制冷机中溴化锂溶液腐蚀性研究

溴化锂吸收式制冷机具有热效率高、热源广泛、能耗低以及零排放等优点,近年来得到广泛的应用.而作为强腐蚀性介质,高浓度溴化锂水溶液在循环条件下会引起碳钢、铜以及铜合金等金属材料严重的腐蚀.由高温溴化锂水溶液中的耐腐蚀性实验表明,溴化锂水溶液腐蚀性受金属材料和外界条件的影响,文章对溴化锂水溶液腐蚀性这一问题的研究进而提出防腐...     

Electrochemical and spectroscopic study of arsenate removal from water using zero-valent iron media

This study investigated the mechanisms involved in removing arsenate from drinking water supplies using zero-valent iron media. Batch experiments utilizing iron wires suspended in anaerobic arsenate solutions were performed to determine arsenate removal rates as a function of the arsenate solution concentration. Corrosion rates of the iron wires were determined as a function of elapsed time using Tafel analysis. The removal kinetics in the batch reactors were best described by a dual-rate model in which arsenate removal was pseudo-first-order at low concentrations and approached zero-order in the limit of high arsenate concentrations. The presence of arsenate decreased iron corrosion rates as compared to those in blank 3 mM CaSO4 background electrolyte solutions. However, constant corrosion rates were attained after approximately 10 days elapsed, indicating that the passivation processes had reached steady state. The cathodic Tafel slopes were the same in the arsenate and the blank electrolyte solutions. This indicates that water was the primary oxidant for iron corrosion and that arsenate did not directly oxidize the iron wires. The anodic Tafel slopes were greater in the arsenate solutions, indicating that arsenate formed complexes with iron corrosion products released at anodic sites on the iron surfaces. Ion chromatography analyses indicated that there was no measurable reduction of As(V) to As(III). X-ray absorption spectroscopy analyses indicated that all arsenic associated with the zero-valent iron surfaces was in the oxidation state. Interatomic arsenic-iron distances determined from EXAFS analyses were consistent with bidentate corner-sharing among arsenate tetrahedra and iron octahedra. Results from this study show that under conditions applicable to drinking water treatment, arsenate removal by zero-valent iron media involves surface complexation only and does not involve reduction to metallic arsenic.     

陶瓷片密封水嘴铅析出量超标原因分析

目的研究某品牌陶瓷片密封水嘴铅析出量超标的主要因素。方法将水嘴样品按不同材质拆解成部件,采用X射线荧光光谱(X-ray fluorescence spectrometry, XRF)对部件中铅含量进行快速筛查,将筛查出的铅含量高的部件消解,采用电感耦合等离子体发射光谱法(inductivelycoupledplasmaopticalemission spectrometery, ICP-OES)测定其中铅含量。通过测定铅含量高部件的铅析出量,对水嘴铅析出量超标原因进行了深入分析。结果 XRF筛查试验结果表明进水软管铜接头和进水软管橡胶管是铅含量高部件,ICP-OES测试对这一结果进行了确证。进水软管橡胶管铅析出量高于进水软管铜接头。结论推测认为进水软管橡胶管中的铅是引起该产品铅析出超标的主要原因。     

Influence of metal ion sorption on colloidal surface forces measured by atomic force microscopy

Atomic force microscopy (AFM) is employed to directly measure colloidal surface forces between a silica particle and a smooth glass plate in an aqueous solution with or without the presence of copper ions. Without the presence of copper ions, results show that the force between these two surfaces is repulsive and that its magnitude decreases with increasing ionic strength and decreasing pH. The surface forces are calculated based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for constant surface charge and are then compared with AFM force measurements. A good agreement between theory and experimental data is reported except at very small separation distances (<3 nm) between the silica particle and the glass plate. This behavior may be attributed to non-DLVO forces, such as the hydration effect that results from the bounded water molecules on the surface of the silica particle, or to surface roughness. When copper ions are present in acidic aqueous solutions, the magnitude of the force is found to be the same as that without the presence of copper ions, which indicates that no sorption of copper ions by the silica particle occurs under these conditions. Near neutral pH, sorption of copper ions causes charge reversal for the silica particle from negative to positive. Therefore, the force between the silica particle and the glass plate changes from repulsive to attractive. The transient zeta-potential of the silica particle during sorption of copper ions is determined by representing the experimental data with the DLVO theory. In alkaline solutions, where removal of copper ions is known to occur mainly by bulk precipitation, the measured force is similar to that without the presence of copper ions, which suggests that sorption does not occur under such conditions.     

