Kinetic and microscopic studies of reductive transformations of organic contaminants on goethite

Reactions mediated by iron mineral surfaces play an important role in the fate of organic contaminants in both natural and engineered systems. As such reactions proceed, the size, morphology, and even the phase of iron oxide minerals can change, leading to altered reactivity. The reductive degradation of 4-chloronitrobenzene and trichloronitromethane by Fe(II) associated with goethite (alpha-FeOOH) was examined by performing sequential-spike batch experiments. The particle size and size distribution of the pre- and postreaction particles were quantified using transmission electron microscopy (TEM). Results demonstrate that the degradation reactions result in goethite growth in the c-direction. Furthermore, pseudo-first-order reaction rate constants for the degradation of 4-chloronitrobenzene and trichloronitromethane and for the loss of aqueous Fe(II) decrease dramatically with each subsequent injection of organic compound and Fe(II). This result indicates that the newly formed material, which TEM and X-ray diffraction results confirm is goethite, is progressively less reactive than the original goethite. These results represent an important step toward elucidating the link between mineral surface changes and the evolving kinetics of contaminant degradation at the mineral-water interface.     

Interaction between calcium and phosphate adsorption on goethite

Quantitatively, little is known about the ion interaction processes that are responsible for the binding of phosphate in soil, water, and sediment, which determine the bioavailability and mobility of phosphate. Studies have shown that metal hydroxides are often responsible for the binding of PO4 in soils and sediments, but the binding behavior of PO4 in these systems often differs significantly from adsorption studies on metal hydroxides in laboratory. The interaction between PO4 and Ca adsorption was studied on goethite because Ca can influence the PO4 adsorption equilibria. Since adsorption interactions are very difficult to discriminate from precipitation reactions, conditions were chosen to prevent precipitation of Ca-PO4 solids. Adsorption experiments of PO4 and Ca, individually and in combination, show a strong interaction between adsorbed Ca and PO4 on goethite for conditions below the saturation index of apatite. It is shown that it is possible to predict the adsorption and interaction of PO4 and Ca on electrostatic arguments using the model parameter values derived from the single-ion systems and without invoking ternary complex formation or precipitation. The model enables the prediction of the Ca-PO4 interaction for environmentally relevant calcium and phosphate concentrations.     

Bidentate complexation modeling of heavy metal adsorption and competition on goethite

Accurate sorption modeling is critical for environmental risk assessment and development of sound remedial technologies. Adsorption to iron oxide phases is one of the important sorption processes regulating the bioavailability and toxicity of metal ions in natural systems. In this study, we used spectroscopically derived bidentate surface species to constrain surface complexation modeling in addressing Ni(ll) and Zn(ll) adsorption and competition on goethite surfaces. The 2-pK(a) triple layer model successfully predicted adsorption in single adsorbate systems. The curvature in adsorption isotherms was accurately depicted using two types of sites: high affinity and low affinity, and mononuclear bidentate surface complexes. A constrained set of parameters was found for each metal (log K(L) = -6.63 and log K(H) = -2.45 for Ni, log K(L) = -3.92 and log K(H) = 2.14 for Zn) that successfully described adsorption over a large range of experimental conditions, covering 6 to 7 orders of magnitude in concentration, ionic strength from 10(-3) to 10(-2), and environmentally relevant pH range between 4 and 6.5. Adsorption competition was predicted using the bidentate surface species with parameters calibrated using single adsorbate data.     

Aminomethylphosphonic acid and glyphosate adsorption onto goethite: a comparative study

Glyphosate is a non-selective, broad spectrum, post-emergent herbicide widely used in weed control. Aminomethylphosphonic acid (AMPA) is one of the main products of biodegradation of glyphosate in natural systems before its ultimate mineralization and also the breakdown product of more complex phosphonates such as nitrilotris-(methylenephosphonic acid). The adsorption isotherms and surface coverage of AMPA and glyphosate (N-phosphomethylglycine, PMG) in aqueous suspensions of goethite as a function of pH were measured. Electrophoretic mobility curves forthe PMG/goethite system were also determined. The ATR-FTIR interfacial spectra of the surface complexes of AMPA and PMG onto goethite were analyzed as a function of the pH and the surface coverage. The phosphonate moiety of these two ligands coordinates to the iron oxide surface with similar structures as the methylphosphonic acid despite the presence of the amino and/or carboxylate groups of their molecules. Two predominating complexes have been identified where the phosphonate group in PMG or AMPA bonds monodentately or bridges bidentately to the surface of iron oxide in an inner sphere mode, while the carboxylate and amino group are noncoordinated to the surface. The stability constants of the surface complexes (triple bond)FeO-P(O)(OH)--R, (triple bond)FeO--P(O)2--R, and ((triple bond)FeO)2--P(O)--R were calculated using the constant capacitance model.     

