粘土对地下水中U(Ⅵ)的吸附作用及其污染控制研究

进行了U(Ⅵ)在粘土上吸附的批实验,其中,粘土样采自我国南方某大型铀尾矿库库底.实验结果表明,U(Ⅵ)在粘土上的吸附与浸泡液的pH值呈强烈的非线性关系,在pH值近中性时,U(Ⅵ)在粘土上的吸附达到了一个最大值,而在偏酸性或偏碱性条件下,U(Ⅵ)在粘土上的吸附迅速减少;运用表面络合理论建立了U(Ⅵ)在粘土上吸附的表面络合模型(DLM),该模型很好地拟合了实验数据.模型检验表明,它可以精确预测U(Ⅵ)在不同热力学条件下的吸附行为;此外,模拟结果表明,U(Ⅵ)的粘土上吸附在酸性条件下受固液比(M/V)影响明显,而在碱性条件下主要受浸泡液中HCO3-和CO2-3的控制.     

运用原位衰减全反射红外光谱法研究铬磁铁矿对磷酸根的吸附作用

采用原位衰减全反射红外光谱技术(ATR-FTIR)探讨pH值和磷酸根浓度对磷酸根在磁铁矿表面吸附形态的影响。结果表明:随着pH值降低,磷酸根浓度增大,磷酸根在磁铁矿表面的吸附量随之增加,形成内层吸附。发现有3种吸附模型:(1)在低pH值时,主要形成对称性为C1的吸附形态,可能主要是单质子化双齿双核络合形态;(2)在高pH值条件下发现有2种形态,高磷酸根浓度条件下,形成1种对称性为C3ν吸附形态,主要是单齿单核络合形态,在低浓度条件下,发现1种C2ν对称性吸附形态,可能是去质子化双齿双核络合形态,与单齿单核络合形态的物种在低浓度条件下共同存在。     

矿物溶解的表面化学动力学机理

本文应用表面化学理论分析了矿物在水溶液中的溶解反应动力学机理。表面化学的催化作用使矿物溶解反应的活化能显著降低。矿物溶解速率受表面吸附、表面交换反应和解吸反应等表面化学过程的控制并与溶液的pH值有关，正比于溶液αH＋值的nθ次幂。受表面吸附控制时，nθ＝1，溶解速率随pH增大而减小；受表面交换反应控制时，nθ＝0，溶解速率与pH无关；受解吸反应控制时，酸性条件下nθ为0～1内的正小数，碱性条件下nθ为-1～0之内的负小数。大多数矿物的溶解作用在酸性条件下受表面吸附和／或表面交换反应控制，在碱性条件下受解吸反应的控制。     

基于PHT3D的地下水中六价铀吸附反应运移数值模拟

在铀尾矿地区溶解态U(Ⅵ)渗漏到含水层中对周围环境造成严重的威胁。本研究利用反应运移软件PHT3D对U(Ⅵ)吸附实验进行模拟,并与传统Kd吸附经验模型进行对比。模拟结果表明:传统Kd吸附经验模型在地球化学条件发生变化时无法刻画表面吸附的动态变化;由表面络合模型计算的Kd值在时空是不断变化的,其更接近实际中多变水化学条件下的吸附;应用PHT3D进行反应模拟能够在复杂地下水流条件中获得较好的效果。     

13X沸石对Ni2+吸附性能的实验研究

在静态条件下，实验研究了13X沸石的用量、温度、时间、溶液pH值、初始Ni^2 质量浓度对Ni^2 吸附性能的。结果表明：在室温下，13X沸石对Ni^2 的吸附平衡时间为15min，对Ni^2 的最大吸附量为49.7mg/g沸石；静态等温吸附过程符合Langmiur吸附等温方程式；13X沸石对Ni^2 的吸附机理为离子交换吸附和表面络合吸附。     

天然锰钾矿吸附水溶液中Hg^2＋的实验研究

利用粉碎分级的天然锰钾矿去除水溶液中Hg^2 的实验研究表明：反应平衡时间约为20小时；pH值对其吸附率影响很大，在中性（氯化物在偏碱性）条件下吸附率较高；溶液中阳离子的存在会产生竞争吸附而降低对Hg^2 的吸附量，2价金属离子较1价金属离子对Hg^2 竞争干扰明显；溶液中Cl^-的存在能明显降低对Hg^2 的吸附量。对等温吸附曲线的回归分析得出在浓度为5～350mg/L段能很好地符合Langmuir单吸附位吸附曲线，并计算出在该实验条件下其最大理论吸附量为27.6mg/g。解吸实验结果表明，在无其他电解质参与的条件下解吸量较少，受多种电解质干扰时其解吸率不超过20%。     

