Profiling iron corrosion coating on iron grains in a zerovalent iron system under the influence of dissolved oxygen

Rapid oxidation of Fe(0) by O(2) occurred when Fe(0) grains were bathed in 0.54 mM FeCl(2) solution saturated with dissolved oxygen (DO), forming a substantial corrosion coating on Fe(0) grains. A sonication method was developed to strip the corrosion coating off the iron grains layer by layer. The transformation of the constituents and the morphology of the corrosion coating along its depth and over reaction time were investigated with composition analysis, X-ray diffraction and scanning electron microscopy. Results indicate that the sonication method could consistently recover >90% iron oxides produced by the Fe(0)-DO redox reaction. Magnetite (Fe(3)O(4)) and lepidocrocite (gamma-FeOOH) were identified as the corrosion products. Initially, lepidocrocite was the preferential product in the presence of DO. As the oxide coating thickened, the inner layer transformed to magnetite, which retained as the only stable corrosion product once DO was depleted. The study confirms the phase transformations between gamma-FeOOH and Fe(3)O(4) within a stratified corrosion coating. The sonication technique exemplifies a new approach for investigating more complicated processes in Fe(0)/oxides/contaminants systems.     

Effects of low pH on nitrate reduction by iron powder

The effect of low pH (2-4.5) on nitrate reduction in an iron/nitrate/water system was investigated through batch experiments conducted in a pH-stat. The results showed that nitrate could be rapidly reduced to ammonium at pH 2-4.5. A black coating, consisted of both Fe(II) and Fe(III), was formed on the surface of iron grains as an iron corrosion product. X-ray diffractometry indicated that the black coating was poorly crystalline, and its spectrum could not be matched with commonly known iron oxides/hydroxides/oxide hydroxides or green rust I/II. The black coating does not inhibit the reactivity of Fe0 (at least at pH < 3). The black coating was unstable and evolved with time into other oxides under certain conditions. A kinetic model incorporating the effects of pH on nitrate reduction and Langmuir adsorption of nitrate was proposed, and the parameters were estimated by nonlinear curve fitting. Based on this model, the two major effects of pH on the kinetics of nitrate reduction are that: (a) H+ ions directly participate in the redox reaction of nitrate reduction following first-order kinetics; and (b) H+ ions affect the nitrate adsorption onto reactive sites.     

A novel hybrid nano zerovalent iron initiated oxidation--biological degradation approach for remediation of recalcitrant waste metalworking fluids

Disposal of operationally exhausted metal working fluids (MWF) through a biological route is an attractive option, since it is effective with relatively low energy demands. However, it is enormously challenging since these fluids are chemically complex, including the addition of toxic biocides which are added specifically to retard bio-deterioration whilst the fluids are operational. Nano-sized elemental iron represents a new generation of environmental remediation technologies. Laboratory scale batch studies were performed to test the degradation ability of a semi-synthetic metalworking fluid (MWF) wastewater (which was found to be resistant to initial bacterial treatment in specifically established bioreactors) by employing a novel hybrid approach. The approach was to combine the synergistic effects of nano zerovalent iron (nZVI) induced oxidation, followed by biodegradation, specifically for the remediation of recalcitrant components of MWF effluent. Addition of nZVI particles to oxygenated wastewater resulted in oxidation of organic contaminants present. Our studies confirmed 78% reduction in chemical oxygen demand (COD) by nZVI oxidation at pH 3.0 and 67% reduction in neutral pH (7.5), and 85% concurrent reduction in toxicity. Importantly, this low toxicity made the nZVI treated effluent more amenable for a second stage biological oxidation step. An overall COD reduction of 95.5% was achieved by the novel combined treatment described, demonstrating that nZVI oxidation can be exploited for enhancing the biodegradability of a recalcitrant wastewater in treatment processes.     

