REE在苏州高岭土／水界面的动力学实验结果表明：短时间内（几分钟）稀土快速吸附在高岭土：接着因为粘土的层状结构，在20h内粘土层间金属与REE发生交换，稀土分配系数变化较大；20h以后能达到稳定的吸附／解吸平衡。因此本次研究采用的平衡时间为24h。3、pH分别为4.5和6.5时REE在苏州高岭土冰界面的分配能用Langmuir吸附等温线模拟和MINEQL＋软件表达。与静电吸附相对应，pH值越高REE最大吸附量越大。同时REE浓度的差异造成了REE分馏，总的趋势是REE含量越高，分馏越不明显。4、近中性（pH＝6.5）条件下不同阴离子的存在对REE在苏州高岭土／水界面分配和分馏的影响表明：随阴离子（Cl-、ClO4-、SO42-）含量升高REE吸附率降低，其中SO42-对REE吸附的影响最大，说明Na＋质量效应和阴离子配合的影响；同时由于不同阴离子与轻重R陇的络合差异所致，阴离子含量越高，轻重稀土的分馏越明显（La／Yb＝0.14-0.96），一般为阴离子含量的增加使得重稀土更多的被吸附，其中C1-和SO42+的影响最为明显。HCO3-虽然与REE有较强配合，但可能由于我们的HCO3-实验浓度低（＜0.0O25mol／L），在我们的实验结果中其对REE吸附和分馏的影响较小。5、由于不同pH和介质条件下，REE的络合形态分布不同，它们可以影响其在水／粒界面的分配。应用MINEQL＋模型，考虑REE的氢氧化物、碳酸盐和腐殖酸的影响，研究了REE的形态分布，结果表明fIA的存在对REE形态有很大影响：在HA不存在时，pH7-8间REECO3＋为主要的REEs形态，在更低和更高pH值，REE主要存在形式分别为REE加和REE（CO3）2-；而当HA存在时，在1）H值3-9，REEHA成为主要形态，在低pH（＜3）和高pH（＞9）时REE3+和REE（CO3）2-分别为主要形态。6、在较宽的pH范围HA能吸附在粘土上意味着在大多数含HA的天然水体中，粘土表面被HA覆盖。随H增加粘土对HA的吸附降低，反应了配位体交换或表面络合反应引起的专属吸附，其他如疏水性、、腐殖物质的溶解和HA的结构变化可能也影响了吸附。HA含量、矿物表面积和离子强度等理化条件对HA吸附会产生影响，从而影响HA对粘土表面的覆盖和接下来的粘土对REE的吸附。7、溶液介质条件对REE在粘土（Kga-1b和SWy-2）／水界面分配和分馏的影响表明：主要与静电相互作用、离子交换反应相对应，除低PH外，REE在高岭土上的吸附表现出弱的pH依赖性；而随pH增加REE在蒙脱土上的吸附呈下降趋势，显示交换反应为吸附过程的主要因素。在两种粘土中REE吸附均为随离子强度增加而降低，反应了Na质量效应。8、腐殖物质在粘土表面的吸附改变了吸附剂的属性。HA存在时REE在固液界面的分配反应了REEHA在固液界面的分配和HA在高岭土或蒙脱土／水界面上的分配，其他如静电吸附等机制也影响了吸附：在高岭土中，HA会增加低pH（＜4）吸附，随pH增加（＞5）HA会降低吸附。与此不同，在整个PH范围（3-10），HA的存在明显降低了REE在蒙脱土上的吸附。REE吸附在高岭土上随队含量增加是先增加后降低。而蒙脱土实验中，在低HA含量（＜5mg／L）处，RE阮吸附率与HA含量增加呈线性降低至几个百分比，而在高队含量处，REEs吸，附率无明显变化。这些清楚地说明水体环境中有机物的存在通常降低微量金属吸，附在微粒上，增加微量金属在水体中的溶解量，从而促进微量金属在水体环境中的长距离迁移。9、HA存在和不存在时，吸附／解吸过程中的REE分馏随pH或离子强度的变化都不明显，但由于REE系列与腐殖物质和矿物络合的差异，会随队含量的变化发生明显变化。通常溶液中高队含量增加了LREE在高岭土／蒙脱土上的吸附。这些结果是在HA存在时，微粒相上产生LREE富集的一个实验证实，也和大多数天然水体中的REEs分馏相一致。 |
| Other Abstract | In recent decades, the studies of REE distribution and behavior are the necessary parts of trace element geochemistry, because REE constrain the sources of materials and their evolution processes in many fields of earth science, furthermore, REE are sometimes used as chemical hornologues for radionuclide (i.e. Am +, Cm +, and Cr+). Although extensive experimental studies have been carried out on the control of particle/water interaction on the distribution of the REE in the aquatic environment. Several studies now are available concerning the REE adsorption onto colloid or particulate material, moreover, the present studies failed to discuss the: effect of solution chemistry (e. g. pH, ionic strength, ligand species, solid/solution ratio) and natural organic material. It is still short of experimental basis about the variety of REE and other minor elements concentration in aquatic system. We carried out the research on the batch adsorption experiments of REE on kaolin from SuZhou and American Clay Minerals Society(Kga-lb) and montmorillonite from American Clay Minerals Society(Swy-2), considering the effect of solution chemistry(e. g. pH, ionic strength, solid/solution ratio), ligand (Cl- ClO4-, SO42-, HCO3-) and Fluka humic acid, and discussing the interaction of HA and clay and the REE speciation in the presence and absence of humic acid. The important conclusions have been summarized as follows: 1 The reproductive experiments results of REE distribution in the SuZhou kaolin/water interface were: the most value of the relative standard deviations of distribution coefficient (D) was 8.4% for Eu, others were between 5.0 and 6.6. The most value of the relative standard deviations of adsorption ratio (Rd) was 2.2% for Dy, most of others were under 2%. The little error means that we can use this experiment method to study REE distribution and fractionation in the water/clay interface. 2, The kinetic experimental results of REE adsorption on the SuZhou kaolin showed: REE were adsorbed onto the kaolin in short time (several minutes), then the D for REE varied due to the layer structure of kaolin and exchange beiween the metals among the clay layers and REE. The reaction reach a "steady state" after 20h. Therefore, we performed our experiments in a 24-h reaction time. 3 Langmuir isotherm can model the REE adsorption on SuZhou kaolin at pH 4.5 and 6.5. At the same time, MINEQL+ software can describe the Langmuir isotherm. It is consistent with electrostatic adsorption that the amount of adsorbate required to rbrm a monalyer on available surface sites was bigger at pH 6.5 than at pH 4.5. REE fra-ctionation occured at different REE concentration. The trend is REE is insignificant in hi^h REE concentration. 