Iron Sulfide Deposits Research Articles

Iron Production By Molten Sulfide Electrolysis

With urgency and incentives to cut CO2 emissions, alongside increasing demand for steel, there is a need for technologies that use solely electricity for iron ore reduction, eliminating the role of carbon as a reductant. Herein, we propose the electrolytic production of liquid cast iron using a novel sulfide route, molten sulfide electrolysis (MSE). The process operates using sulfide chemistry and an inert anode. Sulfides are well known from non-ferrous metallurgy1 and the exclusion of oxygen supports a virtual elimination of green-house gases(GHG) emissions from the reduction step. The electrolytic decomposition of iron sulfide into iron and elemental sulfur gas operates in a multi-component molten sulfide electrolyte. The underlying thermodynamics suggests the absence of trivalent iron species (Fe3+) in such conditions, supporting the reduction of only divalent iron (Fe2+) and reducing the energy need proportionally, as compared to other oxide-based routes. Iron sulfide deposits or tailings, as well as conventional iron oxide ores after sulfidation2 are some of the suitable feedstocks for MSE.Both thermal only, and galvanostatic electrochemical experiments were carried out on electrolyte droplets (~200mg) in a thermal imaging furnace, to confirm the electrolytic deposition of Fe and the evolution of sulfur in a 2-electrode set-up. Faradaic efficiency estimates based on mass-loss measurements – i.e. with respect to gaseous sulfur anodic evolution – are of the order of 90%. Key electrochemical attributes of MSE to be reported include impedance measurement at various fixed DC potentials, measurements at various current densities up to 2A/cm2, and the role of the total charge passed, to highlight the potential limitations observed in such an experimental set up. Characterization of the electrochemical deposits are also presented.

Evaluation of compatibility between formation and Injection water into the Reservoir Rock

Scale deposition represents a critical challenge encountered in water injection systems. The objective of this study is to assess the compatibility between the candidate smart water and the formation water in an oil reservoir rock sample. To achieve this, water samples were collected and analyzed to evaluate the extent of deposit formation under varying temperature and pressure conditions. Additionally, the study also examined the combined influence of temperature and pressure on deposit formation. The results indicated that as the temperature increased, there was a decrease in the concentration of sulfate in the seawater. Taking into account the low concentration of barium (zero) in seawater and the unchanged strontium concentration, the decrease in sulfate concentration can be attributed to the deposition of calcium sulfate. Contrarily, in various ratios of smart water, the sulfate concentration has shown an increase with rising temperatures. This can be attributed to the transformation of sulfite present in the formation water into sulfate due to the influence of temperature. The presence of a low concentration of barium in the formation water resulted in insignificant changes in sulfate concentration due to the precipitation of barium sulfate. Additionally, despite the high concentration of strontium, strontium sulfate deposition did not occur, possibly due to the solubility product constant. The analysis of different smart water ratios under various pressures at ambient temperature revealed that pressure had a minimal effect on the solubility of sulfate and calcium salts. During the sediment analysis, no evidence of strontium sulfate sediment formation was observed. However, the analysis indicated a high possibility of iron sulfide and iron oxide deposits forming. Ultimately, under the experimental conditions, significant sediment formation was not observed.

The metallogeny of the Devonian sediment-hosted sulfide deposits, South China: A case study of the Huodehong deposit

