The Effect of Chloride and Sulfate on the Mineralogy and Morphology Of

THE EFFECT OF CHLORIDE AND SULFATE ON THE MINERALOGY AND MORPHOLOGY OF

SYNTHETICALLY PRECIPITATED COPPER SOLIDS

Thesis

Submitted to

The School of Engineering of the

UNIVERSITY OF DAYTON

In Partial Fulfillment of the Requirements for

The Degree of

Master of Science in Civil Engineering

Lisa Nicole Melton

Dayton, OH

December, 2013

i THE EFFECT OF CHLORIDE AND SULFATE ON THE MINERALOGY AND MORPHOLOGY OF

SYNTHETICALLY PRECIPITATED COPPER SOLIDS

Name: Melton, Lisa Nicole

APPROVED BY:

______Denise Taylor, Ph.D., P.E. Kenya Crosson, Ph.D. Advisory Committee Chairman Committee Member Assistant Professor Assistant Professor Department of Civil and Environmental Department of Civil and Environmental Engineering and Engineering Mechanics Engineering and Engineering Mechanics

______Darren Lytle, Ph.D., P.E. Committee Member Acting Branch Chief (TTEB) & Environmental Engineer U.S. Environmental Protection Agency

______John G. Weber, Ph.D. Tony E. Saliba, Ph.D. Associate Dean Dean, School of Engineering School of Engineering & Wilke Distinguished Professor

ii ABSTRACT

THE EFFECT OF CHLORIDE AND SULFATE ON THE MINERALOGY AND MORPHOLOGY OF

SYNTHETICALLY PRECIPITATED COPPER SOLIDS

Name: Melton, Lisa Nicole University of Dayton

Advisor: Dr. Denise Taylor

Since the implementation of the Lead and Copper Rule in 1991, multiple studies have been completed to explain, predict and mitigate the problems of copper corrosion. Water chemistry is a leading factor in initiating corrosion and a number of parameters have been postulated to be responsible, including pH, alkalinity, chloride and sulfate.

The purpose of this research is to identify aqueous conditions that support the formation of copper corrosion by-products found in distribution systems. Specifically, this work attempted to understand: 1) the role of aggressive ions, chloride and sulfate, in the formation synthetically precipitated particles; 2) the effect of aging on solubility and morphology; 3) evaluate morphology associated with solids. Precipitation experiments were conducted at pH seven and nine, with varied dissolved inorganic carbon (10, 50 mg C/L), and ratios of chloride and sulfate at 1:1, 5:1 and 1:5. Copper was added as cupric perchlorate solution at a concentration of 15 mg/L. Analysis of solubility, mineralogy, and morphological changes were conducted over three months using induced coupled argon plasma spectrometry, x-ray diffraction and scanning electron microscope.

iii This research generally supports results previously reported in literature: high pH conditions over a range of DIC levels favor the formation of tenorite (CuO). High DIC, neutral pH water favors formation of malachite [Cu2(CO3)(OH)2] and experience higher solubility levels. The effect of chloride and sulfate was most evident at low pH, low DIC conditions where connellite

[Cu19SO4Cl4(OH)32*3H2O], langite [Cu4(OH)6SO4H2O] and an unidentified mineral were formed.

The effect of aging was evident through x-ray diffraction as particles transitioned from amorphous to slightly crystalline. This transition was most evident within 28 days of precipitation, which also correlated to a reduction in solubility. Microscopy analysis provided confirmation on the morphology habits associated with tenorite, malachite, connellite and langite. In additional tenorite and malachite were compared to scale from distribution systems and were comparable in surface features, size and habit.

iv ACKNOWLEDGEMENTS

I thank my committee members, Dr. Denise Taylor, Dr. Darren Lytle and Dr. Kenya

Crosson for their support, time, insight and direction. I would not have been able to complete this without their guidance and patience. I express my appreciation to Christy Muhlen, Colin

White and Alyssa O’Donnell for their assistance in the lab and data collection for this research.

I am deeply appreciative to Dr. Joe Saliba and Mace Cofield for their support and continued encouragement in the pursuit of graduate studies. I am particularly grateful to Hazen and Sawyer for affording the time to complete this process and my many co-workers who offered valuable insight and assistance.

I dedicate this work to my mother, Beatrice Antoinette Melton and my sister Dr.

Michelle Melton. Without their love, strength and reassurance, I would not have been able to achieve all that I have. Thank you for encouraging me to start and complete the journey.

v TABLE OF CONTENTS

ABSTRACT ...... iii ACKNOWLEDGEMENTS ...... v LIST OF FIGURES ...... viii LIST OF TABLES ...... x LIST OF ABBREVIATIONS AND NOTATIONS ...... xi CHAPTER 1: INTRODUCTION ...... 1 1.1 PROBLEM STATEMENT ...... 1 1.2 BACKGROUND ...... 1 1.3 EXPERIMENT OBJECTIVES ...... 3 CHAPTER 2: LITERATURE REVIEW ...... 4 2.1 SIGNIFICANCE ...... 4 2.2 DOMESTIC PLUMBING AND CONSUMER IMPACTS ...... 5 2.3 REGULATORY MONITORING ...... 5 2.4 COPPER CORROSION, PASSIVATION AND IMMUNITY ...... 6 2.5 COPPER CORROSION SOLIDS ...... 8 2.6 FORMS OF COPPER CORROSION ...... 10 2.7 FACTORS AFFECTING COPPER CORROSION ...... 12 2.8 CORROSION MANAGEMENT ...... 13 2.9 RESEARCH OBJECTIVE ...... 14 CHAPTER 3: IMPACT OF WATER CHEMISTRY ON SYNTHETICALLY PRECIPITATED COPPER PARTICLES ...... 15 ABSTRACT ...... 15 3.1 BACKGROUND ...... 16 3.2 MATERIAL AND METHODS ...... 18 3.3 RESULTS AND DISCUSSION ...... 20

vi 3.4 CONCLUSIONS ...... 28 CHAPTER 4: CHARACTERIZATION AND MORPHOLOGY OF SYNTHETICALLY PRECIPITATED COPPER PARTICLES ...... 30 ABSTRACT ...... 30 4.1 INTRODUCTION ...... 31 4.2 MATERIAL AND METHODS ...... 33 4.3 RESULTS AND DISCUSSION ...... 36 4.4 CONCLUSIONS ...... 54 CHAPTER 5: CONCLUSION AND RECOMMENDATIONS ...... 56 REFERENCES ...... 59 APPENDIX A ...... 61 APPENDIX B ...... 64 APPENDIX C ...... 65 APPENDIX D ...... 74 APPENDIX E ...... 119

vii LIST OF FIGURES

Figure 2– 1: Regions of Corrosion, Passivation, and Immunity for Copper at 25oC...... 7

Figure 2– 2: Potential-pH Equilibrium Diagram for Copper in Water System at 25oC.

From Nguyen, 2005...... 8

Figure 2 – 3: Autocatalytic Process Occurring in Pitting Corrosion ...... 11

Figure 3 – 1: Jar Test Experiment Set-up ...... 18

Figure 3 – 2: Water Chemistry at pH 7 at Day Zero ...... 21

Figure 3 – 3: Water Chemistry at pH 9 at Day Zero. (*Experimental condition

at pH=9, DIC=50 mg/L, varied from targeted water chemistry) ...... 21

Figure 3 – 4: Copper Solubility at pH 7 and DIC 10 mg C/L ...... 22

Figure 3 – 5: Copper Solubility at pH 7 and DIC 50 mg C/L ...... 24

Figure 3 – 6: Copper Solubility at pH 9 and DIC 10 mg C/L ...... 26

Figure 3 – 7: Copper Solubility at pH 9 and DIC 50 mg C/L (*Experiment condition

varied from targeted water chemistry) ...... 27

Figure 4 – 1: XRD Spectra of Blank Filter and Experiment 6 at Initial Precipitation ...... 39

Figure 4 – 2: XRD Spectra of Connellite (Experimental Run 1) at 28 Days ...... 41

Figure 4 – 3: Connellite (Experimental Run 1) at 28 Days ...... 42

Figure 4 – 4: Experiment 2 (71-2010) SEM at 28 days ...... 43

Figure 4 – 5: Experiment 2 (71-2010) XRD Spectra at 28 days ...... 44

Figure 4 – 6: SEM for Malachite, Experiment 5 (75-1020) at 28 days ...... 46

viii Figure 4 – 7: XRD Spectra for Malachite, Experiment 5 (75-1020) at 28 days ...... 47

Figure 4 – 8: SEM for Tenorite (a) Experiment 9 (91-1020) and (b) Experiment 10 (91-2010) at 28 days ...... 48

Figure 4 – 9: XRD Spectra for Tenorite in Experiment 10 (91-2010) at 28 days ...... 49

Figure 4 – 10: SEM Images of Malachite from Distribution Piping (a, b) (O’Donnell and

Lytle 2008) and Precipitation Experiments (c, d) ...... 52

Figure 4 – 11: SEM Images of Tenorite from Distribution Piping (a, b) (O’Donnell and

Lytle 2008) and Precipitation Experiments (c, d) ...... 53

ix LIST OF TABLES

Table 2 – 1: Copper Corrosion Minerals ...... 9

Table 3 – 1: Target Water Quality Conditions ...... 19

Table 4 – 1: Target Test Conditions ...... 34

Table 4 – 2: Solids Water Quality Conditions ...... 37

Table 4 – 3: Mineralogy Results from X-ray Diffraction ...... 38

Table 4 – 4: Mineralogy with Age ...... 40

x LIST OF ABBREVIATIONS AND NOTATIONS

Cl- Chloride Cu Copper

. Cu19Cl4(SO4)(OH)32 3H20 Connellite

Cu(OH)2 Cupric Hydroxide

Cu2O Cuprite

Cu4(OH)6SO4H20 Langite

Cu(CO)3(OH)2 Malachite CuO Tenorite CDA Copper Development Association DIC Dissolved Inorganic Carbon LCR Lead and Copper Rule MIC Microbiologically Induced Corrosion SEM Scanning Electron Microscopy

2- SO4 Sulfate TEM Transmission Electron Microscopy XRD X-ray Diffraction

xi CHAPTER 1

INTRODUCTION

1.1 PROBLEM STATEMENT

The purpose of this research project is to investigate the effect of pH, dissolved inorganic carbon

(DIC), chloride and sulfate on corrosion by-products associated with copper pipelines. Localized corrosion, or “pitting” corrosion, is a major cause of household plumbing failure. In relatively short periods of time, corrosion propagation leads to pipe failure in the form of pinhole leaks, resulting in costly repairs and water damage. Water chemistry is a leading factor in initiating corrosion and a number of parameters have been postulated to be responsible, including pH, alkalinity, chloride, silica, bicarbonate and sulfate (Duthil et al. 1996). The scope of this research will focus on the synergetic effects of aggressive ions, chloride and sulfate, in forming pitting corrosion products.