EXAFS analysis of arsenite adsorption onto two-line ferrihydrite, hematite, goethite, and lepidocrocite

The modes of As(III) sorption onto two-line ferrihydrite (Fh), hematite (Hm), goethite (Gt), and lepidocrocite (Lp) have been investigated under anoxic condition using X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure spectroscopy (XANES) indicates that the absence of oxygen minimized As(III) oxidation due to Fenton reactions. Extended X-ray absorption fine structure spectroscopy (EXAFS) indicates thatAs(III)forms similar inner-sphere surface complexes on two-line ferrihydrite and hematite that differ from those formed on goethite and lepidocrocite. At high surface coverage, the dominant complex types on Fh and Hm are bidentate mononuclear edge-sharing (2E) and bidentate binuclear corner-sharing (2C), with As-Fe distances of 2.90 +/- 0.05 and 3.35 +/- 0.05 A, respectively. The same surface complexes are observed for ferrihydrite at low surface coverage. In contrast, As(III) forms dominantly bidentate binuclear corner-sharing (2C) sorption complexes on Gt and Lp [d(As-Fe) = 3.3-3.4 A], with a minor amount of monodentate mononuclear corner-sharing (1V) complexes [d(As-Fe) = 3.5-3.6 A]. Bidentate mononuclear edge-sharing (2E) complexes are virtually absent in Gt and Lp at the high surface coverages that were investigated in the present study. These results are compared with available literature data and discussed in terms of the reactivity of iron(III) (oxyhydr)oxide surface sites.     

Pu(V)O2+ adsorption and reduction by synthetic hematite and goethite

Changes in aqueous- and solid-phase plutonium oxidation state were monitored over time in hematite (alpha-Fe2O3) and goethite (alpha-FeOOH) suspensions containing 239Pu(V)-amended 0.01 M NaCl. Solid-phase oxidation state distribution was quantified by leaching plutonium into the aqueous phase and applying an ultrafiltration/solvent extraction technique. The technique was verified using oxidation state analogues of plutonium and sediment-free controls of known Pu oxidation state. Batch kinetic experiments were conducted at hematite and goethite concentrations between 10 and 500 m2 L(-1) in the pH range of 3-8. Surface-mediated reduction of Pu(V) was observed for both minerals at pH values of 4.5 and greater. At pH 3 no adsorption of Pu(V) was observed on either goethite or hematite; consequently, no reduction was observed. For hematite, adsorption of Pu(V) was the rate-limiting step in the adsorption/reduction process. In the pH range of 5-8, the overall removal of Pu(V) from the system (solid and aqueous phases) was found to be approximately second order with respect to hematite concentration and of order -0.39 with respect to the hydrogen ion concentration. The overall reaction rate constant (k(rxn)), including both adsorption and reduction of Pu(V), was 1.75+/-2.05 x 10(-10) (m(-2) L)(-2.08) (mol(-1) L)(-0.39) (s(-1)). In contrast to hematite, Pu(V) adsorption to goethite occurred rapidly relative to reduction. At a given pH,the reduction rate was approximately independent of the goethite concentration, although the hydrogen ion concentration (pH) had only a slight effect on the overall reaction rate. For goethite, the overall reaction rates at pH 5 and pH 8 were 6.0 x 10(-5) and 1.5 x 10(-4) s(-1), respectively. For hematite, the reaction rate increased by 3 orders of magnitude across the same pH range.     

Adsorption of glyphosate on goethite (alpha-FeOOH): surface complexation modeling combining spectroscopic and adsorption data

N-(phosphonomethyl)glycine (glyphosate, PMG) is the most widely used herbicide, and its adsorption onto soil minerals plays a significant role in its mobility and rate of degradation. In this work, we present the results of the first serious effort to find a realistic surface complexation modelthatfits both adsorption and total proton concentration data for PMG on the common soil mineral, goethite. Special attention was focused on making sure that the final model was in good semiquantitative agreement with previously reported X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopic measurements. Electrostatic effects were accounted for using the Basic Stern model, and the charges of the PMG-containing surface complexes were assumed to be distributed across the 0- and beta-planes. The reactions for the protonation of the goethite surface were described using the 1 pK model. We optimized on the intrinsic formation constants and the charge distributions of the complexes, as well as the initial total proton concentration (I = 0.1 M Na(NO3), 25.0 degrees C), and the following model was obtained. triple bond FeOH(0.5-) + H3L <==> triple bond FeHL(1.5-) + H(+) + H2O Log10beta = 4.70 +/- 0.08, Q0 = -0.18 +/- 0.02 triple bond FeOH(0.5-) + H3L <==> FeL(2.5-) + 2H(+) + H2O Log10beta = -3.9 +/- 0.1, Q0 = -0.7 +/- 0.1 Here, beta is the intrinsic formation constant, Q0 is the charge at the 0-plane, and the errors are reported as one standard deviation. The charge distributions of the complexes are rationalized by considering intramolecular hydrogen bonding between the protons of the amine group and both the phosphonate and carboxylate groups.     

