Author: David Earl MacNevin
Publisher:
ISBN:
Category : Copper
Languages : en
Pages : 143

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The effects of corrosion inhibitors on water quality and the distribution system were studied. This dissertation investigates the effect of inhibitors on iron surface roughness, copper surface roughness, and copper release. Corrosion inhibitors included blended poly/ortho phosphate, sodium orthophosphate, zinc orthophosphate, and sodium silicate. These inhibitors were added to a blend of surface water, groundwater, and desalinated brackish water. Surface roughness of galvanized iron, unlined cast iron, lined cast iron, and polyvinyl chloride was measured using pipe coupons exposed for three months. Roughness of each pipe coupon was measured with an optical surface profiler before and after exposure to inhibitors. For most materials, inhibitor did not have a significant effect on surface roughness; instead, the most significant factor determining the final surface roughness was the initial surface roughness. Coupons with low initial surface roughness tended to have an increase in surface roughness during exposure, and vice versa, implying that surface roughness tended to regress towards an average or equilibrium value. For unlined cast iron, increased alkalinity and increased temperature tended to correspond with increases in surface roughness. Unlined cast iron coupons receiving phosphate inhibitors were more likely to have a significant change in surface roughness, suggesting that phosphate inhibitors affect stability of iron pipe scales. Similar roughness data collected with new copper coupons showed that elevated orthophosphate, alkalinity, and temperature were all factors associated with increased copper surface roughness. The greatest increases in surface roughness were observed with copper coupons receiving phosphate inhibitors. Smaller increases were observed with copper coupons receiving silicate inhibitor or no inhibitor. With phosphate inhibitors, elevated temperature and alkalinity were associated with larger increases in surface roughness and blue-green copper (II) scales. Otherwise a compact, dull red copper (I) scale was observed. These data suggest that phosphate inhibitor addition corresponds with changes in surface morphology, and surface composition, including the oxidation state of copper solids. The effects of corrosion inhibitors on copper surface chemistry and cuprosolvency were investigated. Most copper scales had X-ray photoelectron spectroscopy binding energies consistent with a mixture of Cu2O, CuO, Cu(OH)2, and other copper (II) salts. Orthophosphate and silica were detected on copper surfaces exposed to each inhibitor. All phosphate and silicate inhibitors reduced copper release relative to the no inhibitor treatments, keeping total copper below the 1.3 mg/L MCLG for all water quality blends. All three kinds of phosphate inhibitors, when added at 1 mg/L as P, corresponded with a 60% reduction in copper release relative to the no inhibitor control. On average, this percent reduction was consistent across varying water quality conditions in all four phases. Similarly when silicate inhibitor was added at 6 mg/L as SiO2, this corresponded with a 25-40% reduction in copper release relative to the no inhibitor control. Hence, on average, for the given inhibitors and doses, phosphate inhibitors provided more predictable control of copper release across changing water quality conditions. A plot of cupric ion concentration versus orthophosphate concentration showed a decrease in copper release consistent with mechanistic control by either cupric phosphate solubility or a diffusion limiting phosphate film. Thermodynamic models were developed to identify feasible controlling solids. For the no inhibitor treatment, Cu(OH)2 provided the closest prediction of copper release. With phosphate inhibitors both Cu(OH)2 and Cu(PO4)·2H2O models provided plausible predictions. Similarly, with silicate inhibitor, the Cu(OH)2 and CuSiO3·H2O models provided plausible predictions.

Author: Phillip Andrew Lintereur
Publisher:
ISBN:
Category : Silicates
Languages : en
Pages : 191

