Biosorption of Cadmium by Citrobacter sp. JH 11-2 Isolated from Mining Site Soil

The wide use of cadmium (Cd) in batteries and semiconductors poses human and environmental health hazards when these materials are disposed. Citrobacter sp. JH 11-2, isolated from soil at an abandoned mining site, shows potential for use as a biosorbent for Cd removal from aqueous solution. A minimal inhibitory concentration of 300 mg L^?1 indicated high tolerance of the strain to Cd. The strain effectively removed 47.7% of the Cd from a 100 mg L^?1 solution within 160 h. Cell fractioning revealed that most of the Cd (43.5%) was in the membrane fraction, while 38.5% was in the peptidoglycan layer and 18.0% was in the cytoplasmic fraction. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of functional groups on dried Citrobacter sp. JH 11-2 cells that can adsorb or complex Cd ions. A Langmuir model provided a good fit to Cd removal by the cells, which followed pseudo-second-order kinetics. Results support further development of Citrobacter sp. JH 11-2 as a biosorbent for Cd removal.     

Enhancement of uranium bioaccumulation by a Citrobacter sp. via enzymically-mediated growth of polycrystalline NH4UO2PO4

The objective of this work was to study the effect of pH and ionic matrix on product release and on the removal of uranyl ion by a Citrobacter. sp phosphatase enzyme-catalysed reaction. An improvement in the efficiency of uranyl removal was obtained by incorporating ammonium acetate (NH₄Ac) into the solution. It was confirmed using X-ray diffraction (XRD), and other analytical techniques, that the insoluble, cell-bound product was NH₄UO₂PO₄.     

Enzymatically-mediated uranium accumulation and uranium recovery using a Citrobacter sp. Immobilised as a biofilm within a plug-flow reactor

Biofilm-immobilised Citrobacter sp. removed uranyl ion from flows supplemented with glycerol 2-phosphate. The metal uptake mechanism was mediated by the activity of a cell-surface bound phosphatase that precipitated liberated inorganic phosphate with uranyl ion as HUO₂PO₄·4H₂O at the bacterial surface. A modified integrated form of the Michaelis–Menten equation is proposed to describe the removal of metal ion by a columnar bioreactor, where the efficiency of metal removal is semi-quantitatively related to the input flow rate, the total enzyme loading (E₀) and the bioreactor activity. With biofilm-immobilised bacteria, E₀ was further divisible (split) into subparameters of phosphatase titre per bacterium and total biomass surface area. Varying the split E₀ and the reaction temperature modified the bioreactor performance. The immobilised bacteria retained high metal loads without loss in steady-state activity. Accumulated metal was recovered as a concentrated solution.     

The role of sulfate as a competitive inhibitor of enzymatically‐mediated heavy metal uptake by Citrobacter sp: implications in the bioremediation of acid mine drainage water using biogenic phosphate precipitant

Heavy metals can be removed from solution via biocrystallization with enzymatically‐liberated inorganic phosphate, according to Michaelis–Menten kinetics, in free whole cells and cells immobilized within polyacrylamide gel in a flow‐through reactor. Sulfate is a competitive inhibitor of phosphate release and a predictive model was developed and shown to describe the effect of sulfate on the efficiency of phosphate release by flow‐through columns. The inhibitory effect was substantially less than anticipated in the case of metal removal by the columns. In the case of lanthanum removal metal removal efficiency was restored by increasing the substrate concentration in accordance with model predictions. In the case of uranyl ion its removal with an equivalent substrate supplement increased the activity by 20% over the initial value at a limiting flow rate. Since the initial loss in activity in the presence of 40 mmol dm⁻³ SO₄²⁻ (approximately twice the K_i value) was only approximately 20% with both metals this was considered to be a minor problem for bioprocess application. In confirmation, calculations made from a published ‘case history’ of application of the system to the bioremediation of acid mine drainage water (AMD) containing 0.22 mmol dm⁻³ of uranyl ion and 35 mmol dm⁻³ of SO showed that the benchscale model is a good representation of performance under actual load conditions. © 1999 Society of Chemical Industry     

Citrobacter farmeri降解间甲酚的特性分析

从某焦化厂废水好氧生物处理的污泥中分离出一株能以间甲酚为唯一碳源、能源生长代谢的菌株Citrobacter farmeri.考察了间甲酚在不同初始浓度下Citrobacter farmeri细菌生长动力学,4种等浓度酚类物质的降解先后顺序,分别添加共基质葡萄糖和蛋白胨对低浓度和高浓度间甲酚降解的影响,以及在添加共基质葡...     