不同因素对砂岩含水层介质吸附铀的影响

铀矿开采过程中及井场退役后,含铀浸出液的扩散会对地下水造成一定影响,该影响范围和程度决定了铀的天然衰减特征。本文以北方某地浸铀矿区砂岩含水介质为研究对象,研究了溶液化学特征和黄铁矿含量对砂岩吸附和转化铀的影响。结果表明,砂岩颗粒对U(VI)的吸附基本在12 h可达平衡。线性等温吸附模型可以很好地描述吸附特征;砂岩颗粒对U(VI)的吸附率总体随着粒径增大而减小,当岩石粒径增大到0.200.25 mm时,吸附率趋于稳定。溶液pH值是影响吸附的主要因素,通过控制溶液中U(VI)的络合形态和岩石颗粒表面带电荷情况,在库仑力的作用下促进或者抑制吸附,在pH=6时,达到最佳吸附状态。共存离子对U(VI)吸附的抑制程度是: {\mathrm{HCO}}_3^{-}>Ca²⁺>Mg²⁺> {\mathrm{SO}}_4^{2-}。 {\mathrm{HCO}}_3^{-}主要通过与 {\mathrm{UO}}_2^{2+}络合形成带负电荷的络合阴离子抑制U(VI)吸附。近中性pH值试验条件下,黄铁矿含量的增加对U的去除起到显著的促进作用,这种促进作用体现在吸附和还原作用,被吸附的Fe²⁺在吸附剂表面通过电子转移还原吸附态的U(VI),还原产物是UO_2+x,吸附和还原是个相互促进的过程;在弱碱性pH值试验条件下,黄铁矿对U(VI)去除的影响不明显,水解沉淀作用和较低的吸附率抑制了还原反应的发生。     

坡缕石对Zn^2＋的吸附性能及吸附工艺条件优化研究

从坡缕石粘土提纯人手，进行了坡缕石吸附Zn^2 的实验研究，结果表明坡缕石对水中Zn^2 的吸附性能主要受振荡速度、吸附时间、溶液pH值、吸附剂用量等因素影响，30℃时坡缕石对Zn^2 的等温吸附曲线同时符合Langmuir方程和BET方程。在本实验条件下，坡缕石对水中的Zn^2 (20mL，Zn^2 浓度均为50mg／L)的最佳吸附工艺条件为：振荡速度150r／min，吸附时间120min，吸附剂用量0．120g，溶液pH为6．2，此条件下去除率达到T95．5％。     

零价铁吸附-还原溶液中U(VI)的实验研究

研究零价铁(Zero-valent iron,ZVI)去除溶液中的U(VI),分析了pH值、反应时间、ZVI投加量、铀溶液初始浓度、其它离子(Mg2+、Mn2+、Cl-、NO-3、CO2-3和Cu2+)等条件因素对U(VI)去除效果的影响,并讨论其去除机理。结果表明:ZVI对溶液中U(VI)有较好的去除作用,在pH=4,振荡时间为120min,ZVI投加量为1.6g/L,铀溶液初始浓度为10mg/L,铀去除量为4mg/g时,U(VI)的去除率可达到63.7%。其它离子实验结果表明:Mg2+、Mn2+、Cl-、NO-3对ZVI去除U(VI)影响不超过3%,CO2-3和Cu2+影响相对较大。ZVI去除溶液中U(VI)以还原沉淀和吸附作用为主,吸附-还原反应遵循一级化学反应动力学方程。     

天然沸石对Pb(Ⅱ)和Ni(Ⅱ)离子的吸附作用研究

在静态条件下,研究了沸石对重金属离子（如Ｐｂ＾２＋和Ｎｉ＾２＋）的吸附与交换。结果表明,沸石对重金属离子具有较强的吸附性能,ｐＨ值的影响吸附的主要因素,离子交换和表面络合反应是主要吸附形式。     