The Devonian sedimentary rocks in South China host numerous sulfide deposits (e.g. the Siding and Beishan Pb-Zn sulfide deposits, and the Yingde iron sulfide deposits) that are distinctly characterized by a wide variation of δ34S values in sulfides (−28.7‰ to +42.8‰). Such signature, however, has not been investigated in depth and thus the metallogeny of these deposits remain poorly understood. This paper investigated the Huodehong deposit hosted by sedimentary rocks of the Middle Devonian in the western Yangtze Block, South China. A complex paragenesis has been defined: I) micro-grained pyrite (Py1) associated with organic materials; II) radial and crustiform pyrite (Py2) and marcasite (Mc1) aggregates; III) subhedral-anhedral pyrite (Py3), microcrystal colloform sphalerite (Sp1), and dendritic galena; and IV) coarse-grained euhedral sphalerite (Sp2) occurred as veinlets. The mineralogical evidence shows that the Py1 occurred as syn-sedimentary pyritic stromatolites, which is overprinted by cavity-filling hydrothermal Py2, Py3, Sp1, and Sp2. In situ S isotopes show that the δ34S values of Py1-Py3 and Sp1 range from –22.8‰ to −10.8‰. Such highly depleted heavy sulfur isotopes indicate that the reduced sulfur was mainly derived from bacterially reduced seawater sulfate in an open system. The Sp1 has similar δ34S values to its reworking Py1, implying that part of reduced sulfur was sourced from sedimentary pyrite. Such sedimentary pyrite might act as a geochemical barrier in accelerating sulfate reduction via the hydrolysis of Fe2+ resulting an increase in the H+ concentration and the formation of HSO4−. In addition, the Sp2 has slightly depleted heavy sulfur isotopes (δ34S = −9.3‰ to −1.1‰), implying the late input of heavy sulfur isotopes component. Hence, the highly heterogeneous sulfur isotopes at Huodehong likely resulted from bacterial sulfate reduction coupled with reworking sedimentary pyrite, and subordinate incorporation of 34S-rich sulfur. The reduced sulfur of the Huodehong deposit has multiple sources (i.e. sedimentary pyrite and sulfate-bearing evaporites), and the ore formation has experienced the epigenetic hydrothermal mineralization with mixture of metals from the metamorphic basement rocks. The outcomes will have a great implication for understanding the origin and exploration of the Devonian sulfide deposits in South China.

Genesis of the argillite-hosted cupriferous iron sulfide deposits of the Shimokawa mine in the Hidaka Belt, northern Hokkaido, Japan

Genesis of the argillite-hosted cupriferous iron sulfide deposits of the Shimokawa mine in the Hidaka Belt, northern Hokkaido, Japan

Fouling propensity of nonstoichiometric pyrrhotite polytypes in glycol gas dehydration units

Fouling formation in gas dehydration units is performed mainly by gradual accumulation of sulfur-containing compounds and its corrosion products in glycol streams. High concentrations of iron-sulfur species in glycol media increase the fouling propensity on the tube surfaces of heat exchangers. Therefore, the factors affecting the fouling formation and their ranks were determined in a pilot plant gas dehydration unit. Then, the morphology and composition of the fouling layers were studied by qualitative and quantitative XRD patterns. The results revealed that among studied parameters, the concentration of dissolved iron in glycolic media is the main factor responsible for the formation of iron-sulfide deposits. Moreover, it was showed that non-stoichiometric pyrrhotite polytypes 4C, 5C and 6C are the base components of fouling scales deposited on the surface of heat exchangers. Distribution of iron-based species was also determined in the cross-section of a typical heat exchanger and the results showed that the deposited layers are consisted of hydrocarbon residues and pyrrhotite polytypes. Over the time, the pyrrhotite polytypes in deposited layers are covered by paraffin residues absorbed by TEG phase from the natural gas stream.

Vapor‐Deposited Minerals Contributed to the Martian Surface During Magmatic Degassing

AbstractMartian magmas were likely enriched in S and Cl with respect to H2O. Exsolution of a vapor phase from these magmas and ascent of the gas bubbles through the magma plumbing system would have given rise to shallow magmas that were gas‐charged. Release and cooling of this gas from lava flows during eruption may have resulted in the addition of a significant amount of vapor‐deposited phases to the fines of the surface. Experiments were conducted to simulate degassing of gas‐charged lava flows and shallow intrusions in order to determine the nature of vapor‐deposited phases that may form through this process. The results indicate that magmatic gas may have contributed a large amount of Fe, S, and Cl to the Martian surface through the deposition of iron oxides (magnetite, maghemite, and hematite), chlorides (molysite, halite, and sylvite), sulfur, and sulfides (pyrrhotite and pyrite). Primary magmatic vapor‐deposited minerals may react during cooling to form a variety of secondary products, including iron oxychloride (FeOCl), akaganéite (Fe3+O (OH,Cl)), and jarosite (KFe3+3(OH)6(SO4)2). Vapor‐deposition does not transport significant amounts of Ca, Al, or Mg from the magma and hence, this process does not directly deposit Ca‐ or Mg‐sulfates.