水热法制备纳米二氧化锆及其动力学研究

研究了水热法制备纳米二氧化锆过程中,制备前驱物的投料比n(NH3·H2O)∶n(ZrOCl2·8H2O)、水热反应的温度及保温时间对平均粒径dXRD及结晶率Xc的影响,研究结果表明:随着反应温度提高,晶体生长速率增大,晶化率提高,同时平均晶体粒径增大;水热时间延长,晶化率上升。其动力方程用Avrami动力学方程表示,分别求出在水热温度为 180℃时,动力学方程为ln[-ln(1-Xc) ] =ln1.28 0.578lnt;当水热温度为 240℃时,动力学方程为ln[-ln(1-Xc) ] =ln1.80 0.327lnt;当保温时间≥1h时,方程计算结果与实测数据基本吻合,其相对误差≤2. 6%。     

Polymerization of ethylene by supported zirconium alkoxide complex

Dichlorobis(3‐hydroxy‐2‐methyl‐4‐pyrone)Zr(IV) was grafted onto different inorganic supports, namely SiO₂, MAO‐modified SiO₂, MCM‐41, Al₂O₃, and MgO. The resulting supported catalysts were shown to be active in ethylene polymerization using methylaluminoxane (MAO) as the catalyst. Catalysts were characterized by Rutherford Backscattering Spectrometry (RBS) and nitrogen adsorption method. The highest catalyst activities were observed for the zirconium complex supported on MCM‐41. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of fine zirconium carbide powder by carbothermal reaction of carbon‐coated zirconia particles

In this study, a novel method for the synthesis of fine ZrC powder was presented. It consists of chemical vapor deposition (CVD) of C from CH₄ on ZrO₂ particles followed by carbothermal reaction. Firstly, optimal CVD conditions (1300 K and 30 minutes) yielding the stoichiometric amount of C deposit (23 wt%) were determined. Carbothermal reaction behavior of the carbon‐coated oxide particles was then investigated in Ar flow at 1700‐1800 K for 0‐120 minutes. Mass measurements, XRD and SEM techniques were used to characterize the products at various stages of the process. Lattice constants and mass losses of the samples increased to the levels of ZrC with increasing temperature and time. Almost pure ZrC powder (oxygen content: 0.59 wt%) with a mean particle size of ~170 nm was synthesized at 1800 K within 120 minutes. The present study demonstrates that ZrC powder can be synthesized at lower temperatures and shorter reaction times using C‐coated ZrO₂ powders compared with the conventional method which uses a mixture of ZrO₂ and solid C particles.     

分光光度法测定光亮镍及珍珠镍镀液中的镍含量

光亮镍和珍珠镍镀中镍的测定定通常采用EDTM滴定法,该法选择性低,易造成环境污染,本文采用分光光度法进行分析,探讨了测量波长,硫酸浓度及干扰元素等的影响,该法在镍含量为0－200mg范围内遵守比耳定律,测量结果准确,能满足实际生产的要求。     

Visualization of the Function of a Biofilm Reactor by Magnetic Resonance Imaging

This study demonstrates that Magnetic Resonance Imaging (MRI) can visualize the growth of biofilm on an inert support matrix, and quantitate the blocking effects caused by precipitation of metal ions from a stream of effluent flowing through the resultant bioreactor. The measurements were based on glass tubes (16 mm diameter, 70 mm length) packed with cubes of polyurethane foam coated with Citrobacter sp. biofilm. Each bioreactor was challenged with a buffered aqueous solution of lanthanum and/or copper ions plus an organic phosphate source which, in the presence of phosphatase in the biofilm, react together to produce a precipitate of metal phosphate. MRI can distinguish the solid metal phosphate from the surrounding fluid, and provide velocity maps that quantitate the effect of blockage on the flow field through the entire bioreactor. The use of these data to aid the design of an efficient bioreactor is discussed.     

机械活化辅助浸出硫化镍矿中有价金属

随着高镍三元锂电池在新能源电动汽车领域的规模化应用,全球镍资源的需求量日益增加,绿色、高效、低成本地从硫化镍矿资源中提取镍的技术备受关注。本工作提出了机械活化辅助氧化浸出硫化镍矿的提取路径,在机械活化过程中通过改变硫化镍矿结构、增加晶体无序化程度、减小粒度和增加比表面积增加硫化镍矿的反应活性,再通过Na2S2O8氧化浸出实现了常压环境中硫化镍矿中有价金属的高效浸出。考察了机械活化和浸出过程中各因素对硫化镍精矿浸出的影响,确定了较优条件。在较优条件球磨转速613 r/min、球料比20:1、球磨时间120 min、酸浓度2 mol/L、过硫酸钠浓度0.42 mol/L、浸出时间60 min、液固比5:1、搅拌速率400 r/min和浸出温度80℃下,Ni, Co, Cu和Fe的浸出率分别达98.9%, 97.7%, 98.2%和98.7%。     