Electroosmotic flow stimulates the release of alginate-bound phenanthrene

There is growing interest in employing electro-bioremediation, a hybrid technology of bioremediation and electrokinetics for the treatment of contaminated soil. Most present applications of electrokinetics aim at pollutant extraction, which requires transport over large distances facilitated by electroosmotic flow (EOF). They do not explicitly account for the possibility that EOF passing along soil particles stimulates the release of hydrophobic organic compounds (HOC) and locally improves pollutant bioavailability. Here, we report on the stimulated release of polycyclic aromatic hydrocarbon (phenanthrene) from model organic matter in the presence of direct current (DC)-electric fields (0.5-2 V cm(-1)) typically used in electrobioremediation measures. Alginate beads were employed as a model polymer release system (MPRS) exhibiting similar release behavior as natural organic matter (NOM). In the presence of EOF the phenanthrene release flux from alginate beads was between 1.4- and 1.8-fold higher than under hydraulic flow conditions with equal bulk water velocity and 30-120-fold higherthan under stagnantwater conditions. Our data suggest that DC-electric fields (0.5-2 V cm(-1)) can stimulate the release of PAH bound to particles exposed to stagnant water zones often found at hydraulic flow regimes restricted by low permeability.     

碱回收炉受热面腐蚀原因分析

本研究以某企业2200 tds/d碱回收炉为研究对象,通过分析黑液特性、测量碱回收炉受热面厚度变化,以及对水冷壁割管进行SEM分析及腐蚀产物XRD分析来研究碱回收炉运行中受热面腐蚀的原因。结果表明,碱回收炉在燃烧黑液过程中的腐蚀主要发生在中下层水冷壁墙面、各层燃烧器等高处的高温负荷区和局部低温受热面;碱回收炉内的腐蚀是不断扩散和加剧的,主要是由黑液燃烧产生的腐蚀气体、具有高温腐蚀性的可扩散腐蚀产物与高温氧化还原及硫化的作用造成;尾部气流速度场不均,导致低温受热面部位腐蚀;炉膛上部一级过热器烟气设计流速大,腐蚀和磨损交替破坏受热面。并对此提出了合理的防腐措施。     

飞机发动机操纵钢索断丝原因分析及改进措施

针对某型号飞机飞行中发动机操纵钢索发生断丝卡滞问题,根据油门操纵拉杆的结构及工作原理进行分析。采用扫描电镜和化学成分分析等方法,综合分析后得出产生断丝卡滞的主要原因是钢索捻制时有倒刺,拉杆制造过程中该部位恰好位于压接头附近,在后续使用维护中油门操纵拉杆受到推拉作用,钢丝刺出钢索表面而发生卡滞。对上述现象提出改进措施:加强油门操纵拉杆的使用维护和保养,防止因摩擦力过大导致拉杆运动受阻;加强油门操纵拉杆钢索的表面质量检查,发现钢索有断头、生锈、松散等现象应及时更换;注意检查外套铜管内腔,防止外来多余物进入铜管导致油门拉杆运动受阻而卡滞。     

Fat-crystal stabilised w/o emulsions for controlled salt release

The potential of fat-crystal stabilised w/o emulsions to control the release of salt contained within their aqueous phase has been investigated. A mixture of mono- and triglyceride crystals was used to obtain Pickering-stabilised 60:40 w/o emulsions. Salt release was monitored by placing small amounts of these emulsions into a bulk aqueous phase (this was either pure water or glucose aqueous solutions in order to vary osmotic pressure gradients) and measuring changes in conductivity over time. Less than 5% of total salt was released after 1 month in emulsions containing a mixture of mono- and triglycerides. Emulsions containing only monoglycerides released more than 40% salt in this period. SEM pictures showed that crystals have sintered at the interface to give total surface coverage with no or very few defects. Stability measurements at varying temperatures and Differential Scanning Calorimetry (DSC) indicate that any release is the result of partial melting of the crystals. Finally, varying the osmotic pressure gradient has no impact on salt release.     