Iron-sulfur distribution and its environmental significance in three typical areas of western Lake Taihu

以太湖西岸聚藻区、清淤区和开阔水域3种典型区域为对象，对沉积物中硫铁的分布进行研究.结果显示，各区域沉积物中铁还原均比硫还原活跃，硫铁氧化还原菌的分布表明硫铁循环主要集中于0~15 cm表层沉积物.开阔水域未发现明显硫离子（dS^2-）释放与酸性可挥发性硫化物（AVS）沉积，硫还原较弱；二价铁离子（dFe²⁺）平均浓度为dS^2-的5.2倍，说明沉积物仍以铁还原为主导.清淤区硫酸盐还原菌（SRB）相对丰度与dS^2-含量均为所有区域中最低，且未见明显dFe²⁺释放，表明清淤抑制了硫铁还原的进行.聚藻区表层沉积物SRB相对丰度达到2.7%，且出现dS^2-和AVS的显著升高，说明沉积物中发生着强烈的微生物硫还原.在表层沉积物也出现了明显的dFe²⁺释放，反映出强烈的铁还原，但沉积物中铁还原菌（FeRB）的平均丰度仅为0.6%，这一数值与其他区域相似，显然无法解释聚藻区与其他区域巨大的dFe²⁺差异，因此微生物铁还原并不是铁还原的主要途径.考虑到硫铁化合物的沉积与Fe（Ⅲ）氧化物的消耗一致，沉积物中的铁还原是由ΣS^2-诱导的化学铁还原主导.dFe²⁺平均浓度为dS^2-的4.8倍，监测培养沉积物的dS^2-、dFe²⁺变化所得的铁还原速率是硫还原速率的7.4倍，说明铁还原仍比硫还原活跃.但由于AVS的沉积对ΣS^2-的消耗，真实硫还原速率应高于测量值.;Geochemical characteristic of sulfur and iron was investigated in three types of sediments including algae accumulated sediment, dredged sediment and sediment away from lake shore. It was found that iron reduction dominated in all sediments rather than sulfate reduction. Both reduction concentrated in 0-15 cm surface sediments according to the distribution of microorganisms of iron and sulfur species. Accumulation of dS^2- and acid volatile sulfide(AVS)was not observed in sediment away from lake shore, indicating that sulfate reduction is minor. Iron reduction was more active than sulfate reduction as the mean concentration of dFe²⁺ was 5.2 folds of dS^2-. Sulfate reducing bacteria (SRB) abundance and dS^2- content in dredged sediments were the lowest and dFe²⁺ release was not found, suggesting the depressed iron and sulfate reduction by dredging. SRB abundance in algae accumulated sediment reached to 2.7% and intensive dS^2- release and AVS deposition were found, indicating the strong sulfate reduction. Active iron reduction was also found with high dFe²⁺ concentration in algae accumulated sediment. However, the mean abundance of iron reducing bacteria (FeRB) was only 0.6%, which was similar to other sediments and was obviously not able to explain the huge difference of dFe²⁺ concentrations. Thus, microbial iron reduction was not the main pathway of iron reduction. Considering the corresponding dissolution of Fe(Ⅲ) oxides and deposition of iron sulfides, sulfide-mediated chemical iron reduction was the dominating pathway. The mean concentration of dFe²⁺ was 4.8 folds of dS^2-, and iron reduction rate was 7.4 folds of sulfate reduction rate by monitoring dS^2- and dFe²⁺ variations, suggesting iron reduction was more active than sulfate reduction. However, as AVS generation could consume dS^2-, the real rate of sulfate reduction was higher than the measured rate. Transition of iron and sulfur cycling would cause various negative effects and even extreme cases including dead zones in marine and black bloom in freshwater lakes. Although similar phenomenon was only observed in algae accumulated sediment, concern should still be raised.

