Iron Corrosion Products Research Articles

X-ray absorption spectroscopy study of the various forms of phosphorus in ancient iron samples

Several ancient world heritage iron-based structures present quite good corrosion resistance that is generally related to the presence of phosphorus in their metallic substrate. However, the exact protection mechanisms have not yet been explained. In order to better understand the role of this element, in the conditions of atmospheric corrosion, both its distribution and speciation were investigated. To do so, a combination of microXRF and microXANES at the P K-edge was used, together with micro-Raman investigations. This methodology was applied on two types of ancient ferrous samples. For both types, two sources of phosphorus, global endogenous as well as localised exogenous were revealed. From these two sources, the phosphorus was seen to be heterogeneously distributed in the corrosion products. The shape of the XANES spectra demonstrated that the phosphorus is present as phosphate complexes with all the iron corrosion products present in the layers.

Zero-valent iron and iron oxide-coated sand as a combination for removal of co-present chromate and arsenate from groundwater with humic acid

The combination of zero-valent iron (Fe0) and iron oxide-coated sand (IOCS) was used to remove Cr(VI) and As(V) from groundwater in this study. The efficiency and the removal mechanism of Cr(VI) and As(V) by using this combination, with the influence of humic acid (HA), were investigated using batch experiments. Results showed that, compared to using Fe0 or IOCS alone, the Fe0–IOCS can perform better on the removal of both Cr(VI) and As(V). Metal extraction studies showed that As(V) was mainly removed by IOCS and iron corrosion products while Cr(VI) was mainly removed by Fe0 and its corrosion products. Competition was found between Cr(VI) and As(V) for the adsorption sites on the iron corrosion products. HA had shown insignificant effects on Cr(VI) removal but some effects on As(V) removal kinetics. As(V) was adsorbed on IOCS at the earlier stage, but adsorbed/coprecipitated with the iron corrosion products at the later stage.

Review: The fundamental mechanism of aqueous contaminant removal by metallic iron

Contaminant co-precipitation with continuously generated and transformed iron corrosion products has received relatively little attention in comparison to other possible removal mechanisms (adsorption, oxidation, precipitation) in Fe0/H 2 O systems at

Reductive transformation and dechlorination of chloronitrobenzenes in UASB reactor enhanced with zero-valent iron addition

BACKGROUND: Zero-valent iron (ZVI) is increasingly being applied in biological wastewater treatment to enhance the conversion of various contaminants. The objective of this present study was to investigate the effect of ZVI on the anaerobic biotransformation and dechlorination of chloronitrobenzenes (3,4-DClNB and 4-ClNB). Experiments were conducted in two upflow anaerobic sludge blanket (UASB) reactors, one (R2) with 30 g L−1 ZVI added, and the other (R1), serving as control reactor. RESULTS: ZVI-based anaerobic granular sludge (ZVI-AGS) composed of bacteria associated with precipitated FeCO3 and FeS was successfully developed within 5 months in reactor R2. ZVI addition obviously enhanced 3,4-DClNB transformation and dechlorination efficiencies under high 3,4-DClNB loads, and further promoted dechlorination of 4-chloroaniline (4-ClAn) to aniline. Compared with the AGS formed in R1 reactor, iron and its corrosion products were observed and colonized with anaerobes such as methanothrix in ZVI-AGS, and the specific transformation rates of 3,4-DClNB and 4-ClNB using ZVI-AGS were improved by 34.0% and 64.4%, respectively. Furthermore, ZVI-AGS provided higher 3,4-dichloronailine and 4-ClAn dechlorination efficiency than AGS. Abiotic transformation of ClNBs by ZVI, appropriate concentration of iron corrosion products, lower redox potential and greater hydrogen production were the main factors providing enhanced transformation and dechlorination of ClNBs in the UASB reactor. CONCLUSION: Addition of ZVI to a UASB reactor enhanced the reductive transformation and dechlorination of ClNBs. It provides a feasible proposal for the design and optimization of a high-rate anaerobic wastewater treatment technique for industrial wastewater. Copyright © 2010 Society of Chemical Industry