1.2 BACKGROUND

Copper piping is a common material in home plumbing systems, offering a lighter, stronger and cheaper alternative to other metals. Although copper is insoluble in pure water, pipe in contact with oxidizing environments will experience corrosion until equilibrium is established. This degradation can be uniform or localized and varies based on the water quality parameters, copper pipe characteristics and use of corrosion inhibitors (Merkel 2006). Uniform corrosion is

1 typical of new piping installations which form a highly soluble cupric oxide film (cuprite) when exposed to aerated water sources. Corrosion continues until the scale comes into equilibrium with the surrounding environment, forming a protective barrier on the pipe surface. Research has shown that the soluble copper levels may exceed the 1.3 mg/L action level established by the Lead and Copper Rule, during the formation of this passivating layer. The ramifications of high levels of dissolved copper include gastrointestinal distress, liver and kidney damage. Efforts to minimize uniform corrosion include raising the pH of the treated water or the addition of corrosion inhibitors at the treatment facility.

Copper distribution systems are also susceptible to non-uniform corrosion (pitting). Pitting occurs where there has been a disruption in the protective scale allowing non-uniform loss of material on the pipe surface. Pitting is one of the most destructive forms of corrosion, resulting in a small percentage of metal loss that compromises the integrity of pipeline. Pinhole leaks can cause extensive home damage to drywall and set-up conditions for mold growth. Repairs associated with plumbing failure can be extensive and time consuming, resulting in lost time from work, emotional stress and significant cost. It is estimated that pinhole leak repairs and prevention costs in the United States is nearly $930 million a year (Scardina et al. 2007).

Reliably establishing the underlying source of pitting corrosion in a drinking water distribution system is complicated. Aggressive anions (e.g. chloride and sulfate) have been shown to affect the protective nature on the internal surfaces of pipes and have documented corrosion affects individually (Cong et al. 2009; Duthil et al. 1996; Lytle and Schock 2008; Schock et al. 1999).

Chloride has been shown to initiate pits, and has been documented by the Copper Development

Associate as the largest cause of failure in cold water pipes (Farooqi, 2006). Sulfate also exhibits aggressive corrosion of copper and may be a more influential anion than chloride, since copper sulfate byproducts are very soluble (Cong, 2009). Electrochemical studies also confirm 2 that when both anions are present, they can have either an accelerating or inhibiting effect depending on the relative concentrations of chloride and sulfate (Mankowski et al. 1997; Duthil et al. 1996).

1.3 EXPERIMENT OBJECTIVES

This research is intended to advance knowledge in the field related to the competing effect of chloride and sulfate on corrosion by-product development, over time. Four specific questions were considered:

1. Can we spontaneously precipitate similar minerals formed in areas of localized

corrosion? Do extreme water quality conditions (high anion concentrations) aid in the

synthesis of particles? What is the nature of these solids?

2. What is the effect of aging on mineral identification and morphology? Does chloride or

sulfate affect the aging process?

3. Does cuprosolvency change over time due to pH, dissolved inorganic carbon, chloride or

sulfate?

4. How well do synthetically precipitated solids coincide with the morphology and

mineralogy of actual distribution system scale?

This work combines elements of a tradition thesis, including an introduction (Chapter 1) and summary of literature (Chapter 2). Chapters 3 and 4 are written as complete manuscripts for submission to peer reviewed journals (Environmental Science & Technology; Journal American

Water Works). Each article includes an overview of methods, results, discussion and conclusions. Final conclusions and recommendations are presented in Chapter 5.

3 CHAPTER 2

LITERATURE REVIEW

2.1 SIGNIFICANCE

In the USA, approximately 90% of home distribution systems use copper pipelines (Loganathan and Lee 2005). Copper piping is highly favored for potable plumbing because of its availability, ease of installation, affordability and durability. While copper has a high corrosion resistance, it can be susceptible to uniform and localized corrosion which negatively impact consumers with blue-water, high soluble copper levels or leaks.

Copper leaching from water distribution systems has been a major concern over the past decades, mainly attributed to more stringent regulations and rising consumer expectations.

Dissolution of copper scales is the main mechanism by which copper is liberated to drinking water (Schock et al 1995). In new pipes, internal pipe scale favors highly soluble material such as cuprite and cupric hydroxide, which can exceed the Lead and Copper Rule (LCR) action level of 1.3 mg/L (Federal Register 1991a,b). Ingestion of excessive copper levels can cause nausea, cramping, vomiting in the gastrointestinal tract, and cirrhosis of the liver (USEPA 2004). In more established potable plumbing systems, disturbances in the internal copper scale can suspend particulate that cause staining of home fixtures, turbid water and a metallic taste.

Copper is also susceptible to pinhole leaks or pitting corrosion. Pitting is both costly and problematic, causing a small percentage of metal loss that impacts the usable lifespan of a system. It is estimated that the total cost of pinhole leaks and pinhole leak prevention in the US

4 is $930 million annually, with more than 50% of the cost ($564 million) due to single family home repairs (Scardina et al. 2007). This represents a sizable investment for homeowners, who may also experience mental stress, lost time from work or a reduction in property value. End users who encounter pinhole leaks may also choose to replace large portions of their home distribution piping or add point of use treatment systems that may not permanently mitigate the problem. It is estimated that the occurrence of pinhole leaks is significantly under reported because copper pitting is typically not associated with a regulatory violation and there is no compliance issue to report (Lytle and Schock 2008).

2.2 DOMESTIC PLUMBING AND CONSUMER IMPACTS

Utilities and municipalities are responsible to assess and maintain service mains associated with water distribution systems. Buried utility infrastructure is estimated to represent nearly

1,409,800 km of piping in the United States (Kock et al. 2002); however, residential plumbing in buildings and homes, is estimated to far exceed this value (Longanathan and Lee 2005). When leaks are detected, the responsibilities for repairs often fall on businesses or homeowners. Very few sources exist for connecting incidences of pitting corrosion in communities. Despite the large cost associated with pitting corrosion leaks, reporting of pinhole leaks is often understated, mainly because copper pitting is typically not associated with a regulatory violation and there is no noncompliance issue to report (Lytle and Schock 2008).

2.3 REGULATORY MONITORING

A number of regulations exist to monitor drinking water systems and limit constituents of concern which may impact public health. Copper is monitored by the Lead and Copper Rule

(LCR) under the Safe Drinking Water Act of 1986. Copper is a beneficial enzyme necessary for normal metabolic functions, and is found in shellfish, nuts, organ meats and dried legumes. The

LCR seeks to limit exposure to high concentrations of copper which may cause stomach and 5

intestinal distress, liver and kidney damage (long term exposure) and danger to people with

Wilson’s disease (USEPA 2004).

The LCR, first published in 1991, was enacted to protect public health by reducing water corrosivity. The ruling set into effect an action level of 1.3 mg/L for copper, based on 90th percentile level (or 10%) of tap water samples. If copper levels are above the action levels, requirements such as water quality parameter monitoring, corrosion control treatment and public education are implemented. Samples are collected on a 6-month basis unless the system qualifies for reduced monitoring on an annual or triennially basis. Revisions to the LCR in 2000 and 2007 provided revised analytical methods, and streamlined report/record keeping requirements. It also required water suppliers to submit advanced notification of changes in water treatment plans to evaluate effects on distribution system water quality.

2.4 COPPER CORROSION, PASSIVATION AND IMMUNITY

Copper may exist in water in either the monovalent copper (+1) (cuprous) or divalent copper

(+2) (cupric) state. The (+2) form of copper is highly soluble in aqueous conditions while (+1) copper is unstable and will rapidly oxidize to Cu (+2) or will reduce to copper metal through the reactions noted in equation 2.1 and 2.2.

Cu(s)  Cu+ + e- (eqn 2.1)

Cu+  Cu2+ + e- (eqn 2.2)

The corrosion of copper in an aqueous environment is a function of the pH and oxidation potential of a solution. When exposed to aqueous environments copper has three (3) potential states – passivation, corrosion or immunity. The Pourbaix diagrams presented in Figures 2-1 and

2-2 are useful for predicting chemical equilibrium of copper in water. Oxidation potential (Eh) is graphed against pH and regions of corrosion, passivation and immunity are demarcated by the heavy black lines. The dashed lines outline the stability boundary of water (at 1 atm). Positive 6

values of pE indicate oxidizing regions and negative values are reducing regions. Combinations of pE and pH that form oxidized protective layers are labeled as passive. Areas of immunity are where copper is thermodynamically stable.

Figure 2– 1: Regions of Corrosion, Passivation, and Immunity for Copper at 25oC

Copper and its alloys belong to a group of materials that form a kinetically stable passive film in neutral pH environments. As shown in Figure 2 – 2 the protective copper oxide films cuprite

(Cu2O) and tenorite are preferred in oxidizing/alkaline regions. In very low or high pH

2+ - environments copper corrodes into soluble ions Cu or CuO2 , respectively. When exposed to reducing environments copper is stable.

Figure 2– 2: Potential-pH Equilibrium Diagram for Copper in Water System at 25oC. From

Nguyen, 2005.

2.5 COPPER CORROSION SOLIDS

When exposed to aqueous environments copper will corrode, passivate (form protective barrier) or remain immune. Due to the noble nature of copper, it will readily precipitate a passivating layer in oxidizing environments. Most often on fresh Cu pipe this protective layer is

Cu2O (cuprite) per equation 2.3. Cuprite is not thermodynamically stable, and forms in a narrow range of oxidation potential (Eh), as shown in Figure 2-2. Instead Cu (+1) will rapidly oxidize to

Cu (+2), to form cupric hydroxide (equation 2.2). In typical distribution systems, the dissolution of cuprite is incomplete leaving a duplex layer of cuprite near the metal surface followed by cupric hydroxide.