Adsorption Behavior of Hexavalent Chromium in Vadose Zone

Adsorption behavior of Cr (VI) in vadose zone, which is silty clay and clayey soil, was studied through kinetics experiments, isothermal adsorption experiments under various conditions, including different ph, temperature and organic contents. The results from kinetics experiments showed that the sorption progress of Cr (VI) has clear features in different stages, and adsorption equilibrium showed at 30 min, the adsorption rate of silty clay and clayey soil were 60%. The isothermal adsorption curve of Cr (VI) fitted closely with Freundlich equation model. When pH is 3-5 a plateau were seen, thereafter with increase in pH the adsorption rate of Cr (VI) dropped sharply and the minimum achieved at pH 10, the adsorption rate were only 35%. Adsorption rate of Cr (VI) increased gradually with the increase of temperature, the temperature of vadose zone is 14.7 ℃, according to the experimental results, the adsorption rate of Cr (VI) is about 40%. The use of organics represents an important contribution to the sorption of Cr (VI), sorption rate up to 100% when 30% of organic content. These studies will provide basis for manager to minimize the impacts, and provide basic data for pollution prevention and remediation of vadose zone.     

Approaches to surface complexation modeling of Uranium(VI) adsorption on aquifer sediments

Uranium(VI) adsorption onto aquifer sediments was studied in batch experiments as a function of pH and U(VI) and dissolved carbonate concentrations in artificial groundwater solutions. The sediments were collected from an alluvial aquifer at a location upgradient of contamination from a former uranium mill operation at Naturita, Colorado (USA). The ranges of aqueous chemical conditions used in the U(VI) adsorption experiments (pH 6.9 to 7.9; U(VI) concentration 2.5 · 10⁻⁸ to 1 · 10⁻⁵ M; partial pressure of carbon dioxide gas 0.05 to 6.8%) were based on the spatial variation in chemical conditions observed in 1999-2000 in the Naturita alluvial aquifer. The major minerals in the sediments were quartz, feldspars, and calcite, with minor amounts of magnetite and clay minerals. Quartz grains commonly exhibited coatings that were greater than 10 nm in thickness and composed of an illite-smectite clay with occluded ferrihydrite and goethite nanoparticles. Chemical extractions of quartz grains removed from the sediments were used to estimate the masses of iron and aluminum present in the coatings. Various surface complexation modeling approaches were compared in terms of the ability to describe the U(VI) experimental data and the data requirements for model application to the sediments. Published models for U(VI) adsorption on reference minerals were applied to predict U(VI) adsorption based on assumptions about the sediment surface composition and physical properties (e.g., surface area and electrical double layer). Predictions from these models were highly variable, with results overpredicting or underpredicting the experimental data, depending on the assumptions used to apply the model. Although the models for reference minerals are supported by detailed experimental studies (and in ideal cases, surface spectroscopy), the results suggest that errors are caused in applying the models directly to the sediments by uncertain knowledge of: 1) the proportion and types of surface functional groups available for adsorption in the surface coatings; 2) the electric field at the mineral-water interface; and 3) surface reactions of major ions in the aqueous phase, such as Ca²⁺, Mg²⁺, HCO₃⁻, SO₄²⁻, H₄SiO₄, and organic acids. In contrast, a semi-empirical surface complexation modeling approach can be used to describe the U(VI) experimental data more precisely as a function of aqueous chemical conditions. This approach is useful as a tool to describe the variation in U(VI) retardation as a function of chemical conditions in field-scale reactive transport simulations, and the approach can be used at other field sites. However, the semi-empirical approach is limited by the site-specific nature of the model parameters.     

Interactions of uranium with bacteria and kaolinite clay

We assessed the accumulation of uranium (VI) by a bacterium, Bacillus subtilis, suspended in a slurry of kaolinite clay, to elucidate the role of microbes on the mobility of U(VI). Various mixtures of bacteria and the koalinite were exposed to solutions of 8 × 10^− 6 M- and 4 × 10^− 4 M-U(VI) in 0.01 M NaCl at pH 4.7. After 48 h, the mixtures were separated from the solutions by centrifugation, and treated with a 1 M CH₃COOK for 24 h to determine the associations of U within the mixture. The mixture exposed to 4 × 10^− 4 M U was analyzed by transmission electron microscope (TEM) equipped with EDS. The accumulation of U by the mixture increased with an increase in the amount of B. subtilis cells present at both U concentrations. Treatment of kaolinite with CH₃COOK, removed approximately 80% of the associated uranium. However, in the presence of B. subtilis the amount of U removed was much less. TEM–EDS analysis confirmed that most of the U removed from solution was associated with B. subtilis. XANES analysis of the oxidation state of uranium associated with B. subtilis, kaolinite, and with the mixture containing both revealed that it was present as U(VI). These results suggest that the bacteria have a higher affinity for U than the kaolinite clay mineral under the experimental conditions tested, and that they can immobilize significant amount of uranium.     