In situ structural characterisation of nonstable phases involved in atmospheric corrosion of ferrous heritage artefacts

The prediction of very long term corrosion of iron and low alloy steel in atmospheric conditions or in hydraulic binder media is a crucial issue for the conservation and restoration of heritage artefacts. For both media, the typical iron corrosion product layers (CPL) can be described as a matrix of goethite (α-FeOOH) crossed by marblings of reactive phases: maghemite (γ-Fe2O3), ferrihydrite (Fe5HO8.4H2O), feroxyhyte (δ-FeOOH), etc. The aim of the experiments presented here is to bring new insights on the role that the maghemite could potentially play in the mechanisms of corrosion. For that purpose, electrochemical reductions have been coupled with in situ Raman microspectroscopy. These experiments enable the authors to propose a hypothesis of local mechanisms in the specific case of marblings of maghemite connected to the metallic substrate. These local mechanisms could drastically influence the global corrosion rate.

The suitability of metallic iron for environmental remediation

AbstractAqueous contaminant removal in the presence of metallic iron is often regarded as a reductive transformation mediated by the Fe0 surface. However, successful removal of theoretically nonreducible contaminants has been largely reported. This article presents a rebuttal of the concept of contaminant reductive transformation. It is argued through a careful examination of the evolution of the volume and adsorptive properties of iron and its corrosion products that contaminants are primarily adsorbed and coprecipitated with iron corrosion products. One may wonder how the Fe0 technology will develop with the new concept. © 2009 American Institute of Chemical Engineers Environ Prog, 2010

Influences of Humic Acid on Cr(VI) Removal by Zero-Valent Iron From Groundwater with Various Constituents: Implication for Long-Term PRB Performance

A 9-month-long continuous flow column study was carried out to investigate Cr(VI) removal by Fe0 with the presence of humic acid. The study focused on the influences of humic acid promoted dissolved iron release and humic acid aggregation in Fe0 columns receiving synthetic Cr(VI) contaminated groundwater containing various components such as bicarbonate and Ca. The effects of humic acid varied significantly depending on the presence of Ca. In Ca-free columns, the presence of humic acid promoted the release of dissolved iron in the forms of soluble Fe-humic acid complexes and stabilized fine Fe (hydr)oxide colloids. As a result, the precipitation of iron corrosion products was suppressed and the accumulation of secondary minerals on Fe0 surfaces was diminished, and a slight increase in Cr(VI) removal capacity by 18% was record compared with that of humic acid-free column. In contrast, in the presence of Ca, as evidenced by the SEM and FTIR results, humic acid greatly co-aggregated with Fe (hydr)oxides and deposited on Fe0 surfaces. This largely inhibited electron transfer from Fe0 surfaces to Cr(VI) and reduced the drainable porosity of the Fe0 matrix, resulting in a significant decrease in Cr(VI) removal capacity of Fe0. The Cr(VI) removal capacity was decreased by 24.4% and 42.7% in humic acid and Ca receiving columns, with and without bicarbonate respectively, compared with that of Ca and humic acid-free column. This study yields new considerations for the performance prediction and design of Fe0 PRBs in the environments rich in natural organic matter (NOM).

Enhancing sustainability of household water filters by mixing metallic iron with porous materials

This study conceptually discusses the feasibility of enhancing the sustainability of conventional iron/sand filter (Fe 0/sand filter) for safe drinking water by partially or totally substituting sand (quartz) by porous materials. Relevant materials included activated carbon, dolomites, limestone, pumice, sandstone, and zeolites. The rational was to use the internal volume of porous additives as storage room for in situ generated iron oxyhydroxides (iron corrosion products) and thus delay time to filter clogging. Based on previous works a filter with a volumetric Fe 0:quartz ratio of 51:49 was used as reference system. The reference system is clogged upon Fe 0 depletion. Results showed that totally substituting quartz by pumice particles having a porosity of 80% yields to a residual porosity of 41%. This encouraging result suggested that the possibility of using Fe 0/MnO 2/pumice systems for a synergic promotion of Fe 0 reactivity (by MnO 2) and filter permeability (by pumice) should be investigated in more details.