Arsenic(III) and arsenic(V) reactions with zerovalent iron corrosion products

Zerovalent iron (Fe0) has tremendous potential as a remediation material for removal of arsenic from groundwater and drinking water. This study investigates the speciation of arsenate (As(V)) and arsenite (As(III)) after reaction with two Fe0 materials, their iron oxide corrosion products, and several model iron oxides. A variety of analytical techniques were used to study the reaction products including HPLC-hydride generation atomic absorption spectrometry, X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray analysis, and X-ray absorption spectroscopy. The products of corrosion of Fe0 include lepidocrocite (gamma-FeOOH), magnetite (Fe3O4), and/or maghemite (gamma-Fe2O3), all of which indicate Fe(II) oxidation as an intermediate step in the Fe0 corrosion process. The in-situ Fe0 corrosion reaction caused a high As(III) and As(V) uptake with both Fe0 materials studied. Under aerobic conditions, the Fe0 corrosion reaction did not cause As(V) reduction to As(III) but did cause As(III) oxidation to As(V). Oxidation of As(III) was also caused by maghemite and hematite minerals indicating that the formation of certain iron oxides during Fe0 corrosion favors the As(V) species. Water reduction and the release of OH- to solution on the surface of corroding Fe0 may also promote As(III) oxidation. Analysis of As(III) and As(V) adsorption complexes in the Fe0 corrosion products and synthetic iron oxides by extended X-ray absorption fine structure spectroscopy (EXAFS) gave predominant As-Fe interatomic distances of 3.30-3.36 A. This was attributed to inner-sphere, bidentate As(III) and As(V) complexes. The results of this study suggest that Fe0 can be used as a versatile and economical sorbent for in-situ treatment of groundwater containing As(III) and As(V).     

Evidence for Escherichia coli O157:H7 attachment to water distribution pipe materials by scanning electron microscopy

Scanning electron microscopy observation was used to investigate the adhesion of Escherichia coli O157:H7 on water distribution pipe surfaces such as copper and polyethylene plastic at different contact times and storage temperatures. Our results indicated that E. coli cells could easily attach to both surface types after exposures as short as 1 or 4 h at ambient (20 degrees C) and refrigeration temperatures (4 degrees C). Also, we found that copper surfaces have a higher number of attached E. coli cells than plastic surfaces. The number of cells attached to each type of material depended on the nature of the water distribution pipe surfaces and the length of contact time. In addition, the surface energy value of each surface estimated by contact angle measurements using water, alpha-bromonaphthalene, and dimethyl sulfoxide as wetting agents showed that both copper (41.2 megajoules [MJ] m(-2)) and plastic (45.8 MJ x m(-2)) have a low energy surface. In no cases could evidence of extracellular material be observed on surfaces with either exposure condition.     

The release of nickel and other trace elements from electric kettles and coffee machines

The release of nickel, chromium and lead from electric kettles to water under conditions simulating regular household use was investigated. Ten out of 26 kettles sold on the Danish market released more than 50 μg/l nickel to water, whereas neither lead nor chromium was released in any significant amount. Fifty mug/l of nickel in water was chosen as the threshold of action, because concentrations below this value were considered unlikely to provide outbreaks of eczema for those consumers suffering from contact allergy to nickel, who are also sensitive to the content of nickel in the diet. This first part of the study was followed up by a dialogue between the kettle producers and the Danish authorities, leading to a change of construction or design for those kettles that did not comply with the criteria. As a follow-up study another ten kettles were studied to check whether compliance was improved. Two of these ten kettles still released more than 50 μg/l nickel to water under the test conditions. These two kettles, however, were subsequently withdrawn from the market. Coffee machines tested similarly did not release aluminium, lead, chromium or nickel in quantities of any significance.     