Melanosis? Think Again: A Case of Pseudomelanosis duodeni and Jejunal Hemangiomas

Melanosis coli is a common cause of hyperpigmented lesions in the GI tract that typically result from laxative overuse. Herein we describe a case of pseudomelanosis duodeni and jejunal hemangiomas discovered after push enteroscopy for an un-localized GI bleed. Though similar in appearance, pseudomelanosis is actually due to deposition of hemosiderin in lamina propria (LP) macrophages. An 83-year-old Asian female presented with recurrent hospitalizations for melena and severe anemia. Past medical history included transfusion-dependent iron deficiency anemia from chronic GI bleeding, hypertension, diabetes, heart failure, and atrial fibrillation not on anticoagulation. Her initial workup began in 2014 and EGD demonstrated erosive gastropathy with negative H. pylori. Colonoscopy demonstrated three 3-5 mm polyps and diverticulosis but no signs of acute bleeding. Repeat hospitalization for anemia with EGD in 2015 showed no source of bleeding. Colonoscopy showed two 5-8 mm polyps and diverticulosis but no bleeding. Outpatient capsule endoscopy in 2015 was unrevealing. Repeat hospitalization in April 2018 with colonoscopy revealed melena from the ileum and several small polyps in the cecal region. Push-enteroscopy revealed dark speckled pigmentation in the duodenum and jejunum. Two bleeding hemangiomas in the jejunum were found and ablated with APC then clipped. Duodenal biopsies demonstrated hemosiderin deposition within the LP macrophages consistent with a diagnosis of pseudomelanosis duodeni. Pseudomelanosis duodeni is characterized by the presence of brownish or blackish pigmentation in duodenal mucosa. It is associated with various medical conditions including, diabetes, renal disease, GI bleeding, hypertension, heart failure, oral iron intake, and use of erythropoiesis-stimulating agents. Histologic differential includes hemochromatosis, brown bowel syndrome, and malignant melanoma. Pseudomelanosis duodeni has histology notable for iron sulfide and hemosiderin deposits in the LP macrophages. This is in contrast to the accumulation of lipofuscin in the LP macrophages due to laxative overuse seen in melanosis coli. Interestingly, the hyperpigmentation made it easier to identify the jejunal hemangiomas; in a similar fashion to melanosis coli making it easier to identify polyps. Although this disease is quite rare and benign, it warrants tissue biopsy to rule out other worrisome etiologies.2546_A Figure 1. Dark speckled pigmentation scattered throughout the small bowel.2546_B Figure 2. Hemangiomas in the jejunum (blue/white arrows). Right image shows bleeding hemangioma (blue/white arrow).2546_C Figure 3. Left image demonstrates mucosal changes after APC ablation of bleeding hemangiomas (white/blue arrows). Right image demonstrates clips placed (red/white arrow) after APC ablation.

Biogeochemical conversion of sulfur species in saline lakes of Steppe Altai

The aim of the present research is to identify the main mechanisms of sulfur behavior in saline lakes in the course of time and followed transformations in their chemical composition. The influence of water on chemical composition of biochemical processes involved in decomposition of organic matter was determined by the study of behavior of reduced forms of sulfur in lakes. The determination of reduced forms of sulfur was carried out by successive transfer of each form of sulfur to hydrogen sulfide followed by photometric measurements. The other chemical components were determined by standard methods (atomic absorption, potentiometric method, titration method and others). The salt lakes of the Altai steppe were studied in summer season 2013–2015. Analysis of the chemical composition of the saline lakes of Altai Krai has shown that carbonate-, hydrocarbonate- and chloride ions dominate among anions; sodium is main cation; sulfates are found in subordinate amounts. Reduced forms of sulfur occur everywhere: hydrogen and hydrosulfide sulfur S2- prevail in the bottom sediments; its derivative—elemental S0 —prevails in the lakes water. The second important species in water of soda lakes is hydrosulfide sulfur S2-, and in chloride lakes is thiosulfate sulfur S2 O32-. The lag in the accumulation of sulfates in soda lakes in comparison to chloride lakes can be explained by their bacterial reduction, followed by the formation and deposition of iron sulfides in sediments. In chloride lakes gypsum is a predominantly barrier for sulfates.