Arsenate removal from water by zero-valent iron/activated carbon galvanic couples

Galvanic couples composed of zero-valent iron and activated carbon (Fe 0/AC) were investigated for As(V) removal from water. The effects of Fe 0 to AC mass ratio (FCR), solution pH, ionic strength and co-existing anions (phosphate, carbonate, silicate, nitrate, chloride and sulfate) and humic acid (HA) on As(V) removal were evaluated. The results showed that the optimum mass ratio was 1:1, and Fe 0/AC with this ratio was more effective for As(V) removal than Fe 0 and AC alone at pH of 7 and ion strength of 0.03 M NaCl. The enhanced performance for As(V) removal was fulfilled through an accelerated corrosion process of Fe 0, which meant more corrosion products for efficient As(V) removal. The As(V) removal followed a pseudo-first order reaction. The rate constants ( k) for 1:1 Fe 0/AC and Fe 0 alone were 0.802 and 0.330 h −1, respectively. Potentiodynamic polarization scans further confirmed that Fe 0 corrosion was promoted when Fe 0 was coupled with AC. Except silicates, other co-existing anions promoted As(V) removal. No reduction form of As (As(III) or As(0)) could be detected on iron corrosion products (ICPs) and in solutions. Identified ICPs included poorly crystallized lepidocrocite (γ-FeOOH) and magnetite/maghemite (Fe 3O 4/γ-Fe 2O 3) for both of Fe 0/AC and Fe 0 systems. In conclusion, the Fe 0/AC couple exhibited higher As removal performance than that of Fe 0 alone from water.

Experimental Study of Removing Surface Corrosion Products from Archaeological Iron Objects and Alternating Iron Corrosion Products by Nd:YAG Laser Cleaning System

The corrosion product of archaeological iron objects is supposed to be removed because it causes re-corrosion. So far it is removed by scapel and sand blaster but they depend on the skill and experience of a conservator and the glass-dust of the sand blaster is harmful to humans. Therefore this study applies a laser cleaning system which is used in various industrial cleaning processes, to remove corrosion product from archaeological iron objects. In addition, this work studies the alternation of corrosion product after laser irradiation, which evaluates the reliability of the laser cleaning system. Optical microscopy, SEM-EDS, XRD, Raman have been used to observe and analyse the surface of the objects. The results show the capacity of laser cleaning some corrosion product, but blackening appears with increasing pulses and laser energy, and some corrosion products, goethite and hematite, are partially altered to magnetite. These problems, blackening and alternation of corrosion product, should be solved by further studies which find the optimal laser irradiation condition and use a wetting agent. (Received January 30, 2012)

The Initial Stages of Atmospheric Corrosion of Iron in a Saline Environment Studied with Time-Resolved In Situ X-Ray Transmission Microscopy

We have investigated atmospheric corrosion of a 50 nm layer of iron covered with a thin layer of NaCl by in situ X-ray transmission spectromicroscopy. We find that upon its deliquescence, a small part of the NaCl layer is rapidly transformed into a sodium oxide (NaOH) species. A large part of the sodium and chlorine ions forms a concentrated solution on the iron surface and becomes segregated, whereby the sodium ions appear stationary and passive during further corrosion progression. In contrast, the chlorine ions appear highly mobile and become concentrated at and travel with the corrosion front, apparently acting as a corrosion catalyst. The corrosion front progression is partly of filiform and partly of radial type. The early iron corrosion products (chloride-containing oxyhydroxides) are short-lived (for some hours) and undergo a transformation as the corrosion front sweeps by from a chlorinated species to a less chlorinated species.