Effects of dissolved oxygen on formation of corrosion products and concomitant oxygen and nitrate reduction in zero-valent iron systems with or without aqueous Fe2+

Batch tests were conducted in zero-valent iron (ZVI or Fe0) systems to investigate oxygen consumption and the effect of dissolved oxygen (DO) on formation of iron corrosion products, nitrate reduction, the reactivity of Fe0, the role Fe2+ (aq) played, and the fate of Fe2+. The study indicates that without augmenting Fe2+ (aq), neither nitrate nor DO could be removed efficiently by Fe0. In the presence of Fe2+ (aq), nitrate and DO could be reduced concomitantly with limited interference with each other. Unlike nitrate reduction, DO removal by Fe0 did not consume Fe2+ (aq). A two-layer structure, with an inner layer of magnetite and an outer layer of lepidocrocite, may be formed in the presence of DO. When DO depleted, the outer lepidocrocite layer was transformed to magnetite. The inner layer of magnetite, even in a substantial thickness, might not impede the Fe0 reactivity as much as the thin interfacial layer between the oxide coating and liquid. Surface-bound Fe2+ may greatly enhance the electron transfer from the Fe0 core to the solid-liquid interface, and thus improve the performance of the Fe0 process.     

The effects of biofilm on the transport of stabilized zerovalent iron nanoparticles in saturated porous media

The transport of stabilized zerovalent iron nanoparticles (nZVI) has recently been the topic of extensive research due to its proven potential as an in situ remediation tool. However, these studies have ignored the effects of biofilms—complex aggregations of bacterial cells and excreted extracellular polymeric substances present in nearly all aquatic systems—on the transport of these particles. This study examines the effects of Pseudomonas aeruginosa (PAO1) biofilm, at a cell concentration similar to that reported for saturated aquifers, on the transport of commercially available, poly (acrylic acid) stabilized nZVI (pnZVI) in 14 cm long columns packed with saturated glass beads at salt concentrations of 1 and 25 mM NaCl. Compared to retention on uncoated columns, in the presence of biofilm the retention of pnZVI increased at higher ionic strength, while ionic strength played no role in retention of these nanoparticles in the absence of biofilm. The Tufenkji-Elimelech correlation equation predicts lower retention of pnZVI on biofilm coated columns compared to uncoated columns due to a lower Hamaker constant, and DLVO energy considerations predict the most favorable attachment to uncoated porous media at higher ionic strength. A steric (polymer-mediated) model that considers the combined influence of steric effects of polymers and DLVO interactions is shown to adequately describe particle retention in columns.     

Control of sulfide in sewer systems by dosage of iron salts: comparison between theoretical and experimental results, and practical implications

Removal of sulfide species from municipal sewage conveyance systems by dosage of iron salts is a relatively common practice. However, the reactions that occur between dissolved iron and sulfide species in municipal sewage media have not yet been fully quantified, and practical application relies heavily on empirical experience, which is often site specific. The aim of this work was to combine theoretical considerations and empirical observations to enable a more reliable prediction of the sulfide removal efficiency for a given dosing strategy. Two main questions were addressed, regarding the dominant sulfur species that results from the oxidation of sulfide by Fe(III) and the dominant precipitation reaction between Fe(II) and sulfide species. Comparison of thermodynamic prediction obtained by an equilibrium chemistry-based computer program (MINEQL+) with experimental results obtained by dosing ferrous salts showed that the product of precipitation is FeS under all operational conditions tested. Regarding the reaction between ferric salts and sulfide species, analysis of thermodynamic data suggested that the dominant product of sulfide oxidation under typical pe/pH conditions prevailing in municipal raw wastewater is SO(4)(2-). However, comparison between sulfide removal in laboratory experiments conducted with multiple samples of raw municipal sewage with a varying composition, and the prediction of MINEQL+ showed the main sulfide oxidation product to be S(0). In order to reduce sulfide in sewage to <0.1 mgS/l a minimal molar ratio of around 1.3 Fe to 1 S should be applied when ferrous salts are used, as compared with a minimal ratio of 0.9 Fe to 1 S required when ferric salts or a mixture of ferrous and ferric salts (at a 2 Fe(III) to 1 Fe(II) ratio) are used. It appears that the high Fe to S(-II) ratios often recommended in practice can be reduced considerably by applying tight in-line control.     