+ + 2Cu + H20  Cu2O (s) + 2H (eqn 2.3) Cuprite 8

+2 + Cu + 2H20  Cu(OH)2 (s) + 2H (eqn 2.4) Cupric Hydroxide Cupric hydroxide has a relatively high solubility and will transition to a more thermodynamically stable solid with time. The aging process of copper involves the re-crystallzation and dehydration of copper hydroxide into tenorite (CuO) and the slow formation of malachite

[Cu(CO3)(OH)2] in pH ranges below tenorite’s general stability boundary (Schock et al. 1995).

Malachite forms preferentially at a pH range less than 7, while tenorite precipitates in a pH range of 7-9. The associated formation of tenorite and malachite are noted in equations 2.3 –

2.4.

Cu(OH)2 (s)  CuO(s) + H2O (eqn 2.5) Tenorite + 2- + 2Cu + 2H20 + CO3  Cu2(OH)2CO3 (s) + 2H (eqn 2.6) Malachite

The most common copper compounds found on pipe walls are cuprite (Cu2O), tenorite (CuO), malachite [Cu2(CO3)(OH)2], langite [Cu4(SO4)(OH)6.2(H2O)], atacamite [Cu2(OH)3Cl], brochantite

[Cu4(SO4)(OH)6 ] , azurite [2CuCO3Cu(OH)2 ], and cupric hydroxide [Cu(OH)2)] (Lagos 2001).

Additional corrosion products associated with the interaction of copper with ions in drinking water are note in Table 2-1.

Table 2 – 1: Copper Corrosion Minerals Mineral Formula Copper metal Cu Cuprite Cu2O Cupric Hydroxide Cu(OH)2 Tenorite CuO Malachite Cu2(CO3)(OH)2 Nantokite CuCl Copper (II) hydroxy-chloride -

Copper Hydroxide Sulfate Hydrate Cu4(SO4)(OH)6.2(H2O)

Brochantite Cu4(SO4)(OH)6 Langite Cu4(SO4)(OH)6.2(H2O) Posnjakite Cu4(SO4)(OH)6.(H2O)

2.6 FORMS OF COPPER CORROSION

Many types of corrosion exist, however the types most affected by water quality are presented below, including: uniform, pitting, tuberculation and microbiologically induced corrosion. The kind of attack depends on the pipe material, the construction of the system, and the scale/ oxide film formation (Schock 1999).

2.6.1 Uniform Corrosion

Uniform corrosion is categorized as an attack occurring over the entire surface of an object. This type of corrosion is associated with the slow loss (thinning) of piping material. Uniform corrosion is easily monitored and there is ample warning when components must be replaced.

In domestic distribution systems, uniform corrosion is rarely the source of pipe failure. In severe cases, uniform corrosion may result in “blue/green-water” from colloidal particulate or an increase in soluble copper levels. The potential for leaching of copper increases in stagnant conditions as copper scale dissolves and comes into equilibrium with the aqueous environment.

Internal plumbing exposed to corrosive water have a likelihood of elevated levels at the tap. As noted in previous studies (Schock et al. 1995, 1999), uniform corrosion rapidly increases with decreasing pH (<6). At higher pH (>7), the rate of uniform corrosion is low, and localized corrosion becomes the dominant mechanism.

2.6.2 Pitting Corrosion

Non-uniform (pitting corrosion) corrosion is an area of localized attack quantified by a pitting factor: (P/d), where P is the deepest metal penetration and d is the average metal penetration.

Localized corrosion is a major concern for homeowners, although the mechanisms involved are not well understood. Copper pitting is generally regarded as a two-step process in which pits are first initiated and then gradually penetrate through a metal surface. Pitting requires the presence of an anode and cathode which are electrically connected and immersed in a 10

conductive electrolyte (Figure 2 – 1). Imperfections or breakdowns on the surface of passivating scale, establishes an anode where copper is oxidized and cuprous (+1) copper is released into solution. The neighboring cathode experiences reduction as electrons travel to the surface. Negatively charged anions are attracted to the pit to counterbalance the presence of metal ions. Pitting corrosion is autocatalytic (self-propagating) in nature and continues until the system fails or the tubercle provides a protective barrier.

Figure 2 – 3: Autocatalytic Process Occurring in Pitting Corrosion

2.6.3 Tuberculation

Tuberculation is an extension of pitting corrosion. As copper becomes pitted, tubercle deposits of basic cupric carbonate, sulfate or chlorides salts buildup at the anode resulting in reduced internal surface area of a pipe. While tubercle accumulation in copper pipes is often small (0.5 -

2 mm) typical residential plumbing is small (¼ to 1-inch o.d.), resulting in significant loss of cross sectional area. Tuberculation is often associated with poorly buffered waters, where pH can become extremely high under localized surface conditions (Schock 1999). Tuberculation is minimized with sufficient alkalinity in a system.

11 2.6.4 Microbiologically Induced Corrosion

Microbiologically induced corrosion (MIC) occurs in environments where bacteria thrive on nutrients in the water. MIC typically occurs at the farthest points of the distribution system, at dead ends and a low points where water stagnates, sediment accumulates and disinfection residuals are low (AWWA 2011). Reduction in total organic carbon, and natural organic matter have been shown to lessen MIC activity (Schock 1999).

2.7 FACTORS AFFECTING COPPER CORROSION

Factors affecting internal corrosion of copper pipe lines fall within two (2) categories – physical and chemical parameters. Physical factors include pressure, velocity and temperature of the operating system. Chemical parameters encompass pH, alkalinity, hardness, dissolved oxygen, chloride, sulfate, nitrate and aluminum. The focus of this study includes pH, dissolved inorganic carbon, chloride and sulfate, which are discussed in more detail below.

2.7.1 DIC and pH

Dissolved inorganic carbon (DIC) is the sum of all dissolved inorganic carbon containing species and is one of the most critical parameters to controlling internal corrosion (AWWA 2011). DIC is composed of bicarbonate, carbonate and dissolved carbon dioxide gas as shown in equation 2.4, and is measured in milligrams of carbon per liter. DIC is an indicator of buffer capacity and is required to maintain a constant pH in a distribution system. Studies have shown that as DIC concentrations increase, cuprosolvency increases.

2- DIC = [H2CO3] + [HCO3] + [CO3 ] (eqn 2.4)

The activity of hydrogen ions, H+, is a critical parameter in the formation of uniform and localized corrosion. Often pH is the controlling factor in the formation of copper oxide and copper carbonate minerals. Low pH can directly increase the solubility of metals, while high pH 12

conditions enhance the formation of uniform corrosion scales. For pitting corrosion, pH is an important parameter and in the absence of passivating coatings can encourage pitting between a pH of 5-9 (Schock 1999).

2.7.2 Chloride and Sulfate

2- Both Cl- and SO4 are aggressive anions that have the ability to accelerate corrosion in copper, by interfering with the formation of normal oxide or hydroxycarbonate passive films (Schock

1999). The formation of chloride is the result of disinfection with gaseous or solid chlorine as shown in equation 2.5. Researchers have repeatedly identified chloride as the major culprit leading to copper pitting; and reports by the CDA support copper induced pitting as the largest cause of failure in cold water pipes (Farooqi 2006). Chlorine has been shown to reduce the formation of protective layers by competing with other oxidizing agents (e.g. dissolved oxygen) in the formation of passiviation barriers.

- - Cl2 + 2e  2Cl (eqn 2.5)

Sulfate has also been identified as an active anion in pitting. Sources of sulfate in finished water stem from coagulants and coagulate aids used in drinking water treatment. Sulfate is more active, than chloride, in pitting corrosion due to the formation of highly soluble copper sulfate minerals (e.g. brochantite [Cu4(OH)6(SO4)]). Together sulfate and chloride can form a synergetic effect, in causing pitting, as noted by previous research by Mankowski et al. (1997).

2.8 CORROSION MANAGEMENT

While corrosion inhibitors were not an express part of this work, it is worth noting that various techniques are often employed by utilities to rectify pitting and uniform corrosion issues for end users. Corrosion management is an area of continued development as researchers attempt to optimize treatment technologies with minimal impacts on distribution piping. Sequestering of 13

copper is usually accomplished through corrosion inhibitors or water quality modifications.

Many utilities (20%) utilize an orthophosphate based inhibitor, which is very effective on copper

(Rushing et al. 2002). Orthophosphate is also used regularly by utilities; but is ineffective outside a pH range of 7.0 – 8.0.

Water quality adjustments to pH and DIC have been very successful in controlling copper corrosion. Minimal cost is often associated with pH modifications, with a dual benefit of optimizing the environment for corrosion inhibitors. Caustic soda (sodium hydroxide), soda ash, potassium hydroxide, and aeration/air stripping are principal methods for increasing pH (AWWA

2011). Employing water chemistry adjustment, whether it is corrosion inhibitor addition, pH adjustment, or DIC adjustment, requires a commitment to continually maintaining a consistent operation (Schock 1995).

2.9 RESEARCH OBJECTIVE

The objective of this work is to further examine the role of chloride, sulfate, pH and DIC on copper corrosion byproducts. An attempt is made to synthesize the conditions which form common Cu compounds found in domestic copper plumbing. Special attention is paid to the aging process, morphology and solubility impacts of solids precipitated in the presence of aggressive anions (chloride and sulfate). It is the intent to elucidate the competing effects of chloride and sulfate over a range of pH and DIC values.

14 CHAPTER 3

IMPACT OF WATER CHEMISTRY ON SYNTHETICALLY PRECIPITATED COPPER PARTICLES

ABSTRACT

Water chemistry is a leading factor in initiating copper corrosion and a number of parameters have been postulated to be responsible. This study attempts to examine the role of chloride, sulfate, pH and DIC on copper solubility. Special attention is paid to the aging process and solubility impacts of samples precipitated in the presence of aggressive anions (chloride and sulfate). Precipitation experiments were conducted, over pH seven and nine, with varied dissolved inorganic carbon (10, 50 mg/L), and ratios of chloride and sulfate at 1:1, 5:1 and 1:5.

Water quality parameters, pH and DIC are significant factors in controlling the solubility of copper.