Understanding chromate reaction kinetics with corroding iron media using Tafel analysis and electrochemical impedance spectroscopy

The kinetics of chromate removal from contaminated water by zerovalent iron media are not well understood. This study investigated the reactions occurring on iron surfaces in chromate solutions in order to understand the removal kinetics and to assess the long-term ability of zerovalent iron for removing Cr(VI) from contaminated water. Tafel polarization analysis and electrochemical impedance spectroscopy were used to determine the corrosion rates and charge-transfer resistances associated with Cr(VI) removal by iron wires suspended in electrolyte solutions with initial Cr(VI) concentrations of 10,000 microg/L. The condition of the iron surfaces at the time of their exposure to chromate determined the effectiveness of the iron for chromate removal. Both iron coated with a water-formed oxide and initially oxide-free iron were effective for chromate removal. However, iron coated with an air-formed oxide was an order of magnitude less effective for removing soluble chromium. Although iron with the air-formed oxide was largely passivated with respect to chromate removal, its overall rate of corrosion was similar to that for iron with the other initial surface conditions. This indicates that water, but not chromate, was able to penetrate the air-formed oxide coating and access cathodic sites. For all initial surface conditions, addition of chromate decreased the corrosion rate by increasing the corrosion potential and the anodic charge transfer resistance. Although Cr(VI) is a strong oxidant rates of iron corrosion were not proportional to the aqueous Cr(VI) concentrations due to anodic control of iron corrosion. Under anodically controlled conditions, the rate of corrosion was limited by the rate at which Fe2+ could be released at anodic sites and not by the rate at which oxidants were able to accept electrons. This study shows that the zero order removal kinetics of Cr(VI) by iron media can be explained by anodic control of iron corrosion and the concomitant anodic control of Cr(VI) reduction.     

Nitrification in premise plumbing: role of phosphate, pH and pipe corrosion

Nitrification in PVC premise plumbing is a weak function of pH over the range 6.5--8.5 and is insensitive to phosphate concentrations 5--1000 ppb. Lead pipe enhanced nitrification relative to PVC, consistent with expectations that nitrifiers could benefit from ammonia recycled from nitrate via lead corrosion. Relatively new copper pipe (< 1.5-years-old) did not allow nitrifiers to establish, but nitrifiers gradually colonized over a period of months in brass pipes when copper concentrations were reduced by pH adjustment or orthophosphate. Nitrifiers were inhibited by trace copper, but not by lead levels up to 8000 ppb. In some systems using chloramines, brass in plastic plumbing systems might be more susceptible to lead/copper leaching, and accelerated dezincification, due to lower pH values resulting from nitrification.     

Electrochemical study of arsenate and water reduction on iron media used for arsenic removal from potable water

Zerovalent iron filings have been proposed as a filter medium for removing As(III) and As(V) compounds from potable water. The removal mechanism involves complex formation of arsenite and arsenate with the iron surface and with iron oxides produced from iron corrosion. There is conflicting evidence in the literature on whether As(V) can be reduced to As(III) by iron filter media. This research uses electrochemical methods to investigate the redox reactions that occur on the surface of zerovalent iron in arsenic solutions. The effect of arsenic on the corrosion rate of zerovalent iron was investigated by analysis of Tafel diagrams for iron wire electrodes in anaerobic solutions with As(V) concentrations between 100 and 20,000 microg/L. As(V) reduction in the absence of surface oxides was investigated by analysis of chronoamperometry profiles for iron wire electrodes in solutions with As(V) concentrations ranging from 10000 to 106 microg/L. The effect of pH on As(V) reduction was investigated by analyses of chronopotentiometry profiles for iron wire electrodes at pH values of 2, 6.5, and 11. For freely corroding iron, the presence of As(III) and As(V) decreased the iron corrosion rate by a factor of 5 as compared to that in a 3 mM CaSO4 blank electrolyte solution. The decrease in corrosion rate was independent of the arsenic concentration and was due to the blocking of cathodic sites for water reduction by arsenic compounds chemisorbed to the iron surface. The chronoamperometry and chronopotentiometry experiments showed that elevated pH and increased As(III) to As(V) ratios near the iron surface decreased the thermodynamic favorability for As(V) reduction. Therefore, reduction of As(V) occurred only at potentials that were significantly below the apparent equilibrium potentials based on bulk solution pH values and As(III) to As(V) ratios. The potentials required to reduce more than 1% of the As(V) to As(III) were below those that are obtainable in freely corroding iron media. This indicates that there will be minimal or no reduction of As(V) in iron media filters under conditions relevant to potable water treatment.     