Immobilization of arsenic in a tailings material by ferrous iron treatment

Weathering and internal dissolution processes in mining waste materials may mobilize elevated levels of arsenic (As), contaminating ground and surface waters. Treating the polluted waters with iron oxyhydroxides is an established remediation method. By contrast, little knowledge is available to stabilize As in source materials by treating it with Fe precipitates and, on this way, to prevent the generation of polluted waters. In the present work the efficiency of Fe(II) treatment on As immobilization in a tailings material (TM) was studied with regard to the Fe:As molar ratio, the influence of CaCO3 amendment, and the As desorption at continued intensive leaching of Fe-treated TM. Fe precipitates were created by aerobic treatment of TM with Fe(II)sulfate at several Fe:As molar ratios with or without adding CaCO3, followed by aging the Fe-treated TM. The As retention in the treated tailings was studied by 4-fold elution with water, and the As desorption kinetics was examined by suspension leaching in laboratory microcosms over 3 weeks. Fe(II) treatment of TM reduced the water-extractable total As to <10 microg/L as the Fe:As molar ratio increased from 0 to 8. The water-soluble As of Fe-treated tailings could be reduced to 10-30 microg/L also under conditions of intensive leaching. Stabilizing the pH with CaCO3 resulted in consistently higher As release. The As desorption data followed the first-order kinetics in the early time stages of the desorption whereas at longer times the parabolic diffusion model was valid.     

钢筋混凝土梁内部钢筋锈蚀程度检测研究

结合钢筋混凝土结构在工程中的广泛应用,分析了混凝土中钢筋的锈蚀机理,介绍了钢筋锈蚀的检测方法,进行了钢筋混凝土梁内部钢筋锈蚀现场测试,并对检测结果进行了分析,对于实际工程中防止钢筋锈蚀具有一定的意义。     

The role of nitrobenzene on the yield of trihalomethane formation potential in aqueous solutions with Microcystis aeruginosa

Algae are one of the most important disinfection by-product (DBP) precursors in aquatic environments. The contents of DBP precursors in algae are influenced by not only environmental factors but also some xenobiotics. Trihalomethane formation potential (THMFP) in both the separate and interactive pollution of Microcystis aeruginosa and Nitrobenzene (NB) was investigated in batch experiment to discover the effects of xenobiotics on the yield of DBP precursors in the algal solution. The results show that in the separate NB solution, NB did not react with Cl₂ to form trihalomethane (THM), whereas in the algae solution, THMFP had a significant positive linear correlation with M. aeruginosa density in both solution and extracellular organic matter (EOM). The correlation coefficients were 0.9845 (p = 3.567 × 10⁻⁴) and 0.9854 (p = 1.406 × 10⁻⁴), respectively. According to regression results, about 77.9% of the total THMFP came from the algal cells, while the rest came from EOM. When the interactive pollution of M. aeruginosa and NB occurred, the growth of algae was inhibited by NB. The density of M. aeruginosa in a high concentration NB solution (280 μg/L) was only 71.1% of that in the solution without NB after 5 days of incubation. However, THMFP in the mixture (algae and NB) and the EOM did not change significantly, and the productivity of THMFP by the algae (THMFP/10⁸cells) increased with the increase in NB concentration. There was a significant linear correlation between THMFP/10⁸cell and NB concentration (r = 0.9117, p < 0.01), which shows the contribution of the algae to THM formation was enhanced by NB. This result might be caused by the increased protein productivity and the biodegradation of NB by M. aeruginosa.     

Evaluation of nanoscale zerovalent iron particles for trichloroethene degradation in clayey soils

The longevity and reactivity of nanoscale zerovalent iron (nZVI) and palladized bimetallic particles (BNP) were evaluated in batch and column experiments for remediation of a trichloroethene (TCE)-contaminated plume within a clayey soil from Oak Ridge Reservation (ORR). Comparative studies assessing the viability of BNP and nZVI confirmed that particle behavior is severely affected by clay sediments. Surface morphology and composition analyses using SEM and SEM-energy-dispersive spectroscopy spectrum revealed particle agglomeration through the formation of clay-iron aggregates of greater mass during the early phase of the experiment. Batch study results suggest that TCE degradation in ORR clayey soil follows a pseudo-first-order kinetic model exhibiting reaction rate constants (k) of 0.05-0.24 day^− 1 at varied iron-to-soil ratios. Despite high reactivity in water, BNP were less effective in the site-derived clay sediment with calculated TCE removal efficiencies of 98.7% and 19.59%, respectively.A column experiment was conducted to investigate particle longevity and indicator parameters of the TCE degradation process under flow conditions. It revealed that the TCE removal efficiency gradually declined over the course of the experiment from 86-93% to 51-52%, correlating to a progressive increase in oxidation-reduction potential (ORP) from − 485 to − 250 mV and pH drop from 8.2-8.6 to 7.4-7.5. The rate of nZVI deactivation reaction was found to be a first order with a k_d value of 0.0058 day^− 1. SEM images of residual nZVI revealed heavily agglomerated particles. However, despite widespread oxidation and agglomeration, particles managed to maintain some capacity for oxidation. A quantitative analysis of nZVI deactivation has the potential of predicting nZVI longevity in order to improve the design strategy of TCE remediation.     