Modeling the kinetics of the competitive adsorption and desorption of glyphosate and phosphate on goethite and gibbsite and in soils

The herbicide glyphosate and inorganic phosphate compete for adsorption sites in soil and on oxides. This competition may have consequences for the transport of both compounds in soil and hence for the contamination of groundwater. We present and evaluate six simple, kinetic models that only take time and concentrations into account. Three of the models were found suitable to describe the competition in soil. These three models all assumed both competitive and additive adsorption, but with different equations used to describe the adsorption. For the oxides, three additional models assuming only competitive adsorption were also found suitable. This is in accordance with the observation that the adsorption in soil is both competitive and additive, whereas the adsorption on oxides is competitive. All models can be incorporated in transport models such as the convection-dispersion equation.     

泡菜中高耐镉乳酸菌的选育及吸附特性

以筛选耐镉乳酸菌并研究其吸附特性为目的,利用高镉MRS培养基从泡菜中初筛出乳酸菌,并通过提高镉浓度对菌株进行驯化、复筛,以提高其耐镉能力,最终筛选出1株高耐镉乳酸菌ZY-6,固体最高耐镉质量浓度为10 000 mg/L,液体最高为900 mg/L,且p H值为7、Na Cl质量浓度为10 g/L、温度为37℃时菌株生长情况最好。经形态学观察、生理生化实验及分子生物学鉴定,该菌株为绿色魏斯菌(Weissella viridescens),在含50 mg/L的镉溶液中吸附率为61. 78%,对其他重金属如铅、铜和锰也显示出一定的吸附能力,研究结果为乳酸菌作为潜在的食品级重金属吸附剂提供了一定依据。     

Kinetic studies on cooking of tropical milled rice

Four aged tropical milled rices differing in amylose content and/or starch gelatinization temperature (GT) were presoaked for 30 min and cooked in calculated weights of water based on amylose content at 80, 90, 100, 110 and 120°C. Differences in cooking rates were evident below 100°C. Activation energy of cooking, derived from Arrhenius plots of cooking rate constant and reciprocal temperature, ranged from 76 to 121 kJ/mole at 80–90°C and 31–57 kJ/mole at 90–120°C. Cooking rates were lower and activation energy values were higher for intermediate GT samples than for low GT samples.     

分子印迹交联壳聚糖树脂对镉的吸附性能研究

采用分子印迹交联壳聚糖树脂（MICCR）为基础材料,研究MICCR对重金属Cd（Ⅱ）的吸附性能,考察pH对MICCR吸附性能的影响以及MICCR的重复吸附性能。结果表明:MICCR对重金属Cd（Ⅱ）的吸附容量为170.4mg/g,MICCR吸附Cd（Ⅱ）的最佳pH为4.5,其吸附较好地符合二级动力学模型,且吸附速率为6.97g·g^-1·h^-1。通过交联反应和分子印迹技术改进了壳聚糖吸附剂的重复吸附性能,且MICCR吸附镉的性能稳定。      

分子印迹交联壳聚糖树脂对镉的吸附性能研究

采用分子印迹交联壳聚糖树脂(MICCR)为基础材料,研究MiCCR对重金属Cd(Ⅱ)的吸附性能,考察pH对MICCR吸附性能的影响以及MICCR的重复吸附性能.结果表明:MICCR对重金属Cd(Ⅱ)的吸附容量为170.4mg/g,MICCR吸附Cd(Ⅱ)的最佳pH为4.5,其吸附较好地符合二级动力学模型,且吸附速率为6.97g·g-1·h-1.通过交联反应和分子印迹技术改进了壳聚糖吸附剂的重复吸附性能,且MICCR吸附镉的性能稳定.     