Modeling kinetics of Cu and Zn release from soils

Kinetics of Cu and Zn release from soil particles was studied using two surface soils with a stirred-flow method. Different solution pH, dissolved organic matter (DOM) concentrations, and flow rates were tested in this study. A model for kinetics controlled sorption/desorption reactions between soils and solutions was globally fit to all experimental data simultaneously. Results were compared to a model that assumes local instantaneous equilibrium. We obtained one unique set of model parameters applicable to different pH, dissolved organic carbon (DOC), and flow conditions. We included DOM complexation of copper ions, which decreased their sorption. The effect of pH was included by assuming proton competition with metal ions for binding sites on soil particles. These results provide the basis for developing predictive models for metal release from soil particles to surface waters and soil solution.     

Potential sources of copper contamination of farm milk supplies measured by atomic absorption spectrophotometry.

A method was developed to use atomic absorption spectrophotometry for copper measurements in milk filtrates prepared from equal volumes of milk and 20% trichloracetic acid. Results are reported for 11 farms for water supplies, wash and rinse solutions, and milk. Copper below 10 mug/liter was found at the well for the 5 farms with their own spring supply. Averages and ranges for all 11 farms in mug/liter were 33 (0 to 156) at the cold water tap in the milk house, 220 (8 to 1,360) at the hot water tap, 246 (8 to 1,722) in the wash sink with added detergent and hot water, and 275 (9 to 1,823) after using the wash solution. Rinse solution with hypochlorite in cold water showed a rise from 31 (1 to 157) before use to 51 (5 to 206) after use. Copper in milk averaged 99 mug/liter (72 to 163). In spite of relatively high copper in wash solutions, copper in milk was not correlated postively, giving rise to question whether adsorbed copper from such solutions can contribute much copper to milk. Thorough rinsing with low copper cold water and a high dilution ratio in milk were seen as mitigating factors. Direct contact of milk with copper bearing metals presented a greater opportunity for contamination. Removal of substantial amounts of copper from pipe lines and bulk tanks with sulfamic acid was demonstrated.     

Morphology and breaking of latex particle deposits at a cylindrical collector in a microfluidic chamber

We report an analysis for the morphology and breaking behavior of deposits of spherical latex particles (1 and 3.6 μm in diameter) at a cylindrical collector in a microfluidic channel fabricated by soft-lithography. In-situ observation of particle deposition over a large range of flow rate conditions evidence the relationship between deposit morphology and mode of particle transport toward the collector. For low Pe?clet number (Pe), particle deposits are nearly uniform all over the collector surface except at the rear where particles do not attach. Upon increase of Pe, deposits gradually adopt a columnar morphology at the collector stagnation point. These results are qualitatively consistent with previously reported Monte Carlo simulations of deposits formation in stagnation point flow systems. However, these simulations fail to quantitatively predict the observed deposition at the rear of the collector for sufficiently high flow rate. Additional deposit breaking experiments together with numerical evaluations of particle flux around the collector suggest that such "anomalous" deposition at large Pe is significantly governed by concomitant detachment of deposited particles at the stagnation point and the presence of recirculation flow at the collector rear. Finally, kinetics of deposition are discussed in connection with particle size-dependence of deposit breaking features.     

Microscopic observations of reductive manganite dissolution under oxic conditions