High pH conditions reduced copper solubility in addition to low DIC levels. Chloride and sulfate appear to provide some benefit to reducing cuprosolvency at initial precipitation, as exhibited in all test conditions. The effect of chloride and sulfate during aging was variable. Under low pH/low DIC conditions chloride and sulfate appear to enhance solubility, in particular at ratios favoring sulfate concentrations. Low pH/high DIC conditions exhibited an increase in solubility

(due to DIC levels), but chloride and sulfate reduced cuprosolvency after 28 days. The effect of chloride and sulfate at high pH/low DIC conditions was ambiguous; while at high pH/high DIC chloride and sulfate do not have a distinguishable affect.

3.1 BACKGROUND

As the use of domestic copper plumbing has increased, issues related to localized corrosion

(pitting) and uniform corrosion (blue water) have become widely researched topics. Since the implementation of the Lead and Copper Rule (LCR) in 1991 (Federal Register 1991 a,b), multiple studies have been completed to explain, predict and mitigate the problems of copper corrosion.

The LCR requires systems to control the corrosiveness of their water by limiting soluble copper levels to 1.3 mg/L in 10% of tap water samples. Water chemistry is a critical component to controlling scale solubility, particulate suspension and pinhole leaks.

Interior corrosion of copper surfaces can be uniform or localized. Due to the noble nature of copper, it will readily precipitate a passivating layer in oxidizing environments. This film is a protective coating on the interior of the pipe and continues to form until equilibrium is reached with the surrounding environment. In younger copper plumbing cuprite (Cu20) and cupric hydroxide [Cu(OH)2] are often detected, as monovalent copper is oxidized to a divalent state as referenced below as an excerpt from background provided in Chapter 2 .

+ + 2Cu + H20  Cu2O (s) + 2H (eqn 2.3) Cuprite +2 + Cu + 2H20  Cu(OH)2 (s) + 2H (eqn 2.4) Cupric Hydroxide

Typically the dissolution of cuprite is incomplete leaving a duplex layer of cuprite near the metal surface followed by cupric hydroxide. Dissolution of copper scales is the main mechanism by which copper is liberated to drinking water (Schock et al. 1995).

During the aging process soluble copper levels are reduced in solution as surface minerals undergo phase change and precipitate to the most stable solid. In established (aged) distribution systems tenorite and malachite are often present (Lytle and Schock 2008; Edwards

1994). The interaction of various ions present in the aqueous environment can also affect the

2- copper solids formed as systems transition to steady state. Both Cl- and SO4 are aggressive anions that have the ability to accelerate corrosion in copper. Chloride has been shown to reduce the formation of protective layers, by competing with other oxidizing agents (e.g. dissolved oxygen) in the formation of passiviation barriers (Edwards 1994; Cong 2009; Farooqi

2006). Research by Lytle and Schock (2008) has suggested that water with high pH and chlorine are aggressive in the formation of pits. Likewise, Duthil et al (1996) found that chloride and sulfate have synergistic effects on copper corrosion, and that varying the chloride sulfate concentration can have an accelerating or inhibiting influence.

Localized corrosion poses a unique set of issues. While pitting corrosion does not result in increased copper levels, it is problematic as fully-penetrating pinholes burden consumers with the cost of repairs and associated damage. The mechanism of copper pitting is generally regarded as a two-step process in which pits are first formed (e.g. initiation) and then gradually penetrates through a metal surface (e.g., propagation) (Sarver, 2012). Pits can initiate at specific locations, including imperfections or breakdowns in the passive film layer that naturally occurs on copper surfaces in potable water or under particulate deposits that have settled into the pipe surface. Studies have shown that potable water sources with varying concentrations of dissolved inorganic carbon (DIC), pH, and chloride to be catalyst in the formation of pitting corrosion in copper pipe loop studies (Lytle and Schock 2008; Rushing 2002; Sarver et al. 2012).

The objective of this work is to further examine the role of chloride, sulfate, pH and DIC on copper solubility. An attempt is made to synthesize the aqueous conditions under which Cu corrosion is observed in domestic copper plumbing. Special attention is paid to the aging process and solubility impacts of samples precipitated in the presence of aggressive anions

(chloride and sulfate). It is the intent to elucidate the competing effects of chloride and sulfate over a range of pH and DIC values.

3.2 MATERIAL AND METHODS

3.2.1 Procedure

Jar testing was conducted in 3L of deionized water, with motorized mixing and automated pH monitoring (Figure 3 – 1). A 2 x 2 x 4 sample matrix was created varying pH, dissolved inorganic carbon, chloride and sulfate (Table 3 – 1). Controls were created without chloride and sulfate.

Reagent grade chemicals were used for experiments. Sodium bicarbonate was added as the source of dissolved inorganic carbon, sulfate was added as sodium sulfate and chloride was added as sodium chloride. Copper was added as cupric perchlorate, from stock solution to give an initial copper concentration of 15 mg/L. The pH was monitored and held constant (+/- 0.1 su) through a Hach Company (Loveland, CO) EC40 benchtop pH/ISE meter (Model 50125) and pH electrode (Model 48600). Calibration was completed daily using pH 7 and 10 standard solutions.

The computer controlled titrator system added small increments of nitric acid (0.5N) and potassium hydroxide (0.6N) to maintain constant pH. The solution was mixed for 30 minutes, at

20 rpm, during which time particle formation was observed.

Figure 3 – 1: Jar Test Experiment Set-up

Table 3 – 1: Target Water Quality Conditions

Condition Description Copper 15 mg/L of Cu 7 s.u. pH 9 s.u. 10 mg C/L Alkalinity 50 mg C/L 5:1 with Chloride concentration of 1000 mg/L, Sulfate concentration of 200 mg/L 1:5 with Chloride concentration of 200 mg/L, Chloride-Sulfate Sulfate concentration of 1000 mg/L

Ratio 1:1 L with Chloride concentration of 200 mg/L, Sulfate concentration of 200 mg/L

1:1 H Chloride concentration of 800 mg/L, Sulfate concentration of 800 mg/L

3.2.2 Water Chemistry Analysis

At the end of 30-minutes, 160 mL of sample was removed for anion analysis. The following analytical methods were used to confirm water quality: chloride (ion chromatography, EPA

Method 300.0), sulfate and copper (ICAP, EPA Method 200.7) and total inorganic carbon

(coulometric, ASTM method D-513-92). Sample volumes included 60 mL for chloride and sulfate, 60 mL for copper and 40 mL for total inorganic carbon.

The copper sample was further divided to measure for total and soluble concentrations. Total copper was quantified in an unfiltered sample while soluble copper was filtered through a 0.20

µm inorganic membrane syringe filter with polypropylene housing to separate colloidal copper.

The inorganic membrane filters contained a pre-filter which was found to adsorb copper.

Solubility samples were repeated under the target water quality conditions and filtered through a 0.20 µm, 25 mm polypropylene filter with polypropylene housing. No additional sorption of copper or other ions was observed. Filtered and non-filtered samples were acidified prior to analysis with 0.15 percent nitric acid to a pH of 2.0.

Remaining jar test volumes from each test condition were stored in 250 mL HDPE bottles at 21oC to study the effects of aging. A bottle from each experiment was removed for analysis on day 0,

7, 28, 60 and 90. The pH of each solution was measured prior to removing aliquots for water chemistry analysis as noted above.

3.2.3 Other Methods

Glassware used for standards and solutions were cleaned using a 5% solution of detergent. All glassware was thoroughly rinsed with deionized water. Reused glassware was immediately cleaned by soaking in 10% (v/v) concentrated HNO3 and rinsed with deionized water. Air displacement micropipettes with disposable tips were used for handling and transferring solutions.

3.3 RESULTS AND DISCUSSION

3.3.1 Water Chemistry

Measured water chemistry from each test condition at day zero is noted in Figures 3-2 and 3-3.

Raw data for all tables is shown in Appendix A. Chloride and sulfate ratios of 1:1L (200 mg/L);

1:1H (800 mg/L); 1:5 (200 mg/L:1000 mg/L) and 5:1 (1000 mg/L:200 mg/L) were used.

Figure 3 – 2 confirms samples for pH 7 met target conditions. For pH 9 (Figure 3 – 3) target values varied in one case, at pH = 9, DIC = 50 mg/L with an intended chloride sulfate ratio of 5:1

(1000 mg/L Cl-; 200 mg/L SO4). ICAP analysis revealed that chloride-sulfate concentrations were

190.5 mg/L and 893.7 mg/L respectively, reflecting a ratio of 1:5. Results for this sample are compared to the 1:5 ratio.

1200 pH = 7 pH = 7 DIC = 10 mg/L as C DIC = 50 mg/L as C 1000

800

600 Chloride Sulfate 400 Concentration,mg/L DIC

200

Chloride: Sulfate Mass Ratio

Figure 3 – 2: Water Chemistry at pH 7 at Day Zero

1200 pH = 9 pH = 9 DIC = 10 mg/L as C DIC = 50 mg/L as C 1000

800

600 Chloride

400 Sulfate Concentration,mg/L DIC 200

0 *

Chloride: Sulfate Mass Ratio

Figure 3 – 3: Water Chemistry at pH 9 at Day Zero. (*Experimental condition at pH=9, DIC=50 mg/L, varied from targeted water chemistry)

3.3.2 Solubility and Aging

Soluble copper concentrations were evaluated to determine the effects of pH, DIC, chloride and sulfate on minerals. The solubility of passivating films on the pipe surface is the most important factor in determining whether a given water quality can meet many drinking water regulations based on the health effects of ingested metals (Schock 1999).

Low pH / Low DIC: The solubility of copper particles at pH 7 and DIC of 10 mg C/L are shown in

Figure 3-4. Soluble copper levels initially exceeded the LCR action level of 1.3 mg/L in all test conditions. The control sample (generated without the presence of chloride or sulfate) is anticipated to form malachite over time (Shock et al. 1995), which is thermodynamically favored in low pH conditions.

10.0 5:1 Chloride Sulfate Ratio 1:5 Chloride Sulfate Ratio 1:1 L Chloride Sulfate Ratio 1:1H Chloride Sulfate Ratio Control USEPA copper action level = 1.3 mg/L

1.0

0.1 Soluble Copper, Soluble mg/L Cu

0.0 0 10 20 30 40 50 60 70 80 90 100 Elapsed Time, Days

Figure 3 – 4: Copper Solubility at pH 7 and DIC 10 mg C/L

As particles age, solubility steadily decreased over the course of the three (3) months. Samples transitioned to a soluble concentration below the copper action level within 12 days. The effect of chloride and sulfate is evident throughout the aging process. At day zero, chloride and sulfate provide reduced cuprosolvency levels (20-40% reduction), compared with the control. Copper solubility levels remain highest in the presence of high sulfate concentration (ratio 1:5). In the presence of equal concentrations of chloride and sulfate (1:1 L and 1:1 H) the trends follow closely together and solubility is slightly below the high sulfate concentration in the mass ratio of 1:5. At day 60 the chloride sulfate ratio of 5:1, 1:5 and 1:1 appear to interchange. The presence of high chloride concentration (ratio 5:1) results in the second lowest solubility levels.