Influence of arsenate adsorption to ferrihydrite, goethite, and boehmite on the kinetics of arsenate reduction by Shewanella putrefaciens strain CN-32

The kinetics of As(V) reduction by Shewanella putrefaciens strain CN-32 was investigated in suspensions of 0.2, 2, or 20 g L(-1) ferrihydrite, goethite, or boehmite at low As (10 μM) and lactate (25 μM) concentrations. Experimental data were compared with model predictions based on independently determined sorption isotherms and rates of As(V) desorption, As(III) adsorption, and microbial reduction of dissolved As(V), respectively. The low lactate concentration was chosen to prevent significant Fe(III) reduction, but still allowing complete As(V) reduction. Reduction of dissolved As(V) followed first-order kinetics with a 3 h half-life of As(V). Addition of mineral sorbents resulted in pronounced decreases in reduction rates (32-1540 h As(V) half-life). The magnitude of this effect increased with increasing sorbent concentration and sorption capacity (goethite < boehmite < ferrihydrite). The model consistently underestimated the concentrations of dissolved As(V) and the rates of microbial As(V) reduction after addition of S. putrefaciens (～5 × 10(9) cells mL(-1)), suggesting that attachment of S. putrefaciens cells to oxide mineral surfaces promoted As(V) desorption and thereby facilitated As(V) reduction. The interplay between As(V) sorption to mineral surfaces and bacterially induced desorption may thus be critical in controlling the kinetics of As reduction and release in reducing soils and sediments.     

镉在企鹅珍珠贝组织器官中的分布及其存在形态研究

为研究企鹅珍珠贝组织器官中镉的分布及形态,实验采用石墨炉原子吸收光谱法和凝胶层析技术分析了镉在贝体不同组织器官中的分布、存在形态和相对分子质量分布。结果表明,企鹅珍珠贝各组织器官中镉的含量分别为:全脏器2.33 mg/kg,外套膜2.50 mg/kg,闭壳肌2.40 mg/kg,内脏团2.38 mg/kg,斧足2.24 mg/kg,鳃1.42 mg/kg。全贝中83.3%的镉蓄积在企鹅珍珠贝的内脏团、闭壳肌和外套膜中。企鹅珍珠贝各组织器官中只有不到40%的镉以可溶性蛋白结合态的形式存在。各组织器官的可溶性热稳定蛋白经Sephadex G-50凝胶过滤柱层析分离后,均得到相对分子质量>26000 u和<16000 u的两个蛋白质的紫外吸收峰。内脏团、外套膜和腮中的镉在两种分子质量段的蛋白质中均有分布;闭壳肌中少量镉与大分子蛋白质结合,其余近90%的镉分布在非蛋白组分中;斧足中镉几乎完全与大分子蛋白质结合。研究表明,镉在企鹅珍珠贝组织器官中的分布及形态存在差异性。      

Kinetic migration studies from packaging films into meat products

One of the main concerns regarding safety of food packaging is the possible migration of chemical substances (monomers and other starting substances, additives, residues) from food contact materials into foods. To evaluate the effect of the fat content and of the temperature of storage on the migration from plastics packaging films into meat products as an important class of foodstuffs, the kinetic mass transport of a model migrant (diphenylbutadiene) from low density polyethylene (LDPE) film in contact with different meat products was investigated. From the data, the diffusion coefficients were calculated for the applied test conditions, by use of a mathematical model. The results showed that migration increased with fat content and storage temperature. Analysis of migration data corresponding to minced pork meat containing different amounts of fat, stored for 10 days at 25°C, revealed an excellent relationship between migration level and fat content. This behaviour was also found for other types of meat products (chicken and pork neck). A simplifying mathematical model was applied to derive effective diffusion coefficients in the polymer which, however, do take kinetic effects in the meat also into account. In the case of pork meat contact, the effective diffusion coefficients derived from mathematical modelling were ten times higher for storage at 25°C (1.88×10(-9)cm(2)s(-1)) than for storage at 5°C (1.2×10(-10)cm(2)s(-1)).     

Batch and continuous packed column studies of cadmium biosorption by Hydrilla verticillata biomass

The removal of heavy metal ions by the nonliving biomass of aquatic macrophytes was studied. We investigated Cd biosorption by dry Hydrilla verticillata biomass. Data obtained in batch experiments indicate that H. verticillata is an excellent biosorbent for Cd. Cd was rapidly adsorbed and such adsorption reached equilibrium within 20 min. The initial pH of the solution affected Cd sorption efficiency. Results obtained from the other batch experiments conformed well to those obtained using the Langmuir model. The maximum adsorption capacity q(max) for H. verticillata was 15.0 mg/g for Cd. The breakthrough curve from the continuous flow studies shows that H. verticillata in the fixed-bed column is capable of decreasing Cd concentration from 10 to a value below the detection limit of 0.02 mg/l. The presence of Zn ions affected Cd biosorption. It can be concluded that H. verticillata is a good biosorbent for treating wastewater with a low concentration of Cd contaminants.