Effect of composition of coke deposited in delayed coker furnace tubes on on-line spalling

Delayed coking is one of the most widely used residue upgradation process in crude oil refining where vacuum residue is thermally cracked and converted into distillates and petroleum coke. During heating of vacuum residue in coker furnace, coke is continuously deposited in furnace tubes which is removed at regular intervals by one of the three methods namely (i) pigging, (ii) steam air decoking or (iii) online spalling (OLS). OLS is one of the preferred methods of coke removal from coker furnace tubes. We have noticed very effective as well as “not so effective” OLS in a commercial delayed coker furnace. In present article, the changes in composition and properties of furnace coke during effective and ineffective OLS were systematically analyzed by various analytical tools such as Dilatometer, TGA, HRSEM, SEM-EDX and XRD. Based on these analyses, it was found that inorganic deposits such as iron sulphides and tube metal corrosion products play a major role in failure of OLS. Higher total acid number (TAN) of vacuum residue may be promoting the formation of iron sulfide deposits in furnace tube.

Mineral scaling in two-phase geothermal pipelines: Two case studies

Mineral scaling is a common problem in geothermal power facilities. This scale deposition is usually caused by changes in the geothermal fluid temperature or composition and chemistry. Precipitation of minerals can limit fluid flow within the steam field equipment, reducing plant efficiency and increasing maintenance costs.A layer of scaling is commonly found in most parts of the geothermal steam gathering system. However, significant amounts of deposited mineral scales are usually observed in the pipelines and vessels that handle silica super-saturated brines.This work focuses on a less common scaling in geothermal two-phase pipelines, when fluids are usually high enthalpy and under-saturated with respect to amorphous silica. The scaling is mainly caused by mixing and changes in steam fraction at the two-phase pipelines, when several wells share the same pipeline header to transport the fluid to the downstream facility.Two case studies are discussed in this work reporting mineral scaling due to the mixing of incompatible geothermal fluids within two-phase headers.The first case investigates silica deposition caused by the mixing of a steam-dominated well fluid with fluid from two water-dominated wells. The scale deposition is caused by the small amount of brine entrained in the steam-dominated well fluid, which reacts upon mixing with the fluid from the other water-dominated wells, causing massive localised scaling at the mixing points. The second case investigates iron sulfide and silica deposition caused by the mixing of a low-pH, high-silica fluid with neutral-pH fluid.Header blockage can result in an increase in wellhead pressures causing production from some wells to collapse, at the same time decreasing the flow of geothermal fluids to the separators. The scaling requires regular cleaning to return the pipelines to full flow capacity. Recommended engineering solutions are given for both cases, for possible site implementation.

(Invited) Atomic Layer Deposition of Cobalt, Nickel, and Iron Sulfides: Synthesis and Applications

Transition metal sulfides have recently aroused great attention for a variety of applications in energy conversion and storage devices. Many transition metal sulfides, such as cobalt, nickel, and iron sulfides, have shown superb electrochemical properties, so they are highly promising as candidate active materials for supercapacitors, batteries, and water-splitting electrocatalysis. Atomic layer deposition (ALD) is a well-known nanotechnology for preparing uniform, conformal coating films on complex 3D structures. Recently, ALD has gained particular attention in energy conversion and storage applications, as ALD has been demonstrated as an effective approach to uniformly and conformally load active materials onto complex 3D nanostructured electrodes. For most electrodes, their electrochemical properties are largely determined by the surface properties, and therefore conformally coating the surface by ALD is of particular importance for the device performance, as the optimization of the nanostructured geometry of the electrodes can be decoupled from the modification of the surface properties. On the other hand, however, ALD of metal sulfides is much less explored, as compared to oxides. The ALD processes for many of the important sulfides, such as CoSx, NiSx, and FeSx, are still not well established, which therefore could seriously hinder their applications in energy devices. Herein, we will present our recent progress on the ALD of CoSx, NiSx, and FeSx. The metal sulfides were all deposited using metal amidinates as the metal precursors and H2S as the sulfur source. The saturation behaviors of these ALD processes were carefully studied. Typical film properties, such as microstructure, purity, and morphology, were evaluated by various techniques including TEM, AFM, SEM, RBS, and XPS. With optimal deposition conditions, our ALD processes were able to produce high-quality, pure, smooth, and well-crystallized films of CoSx, NiSx, and FeSx. In addition, all these sulfide films were able to uniformly and conformally cover deep narrow trenches with high aspect ratio of 10:1, which demonstrated the excellent conformality of our ALD processes. We will also present a few examples to demonstrate the promising applications of these ALD sulfides in energy conversion and storage devices. ALD CoSx showed excellent electrochemical redox kinetics in alkaline aqueous solution, and therefore it was a suitable candidate active material for supercapacitors. By conformally depositing CoSx thin film on porous nickel foam electrodes, the synthesized ALD-coated electrodes showed remarkable supercapacitor performance with high specific capacitance, good rate performance, and good cycling stability. Meanwhile, ALD NiSx was found to show excellent electrocatalytic performance toward OER, and therefore it was promising for electrocatalysis and metal-air batteries. Further studies showed that the ALD NiSx converted to porous nickel oxyhydrate during electrochemical aging, and the aged product exhibited superior OER performance with good stability.

