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Thesis (Ph. D.)--University of Hawaii at Manoa, 1996. / Includes bibliographical references (leaves 227-230). / Microfiche. / xxii, 230 leaves, bound ill. 29 cm

Phosphorus chemistry controls key aspects of eutrophication, microbial nutrition, corrosion and other environmental processes. It is commonly assumed that phosphorus occurs exclusively as phosphate (+5) in nature. In fact, although phosphate is undoubtedly dominant in many systems, phosphorus compounds with lower oxidation states (reduced phosphorus) can also be present in the environment and could be of practical importance in many circumstances. Most reduced phosphorus compounds are likely to originate in steel-making or thermal phosphorus plants. It was determined that reduced phosphorus would not be detected in routine environmental analyses even if they were present. A new method was developed to detect these compounds, and in a preliminary survey reduced phosphorus was proven to be present in water that contacts corroding iron pipes, steel slag samples, phosphorus plant wastewater, phosphite fertilizers, and in sewage treatment plant effluent. However, no evidence could be obtained for massive bio-reduction of phosphates that has been proposed by some researchers. Given that phosphorus is often a limiting nutrient, and phosphorus compounds sometimes inhibit and sometimes catalyze practically important reactions (e.g. iron corrosion), future work should examine reduced phosphorus occurrence and chemistry in greater detail. / Ph. D.

Customer complaints of red water problems remain to be a frequent occurrence for water utilities. While material sources may vary, it is generally accepted that iron rust resulting from corrosion of iron based pipes is the predominant cause of red water issues. Recent efforts have lead to the development of a number of models that predict the occurrence of iron release and subsequent red water formation. This paper provides a detailed analysis of recently developed iron corrosion release models. Significant disagreement exists as to the processes and mechanisms leading to the release of iron corrosion materials into the water supply. This lack of consensus is made evident when comparing each of the iron release models. Considerable variation exists as to mechanisms considered and specific modeling goals. While each model may be beneficial for simulating certain aspects of corrosion release, no single model has been developed that provides a comprehensive portrayal of iron corrosion release phenomena. / Master of Science

M.Sc. (Physics) / Please refer to full text to view abstract

The net present replacement value of all publicly and privately owned potable water pipes in the U.S. is on the order of $2.4 trillion dollars, and costs associated with deteriorating iron pipes is billions of dollars per year. Problems arising from iron corrosion include reduced lifetime of the material, scale buildup and energy loss, nonuniform corrosion and leaks, catastrophic failure, "red water," disinfectant loss and bacterial re-growth. Iron corrosion is a very complicated process and is affected by many factors. This research focused on the effect of disinfectant type, sulfate/chloride ratios, nitrate concentration, and magnesium hardness on iron corrosion. For the waters tested, chlorine better controlled red water and microbial activity in the bulk solution than chloramine. Changes in the sulfate/chloride ratio did not have a large effect on iron corrosion. High levels of nitrate increased the rate of chlorine decay as a result of free ammonia formation, and also increased the release of iron. Increased magnesium and zinc decreased the red water caused by high silicate. Microbiological activity is important in iron corrosion, and control of re-growth in water distribution systems is a major challenge for water utilities. A separate study examined the inter-relationship between iron corrosion and bacterial re-growth, with a special focus on the potential of iron pipe to serve as a source of phosphorus. Under some circumstances corroding iron and steel may serve as a source for all macronutrients necessary for bacterial re-growth including fixed carbon, fixed nitrogen and phosphorus. Conceptual models and experimental data illustrate that levels of phosphorus released from corroding iron are significant relative to that necessary to sustain high levels of biofilm bacteria. Consequently, it may be more difficult to limit re-growth on iron surfaces by limiting phosphorus in the bulk water. / Master of Science