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A study was conducted to investigate and quantify the effects of corrosion inhibitors on metal release within a pilot distribution system while varying the source water. The pilot distribution system consisted of pre-existing facilities from Taylor et al (2005). Iron, copper, and lead release data were collected during four separate phases of operation. Each phase was characterized by the particular blend ratios used during the study. A blended source water represented a water that had been derived from a consistent proportion of three different source waters. These source waters included (1) surface water treated through enhanced coagulation/sedimentation/filtration, (2) conventionally treated groundwater, and (3) finished surface water treated using reverse osmosis membranes. The corrosion inhibitors used during the study were blended orthophosphate (BOP), orthophosphate (OP), zinc orthophosphate (ZOP), and sodium silicate (Si). This document was intended to cite the findings from the study associated with corrosion treatment using various doses of sodium silicate. The doses were maintained to 3, 6, and 12 mg/L as SiO2 above the blend-dependent background silica concentration. Sources of iron release within the pilot distribution system consisted of, in the following order of entry, (1) lined cast iron, (2) un-lined cast iron, and (3) galvanized steel. Iron release data from these materials was not collected for each individual iron source. Instead, iron release data represented the measurement of iron upon exposure to the pilot distribution system in general. There was little evidence to suggest that iron release was affected by sodium silicate. Statistical modeling of iron release suggested that iron release could be described by the water quality parameters of alkalinity, chlorides, and pH. The R2 statistic implied that the model could account for only 36% of the total variation within the iron release data set (i.e. R2 = 0.36). The model implies that increases in alkalinity and pH would be expected to decrease iron release on average, while an increase in chlorides would increase iron release. The surface composition of cast iron and galvanized steel coupons were analyzed using X-ray photoelectron spectroscopy (XPS). The surface analysis located binding energies consistent with Fe2O3, Fe3O4, and FeOOH for both cast iron and galvanized steel. Elemental scans detected the presence of silicon as amorphous silica; however, there was no significant difference between scans of coupons treated with sodium silicate and coupons simply exposed to the blended source water. The predominant form of zinc found on the galvanized steel coupons was ZnO. Thermodynamic modeling of the galvanized steel system suggested that zinc release was more appropriately described by Zn5(CO3)2(OH)6. The analysis of the copper release data set suggested that treatment with sodium silicate decreased copper release during the study. On average the low, medium, and high doses decreased copper release, when compared to the original blend source water prior to sodium silicate addition, by approximately 20%, 30%, and 50%, respectively. Statistical modeling found that alkalinity, chlorides, pH, and sodium silicate dose were significant variables (R2 = 0.68). The coefficients of the model implied that increases in pH and sodium silicate dose decreased copper release, while increases in alkalinity and chlorides increased copper release. XPS for copper coupons suggested that the scale composition consisted of Cu2O, CuO, and Cu(OH)2 for both the coupons treated with sodium silicate and those exposed to the blended source water. Analysis of the silicon elemental scan detected amorphous silica on 3/5 copper coupons exposed to sodium silicate. Silicon was not detected on any of the 8 control coupons. This suggested that sodium silicate inhibitor varied the surface composition of the copper scale.

Author: Erica D. Stone
Publisher:
ISBN:
Category : Drinking water
Languages : en
Pages : 188

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This study evaluated the effects of orthophosphate (OP) inhibitor addition on iron, copper, and lead corrosion on coupons exposed to different blends of groundwater, surface water, and desalinated seawater. The effectiveness of OP inhibitor addition on iron, copper, and lead release was analyzed by statistical comparison between OP treated and untreated pilot distribution systems (PDS). Four different doses of OP inhibitor, ranging from zero (control) to 2 mg/L as P, were investigated and non-linear empirical models were developed to predict iron, copper, and lead release from the water quality and OP doses. Surface characterization evaluations were conducted using X-ray Photoelectron Spectroscopy (XPS) analyses for each iron, galvanized steel, copper, and lead/tin coupon tested. Also, a theoretical thermodynamic model was developed and used to validate the controlling solid phases determined by XPS. A comparison of the effects of phosphate-based corrosion inhibitor addition on iron, copper, and lead release from the PDSs exposed to the different blends was also conducted. Three phosphate-based corrosion inhibitors were employed; blended orthophosphate (BOP), orthophosphate (OP), and zinc orthophosphate (ZOP). Non-linear empirical models were developed to predict iron, copper, and lead release from each PDS treated with different doses of inhibitor ranging from zero (control) to 2 mg/L as P. The predictive models were developed using water quality parameters as well as the inhibitor dose. Using these empirical models, simulation of the water quality of different blends with varying alkalinity and pH were used to compare the inhibitors performance for remaining in compliance for iron, copper and lead release. OP inhibitor addition was found to offer limited improvement of iron release for the OP dosages evaluated for the water blends evaluated compared to pH adjustment alone. Empirical models showed increased total phosphorus, pH, and alkalinity reduced iron release while increased silica, chloride, sulfate, and temperature contributed to iron release. Thermodynamic modeling suggested that FePO4 is the controlling solid that forms on iron and galvanized steel surfaces, regardless of blend, when OP inhibitor is added for corrosion control. While FePO4 does not offer much control of the iron release from the cast iron surfaces, it does offer protection of the galvanized steel surfaces reducing zinc release. OP inhibitor addition was found to reduce copper release for the OP dosages evaluated for the water blends evaluated compared to pH adjustment alone. Empirical models showed increases in total phosphorus, silica, and pH reduced copper release while increased alkalinity and chloride contributed to copper release. Thermodynamic modeling suggested that Cu3(PO4)2·2H2O is the controlling solid that forms on copper surfaces, regardless of blend, when OP inhibitor is added for corrosion control. OP inhibitor addition was found to reduce lead release for the OP dosages evaluated for the water blends evaluated compared to pH adjustment alone. Empirical models showed increased total phosphorus and pH reduced lead release while increased alkalinity, chloride, and temperature contributed to lead release. Thermodynamic modeling suggested that hydroxypyromorphite is the controlling solid that forms on lead surfaces, regardless of blend, when OP inhibitor is added for corrosion control. The comparison of phosphate-based inhibitors found increasing pH to reduce iron, copper, and lead metal release, while increasing alkalinity was shown to reduce iron release but increase copper and lead release. The ZOP inhibitor was not predicted by the empirical models to perform as well as BOP and OP at the low dose of 0.5 mg/L as P for iron control, and the OP inhibitor was not predicted to perform as well as BOP and ZOP at the low dose of 0.5 mg/L as P for lead control. The three inhibitors evaluated performed similarly for copper control. Therefore, BOP inhibitor showed the lowest metal release at the low dose of 0.5 mg/L as P for control of iron, copper, and lead corrosion.