Comments on “Decontamination of solutions containing Cu(II) and ligands tartrate, glycine and quardol using metallic iron” [J. Hazard. Mater. (175 (2010) 452–459)

This letter presents ways for an improved discussion of the data provided in a recent article on aqueous removal of Cu II complexes from aqueous solutions using metallic iron (Fe 0) by Gyliene and his co-workers. It is shown that the authors have furnished another brilliant validation of the concept that adsorption onto iron corrosion products and co-precipitation with iron corrosion products are the fundamental mechanisms of dissolved contaminant removal in Fe 0/H 2O systems.

Migration Behavior of Alkali Earth Ions in Compacted Bentonite With Iron Corrosion Product Using Electrochemical Method

AbstractCarbon steel overpack will corrode by consuming oxygen introduced during repository construction after closure of repository, that will keep the environment in the vicinity of repository reducing. The iron corrosion products can migrate in bentonite as ferrous cations (Fe2+) through the interlayer of montmorillonite replacing the exchangeable sodium ions in the interlayer. This replacement of sodium may affect the migration behavior in the altered bentonite not only for redox-sensitive elements but also the other ions. Therefore we have carried out electrochemical analysis, of calcium, strontium or barium with the ferrous ion supplied by anodic corrosion of iron coupons in compacted bentonite. Fifteen micro liters of tracer solution containing 8.6 M of CaCl2 or 3.0 M of SrCl2 or 1.5 M BaCl2 were sspiked on the interface between the iron coupon and bentonite, for which the dry density was in the range of 1.4 to 1.5 Mg/m3, before assembling. The iron coupons were connected as working electrodes to the potentiostat and held at a constant supplied potential between - 500 to +300 mV (vs. Ag/AgCl reference electrode) for up to 7 days. Calcium and strontium could migrate faster and deeper into the bentonite than iron in each condition, while barium could migrate slower than iron. A model using dispersion and electromigration can explain the measured profiles in the bentonite specimens. The fitted value of electromigration velocity was a function of applied electrical potential and 10 to 23 nm/s for calcium, 11 to 19 for strontium, around 4 nm/s for barium and 5 to 15 nm/s for iron, respectively. Alternatively, the fitted value of the dispersion coefficient was not a function of applied potential, and the values were 3 - 8 × 10-12 m2/s for calcium, 2 - 4 × 10-12 m2/s for strontium, 5 - 10 × 10-12m2/s for barium and 3 - 9 × 10-12 m2/s for iron, respectively.

Testing Kd models of Cs + in the near field of a HLW repository in granite with a reactive transport model

Performance assessment models of high-level radioactive waste (HLW) repositories commonly rely on the simplifying assumption of a constant K d for radionuclide sorption. Testing the validity of this assumption has been prevented by the lack of nuclide thermodynamic sorption data and the unavailability of models for handling nuclide migration and sorption together with the geochemical evolution of the near field. The validity of the constant K d assumption has been tested with a multicomponent reactive transport model (RTM) for Cs + in the near field of a HLW repository in granite. Model results show that the apparent K d of Cs +, K d a , increases with time due to the decrease of the ionic strength, I, of the bentonite porewater caused by the out-diffusion of the aqueous species from the bentonite into the granite. Computed values of I are related to those of K d a through the following polynomial expression: I = 253.5 1 K d a 2 + 8.77 1 K d a - 0.005 . A thermodynamic justification for such an expression has been derived from the cation exchange reactions. A constant- K d model fails to reproduce the release rate of Cs + from the near field computed with the RTM. A variable- K d model which incorporates the dependence of K d a on I reproduces adequately the Cs + release rate, thus providing a surrogate for the constant- K d model. The results of the sensitivity runs to changes in model parameters and boundary conditions show that the water flux at the bentonite–granite interface affects strongly the K d a through changes in I while the effective diffusion coefficient of the bentonite plays a minor role on K d a . An increase in the cation exchange capacity leads to an increase of K d a , but it does not affect the time evolution of I. Competing cations such as Ni 2+ and iron corrosion products decrease slightly the K d a of Cs + by competing for exchange sites and by increasing the I.