(Invited) Atomic Layer Deposition of Cobalt, Nickel, and Iron Sulfides: Synthesis and Applications

Recent development on the atomic layer deposition (ALD) of CoSx, NiSx, and FeSx is presented. The sulfides are deposited by using metal amidinates as the metal precursors and H2S as the sulfur source. Ideal saturated, self-limiting growth behaviors are observed for all these ALD processes, and the deposited sulfide films are able to uniformly and conformally cover deep narrow trenches with high aspect ratio of 10:1. Examples of using these ALD processes to synthesize CoSx, NiSx, and FeSx thin films for the respective applications in supercapacitors, electrocatalysis, and chemical catalysis are also presented.

Cocrystallization coefficients of Cr, V, and Fe in hydrothermal ore systems (from experimental data)

The cocrystallization coefficients of Cr, V, and Fe (DMe/Fe) in magnetite and sulfide minerals (pyrite, chalcopyrite, and Fe-containing sphalerite) in multiphase associations are determined in hydrothermal-growth experiments with internal sampling at 450 °C and 100 MPa (1 kbar). The results are compared with previous data on DMn/Fe. Magnetite and pyrite are characterized by the highest DMe/Fe values for both Cr (1.2 and 2) and V (6.6 and 1.1). These minerals also show the highest mineral/solution distribution coefficients of Cr and V. For V and Cr in chalcopyrite, much lower DMe/Fe values (0.03 and 0.04, respectively) were obtained, which, however, are slightly higher than those for Mn in magnetite (0.01). Although the deposition of magnetite and iron sulfides has no significant effect on the evolution of Mn in solution and Mn-Fe partitioning, crystallization of magnetite and pyrite favors a decrease in Cr and V contents relative to Fe content in solution.The data obtained can be used to reconstruct the chemical composition of paleofluids. Spinel minerals with close contents of Mn, V, and Cr can form through a hydrothermal process provided that the solutions are highly enriched in Mn relative to Fe and have V and Cr contents close to the Fe one. Such solutions seem to be exotic. Usually, a magnetite-forming hydrothermal fluid contains V and Cr as millionths of Fe, while the Mn content in it can be of the same order of magnitude as the Fe content. The data obtained may be of interest for reconstructing the evolution of the chemical composition of the World Ocean in different geologic periods.The study has shown that the bulk distribution coefficient of variable-valence elements between mineral and hydrothermal solution varies over a wide range of values even at constant pressure, temperature, and solution composition and can be used only for qualitative estimation of the element compatibility. In contrast, the bulk cocrystallization coefficient of chemically similar elements is less dependent on physicochemical conditions, has a nearly three times lower variation coefficient, and permits an element partitioning analysis in heterogeneous mineral-fluid systems.

Electrochemical Corrosion Rate Measurement Under Iron Sulfide Deposit

Different from other types of pipeline solids such as sand and iron carbonates, iron sulfide is semi-conductive and electrochemically reactive. This adds extra complexity to laboratory testing compared with inert deposits. Previous laboratory testing has shown that the corrosion rate under iron sulfide deposits can be severely overestimated using electrochemical techniques. In the current work, a laboratory iron sulfide synthesis method and an iron sulfide under-deposit corrosion testing methodology were developed to better assess and monitor this type of corrosion in a simulated pipeline environment. Two different types of iron sulfides were used to investigate the corrosion of carbon steel under such deposits. Scanning electron microscopy, x-ray diffraction, and laser light extinction particle size analysis were utilized to characterize the surface morphology, composition, crystal structure, and particle size of the different iron sulfides. A white light interferometric volume loss method was used to ve...