Author: Marc Edwards
Publisher: American Water Works Association
ISBN: 1583210865
Category : Chemical inhibitors
Languages : en
Pages : 170

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The researchers warn that their findings may not apply in every situation, and that much more research needs to be done. They inquire into such questions as whether polyphosphate reversion is likely to be significant in water distribution systems, how important particulate lead and copper corrosion

Author: Young C. Kang
Publisher:
ISBN:
Category :
Languages : en
Pages : 244

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The following work is the study to evaluate the impact of corrosion inhibitors on the copper metal in drinking water and to investigate the corrosion mechanism in the presence and absence of inhibitors. Electrochemical experiments were conducted to understand the effect of specific corrosion inhibitors in synthetic drinking water which was prepared with controlled specific water quality parameters. Water chemistry was studied by Inductively Coupled Plasma--Atomic Emission Spectroscopy (ICP--AES) to investigate the copper leaching rate with time. Surface morphology, crystallinity of corrosion products, copper oxidation status, and surface composition were characterized by various solid surface analysis methods, such as Scanning Electron Microscopy/Energy--Dispersive Spectrometry (SEM/EDS), Grazing-Incidence-angle X-ray Diffraction (GIXRD), X-ray Photoelectron Spectroscopy (XPS), and Time-of-Flight Secondary Ions Mass Spectrometry (ToF-SIMS). The purpose of the first set of experiments was to test various electrochemical techniques for copper corrosion for short term before studying a long term loop system. Surface analysis techniques were carried out to identify and study the corrosion products that form on the fresh copper metal surface when copper coupons were exposed to test solutions for 2 days of experiments time. The second phase of experiments was conducted with a copper pipe loop system in a synthetic tap water over an extended period of time, i.e., 4 months. Copper release and electrochemically measured corrosion activity profiles were monitored carefully with and without corrosion inhibitor, polyphosphate. A correlation between the copper released into the solution and the electrochemically measured corrosion activities was also attempted. To investigate corrosion products on the copper pipe samples, various surface analysis techniques were applied in this study. Especially, static mass spectra acquisition and element distribution mapping were carried out by ToF-SIMS. Dynamic SIMS provided shallow depth profile of corroded copper sample. The third set of the experiments was related to electrochemical noise (EN) measurement through copper coupons to pipes. Calculating corrosion rate of a metal and predicting exactly how long it lasts are problematic since the metal corrosion may be caused by combined corrosion types. Many other metals undergo not only uniform corrosion, but localized corrosion. Uniform corrosion may be conducive for copper pipe to prevent it from further severe corrosion and form passivated film, but localized corrosion causes pinhole leaks and limits the copper pipe applications. The objective of this set of experiment is to discuss the application of electrochemical noise approaches to drinking water copper corrosion problems. Specially, a fundamental description of EN is presented including a discussion of how to interpret the results and technique limitations. Although it was indicated with electrochemical analysis that the corrosion activity was affected by orthophosphate addition in the short-term test, no copper-phosphate complex or compound was found by copper surface characterization. Apparently, orthophosphate can inhibit corrosion by adsorption on the copper surface, but cannot form solid complexes with copper in such a short time, 2 days. When polyphosphate was added into recirculating copper pipe system, copper level increased and polarization resistance decreased. Greenish blue residue on the copper pipe was suspected as copper phosphate complex and corrosion inhibition mechanism was proposed.