In general, samples with chloride and sulfate experience copper levels twice the control concentration. The presence of sulfate appears to have a greater influence in increasing soluble copper levels. While samples follow the general aging pattern, sulfate concentrations equal or greater to the presence of chloride do not transition to a low solubility state. It can be anticipated that distribution systems with high chloride and sulfate ratios at pH 7 and DIC = 10 mg/L would require longer timelines for aging. There is also a potential for higher copper concentrations at the tap, due to the delayed formation of stable passivating films. This data confirms previous research (Cong 2009) copper sulfates exhibit a higher solubility than copper chlorides.

Low pH / High DIC: The solubility of copper particles at pH 7 and DIC of 50 mg C/L are shown in

Figure 3-5. Soluble copper levels initially exceeded the LCR action level of 1.3 mg/L in all test conditions. With the increase in DIC, soluble copper increased to nearly twice the levels associated with 10 mg C/L of DIC. As noted by Schock (1999) and Lytle & Schock (2008), distribution systems with high DIC concentrations typically experience higher soluble copper

levels. The solubility of samples decreases with time as a result of aging. Samples experience the largest decrease in solubility within the first seven (7) days of aging (concentration reduction of 70%). Within four (4) days solubility concentrations are at or below the copper action level.

The aging process in this experiment appears to have accelerated in the presence of 50 mg C/L of DIC.

10.00

USEPA copper action level = 1.3 mg/L

1.00 5:1 Chloride Sulfate Ratio 1:5 Chloride Sulfate Ratio 1:1 L Chloride Sulfate Ratio 1:1H Chloride Sulfate Ratio Control

Soluble Copper, Soluble mg/L Cu 0.10

0.01 0 10 20 30 40 50 60 70 80 90 100 Elapsed Time, Days

Figure 3 – 5: Copper Solubility at pH 7 and DIC 50 mg C/L

Test conditions continued to experience a reduction in solubility with age, and by day 60 are below 0.10 mg/L. The control (created in the absence of chloride and sulfate) provides a benchmark for aging over time and is predicted to form malachite (Shock et al. 1995) over the aging process. The effect of chloride and sulfate are less distinguishable at higher DIC concentrations. Initially samples with chloride and sulfate provide a 30% reduction in solubility

compared to the control. At day seven chloride sulfate ratios of 1:5 (200 mg/L: 1000 mg/L) and

1:1H (800 mg/L) have solubility values slightly above the control. The presence of chloride and sulfate appear to enhance reduction in copper solubility after 30 days where values remain below control. Compared to pH 7 and DIC of 10 mg/L, chloride and sulfate appear to contribute to lower solubility levels after day 30, at a DIC of 50 mg/L.

Based on this study, a DIC concentration of 50 mg/L in neutral aqueous environments would experience quicker reductions in solubility. Municipalities may choose to increase DIC in their finished water to enhance carbonate protective film formation (passivating layer) on distribution piping. This decision must be balanced with available carbonate in the system to prevent precipitation of calcium in pipes, in particular hot water distribution lines in homes or hot water circuits. At chloride and sulfate ratios used in this study additional benefit is gained in reducing solubility. It can be anticipated that distribution systems with high chloride and sulfate ratios at pH 7 and DIC = 50 mg/L would experience low copper concentrations at the tap.

High pH/Low DIC: The solubility of copper particles at pH 9 and 10 mg C/L of DIC is shown in

Figure 3-6. Samples generated at pH 9 had a lower copper solubility than pH 7 conditions. This trend coincides with work by Shock (1999), Farooqi (2006), Grace (2012) and Edwards (1994;

1999) where high pH conditions promote a reduction in solubility. At initial precipitation copper solubility levels were below the LCR action level, with the exception of ratio 5:1 with a concentration of 2.8 mg/L. The trends experienced over the course of aging are highly variable, in particular during the first 28 days. Solubility concentrations at day 7 were not analyzed for ratios of 1:5, 1:1L and 1:1H. In addition, the peaks exhibited in the control (day 7) and ratio 5:1

(day 28) are attributed to breakthrough of copper particles during filtering. After day 28 the solubility trends become more consistent and can be compared. The control (generated

without the presence of chloride or sulfate) is anticipated to form tenorite over time, which is thermodynamically favored in high pH-oxidizing conditions (Shock et al. 1995). Samples containing chloride and sulfate had a lower solubility than the control between day 28-90.

While samples increase slightly in solubility at the end of the experiment, the concentration remains low. The presence of chloride and sulfate appear to provide some benefit in later points of aging.

10.0 5:1 Chloride Sulfate Ratio 1:5 Chloride Sulfate Ratio 1:1 L Chloride Sulfate Ratio 1:1H Chloride Sulfate Ratio 91-control USEPA copper action level = 1.3 mg/L

1.0

Soluble Copper, Soluble mg/L Cu 0.1

0.0 0 10 20 30 40 50 60 70 80 90 100 Elapsed Time, Days

Figure 3 – 6: Copper Solubility at pH 9 and DIC 10 mg C/L

High pH/High DIC: The solubility of copper particles at pH 9 at 50 mg C/L DIC are shown in

Figure 3-7. In the presence of high pH, soluble copper levels precipitated below the LCR action level of 1.3 mg/L. The control (created in the absence of chloride and sulfate) provides a benchmark for aging over time and is predicted to form tenorite (Shock et al. 1995). At day zero

the control has a slightly higher solubility, just above 1.0 mg/L of copper, before concentrations drop to a similar concentration of the other samples. During aging all experimental runs experience a reduction in solubility. The largest decrease in solubility occurs during the first 28 days of aging, where solubility decreases by a factor of three. After 60 days a slight reduction in chloride sulfate ratios (5:1, 1:5 and 1:1h) are observed. As noted in the water chemistry data at this test condition the ratio of 5:1 is similar to 1:5. Sample 5:1 is represented in the data as *1:5.

Both *1:5 and 1:5 ratios follow similar trends, with a standard deviation of 0.29 and 0.30 respectively, over 90 days. All four (4) chloride and sulfate mass ratios exhibit similar aging trends. Based on experimentation, the presence of chloride and sulfate in high pH and high DIC conditions does not readily appear to inhibit copper solubility. In practice utilities typically increase pH in the distribution system to reduce occurrences of corrosion.

10.0 *1:5 Chloride Sulfate Ratio 1:5 Chloride Sulfate Ratio 1:1 L Chloride Sulfate Ratio 1:1H Chloride Sulfate Ratio Control USEPA action level = 1.3 mg/L

1.0

0.1 Soluble Copper, Soluble mg/L Cu

0.0 0 10 20 30 40 50 60 70 80 90 100 Elapsed Time, Days

Figure 3 – 7: Copper Solubility at pH 9 and DIC 50 mg C/L (*Experiment condition varied from targeted water chemistry)

3.4 CONCLUSIONS

In summary, pH and DIC are significant factors in controlling the solubility of copper. As noted in previous research, increasing pH reduces copper solubility while increasing DIC increases copper solubility. Chloride and sulfate appear to provide some benefit to reducing cuprosolvency at initial precipitation, as exhibited in all test conditions. The effect of chloride and sulfate during aging was variable. Under low pH/low DIC conditions chloride and sulfate appeared to impede solubility, in particular at ratios favoring sulfate concentrations. Low pH and high DIC conditions exhibited an increase in solubility; however, the presence of chloride and sulfate enhanced reduction of solubility after 28 days. At high pH-high DIC levels chloride and sulfate do not affect solubility levels. The effect of chloride and sulfate mass ratio at high pH/low DIC conditions was ambiguous.

The pH of a distribution system is a key parameter of concern which should be closely monitored by municipalities to maintain optimal operation of public and private systems. Based on this research, distribution systems operating at lower pH ranges can expect to experience higher solubility levels than operating in alkaline conditions. The presence of DIC to buffer pH also affects the internal corrosion of copper and formation of stable passivating films. High DIC levels (50 mg/L) are predicted to increase copper solubility by an order of magnitude over low

DIC conditions. DIC levels should be balanced with pH to prevent precipitation of calcium carbonate in a system.

The presence of chloride and sulfate in distribution systems has varying affects. In low pH water with lower buffering capacity, chloride and sulfate impeded the formation of stable passivating films from forming. In low pH, high DIC conditions chloride and sulfate appeared to enhance lower solubility conditions. This is likely a result of exhausting the carbonate ion in low

DIC conditions, allowing chloride and sulfate to electron acceptors in the process. The presence

of chloride and sulfate, as noted in previous work, is nearly always associated in one way or another with all forms of pitting (Lytle and Schock 2008). Systems operating with high levels of chloride and sulfate, should consider additional treatment methods to prevent taste and odor issues (e.g. salinity) and corrosion of distribution system piping.

CHAPTER 4

CHARACTERIZATION AND MORPHOLOGY OF SYNTHETICALLY PRECIPITATED COPPER

PARTICLES

ABSTRACT

Precipitation experiments were conducted at varied pH, dissolved inorganic carbon (DIC) and chloride and sulfate ratios to evaluate the effect of water chemistry in producing corrosion byproducts found in distribution systems. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the morphology and mineralogy of particles and to evaluate changes induced by water chemistry and aging. Twelve of the experiments yielded uniform corrosion minerals (tenorite and malachite), while the other four varied in copper- chloride/sulfate composition forming solids atypical of potable water distribution systems.

Particles evolved slowly from amorphous (poorly crystalline) to slightly crystalline, but did not reach a highly crystalline state during the 90 day experiment. SEM provided insight on surface features and particle size to elucidate XRD information. Morphology coincided with previously published habits of tenorite (massive), malachite (botryoidal/stalactitic), and connellite

(acircular). Microscopy analysis was valuable in clarifying the presence of connellite

[Cu19SO4Cl4(OH)32.3H2O] and langite [CU4(OH)6SO4H20] which were unexpected to form; while illuminating the effect of chloride and sulfate on tenorite (CuO) and malachite [CuCO3.Cu(OH)2] formation.