Adsorption of chromium and copper in aqueous solutions using tea residue

In this study, adsorption of copper and chromium was investigated by residue of brewed tea (Tea Waste) from aqueous solutions at various values of pH. It was shown that adsorbent dose, copper and chromium ion concentrations in such solutions influence the degree of these heavy metal ions’ obviation. The adsorption level of the prepared solutions was measured by visible spectrophotometer. The tea residue adsorbed copper (II) and chromium (VI) ions at initial solution pH by 25 % and 3 %, respectively. During the experiments the peak adsorption occured in hydrated copper nitrate aqueous solution at pH range of 5–6. Likewise the maximum adsorption appeared in potassium chromate aqueous solution at pH range of 2–3. In addition, tea residue adsorbed about 60 mg/g of copper (II) ion at pH=5, while chromium adsorption was registered at about 19 mg/g at pH=2. The data obtained at the equilibrium state, was compared with Langmuir and Freundlich models. Results showed that regarding the kinetics of adsorption, the uptake of copper (II) and chromium (VI) ions by tea residue was comparatively faster, with the adsorption process exhaustion completed within the first 20 min of the experiments. Furthermore, results revealed that adsorption data concerning the kinetic phase is closely correlated with a pseudo-second order model with R²> 0.99 for copper (II) and chromium (VI) ions     

Uranyl adsorption onto montmorillonite: Evaluation of binding sites and carbonate complexation

The fate and transport of uranium in contaminated soils and sediments may be affected by adsorption onto the surface of minerals such as montmorillonite. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate the adsorption of uranyl (UO₂²⁺) onto Wyoming montmorillonite. At low pH (∼4) and low ionic strength (10⁻³ M), uranyl has an EXAFS spectrum indistinguishable from the aqueous uranyl cation, indicating binding via cation exchange. At near-neutral pH (∼7) and high ionic strength (1 M), the equatorial oxygen shell of uranyl is split, indicating inner-sphere binding to edge sites. Linear-combination fitting of the spectra of samples reacted under conditions where both types of binding are possible reveals that cation exchange at low ionic strengths on SWy-2 may be more important than predicted by past surface complexation models of U(VI) adsorption on related montmorillonites. Analysis of the binding site on the edges of montmorillonite suggests that U(VI) sorbs preferentially to [Fe(O,OH)₆] octahedral sites over [Al(O,OH)₆] sites. When bound to edge sites, U(VI) occurs as uranyl-carbonato ternary surface complexes in systems equilibrated with atmospheric CO₂. Polymeric surface complexes were not observed under any of the conditions studied. Current surface complexation models of uranyl sorption on clay minerals may need to be reevaluated to account for the possible increased importance of cation exchange reactions at low ionic strengths, the presence of reactive octahedral iron surface sites, and the formation of uranyl-carbonato ternary surface complexes. Considering the adsorption mechanisms observed in this study, future studies of U(VI) transport in the environment should consider how uranium retardation will be affected by changes in key solution parameters, such as pH, ionic strength, exchangeable cation composition, and the presence or absence of CO₂.     

Adsorption of hexavalent chromium from aqueous solutions by wheat bran

In this research, adsorption of chromium (VI) ions on wheat bran has been studied through using batch adsorption techniques. The main objectives of this study are to 1) investigate the chromium adsorption from aqueous solution by wheat bran, 2) study the influence of contact time, pH, adsorbent dose and initial chromium concentration on adsorption process performance and 3) determine appropriate adsorption isotherm and kinetics parameters of chromium (VI) adsorption on wheat bran. The results of this study showed that adsorption of chromium by wheat bran reached to equilibrium after 60 min and after that a little change of chromium removal efficiency was observed. Higher chromium adsorption was observed at lower pHs, and maximum chromium removal (87.8 %) obtained at pH of 2. The adsorption of chromium by wheat bran decreased at the higher initial chromium concentration and lower adsorbent doses. The obtained results showed that the adsorption of chromium (VI) by wheat bran follows Langmuir isotherm equation with a correlation coefficient equal to 0.997. In addition, the kinetics of the adsorption process follows the pseudo second-order kinetics model with a rate constant value of 0.131 g/mg.min The results indicate that wheat bran can be employed as a low cost alternative to commercial adsorbents in the removal of chromium (VI) from water and wastewater.     