连续滴定法测定甘氨酸铝锆中铝和锆的含量

采用连续滴定法测得甘氨酸铝锆中铝和锆的含量。采用EDTA络合滴定的实验方案,先将甘氨酸铝锆固体粉末配制成溶液,并将溶液的pH值调节在0.5～1之间,以二甲酚橙为指示剂,用EDTA滴定测得锆的含量;再将此溶液的pH值调节在5～6之间,然后加入过量的EDTA溶液,让铝离子与EDTA充分络合,最后过量的EDTA用硫酸锌标准溶液进行返滴定,从而测得铝离子的含量。实验证明,该法简便,结果准确。     

重组柠檬酸杆菌合成紫色杆菌素的工艺条件优化

以L-色氨酸为前体物,对弗氏柠檬酸杆菌(Citrobacter freundii)基因工程菌株生产紫色杆菌素的工艺条件进行了优化。通过单因素实验研究了培养基种类、培养温度、碳源、溶氧、种子液的状态、接种量、诱导时机、诱导剂的浓度及初始pH对细胞生长和紫色杆菌素产量的影响,通过正交实验研究了这些因素中可能存在交互作用的4个因素(种子液OD660、接种量、诱导时机、诱导剂浓度)的影响主次,确定了这些因素、水平的最佳搭配方案。结果表明,重组柠檬酸杆菌合成紫色杆菌素的最优培养条件为:种子液培养至OD660=3.6时,以3%的接种量接种于以甘油为碳源、初始pH为6.5的磷酸盐发酵培养基E2(25μg.ml-1卡那霉素),先在37℃、200r.min-1下培养至OD660=1.4,然后加入0.5μl.ml-1的诱导剂正辛烷,同时转入20℃,在150r.min-1下诱导培养31h。在此最优条件下,紫色杆菌素粗提物(紫色杆菌素及脱氧紫色杆菌素的混合物)产量可达1.809g.L-1,比优化前(0.514g.L-1)提高了252%,是目前国际上其他研究小组报道的最高摇瓶产量(0.43g.L-1)的4.2倍。质粒稳定性实验结果表明重组柠檬酸杆菌在抗生素选择压力条件下具有良好的遗传稳定性。     

Electronic structure and thermal conductivity of zirconium carbide with hafnium additions

The lattice thermal conductivity of ZrC with different Hf contents was investigated theoretically. The density of states and electron density differences were calculated for ZrC and (Zr,Hf)C containing 3.125 or 6.25 at% Hf. It was found that the electronic structure did not change significantly with the Hf additions. Lattice thermal conductivities were calculated for all of the compositions by combining first-principles calculations with the Debye–Callaway model. The theoretical lattice thermal conductivity of ZrC was 68 W·m⁻¹·K⁻¹ at room temperature. When adding 3.125 and 6.25 at% Hf into ZrC, the lattice thermal conductivities decreased to 18 and 15 W·m⁻¹·K⁻¹, respectively. The mechanism for the decreased conductivity is that with the addition of Hf impurities, the frequency of the acoustic phonons decreased, which resulted in decreases in the Debye temperature and lattice thermal conductivity.     

EDTA络合滴定法测定锆英石中的锆铪合量

本文介绍了一种测定锆英石中锆铪合量的EDTA络合滴定法,分析了标准样品及实际样品,并验证了该方法的可行性。结果表明,该方法准确、简单、可行性较强。     

纳米级二氧化锆的制备和应用

纳米二氧化锆是一种新型的高科技材料,有着广泛而重要的用途。根据国内外研究制备的最新进展及其发展趋势,综述了纳米级二氧化锆的制备技术和近年来新的应用领域和研究前沿。     

Narrow-range ethoxylation of fatty alcohols promoted by a zirconium alkoxide sulfate catalyst

Zirconium dodecanoxide sulfate is a very active catalyst in promoting fatty alcohol narrow-range ethoxylation. The catalytic activity is initially very high but rapidly decreases after the addition of one mole of ethylene oxide per mole of substrate. This peculiar behavior makes it possible to obtain narrow-range ethoxylated products containing not more than two or three ethylene oxide units. Because the catalyst shows a very feeble Brönsted acidity, it must be concluded that its activity originates from the Lewis acidity. This acidity is strongly enhanced from the introduction of the sulfate group in the catalyst molecule, because of the strong electron-withdrawing effect of this group. A kinetic model was developed for explaining experimental results.     

纳米级二氧化锆粉体的合成及性能测试

以廉价无机盐氧氯化锆为原料，用氨水作沉淀剂，采用溶胶一凝胶法制备纳米级二氧化锆结合XRD和TEM等测试手段进行表征，并考察了二氧化锆的制备机理及此类氧化物的结构特点。