4.1 INTRODUCTION

4.1.1 Background

Copper Rule (LCR). The LCR sets into effect an action level of 1.3 mg/L for copper, based on 90th percentile level (or 10%) of tap water samples (Federal Register 1991a,b). Understanding the water chemistry that promotes uniform and localized corrosion helps utilities in managing water quality and protecting public health.

The incidence of corrosion in copper distribution systems can be costly. It is estimated that the total cost of pinhole leaks and pinhole leak prevention in the US is $930 million annually, with more than 50% of the cost ($564 million) due to single family home repairs (Scardina et al.

2007). This represents a sizable investment for homeowners, who may also experience mental stress, lost time from work or a reduction in property value.

When studying copper corrosion, in particular pitting corrosion, the effect of water chemistry can have a significant impact on the condition of the distribution system. Parameters such as pH and DIC are critical in minimizing soluble copper levels at consumer taps. Ions such as chloride and sulfate, are influential in the formation of pitting byproducts in residential systems

(Cong 2012).

The objective of this work is to further examine the role of chloride, sulfate, pH and DIC on copper corrosion byproducts. An attempt is made to synthesize the conditions which form

common Cu compounds found in domestic copper plumbing. Special attention is paid to the aging process, morphology and microscopy of solids precipitated in the presence of aggressive anions (chloride and sulfate). It is the intent to elucidate the competing effects of chloride and sulfate over a range of pH and DIC values

4.1.2 Solids Analysis

X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques were employed in analyzing solids precipitated during jar tests and subsequent aging of particles over 90 days.

XRD and SEM provide valuable information on the mineralogy and morphology of particles formed to help understand aqueous conditions that promote corrosion.

XRD is a rapid analytical technique used to study crystal structures and atomic spacing, allowing for identification of crystalline materials. Two types of XRD are available – single crystal and powder. Single-crystal analysis is a non-destructive analytical technique that provides detailed information about the internal lattice of solid crystal. Powder diffraction uses finely pulverized or powdered samples mounted on a thin film. Both types of XRD operate through three basic components: an x-ray tube, sample holder and x-ray detector. In this research powder XRD was utilized for specimen identification. A sample was placed on a flat plate and mounted in the sample stage perpendicular to the x-ray beam. The x-ray tube scans over the sample through a range of theta, which allows all possible diffraction directions of the lattice to be obtained. As the incident beam makes an angle theta with the fixed crystal plane, a diffracted beam is generated at an angle of 2-theta. The diffracted rays are captured by the detector and are subsequently processed and counted. Experimental data of importance from XRD include: the position of the diffraction peaks, the peak intensity and the intensity distribution as a function of diffraction angle. This allows simple phase identification of minerals. The counts of each peak are graphed on the y-axis (labeled intensity) against the diffraction angle. Diffraction peaks for

crystals are converted to d-spacing which are unique for each crystal and can be compared to standard reference patterns for identification.

SEM imaging was also used as a secondary analysis method following XRD. Microscopy images helped confirm mineralogy and to observe the influence of water quality (pH, DIC, chloride and sulfate) on particle shape, size and surface structure. SEM has a magnification range of x 10 to x 1,000,000 with a resolution of 0.5 nm. SEM operates on two basic principles: electron irradiation and magnification. The machine is comprised of an electron gun, lenses, cathode ray tube (CRT) and video signal amplifier. The electron gun produces a finely focused electron beam that interacts with atoms on the sample surface. Samples are mounted within a vacuum chamber that permits stable operation of the electron beam. As the beam scans the specimen in both the x-and y-directions, electrons and x-rays are emitted and converted into an electric signal. The signal is amplified by lenses and fed into the CRT (electron detector) for image observation. Image quality was controlled by setting the accelerating voltage (15 kV) and signal output to secondary electrons (SEI) for topographical observation of the surface.

4.2 MATERIAL AND METHODS

4.2.1 Research Design

Jar testing was chosen as the means of mineral formation to better understand water quality parameters (pH, dissolved inorganic carbon, chloride and sulfate) that may lead to uniform and pitting corrosion products. This study combines the results of water chemistry with solids analysis (XRD and SEM) to evaluate the mineralogy and morphology of precipitates formed.

Samples were monitored over the course of three (3) months to better understand the role of aging in copper corrosion.

4.2.2 Procedure

Jar testing was conducted in 3L of deionized water with an automated pH monitoring system and motorized mixing. A 2 x 2 x 4 sample matrix was created varying pH, dissolved inorganic carbon, chloride and sulfate (Table 4 – 1). Reagent grade chemicals were used for experiments.

Sodium bicarbonate was added as the source of dissolved inorganic carbon, sulfate was added as sodium sulfate and chloride was added as sodium chloride. Copper was added as cupric perchlorate, Cu(ClO4)2*6H20, to give an initial copper concentration of 15 mg/L. Chloride and sulfate concentrations selected for the experiment matrix were an order of magnitude higher than typical distribution systems, to simulate pitting conditions. Areas subject to localized corrosion can experience high anion concentrations as negatively charged ions attempt to counterbalance the release of Cu metal, creating a localized water chemistry altered from the bulk water solution.

Table 4 – 1: Target Test Conditions

Ratio 1:1 L with Chloride concentration of 200 mg/L, Sulfate concentration of 200 mg/L

1:1 H Chloride concentration of 800 mg/L, Sulfate concentration of 800 mg/L

The pH was monitored and held constant (+/- 0.1 su) through a Hach Company (Loveland, CO)

EC40 benchtop pH/ISE meter (Model 50125) and pH electrode (Model 48600). Calibration was

completed daily using pH 7 and 10 standard solutions. The computer controlled titrator system added small increments of nitric acid (0.5N) and potassium hydroxide (0.6N) to maintain constant pH. The solution was mixed for 30 minutes, at 20 rpm, during which time particle formation was observed. Due to the size of the sample matrix and duration of monitoring, water quality and solids analysis were not run in replicate.

4.2.3 Water Chemistry Analysis

At the end of 30-minutes, 160 mL of sample was removed to confirm water chemistry: alkalinity

(Standard Method 2320b.4.6), chloride (ion chromatography, EPA Method 300.0), sulfate and copper (ICAP, EPA Method 200.7) and total inorganic carbon (coulometric, ASTM Method D-513-

92). Sample analysis required 40 mL for alkalinity, 60 mL for chloride and sulfate, 60 mL for copper and 40 mL for total inorganic carbon. An additional aliquot was prepared for solids analysis, prior to storing solution for aging.

4.2.4 Solids Analysis

Solids analysis was conducted at day 0, 14, 28, 60 and 90. XRD and SEM were used to evaluate mineralogy and morphology. XRD specimens were prepared from an aliquot of 100 mL filtered on 0.20 µm polycarbonate filters. Particulate was analyzed on a Scintag XDS-2000 theta-theta diffractometer (Scintag, Inc. Santa Clara, CA) with CuKa radiation x-ray tube operated at 35 kV,

40 mA. Scans were performed over a 2-theta range between 5 and 90o with a step of 0.02o with a 1-s count time at each step. Pattern analysis was performed using Jade+ software v.7

(Materials Data, Inc.) with reference to the 1995-2002 ICDD PDF-2 data files (International

Center for Diffraction Data, Newtown Square, PA). A portion of the XRD filter was removed after scanning and mounted on a 12-mm diameter aluminum stud for SEM analysis. A JEOL

(model JSM-6490LV) with accelerating voltage of 15KeV was used for imaging.

4.2.5 Aging

Remaining jar test volumes from each test condition were stored in 250 mL HDPE bottles at 21oC to study the effects of aging. A bottle from each experiment was removed for analysis on day 0,

7, 28, 60 and 90. The pH of each solution was measured prior to removing aliquots for water chemistry and solids analysis. Solid particulate usually adhered to the side of the container, therefore each bottle was sonicated prior to filtering the remaining volume for analysis. Filtered particulate was photographed and visual observations were noted, as discussed in the results.

4.2.6 Other Methods

4.3 RESULTS AND DISCUSSION

4.3.1 Water Chemistry

Sixteen experimental runs were generated under varying pH, DIC, chloride and sulfate conditions. The initial water quality conditions for each sample condition are noted in Table 4-2, in addition to the assigned identification label. Sample identification was generated as a combination of six numbers, indicating the pH, DIC, chloride and sulfate concentrations. The first number in the series specifies pH, followed by DIC as either 1 = 10 mg C/L or 5 = 50 mg C/L.

The 4 digit combination after the dash identifies chloride concentration, followed by sulfate concentration where 10, 20 or 80 represent 1000 mg/L, 200 mg/L and 800 mg/L, respectively.

By example, a sample labeled as 71-1020, indicates a target water chemistry of pH = 7,

DIC = 10 mg/L, chloride = 1000 mg/L and sulfate = 200 mg/L. All samples were created with 15 mg/L of copper.

Table 4 – 2: Solids Water Quality Conditions

Initial - -2 Cl SO4 Final Exp pH DIC ID pH Run (t=30 [mg/L] (t=90 day) min) [mg/L] [mg/L] 1 71-1020† 7.01 na* 61.8 203.7 7.37 2 71-2010 6.93 na* 193.7 984.5 7.25 3 71-2020 7.08 na* 186.2 202.8 7.53 4 71-8080 6.93 na* 780.6 773.0 7.20 5 75-1020‡ 7.96 49.9 na* 210.5 na* 6 75-2010 7.02 38.9 na* 1010.5 7.68 7 75-2020 7.02 45.2 195.5 201.0 7.84 8 75-8080 7.06 47.5 na* 816.4 7.71 9 91-1020 8.91 10.5 953.9 206.5 na* 10 91-2010 8.91 10.1 191.8 1021.8 7.94 11 91-2020 8.91 na* na* 199.9 8.13 12 91-8080 8.90 9.8 na* 808.8 7.83 13 95-1020 8.91 52.0 na* 198.1 8.10 14 95-2010 8.91 49.1 193.8 1009.4 8.74 15 95-2020 8.91 49.4 192.3 199.5 8.74 16 95-8080 8.91 49.0 779.9 812.7 8.89 * na - not analyzed † Chloride concentration varied from target of 1000 mg/L Cl- ‡ pH value varied from target of 7.0 s.u.