Fabrication and characterization of iron oxide ceramic membranes for arsenic removal

Nanoscale iron oxide particles were synthesized and deposited on porous alumina tubes to develop tubular ceramic adsorbers for the removal of arsenic, which is an extremely toxic contaminant even in very low concentrations. Its natural presence affects rural and low-income populations in developing countries in Latin America and around the world, which makes it essential to develop a user-friendly, low energy demanding and low cost treatment technology. The fabricated ceramic membranes can be operated with minimal trans-membrane pressure difference and do not require pumping. The support tubes and final membrane have been characterized by surface area and porosity measurements, permeability tests and scanning electron microscopy (SEM) imaging. Arsenic concentrations were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Due to its low cost and simple operation, the system can be applied as a point of use device for the treatment of arsenic contaminated groundwaters in developing countries.     

Some effects of aqueous silica on the corrosion of iron

Silica is an important natural component of ground and surface waters, and is sometimes added as an inhibitor to control "red water" problems caused by corroding iron pipes. However, the effect of silicates on many aspects of iron corrosion has never been assessed. Experiments with water containing 0.5, 10, 25 or 50mg/L of SiO(2) demonstrated a significant interplay between aqueous silica and iron corrosion. During this 4-month experiment, higher levels of silica caused more iron release to the water and decreased the size of suspended iron particles. The process of iron corrosion also changed aqueous silica concentrations; silica was released into the water from the cast iron during corrosion and was removed from the water by incorporation into the scale layer. Silica also affected the type of scale that formed on the iron coupons. Scale at the lower silica concentrations was fairly uniform and easy to remove from the coupons, while the scale from the high silica reactors was more dense, and was more difficult to remove. Scale from the high concentration silica reactor also developed tall tubercles, and hydrogen gas-containing bubbles were channeled to solution through these tubercles. Iron corrosion occurring via the evolution was significant under all experimental conditions.     

Removal of dissolved metals by zero-valent iron (ZVI): kinetics, equilibria, processes and implications for stormwater runoff treatment

Infiltration of stormwater runoff contaminated with metals is often questionable in several cases due to its long-term potential to cause deterioration of groundwater quality. To ensure the quality of filtrate, a pre-treatment of contaminated runoff is required. This study investigates the processes of copper and zinc ion removal from stormwater runoff using zero-valent iron (ZVI, Fe0). Kinetic and equilibrium tests were performed with laboratory-prepared and in situ stormwater runoff samples collected from roof, street and highway catchments. Based on the results, a substantial portion of Cu2+ is reduced and transformed to insoluble forms of Cu0 and Cu2O. Unlike copper, the adsorption and co-precipitation associated with freshly precipitated iron oxides play important roles for the removal of Zn2+. Investigations under various water quality conditions demonstrated a relatively minor impact on Cu2+ uptake rates. However, the different conditions apparently altered the removal stoichiometry and phases of the copper deposits. The removal rates of Zn2+ increase with higher dissolved oxygen (DO), ionic strength (IS), temperature (T) and pH. Dissolved organic carbon (DOC) in runoff samples forms complexes with metals and Fe2+, thereby kinetically decreasing the metal uptake rates. Furthermore, depending on its composition, a larger molecular weight organic fraction was found to preferentially compete for the adsorption sites. The study demonstrates that ZVI is a promising medium for achieving comparable capacity to a commercial adsorbent like granular ferric hydroxide (GFH). Long-term performance of ZVI, however, may be limited and governed by the formation of non-conductive layers of iron and cuprous oxides.     

Arsenic mobility and stabilization in topsoils

Agricultural topsoil can be polluted with arsenic due to irrigation with contaminated water from geothermal sources. This work evaluates the mobility of arsenic in topsoils and stabilization of arsenic with zero valent iron (ZVI), in short term experiments. The objective of this study was the development of a simplified empirical model that can predict the concentration of iron released from ZVI and the concentration of arsenic remaining in the solution during short term stabilization experiments. The empirical model correlates the release of arsenic from soil with dissolved iron concentration during stabilization experiments, in different pH and ZVI/solution ratios. Reaction time and the ratio of ZVI/soil affect the efficiency of arsenic stabilization in topsoils with ZVI. In addition, the release/desorption experiments and adsorption experiments, under different conditions, showed that the concentration of arsenate desorbed from soil depends on the temperature. Higher concentrations of arsenate were reported, as the temperature increased.     