Iron corrosion is the most important economic and aesthetic problem facing utilities. In the water distribution system, problems caused by iron corrosion include "red water", scale buildup, and pipe failures. It is necessary to improve our mechanistic understanding of anaerobic iron corrosion in order to better address these concerns. Experiments were conducted to investigate the effect of soluble constituents (Fe2+, PO43-, and NH4+) on H2 evolution during anaerobic iron corrosion. At pH 7.0 when sulfide was absent, variable Fe2+ did not have much influence on H2 release rates, whereas PO43- and NH4+ promoted H2 evolution. If present, soluble sulfide controlled H2 release rates in the solutions with Fe2+ or PO43-; however, NH4+ and S2- combined to inhibit H2 release. A simplistic empirical model was developed that fit data on corrosion rates from previous researchers studying effects of sulfate-reducing bacteria (SRB) on iron corrosion. As a whole, the experimental data and the model results support the notion that water quality controls iron corrosion rates in the presence of SRB. The practical relevance of previous research is somewhat in doubt given the atypical levels of nutrients used in relation to those actually present in water and wastewater. A second phase of research was aimed at exploring the equilibrium and kinetic aspects of iron corrosion in the presence of phosphate. The hypothesis that anaerobic iron corrosion is influenced by low pressure H2 (<1 atm) buildup was examined. At pH 2.75 and pH 7.0 in the presence of 100 mg/L P-PO43-, variations in H2 release were measured under different circumstances. Addition of PO43- formed a protective film, possibly vivianite Fe3(PO4)2, on the iron surface that eventually stopped H2 release. However, results were consistent with the idea that corrosion is an irreversible process that is relatively insensitive to low level H2 (<1 atm). Possible alternative explanations were provided to reconcile the past research data that purportedly demonstrated that removal of H2 increased corrosion rates. A reaction that caused "decay" of H2 in the presence of high phosphate was discovered that can not be readily explained. / Master of Science

La présente étude porte sur les problématiques d’entreposage de colis de déchets nucléaires. En France, via le projet Cigéo, il est envisagé d’entreposer les déchets radioactifs de moyenne et haute activité à vie longue à 500 mètres de profondeur dans un conteneur en acier API 5L X65 (chemisage) déposé dans des galeries creusées au sein d’une formation argileuse (argilites). Une température maximum de 90°C est attendue à la surface de l’acier en raison de l’intense radioactivité. Finalement, un coulis cimentaire (matériau de remplissage) sera injecté entre le chemisage et les argilites. La synthèse de couches de produits de corrosion susceptibles d’être rencontrées à la surface de l’acier dans les conditions de stockage a constitué le premier objectif de ce travail. Les conditions pour l’obtention de sidérite (FeCO3), de mackinawite (FeS) et de magnétite (Fe3O4) ont été déterminées. Par la suite, des essais de couplage impliquant deux électrodes recouvertes de produits différents ont été réalisés dans le but de simuler le comportement d’une surface d’acier recouverte d’une couche hétérogène de produits de corrosion. Il est apparu que l’acier recouvert d’une couche de mackinawite se comportait dans chaque cas comme une cathode. Ce phénomène est associé au caractère plutôt protecteur de la couche de mackinawite. Parallèlement, les essais de formation de la mackinawite par polarisation anodique ont montré que la formation d’une couche de produits de corrosion composée de magnétite/mackinawite était associée à un phénomène de corrosion localisée. Le comportement de l’acier au contact du matériau de remplissage envisagé pour combler l’espace entre le chemisage et les argilites a ensuite été étudié. Ce deuxième volet de l’étude a montré que la couche de produits de corrosion se formant à la surface de l’acier était principalement composée de magnétite, associée à des sulfures de fer tels que la mackinawite. L’hétérogénéité du matériau de remplissage, la présence de sulfures en son sein et la présence d’oxygène dissous dans les solutions de test sont les principales causes de l’apparition d’un phénomène de corrosion localisée. Ce résultat traduit également le caractère imparfaitement protecteur des couches d’oxyde se formant sur l’acier au contact du matériau cimentaire. Enfin, la dernière partie de ce travail de recherche a porté sur l’étude d’éventuels effets galvaniques entre une zone recouverte d’argilites et une zone recouverte de matériau de remplissage impliquant la présence de magnétite et de mackinawite et pouvant faire office de cathode. De tels effets n’ont pas été mis en évidence, ce qui est attribué à l’absence d’un véritable état passif de l’acier en contact avec le matériau cimentaire. / The present study relates to the problem of long-term disposal of nuclear waste. In France, with the Cigéo project, it is envisaged to store high and intermediate level long lived radioactive waste at a depth of 500m inside a carbon steel (API 5L X65) casing in a deep geological disposal, drilled in a very stiff clay formation. A maximum temperature of 90°C is expected at the carbon steel surface, because of the intense radioactivity. Finally, a specific cement grout will be injected between the carbon steel casing and the argilites. The synthesis of corrosion product layers likely to form on the steel surface was the first objective of this work. The different parameters to obtain siderite (FeCO3), mackinawite (FeS) and magnetite (Fe3O4) have been determined. Subsequently, coupling tests were carried out with two steel electrodes covered with different corrosion products in order to simulate the behaviour of a steel surface covered with a heterogeneous corrosion product layer. It appeared that the steel electrode covered with mackinawite was in each case the cathode. This phenomenon is associated with the somewhat protective properties of the mackinawite layer. Besides, anodic polarization experiments conducted to prepare mackinawite layers showed that the formation of a corrosion product layer composed of magnetite/mackinawite was associated with localized corrosion. The behaviour of carbon steel in contact with cement grout envisaged to fill the gap between casing and argillites was studied next. This second part of the study showed that the corrosion product layer forming on the steel surface was mainly composed of magnetite, associated with iron sulphides such as mackinawite. Heterogeneity of the cement grout, presence of sulphide within it, and presence of dissolved oxygen in the test solutions are the main causes of the appearance of localized corrosion processes. This result also shows that the oxide layers forming on the steel surface in the specific cement grout only provides an imperfect protection. Finally, the last part of this research work focused on the study of possible galvanic effects between a zone covered with argilites, and a zone covered with cement grout implying the presence of magnetite and mackinawite and thus able to act as cathode. Such effects could not be evidenced which is attributed to the absence of a real passive state of the steel in contact with the cement grout.