Experiment pH was monitored over the course of trials (Appendix B). Variations were noted as samples aged over 90 days. The pH of samples with a target value of 7.0 generally increased while the samples at the target pH of 9.0 decreased. This shift is indicative of a transition in mineral phase as alkalinity is consumed in the formation of particles. Literature has noted the critical role of pH in the formation of copper corrosion by-products (Schock et al. 1995; Edwards et al., 1994; Lytle et al. 2008) as fluctuations in pH values can significantly affect the mineral phase. Effort was taken to minimize this affect by creating air tight seal. It was observed that experiment 1 and 5 differed from the targeted chloride and pH values, respectively.

Experiment 1 (71-1020) had a chloride concentration of 61.8 mg/L, approximately one tenth of the proposed concentration. Sample 5 (75-1020) was generated at a pH of 7.69, slightly higher than the target of 7. The influence of these factors on mineralogy and morphology are discussed in later sections.

4.3.2 Mineralogy and Morphology

Identification of synthetically precipitated particles was completed through XRD as summarized in Table 4-3.

Table 4 – 3: Mineralogy Results from X-ray Diffraction

Exp Run ID XRD Results

1 71-1020† Connellite, Cu19Cl4(SO4)(OH)32*3H20 2 71-2010 Langite?, Cu4(SO4)(OH)6*2(H2O) 3 71-2020 Unidentified 4 71-8080 Connellite, Cu19Cl4(SO4)(OH)32*3H20 5 75-1020‡ Malachite, Cu2(CO3)(OH)2 6 75-2010 Malachite, Cu2(CO3)(OH)2 7 75-2020 Malachite, Cu2(CO3)(OH)2 8 75-8080 Malachite, Cu2(CO3)(OH)2 9 91-1020 Tenorite, CuO 10 91-2010 Tenorite, CuO 11 91-2020 Tenorite, CuO 12 91-8080 Tenorite, CuO 13 95-1020 Tenorite, CuO 14 95-2010 Tenorite, CuO 15 95-2020 Tenorite, CuO 16 95-8080 Tenorite, CuO † Chloride concentration varied from target of 1000 mg/L Cl- ‡ pH value varied from target of 7.0 s.u.

Copper chloride (and sulfate) minerals were present only at pH 7.0, in low DIC conditions

(experiments 1-4). Minerals identified under these conditions include two cases of connellite

(exp 1 and 4), an unidentified mineral (exp 3) and the possible presence of langite (exp 2).

Tenorite and malachite were identified at pH 9.0 (exp 9-16) and pH 7.0 (exp 5-8), respectively.

No additional copper chloride or sulfate minerals were detected in experiment 5 – 16.

Trends in aging were also studied through the course of this experiment. In general the process of aging is described as the transition of a high-solubility compound to the precipitation of a low-solubility compound and is a unidirectional process, provided the water composition and water temperature remain constant (Lagos 2001). The evolution of particles was tracked over

90 days at time points of 7, 28, 60 and 90 days. Results are summarized in Table 4-4.

4.3.3 Amorphous Minerals

At the onset of experiments (day 0), 14 of the 16 samples presented amorphous results as noted in Table 4-4. Amorphous results are characterized by broad or diffuse peaks (Figure 4-1). This is typically indicative of particles that are too small or poorly crystalline to ensure deflection of x- rays. The filter blank is shown in Figure 4-1, with distinguishable peaks at 14 and 17 degrees 2θ.

Experiment 6 (malachite) is shown graphed with the filter blank to clarify the fact that early samples did not show a distinguishable difference from the blank.

Figure 4 – 1: XRD Spectra of Blank Filter and Experiment 6 at Initial Precipitation

The ability to characterize amorphous solids is a key limitation of XRD. However, as minerals age and undergo recrystallizing, dehydration and increase in particle size, this allows for identification.

Table 4 – 4: Mineralogy with Age

Time (days) Exp Run ID 0 7 28 60 90 1 71-1020 † amorphous - Connellite Connellite Connellite 2 71-2010 Unidentified Langite Langite Langite Langite 3 71-2020 amorphous Unidentified Unidentified Unidentified na* 4 71-8080 amorphous na* Connellite Connellite Connellite 5 75-1020 ‡ amorphous amorphous Malachite Malachite Malachite 6 75-2010 amorphous Malachite Malachite Malachite Malachite 7 75-2020 amorphous Malachite na* Malachite Malachite 8 75-8080 amorphous na* Malachite Malachite Malachite 9 91-1020 amorphous amorphous Tenorite Tenorite Tenorite 10 91-2010 amorphous amorphous Tenorite Tenorite Tenorite 11 91-2020 amorphous na* Tenorite Tenorite na* 12 91-8080 na* na* Tenorite Tenorite Tenorite 13 95-1020 amorphous amorphous amorphous Tenorite Tenorite 14 95-2010 amorphous amorphous na* Tenorite Tenorite 15 95-2020 amorphous na* amorphous Tenorite Tenorite 16 95-8080 amorphous amorphous amorphous Tenorite Tenorite * na - not analyzed Unidentified - Solid not detected by XRD indexing † Chloride concentration varied from target of 1000 mg/L Cl- (confirmed Cl- = 62 mg/L) ‡ pH value varied from target of 7.0 s.u. (confirmed pH of 7.96 s.u.)

4.3.4 Connellite

The hydrated copper sulfate-chloride hydroxide, connellite [Cu19Cl4(SO4)(OH)32*3H20], was identified in experiments 1 and 4 through XRD. As summarized in Table 4 – 4 the minerals were initially amorphous before transitioning to a crystalline state, captured at 28 days. Experiment 1

(71-1020), generated at pH 7.0, 10 mg C/L DIC, 62 mg/L Cl-, 204 mg/L SO4 is shown in Figure 4-2.

The spectra presents sharp diffraction peaks matching the Jade software database in two primary locations: 6.2 and 11 degrees 2θ, with minor peaks at 32.6 and 39.6 degrees. The blank filter peak is captured at 17 degrees 2θ. The spectra indicate a crystalline structure at 28 days.

Figure 4 – 2: XRD Spectra of Connellite (Experimental Run 1) at 28 Days

SEM images (Figure 4-3) reveal an acircular crystal structure averaging 5 µm in length. Visually the precipitate appeared green (day 0) and transitioned to a blue color at day 7, as noted in

appendix C. Experiment 4, 71-8080 (pH of 6.9, 10 mg C/L DIC, 780 mg/L Cl-, 773 mg/L SO4), also identified as connellite followed a similar pattern in aging and morphology. The particles were amorphous when initially precipitated and transitioned to crystalline at 28 days. A slight difference was observed in the XRD pattern which had one additional peak at 17 degrees 2θ.

There are no significant changes in the shape or size of connellite between experiment 1 and 4, despite varying ratios of chloride-sulfate.

Figure 4 – 3: Connellite (Experimental Run 1) at 28 Days

Connellite is a mixed sulfate-chloride-hydroxide, typically found in geological environments but rarely in copper distribution systems. It is unexpected that connellite would precipitate in a sulfate dominant environment, which occurs in of both experiments. Connellite has been known to form in chloride rich conditions (with traces of sulfate) as confirmed by Pollard (2009).

A clear explanation for its formation in highly concentrated sulfate conditions is uncertain. A potential theory of formation would indicate that chloride is more competitive in low pH-low

DIC conditions, and more readily bonded with cupric (Cu+2) ions in solution. Pollard’s work also noted that connellite shares thermodynamic stability between paratacamite, brochantite and malachite/tenorite.

The absence of malachite in experiments 1 through 4 was an interesting observation. At lower pH malachite is favored however its formation is limited by the availability of bicarbonate (DIC).

Previous work has shown that sulfate becomes more active in corrosion product formation at low pH/low DIC conditions. Based on work by Farooqi (2006) and Edwards et al (1994), the copper sulfate, brochantite, is predicted in these conditions. This supports experimental observations that DIC limited environments allow sulfate (and chloride) to become more active in mineral formation.

4.3.5 Langite

In experimental 2, a blue precipitate was observed with a morphology corresponding to a snowflake (Appendix C; Figure 4-4).

Figure 4 – 4: Experiment 2 (71-2010) SEM at 28 days

The XRD pattern (Figure 4-5) was inconclusive with a match in the Jade database. Multiplexing of peaks were observed indicating formation of another crystal structure or a secondary phase.

Peaks were narrow and sharp indicating a highly crystalline structure and extended across the full 2θ axis. Experiment 2 was one of the few cases that formed a crystalline pattern early (at day 7) as noted in Table 4-4. The transition at day 7 was marked by prominent peak development at 13, 23, 28, 39 and 52.8. No additional changes in spectra were noted after day

Figure 4 – 5: Experiment 2 (71-2010) XRD Spectra at 28 days

Bragg’s Law (eqn 4.1) was used to determine d-spacing in the absence of a conclusive pattern match in the software.

2d(sin θ) = λ (eqn 4.1) d = d-spacing (Å) θ in degrees λ = 1.5418 (Å) for copper radiation

The five most prominent peaks in the spectra (Figure 4-5) were at 13, 23, 28, 39 and 52.8 degrees (2θ). The corresponding d-spacing of 6.81, 3.86, 3.56, 2.31 and 1.73 Å was compared with published values of 7.06, 3.57, 2.13, 2.49 and 2.66 Å (Anthony 2001). One prominent peak and two (2) minor peaks were close to expected values. A secondary mineral was not found to index remaining peaks. The d-spacing was compared to other cupric-sulfate and cupric-chloride

minerals, such as brochantite (dehydrated form of langite) but no additional matches were detected. One challenge with identifying the mineral is the state of hydration. Samples were stored in a desiccator, which may have altered moisture content. A conclusive match in XRD was not found to corroborate the mineralogy.

While the XRD analysis was inconclusive, SEM suggested the possible presence of langite. The habit matches geological references (Anthony 2001) where langite is documented as exhibiting crystal twinning resulting in snowflake or star-shaped groupings. Langite is meta-stable to brochantite and has been known to precipitate in copper distribution systems as noted in work by Lagos (2001). Langite is a highly soluble mineral associated with young copper systems. The formation of langite is typical in highly concentrated sulfate environments.