Investigating the mechanism of clofibric acid removal in Fe 0/H 2O systems

Since the introduction of iron wall technology, the inherent relationship between contaminant removal and iron corrosion has been mostly attributed to electron transfer from the metal body (direct reduction). This thermodynamically founded premise has failed to explain several experimental facts. Recently, a new concept considering adsorption and co-precipitation as fundamental contaminant removal mechanisms was introduced. This consistent concept has faced very skeptic views and necessarily needs experimental validation. The present work was the first independent attempt to validate the new concept using clofibric acid (CLO) as model compound. For this purpose, a powdered Fe 0 material (Fe 0) was used in CLO removal experiments under various experimental conditions. Additional experiments were performed with plated Fe 0 (mFe 0: Fe 0/Pd 0, Fe 0/Ni 0) to support the discussion of removal mechanism. Main investigated experimental variables included: abundance of O 2, abundance of iron corrosion products (ICPs) and shaking operations. Results corroborated the concept that quantitative contaminant removal in Fe 0/H 2O systems occurs within the oxide-film in the vicinity of Fe 0. Additionally, mixing type and shaking intensity significantly influenced the extent of CLO removal. More importantly, HPLC/MS revealed that the identity of reaction products depends on the extent of iron corrosion or the abundance of ICPs. The investigation of the CLO/Fe 0/H 2O system disproved the popular view that direct reduction mediates contaminant removal in the presence of Fe 0.

Metallic iron for environmental remediation: Learning from electrocoagulation

The interpretation of processes yielding aqueous contaminant removal in the presence of elemental iron (e.g. in Fe(0)/H(2)O systems) is subject to numerous complications. Reductive transformations by Fe(0) and its primary corrosion products (Fe(II) and H/H(2)) as well as adsorption onto and co-precipitation with secondary and tertiary iron corrosion products (iron hydroxides, oxyhydroxides, and mixed valence Fe(II)/Fe(III) green rusts) are considered the main removal mechanisms on a case-to-case basis. Recent progress involving adsorption and co-precipitation as fundamental contaminant removal mechanisms have faced a certain scepticism. This work shows that results from electrocoagulation (EC), using iron as sacrificial electrode, support the adsorption/co-precipitation concept. It is reiterated that despite a century of commercial use of EC, the scientific understanding of the complex chemical and physical processes involved is still incomplete.

Raman Studies of Corrosion Layers Formed on Archaeological Irons in Various Media

The description and identification of corrosion products formed on archaeological iron artefacts need various approaches at different observation scales. Among analytical techniques available to document phase structure at the microscopic range, Raman spectroscopy offers sensitivity and discrimination between iron corrosion products with an easy implementation. Results obtained for iron artefacts corrosion in soils and atmosphere are presented. Corrosion forms observed for anoxic and aerated soils on one hand and indoor atmosphere on the other are documented. Beyond the identification and organisation of corrosion products through hyperspectral imaging, Raman micro-spectroscopy could also provide quantitative phase proportions which will be needed in the proposition of reactivity diagnosis indicators.