At oxic/anoxic transition zones, manganese release from (hydr)oxide minerals into aqueous solution is a dynamic balance between mineral dissolution and Mn2+(aq) oxidation and precipitation, which are processes respectively promoted by organic reductants and molecular oxygen. We employ a flow-through atomic force microscope reactor (AFM-R) to investigate the reductive dissolution of the [010] surface of manganite (gamma-MnOOH) across a range of pH values and ascorbic acid concentrations in aqueous solutions equilibrated with atmospheric CO2 and O2. The apparent dissolution rate increases with higher ascorbic acid concentrations and lower pH values. Concurrent changes in surface morphology show that dissolution proceeds at low pH via etching and step retreat, while at high pH dissolution is concurrent with precipitation. The precipitates are characterized ex situ by X-ray photoelectron spectroscopy (XPS) and found to be Mn(III)-oxide. The onset of precipitation is consistent with an analysis of the thermodynamic driving forces for the reactions of a two-step mechanism. In the first step, Mn2+ is released to aqueous solution by reduction of gamma-MnOOH in reaction with ascorbic acid. This step is thermodynamically favorable under all conditions employed. In the second step, which leads to precipitation, surface adsorbed Mn2+ is oxidized by O2 to yield a Mn(III)-oxide precipitate. This step is thermodynamically possible only at pH > 5 for our experimental conditions. When the second step is active, the apparent dissolution rate equals the intrinsic dissolution rate minus the precipitation rate. Analysis of the growth rates observed in AFM indicates the precipitation rate reaches 71% of the intrinsic dissolution rate under some reactor conditions. Comparison of our gamma-MnOOH results to literature reports for Mn2+ oxidation on gamma-FeOOH indicates gamma-MnOOH is a more effective surface catalyst by a factor of 10(8).     

Attachment of Arcobacter butzleri,a new waterborne pathogen,to water distribution pipe surfaces

The capability of Arcobacter butzleri to attach to various water distribution pipe surfaces, such as stainless steel, copper, and plastic, was evaluated using scanning electron microscopy. Our results indicated that Arcobacter cells could easily attach to all surface types and the number of attached cells depended on the length of exposure and temperatures (4 and 20 degrees C). Extracellular fibrils were also observed on the stainless steel surface, especially after 72 h of contact times at both refrigeration and ambient temperatures. In addition, the surface energy value of each material was estimated by contact angle measurements using water, alpha-bromonaphthalene, and dimethylsulfoxide. The surface energy of A. butzleri was 58.6 mJ x m(-2) and the surface energy values of the three surfaces studied showed that plastic had a low energy surface (26.1 mJ x m(-2)) as did copper (45.8 mJ x m(-2)) and stainless steel (65.7 mJ x m(-2)).     

Significance of iron(II,III) hydroxycarbonate green rust in arsenic remediation using zerovalent iron in laboratory column tests

We examined the corrosion products of zerovalent iron used in three column tests for removing arsenic from water under dynamic flow conditions. Each column test lasted 3-4 months using columns consisting of a 10.3-cm depth of 50:50 (w:w, Peerless iron:sand) in the middle and a 10.3cm depth of a sediment from Elizabeth City, NC, in both upper and lower portions of the 31-cm-long glass column (2.5 cm in diameter). The feeding solutions were 1 mg of As(V) L(-1) + 1 mg of As(III) L(-1) in 7 mM NaCl + 0.86 mM CaSO4 with or without added phosphate (0.5 or 1 mg of P L(-1)) and silicate (10 or 20 mg of Si L(-1)) at pH 6.5. Iron(II,III) hydroxycarbonate green rust (or simply, carbonate green rust) and magnetite were the major iron corrosion products identified with X-ray diffraction for the separated fractions (5 and 1 min sedimentation and residual). The presence of carbonate green rust was confirmed by scanning electron microscopy (hexagonal morphology) and FTIR-photoacoustic spectroscopy (interlayer carbonate stretching mode at 1352-1365 cm(-1)). X-ray photoelectron spectroscopy investigation revealed the presence of predominantly As(V) at the surface of corroded iron particles despite the fact that the feeding solution in contact with Peerless iron contained more As(III) than As(V) as a result of a preferential uptake of As(V) over As(III) by the Elizabeth City sediment. Extraction of separated corrosion products with 1.0 M HCI showed that from 86 to 96% of the total extractable As (6.9-14.6 g kg(-1)) was in the form of As(V) in agreement with the XPS results. Combined microscopic and macroscopic wet chemistry results suggest that sorbed As(III) was partially oxidized by the carbonate green rust at the early stage of iron corrosion. The column experiments suggest that either carbonate green rust is kinetically favored or is thermodynamically more stable than sulfate green rust in the studied Peerless iron corrosion systems.