4- REE adsorption onto SuZhou kaolin in the presence of different Ligands at near neutral showed: Rd for REE decreased as ligand concentration (Cl\ C1O4\ SO42') increased, especially the effect of SO42" was the most, which reflect the effect of Na+ mass action and complexation of anion. Fractionation between LREE and HGREE were more and more significant, La/Yfo=0.14-0.96, as ligand concentration increased due to the difference of the complexation of ligand and REE. Generally, more HREE were absorbed with increasing ligand concentration, especially for Cl- and SQ42+. Although HCO3+ can form stable complex with REE., the effect of HCCV concentration on REE distribution was low maybe dwe to the low HCCV concentration (<0.0025mol/L). 5. In the different pH arid the present of different ligand, REE speciation distribution are different, which would influence REE distribution in the water/particulate interface. We researched on the R￡E speciation distribution using MINEQL+ model and considering the complexation of i*EE with hydrate, carbonate and humate. The results showed there were great effect of .HA on REE speciation distribution: at the absence of HA, REECCV' become predominant between pH7 and 8, REE3+ and REE(CO3)2" predominat at lower and higher pH separat Y- However, in the presence of HA, the results are very different, it would be expected tLSat REEHA species will predominate at pH 3-9, with REE3+ and .REE(CO3)2- predominat at + lower and Ugher pH separately. 6- The adsorption of HA onto clays occurred over a wide pH range, which suggests that in most natural aquatic systems containing HA, mineral surfaces will be coated with HA. Increasing the pH resulted in a decrease in the adsorption of HA onto minerals, which reflect the specific binding by ligand exchange or surface cornplexation reactions, there may also be possible contributions from other effects such as hydrophobicity, solubility of humic material and HA conformational changes. HA concentration, mineral surface and ionic strength also have effects on HA adsorption, and these will determine, along with solution chemistry, whether complete surface coverage of the clay by HA is achieved. As a result, the presence of HA would influence on the REE adsorption onto clay. 7 The effects of solution chemistry on REE adsorption onto the clay (Kga-lb and SWy-2) were as follows: REE adsorption onto the bare kaolin was shown to low pH dependent expect for low pH, which are mainly consistent with electrostatic and ionic exchange; the trend of REE adsorption on montmorillonite decrease with increasing pH, which shows the main mechanism is exchange reactiion. REE adsorption on the kaolin and montmorillonite decreased With increasing ionic strength, the Na mass action may be important. 8. HA coatings on the minerals were able to confer a different characteristic on the clay surface. In the presence of HA, REE adsorption reflect the distribution of REEHA and HA in the solid/water interface, the electrostatic and other mechanisms maybe have effects on the adsorption. The presence of HA caused a enhancement of adsorption of REE in kaolin system at low pH (<4) and a decrease in adsorption at intermediate and high pH. But the presence of HA decreased significantly adsorption of REE in montmorillonite system in the whole pH range (3-10). REE adsorption onto kaolin increased and then decreased with increasing HA concentration. However, in the montmorillonite system, REE adsorptin decreased exponently to several percent at low HA concentration (<5mg/L), and have no significant change at high HA'1 concentration, with increasing HA. The results presented here have shown that the presence of organic material generally lower trace metals adsorption onto particulate and increase the solubility of trace metals in the aquatic environment, therefore, improve the migration of them in long distance. 9. The REE fractionation during adsorption/desorption in both the absence and presence of HA was not remarkable as function of pH or ionic strength, but occurs as function of HA concentration due to difference between complexation of humic substance and mineral with REE series. In general, high concentration of HA in the solution increases the adsorption of light REE onto the kaolin/montmoriilonite. The results are experimental verification of a process that may generate the enrichment of ligh REE in the particulate phase in the presence of humic acid, which is consistence with the fractionation of REE in most of natural waters. |
| Pages | 90 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.gyig.ac.cn/handle/352002/3638 |
| Collection | 研究生_研究生_学位论文 |
| Recommended Citation GB/T 7714 | 万鹰昕. 溶液介质条件和腐殖影响下REE在水/粘土界面分配和分馏的实验研究[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,2003. |
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