Effects of hardness and alkalinity on the removal of arsenic(V) from humic acid-deficient and humic acid-rich groundwater by zero-valent iron

The effects of hardness (Ca 2+) and alkalinity (HCO 3 −) on arsenic(V) removal from humic acid (HA)-deficient and HA-rich groundwater by zero-valent iron (Fe 0) were investigated using batch experiments. Arsenic, in general, is removed from groundwater possibly by adsorption and co-precipitation with the iron corrosion products. However, in the co-presence of HCO 3 − and Ca 2+, the removal rate of arsenic increased with increasing concentrations of either Ca 2+ or HCO 3 −. It was observed that the removal of arsenic was significantly enhanced by the formation of CaCO 3 as a nucleation seed for the growth of large iron (hydr)oxide particles. In the co-existence of Ca 2+, HCO 3 − and HA, the presence of HA diminished the positive role of Ca 2+ due to the formation of Fe-humate complexes in solution and delaying of the formation of CaCO 3. As a result, the formation of the large iron (hydr)oxide particles was inhibited in the earlier stage which, in turn, affected the removal of arsenic. However, after the formation of CaCO 3 and the subsequent growth of such particles, the presence of large iron (hydr)oxide particles resulted in the rapid removing of arsenic and Fe-humate by adsorption and/or co-precipitation.

Biofouling and microbial corrosion problem in the thermo-fluid heat exchanger and cooling water system of a nuclear test reactor

This article discusses aspects of biofouling and corrosion in the thermo-fluid heat exchanger (TFHX) and in the cooling water system of a nuclear test reactor. During inspection, it was observed that >90% of the TFHX tube bundle was clogged with thick fouling deposits. Both X-ray diffraction and Mössbauer analyses of the fouling deposit demonstrated iron corrosion products. The exterior of the tubercle showed the presence of a calcium and magnesium carbonate mixture along with iron oxides. Raman spectroscopy analysis confirmed the presence of calcium carbonate scale in the calcite phase. The interior of the tubercle contained significant iron sulphide, magnetite and iron-oxy-hydroxide. A microbiological assay showed a considerable population of iron oxidizing bacteria and sulphate reducing bacteria (105 to 106 cfu g−1 of deposit). As the temperature of the TFHX is in the range of 45–50°C, the microbiota isolated/assayed from the fouling deposit are designated as thermo-tolerant bacteria. The mean corrosion rate of the CS coupons exposed online was ∼2.0 mpy and the microbial counts of various corrosion causing bacteria were in the range 103 to 105 cfu ml−1 in the cooling water and 106 to 108 cfu ml−1 in the biofilm.

Sorption of Th(IV) onto Iron Corrosion Products: EXAFS Study

Long-term performance assessment of nuclear waste repositories is affected by the ability of the outer barrier systems to retain radionuclides after possible corrosive leakage of waste containers. The mobility of the radionuclides released from the spent fuel depends strongly on the processes that take place in the backfill material. The interaction of steel corrosion products and radionuclides is part of such a scenario. In this work, the sorption of Th(IV) onto 2-line-ferrihydrite (FeOOH x H2O) and magnetite (Fe3O4), used as models for steel corrosion products, has been studied using EXAFS spectroscopy. Sorption samples were prepared in 0.1 M NaClO4 solutions at acidic pH (initial pH values in the range 3.0-4.2) either from undersaturation and supersaturation conditions with respect to amorphous ThO2. Two oxygen subshells, one at 2.37 A and another at 2.54 A, were observed in the first hydration sphere of Th in the case of the ferrihydrite samples. Th-Fe distances for the different ferrihydrite samples are approximately 3.60 A. These results indicate a corner sharing surface complex of Th(IV) ion onto the ferrihydrite surface where the Th atom shares one O atom with each of two coordinated octahedra. The longer Th-O distance accounts for coordinated water molecules. No significant changes in the structural environment of Th in terms of coordination numbers and distances were detected as a function of Th(IV) concentration. Magnetite samples sorbing Th(IV) also showed also a strong distortion of the O shell, but in contrast to ferrihydrite, two types of nearest Fe atoms were detected at 3.50 A and 3.70 A. These results indicate that Th(IV) ion sorbs onto the magnetite surface as bidentate-corner sharing arrangements to [FeO6] octahedra and [FeO4] tetrahedra.