The impact on human health caused by lead release has resulted in stringent lead regulations, which limit the drinking water concentration of lead to 10µg/L. In order to meet regulation guidelines, sources of lead are being removed from the distribution system and premise plumbing. Lead service lines (LSLs) are replaced to minimize the effect of lead release, with LSL contributing as much as 50-75% of total lead at the tap. Adsorption of lead on galvanized iron corrosion scales have been shown to increase lead release in LSL replacements, which is very concerning for utilities considering replacing the LSLs. Adsorption of lead on to iron minerals has been hypothesized as a mechanism for lead exposure. With the significant presence of unlined cast iron pipes in Halifax, the objective of this thesis was to determine the relationship between the iron particles found in cast iron pipes and lead release at the tap.

An electrochemical investigation of the corrosion of iron and Fe18Cr based stainless steel alloys was undertaken with particular emphasis on the nucleation and growth of surface films. Chronoamperometry was shown to be a sensitive technique to investigate the initial stages of film formation and growth. In a variety of acidic (pH < 7), alkaline and alkaline cyanide electrolytes, providing dissolution of the substrate metal could occur rising current transients, similar to those reported in electrocrystallisation studies, were observed when the electrode was stepped to the appropriate potential. This indicated that at these potentials the surface film formed via the nucleation and growth of discrete nuclei. A significant aspect of this study was visual evidence of this nucleation and subsequent growth of the film provided by scanning electron microscopy which supported the electrochemical data and interpretation thereof. Existing electrocrystallisation models were used to evaluate the experimental rising current transients. While these models gave an indication as to the prevailing nucleation and growth mechanism, they were found to be inadequate in describing anodic oxide formation on an oxidising substrate. A qualitative model was proposed. In acidic electrolytes, rising chronoamperometric transients were observed for Fe, Cr and Fe18Cr at passive potentials and for FexCr (x = 16,18, 20,23% Cr) and alloys 444, 4732, 4733, 304L and 316L at transpassive potentials. The transients were shown to be sensitive to variations of potential, temperature, electrolyte and alloy composition. A systematic investigation of the influence of temperature (20 0 C - 1200 C) on the chronoamperometric, cyclic voltammetric and rotating ring - disc electrode behaviour of Fe in O.5M and 1.0M NaOH was also undertaken. In alkaline electrolytes, the formation of a duplex surface film was proposed, with x-ray photoelectron spectroscopy indicating that the protective base layer consisted of FeO while Fez03 and FeOOH constituted the upper layer. Base layer formation was favoured with increasing temperature and increasing hydroxide ion concentration of the electrolyte. Addition of OAM NaCN to O.5M and 1.0M NaOH had a marked effect on the electrochemistry of the system, with CN- inhibiting surface film formation, particularly of the upper layer. A mechanism for the oxidation of Fe in alkaline and alkaline cyanide electrolytes was proposed. / Thesis (Ph.D.)-University of Natal, 1994.