Investigation of a pyrophoric iron fire in a Visbreaker fractionation column provides better cleaning work procedure

An unexpected ignition of pyrophoric iron sulphide deposits took place in the fractionator of a Visbreaker unit. The distillation column had been chemically decontaminated prior to the event. The investigation of the event leads to conclusions concerning chemical decontamination limitations in vessels in coking service. Based on the lessons learned from this case, a prioritization of manual vessel cleaning works in coking service is proposed.

In situ evaluation of model copper-cast iron canisters for spent nuclear fuel: a case of microbiologically influenced corrosion (MIC)

The Swedish method for disposal of spent nuclear fuel in a deep geological repository (KBS-3) relies on the stability of the granitic bed-rock and two engineered barriers: a copper-cast iron canister and highly compacted bentonite clay. In order to develop a better understanding of the internal corrosion processes that could take place if a leak were to occur in the outer copper canister, five miniaturised copper cast iron canisters were installed at a depth of 450 m at the Äspö Hard Rock Laboratory, in Sweden. The experiments differed in the density of the surrounding bentonite buffer, as well as in the number and position of leak points that were introduced in the copper shell. Several electrochemical techniques (e.g. AC impedance, linear polarisation resistance and electrochemical noise) were used to monitor the corrosion of different components of the experiment. Copper specimens were installed for post-test evaluation of the rate of general corrosion, localised corrosion and stress corrosion cracking (SCC). In addition, mechanical and environmental parameters, such as surface strain, hydrostatic pressure, redox potential, pH, water chemistry, dissolved gases, and microbial numbers, diversity, and activity were measured regularly. After five years of in situ exposure one of the canisters was retrieved and analysed to characterise and evaluate the corrosion processes that had occurred during the experiment. Extensive sulphide production by sulphate reducing bacteria led to rapid corrosion of iron, and the formation of iron sulphide deposits on the copper and iron electrodes disturbed the electrochemical measurements. This paper describes the various analyses that were carried out on the model canister and summarises the conclusions that can be drawn.

Electrochemical CO2 Reduction by Ni-containing Iron Sulfides: How Is CO2 Electrochemically Reduced at Bisulfide-Bearing Deep-sea Hydrothermal Precipitates?

The discovery of deep-sea hydrothermal vents on the late 1970's has led to many hypotheses concerning chemical evolution in the prebiotic ocean and the early evolution of energy metabolism in ancient Earth. Such studies stand on the quest for the bioenergetic evolution to utilize reducing chemicals such as H2 for CO2 reduction and carbon assimilation. In addition to the direct reaction of H2 and CO2, the electrical current passing across a bisulfide-bearing chimney structure has pointed to the possible electrocatalytic CO2 reduction at the cold ocean-vent interface (R. Nakamura, et al. Angew. Chem. Int. Ed. 2010, 49, 7692−7694). To confirm the validity of this hypothesis, here, we examined the energetics of electrocatalytic CO2 reduction by iron sulfide (FeS) deposits at slightly acidic pH. Although FeS deposits inefficiently reduced CO2, the efficiency of the reaction was substantially improved by the substitution of Fe with Ni to form FeNi2S4 (violarite), of which surface was further modified with amine compounds. The potential-dependent activity of CO2 reduction demonstrated that CO2 reduction by H2 in hydrothermal fluids was involved in a strong endergonic electron transfer reaction, suggesting that a naturally occurring proton-motive force (PMF) as high as 200mV would be established across the hydrothermal vent chimney wall. However, in the chimney structures, H2 generation competes with CO2 reduction for electrical current, resulting in rapid consumption of the PMF. Therefore, to maintain the PMF and the electrosynthesis of organic compounds in hydrothermal vent mineral deposits, we propose a homeostatic pH regulation mechanism of FeS deposits, in which elemental hydrogen stored in the hydrothermal mineral deposits is used to balance the consumption of the electrochemical gradient by H2 generation.

Geology and Modes of Occurence of Iron Sulphide Deposits in the Yanahara Mining District

Geology and Modes of Occurence of Iron Sulphide Deposits in the Yanahara Mining District

The Cupriferous Iron Sulphide Deposits of the Koryu Mine in Hidaka Province, Hokkaido

The Cupriferous Iron Sulphide Deposits of the Koryu Mine in Hidaka Province, Hokkaido