季胺盐阳离子插层蒙脱土对铀吸附性能的研究

通过十六烷基三甲基溴化铵（CTMAB）与钠基蒙脱土离子交换制备出季胺盐阳离子插层蒙脱土（CTMA’-M）,采用小角X射线衍射仪、傅里叶变换红外光谱仪和高分辨透射电镜表征微观结构,研究CTMA’的插层量、溶液的初始pH值、初始浓度和其他共存离子对吸附铀性能的影响,考察了CTMA’-M处理铀矿水）台废水的应用性能。结果表明：CTMA’插层后蒙脱土的层间距由1．21nm增加到4．09nm,但仍保持钠基蒙脱土原有的晶体结构。随CTMAB用量的增加,插层到蒙脱土层间的CTMA’量增加,对铀离子的吸附容量逐渐增大,当CTMAB的用量超过阳离子交换容量的1．4倍时,铀吸附容量基本保持不变。溶液pH和接触时间对铀离子吸附性能影响较大．CTMA’-M最佳吸附pH值为6．0,平衡吸附时间为80min,CTMA’插层能够改善蒙脱土对铀离子的选择性吸附。在1L含有15mg／L铀的废水中加入1．5gCTMA’-M时,铀的去除率达到98％以上。     

The effect of pH and natural microbial phosphatase activity on the speciation of uranium in subsurface soils

The biomineralization of U(VI) phosphate as a result of microbial phosphatase activity is a promising new bioremediation approach to immobilize uranium in both aerobic and anaerobic conditions. In contrast to reduced uranium minerals such as uraninite, uranium phosphate precipitates are not susceptible to changes in oxidation conditions and may represent a long-term sink for uranium in contaminated environments. So far, the biomineralization of U(VI) phosphate has been demonstrated with pure cultures only. In this study, two uranium contaminated soils from the Department of Energy Oak Ridge Field Research Center (ORFRC) were amended with glycerol phosphate as model organophosphate source in small flow-through columns under aerobic conditions to determine whether natural phosphatase activity of indigenous soil bacteria was able to promote the precipitation of uranium(VI) at pH 5.5 and 7.0. High concentrations of phosphate (1-3 mM) were detected in the effluent of these columns at both pH compared to control columns amended with U(VI) only, suggesting that phosphatase-liberating microorganisms were readily stimulated by the organophosphate substrate. Net phosphate production rates were higher in the low pH soil (0.73 ± 0.17 mM d⁻¹) compared to the circumneutral pH soil (0.43 ± 0.31 mM d⁻¹), suggesting that non-specific acid phosphatase activity was expressed constitutively in these soils. A sequential solid-phase extraction scheme and X-ray absorption spectroscopy measurements were combined to demonstrate that U(VI) was primarily precipitated as uranyl phosphate minerals at low pH, whereas it was mainly adsorbed to iron oxides and partially precipitated as uranyl phosphate at circumneutral pH. These findings suggest that, in the presence of organophosphates, microbial phosphatase activity can contribute to uranium immobilization in both low and circumneutral pH soils through the formation of stable uranyl phosphate minerals.     

A study on the adsorption of chromium on laterite from Guizhou Province,China

The adsorption behaviors of Cr(VI) on laterite from Guizhou Province were studied in this paper, and the adsorption mechanism was discussed as well. Results showed that different mineral compositions in the laterite would cause differences in the capacity of laterite to absorb Cr(VI). Gibbsite, iron oxide minerals and non-crystalloids are the main contributors to enhancing the capacity of laterite to absorb Cr(VI). The pH of the solution is an important factor affecting the adsorption of Cr(VI) on laterite. Acidic environment (pH=2–5) is favorable to the adsorption of Cr(VI). The amount of adsorbed Cr(VI) decreases with increasing pH of the solution. With increasing initial concentrations of Cr(VI), the amount of adsorbed Cr(VI) increases first, and then decreases. The optimal adsorption concentration of Cr(VI) on laterite is 250 μg/mL. The adsorption of Cr(VI) on laterite is a rapid process, about 80% Cr(VI) will be adsorbed within 2 hours. And the adsorption of Cr(VI) on kaolinite is a slow process.