Author: AWWA Staff
Publisher: American Water Works Association
ISBN: 1613001177
Category : Corrosion and anti-corrosives
Languages : en
Pages : 213

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Author: Xiaotao Guan
Publisher:
ISBN:
Category : Corrosion and anti-corrosives
Languages : en
Pages : 180

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The second article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total iron release in a changing water quality environment. Development of empirical models as a function of water quality and ZOP inhibitor dose for total iron release and mass balances analysis for total zinc and total phosphorus data provided insight into the mechanism of ZOP corrosion inhibition regarding iron release in drinking water distribution systems. The third article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total copper release in a changing water quality environment. Empirical model development was undertaken for prediction of total copper release as a function of water quality and inhibitor dose. Thermodynamic models for dissolved copper based on surface characterization of scale that were generated on copper coupons exposed to ZOP inhibitor were also developed. Surface composition was determined by X-ray Photoelectron Spectroscopy (XPS). The fourth article describes the effects of zinc orthophosphate (ZOP) corrosion inhibitor on total lead release in a changing water quality environment. Surface characterization of lead scale on coupons exposed to ZOP inhibitor by X-ray Photoelectron Spectroscopy (XPS) was utilized to identify scale composition. Development of thermodynamic model for lead release based on surface analysis results provided insight into the mechanism of ZOP inhibition and the role of zinc.

Author: Abdulrahman Ali Alshehri
Publisher:
ISBN:
Category : Drinking water
Languages : en
Pages : 200

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The impact of blended orthophosphate (BOP) inhibitor addition on the corrosion of iron, copper, and lead in drinking water distribution systems was studied under changing water quality environment. Release of iron, copper, and lead were monitored at varying inhibitor doses and changing blends of source waters (groundwater, surface water, and desalinated water). Solid corrosion products on pipe surfaces under BOP treatment were evaluated with surface characterization techniques. Performance of the BOP inhibitor was compared to other corrosion control strategies. Iron scales for iron and galvanized steel coupons incubated in different blended waters in the presence of BOP inhibitor were analyzed by X-ray Photoelectron Spectroscopy (XPS) for surface composition. Identified iron corrosion products were ferric oxide (Fe2O3), magnetite (Fe3O4), and hydrated ferric oxide (FeOOH), in addition to ferric phosphate (FePO4) on coupons exposed to BOP inhibitor. Variations of water quality did not significantly affect the distribution of solid iron forms on surface films. Thermodynamic modeling indicated siderite (FeCO3) was the controlling solid phase of iron release. XPS indicated addition of BOP inhibitor produced a solid phosphate film in the iron scale which could inhibit iron release. Impact of BOP, orthophosphate, and pH adjustment on iron release in a distribution system was examined. Iron release was sensitive to water quality variations (alkalinity and chloride) associated with source and blends of finished water. Finished waters with high alkalinity content (between 149 and 164 mg/L as CaCO3) consistently mitigated iron release regardless of inhibitor use. Dissolved iron constituted about 10% of total iron release. Empirical models were developed that related water quality, inhibitor type and dose to iron release. The BOP inhibitor minimized total iron release followed closely by increasing pH (between 7.9 and 8.1), while orthophosphate dose did not affect iron release. Temperature (ranged from 21.2 to 25.3) had limited influence on iron release with BOP treatment. Monitoring copper release showed that dissolved copper was the dominant form in the effluent, at about 88%. BOP inhibitor doses of 0.5 to 2.0 mg/L proved beneficial in controlling copper concentrations to an average of below 0.5 mg/L. Control of copper release improved with increasing BOP dose, despite changes in alkalinity. Elevation of pH by 0.3 unit beyond pHs (between 7.9 and 8.1) resulted in noticeable decrease in copper concentrations of about 30%, but was more sensitive to higher alkalinity (146 to 151 mg/L as CaCO3) than BOP treatment. Developed empirical models confirmed the importance of BOP inhibitor dose, pH increase, and alkalinity content on copper release. Statistical comparison of the corrosion control strategies proved the advantage of BOP inhibitor, at all doses, over pH elevation in controlling copper release. The BOP inhibitor mitigated lead release below action level, and consistently outperformed pH elevation, in all water quality conditions. XPS analysis identified lead dioxide (PbO2), lead oxide (PbO), cerussite (PbCO3), and hydrocerussite (Pb3(CO3)2(OH)2) as the corrosion products in the scale of lead/tin coupons exposed to BOP inhibitor. XPS and Scanning Electron Microscopy (SEM) analysis suggested cerussite or hydrocerussite is the controlling solid phase of lead release. Thermodynamic models for cerussite and hydrocerussite grossly over predicted actual concentrations. Solubility and equilibrium relationships suggested the possibility of a lead orthophosphate solid that would describe the effectiveness of BOP inhibitor, although no lead-phosphate solid was detected by surface analysis. BOP inhibitor appeared to have mitigated lead release by forming a surface film between lead scale and the bulk water.

Author:
Publisher: DIANE Publishing
ISBN: 1428900160
Category :
Languages : en
Pages : 54

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Author:
Publisher: American Water Works Association
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 738

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