Effects of geochemical constituents on the zero‐valent iron reductive removal of nitrobenzene in groundwater

Nitrobenzene (NB) was chosen as the model contaminant, and batches lab scale experiments were conducted to investigate the effects of geochemical compositions on reductive removal of nitrobenzene by zero‐valent iron (ZVI) in groundwater. Experimental results showed that the kinetics of nitrobenzene reduction by ZVI was a pseudo‐first order with an observed rate constant, k_obs, of 3.67 × 10^?4/s; the calculated half‐life of nitrobenzene was 1.89 × 10³/s. The geochemical constituents of groundwater have significant influences on ZVI reactivity and nitrobenzene reduction. The presence of high concentration of nitrate, carbonate, sulphate and hardness had detrimental effects on reduction of nitrobenzene and formation of aniline; chloride had a slight positive effect on the nitrobenzene reduction and the formation of aniline. Bicarbonate enhanced the ZVI reactivity initially at lower concentration and inhibited the nitrobenzene reduction at high concentration. Therefore, the performance and reactivity of ZVI were found to be strongly affected by the geochemical constituents of groundwater.     

铁氧化物沉积对氧化铝氟吸附再生性能的影响

以再生后氧化铝氟吸附容量变化为核心,实验研究了铁氧化物沉积过程的影响。结果表明,NaOH的再生效果良好,但会造成氧化铝表面铁氧化物溶解;再生时间对氟吸附容量没有显著影响;铁氧化物沉积后氧化铝氟吸附容量衰减速率有所降低,其降低程度主要受初始吸附条件制约。     

超薄膨胀型钢结构防火涂料防腐性能的研究

介绍了钢材的腐蚀及防腐机理,研究了以对丙烯酸树脂进行复合改性为基料,研制出的一种既具有高效防火隔热性能,又具有优异防腐蚀性能的超薄膨胀型钢结构防火涂料的防腐性能。     

有机阻锈剂对桥梁混凝土性能及钢筋锈蚀的影响

研究了两种有机阻锈剂(ZX1、ZX2)对混凝土性能的影响,选择ZX1和亚硝酸钙两种阻锈剂,用电化学方法考察了阻锈剂对钢筋的保护效果。研究表明,有机阻锈剂对桥梁混凝土的性能基本无负面影响,但不同种类阻锈剂的影响规律有所不同;电化学工作站对钢筋的线性极化测试表明:随着干湿交变循环次数的增加,掺加有机阻锈剂钢筋试件的腐蚀电流密度较小且较稳定,阻锈剂基本无溶出现象,抗蚀效果明显。     

Bio-reaction of nitrobenzene with Microcystis aeruginosa: characteristics, kinetics and application

The bio-reaction of nitrobenzene (NB) with Microcystis aeruginosa was investigated at different initial algal densities and NB concentrations by performing static experiments. The results showed that the elimination of NB was enhanced by the bio-reaction, and the reaction rate varied as a function of the reaction time. Moreover, the reaction rate was significantly affected by the algal density and NB concentration. A kinetic analysis showed that the elimination of NB in a solution without algae appeared to be pseudo-first-order with respect to the NB concentration, whereas a first-order model was too oversimplified to describe the elimination of NB in a solution with algae. Assuming that different algal cells have the same effect on the bio-reaction under the same conditions, the bio-reaction can be described as dC_NB = −k₀C_A^mA_NBⁿdt (where k₀ is the reaction rate constant, C_A is the algae density and C_NB is the concentration of NB). When the growth of algae was not considered, the value of k₀, m and n were 8.170 × 10⁻⁴, 0.5887 and 1.692, respectively. Alternatively, when algae were in the exponential growth phase, the value of k₀, m and n were 1.6871 × 10⁻⁵, 0.7248 and 2.5407, respectively, according to a nonlinear fitting analysis. The kinetic model was also used to elucidate the effect of nutritional limitation on the bio-reaction.     

沿海区段输电线路铁塔及基础防腐分析

结合工程实例，对沿海区段输电线路铁塔及基础的腐蚀原因进行了分析，结合国内现有防腐技术分类提出了铁塔及基础防腐处理的几种办法，以供类似工程参考借鉴。