The formation of langite indicates the mineral was in the early stage of development and with time could potentially transition to malachite as a stable passivating film. Experiment 2 was

generated at pH 7, DIC 10 mg C/L, 194 mg/L CL- and 985 mg/L SO4 (ID: 71-2010), coinciding with high sulfate conditions anticipated for langite. It could be expected that young distribution systems with large amounts of sulfate, low pH and low buffering capacity may tend to form intermediate corrosion compounds before stable passivating films.

4.3.6 Malachite

In experiments at pH 7 and DIC 50 mg C/L (experiments 5-8) the mineral identified by XRD was copper carbonate, malachite [Cu2(CO3)(OH)2]. The morphology of malachite exhibited stalactite cubes arranged in spherical formation (Figure 4-6), coinciding with published literature classifying the mineral as spherical, with a tendency to form radial fibrous crystal “bundles”

(Anthony 2001). Malachite particles were larger, averaging 20-25 µm, increasing to 60 microns in later stages of aging (28+ days). Malachite particles precipitated as a blue-green color and

eventually transitioned to green. The color transition was observed at day 7 for experiments 6 and 7; and at 14 days for case 5 and 8.

Figure 4 – 6: SEM for Malachite, Experiment 5 (75-1020) at 28 days

The spectra patterns of malachite from experiments 5-8 transitioned from amorphous to slightly crystalline. The timeline of the transition was detected at points similar to the color transition, day 7 for experiments 6 and 7; day 28 for experiments 5 and 8. Experiment 75-1020, generated at pH 8, DIC 50 mg C/L, 1000 mg/L CL- and 210 mg/L SO4 is shown for reference (Figure 4-7). The peaks are sharp and narrow, although of low intensity indicating a crystalline surface that is not fully developed. Dominant peaks were observed at 12.5, 22 and 31 degrees 2θ. One additional peak may be present at 17 degrees (2θ), but was masked by the filter peak. Samples did not crystallize any further after day 28.

The early detection of experiments 6 (75-2010) and 7 (75-2020) also correlated to a difference in

XRD spectra. Two peaks were evident at 12.5 and 22 degrees (2θ), although broad and small

(Appendix D). Both experiment 6 and 7 represent different ratios of chloride and sulfate, 1:5 and 1:1, respectively. No common pattern was present to explain the early formation of the particles, over the other minerals.

Figure 4 – 7: XRD Spectra for Malachite, Experiment 5 (75-1020) at 28 days

Malachite is a stable passivating mineral found in operational distribution systems. Based on work by Edwards et al. (1994) tenorite and malachite are predicted to be dominant cupric solids over a pH range of 5.5 – 9.5. Bicarbonate (DIC) is a critical factor in mineralogy, and in low pH- high DIC concentrations malachite is favored. Malachite has a solubility below tenorite (Schock et al, 1995) and typically develops after long periods of aging in distribution systems. The presence of chloride and sulfate did not promote the formation of copper sulfate or chloride phase minerals and DIC was likely a factor. In the presence of sufficient carbonate the reaction transitioned without interference from anions present.

The formation of malachite is expected in low pH conditions. The presence of chloride and sulfate may accelerate the formation of malachite, but it is inconclusive as to the target

chloride-sulfate ratio to induce this formation. From this work a 1:1 ratio and 1:5 ratio of chloride-sulfate accelerated mineral development. On average malachite was detected within

30 days. The pH and DIC are likely the predominate factors in the development of malachite (pH below 8.0 and DIC around 50 mg/L).

4.3.7 Tenorite

XRD analysis identified the copper oxide tenorite (CuO), exclusively at pH 9, despite DIC, chloride and sulfate conditions. Tenorite precipitated as green particulate and transitioned to black.

Visually SEM images reflected clusters of round particles averaging in size from 1.0-1.50 µm

(Figure 4 – 8a). An exception to the morphology was noted in experiment 10 and 12, reflecting high sulfate conditions (pH 8.91, 10 mg C/L DIC, 192 mg/L Cl-, 1020 mg/L SO4) and (pH 8.91, 10 mg C/L DIC, 800 mg/L CL- and 809 mg/L SO4) respectively. The morphology was altered into a more oblong shape resembling grains of rice (Figure 4 – 8b), but in general remained similar in size, 2.0 µm in diameter. No changes were observed in the XRD pattern for these experiments, which were identified as tenorite despite morphology changes.

a) b)

Figure 4 – 8: SEM for Tenorite (a) Experiment 9 (91-1020) and (b) Experiment 10 (91-2010) at 28 days

The XRD spectra of samples generated at DIC 10 mg C/L and 50 mg C/L had similar peak definition and intensity. Dominant peaks were observed at 35.8 and 39 degrees (2θ), corresponding to tenorite. Both peaks were broad and of low intensity (Figure 4 – 9), indicating a poorly crystalline structure. This is partially explained by the small, anhedral (smooth texture) morphology of tenorite as observed by SEM. The effect of chloride and sulfate was not distinguishable through XRD. However, there was a clear impact from DIC on the timeline of particulate development. As summarized in Table 4 – 4, minerals precipitated at 50 mg/L were not identified until day 60, while 10 mg/L conditions exhibited peaks earlier at 28 days. This trend was also observed in the mineral photographs (Appendix C). The delay in identification and color can be attributed to the higher concentration of DIC which increases solubility and delays the aging process (Edwards et al. 1994;Farooqi 2006).

Figure 4 – 9: XRD Spectra for Tenorite in Experiment 10 (91-2010) at 28 days

Tenorite is the favored mineral of formation in oxygenated alkaline environments, and is a stable passivating film found in aged copper systems. The presence of sulfate and chloride

(ratios of 1:1, 5:1 and 1:5) did not alter the mineralogy of the solids, nor did the varying concentration of DIC (10 and 50 mg/L). The persistent formation of tenorite under high pH conditions is predicted because of the oxidizing environment that results from using cupric perchlorate [Cu(ClO4)2*6H20] in experiments. Work by Edwards et al. (1994) further confirms the formation of tenorite is expected at pH above 7.7 at all DIC concentrations.

Based on this research, formation of a stable, low solubility passivating barrier can occur within

30 days. Where high DIC conditions exist, the increased solubility may delay mineral formation

(up to 60 days). Distribution systems attempting to minimize soluble copper should increase pH and decrease DIC. It is expected that tenorite will form as a protective barrier in pH conditions above 8.0. While recent research has noted that pitting can occur in high pH-low DIC environments in the presence of chloride (Lytle and Schock 2008), it was not observed in this research. It is anticipated that the mechanism for pitting requires a disturbance to the passivating film which establishes a local corrosion cell in which chloride becomes an active anion in the pitting cycle.

Lastly, it can be noted that while morphology is slightly altered by high sulfate conditions

(experiments 10 and 12) the mineralogy remains consistent. Further work is necessary to confirm the performance of tenorite coatings generated in high sulfate conditions.

4.3.8 Distribution System Comparison of Minerals

The solids from experiments 5 (malachite) and 9 (tenorite) were compared to minerals precipitated from pipe loop studies conducted at the USEPA (O’Donnell and Lytle 2008).

O’Donnell’s work was conducted using copper pipe loop system and synthetic experimental

water with varying levels of chloride, sulfate, free chlorine, DIC and polyphosphates to observe the effects of phosphates on copper corrosion and release in water. Two controls (without phosphate) and two phosphate inoculated waters (one using hexametaphosphate the other sodium phosphate) were included in the test matrix. Experiments were monitored every 48 hours over 200 days. The SEM images from the interior of the control experiments were provided for comparison.

Synthetically precipitated solids showed a close resemblance in structure and size to films formed on distribution pipelines. In general the habit or shape of malachite is described as rosettes, sprays or tufts, aggregates of radiating fibrous crystals, while tenorite is earthy, massive and curved (Anthony 2001).

Malachite from the distribution system (Figure 4-10) are comprised of rosettes (figure a) and bundles (figure b) 10 µm in diameter. Bundles are usually indicative of early formation. The precipitated malachite formed a combination of large spheres (100 µm) and bundles 8-10 µm in size as noted in figure c and d, respectively. Likewise, tenorite exhibited strong similarities to distribution scale. Figure 4-11 captures tenorite film that is encrusted with smooth spheres (2.0

µm in diameter). Precipitated tenorite also formed clusters of smooth spherical 2.5 µm in diameter. Confirmation of morphology from actual distribution systems further confirms the validity of jar testing to generate solids found in distribution systems as well as extrapolating information on aqueous conditions conducive to corrosion mineral formation.

a) c)

b) d) Figure 4 – 10: SEM Images of Malachite from Distribution Piping (a, b) (O’Donnell and Lytle 2008) and Precipitation Experiments (c, d)

a) c)

b) d) Figure 4 – 11: SEM Images of Tenorite from Distribution Piping (a, b) (O’Donnell and Lytle 2008) and Precipitation Experiments (c, d)

53 4.4 CONCLUSIONS

Water chemistry significantly affects copper synthesis, particularly pH and DIC. Changes resulting from the presence of chloride and sulfate were ambiguous in most experiments, except in low pH – low DIC conditions (trials 1 – 4) where copper chloride-sulfate minerals were present. Work from experiments confirmed high pH conditions preferentially develop tenorite, and low pH (high DIC) conditions form malachite over the course of aging. This trend is also observed in operational distribution systems. Practices of controlling pH are often required to minimize uniform corrosion in a system.

The precipitation of tenorite and malachite has a strong consistency in morphology with precipitate scale found in actual distribution systems. The impact of chloride and sulfate is not evident from XRD results, but was noted to affect mineral morphology, particularly in the presence of high sulfate environments. XRD and SEM have been shown to be complementary techniques for identifying copper corrosion minerals associated with uniform and pitting corrosion. The use of SEM was critical in providing visual corroboration of the highly crystalline mineral precipitated in low pH-high sulfate conditions, which appears to be langite. Connellite, while not typically precipitated in high sulfate environments was confirmed through XRD and corresponds to known morphologies. Connellite is an unexpected byproduct of the precipitation experiments and is not typically found in domestic distribution systems. The presence of saline conditions may be an underlying factor in the generation of connellite at this condition.

The aging/evolution of particles was captured in XRD results. Minerals transitioned from amorphous to crystalline, with associated changes in XRD spectra and color. The increasing size of minerals during aging is likely a factor in XRD detection. High pH-high DIC conditions resulted

in a delay in particle aging, possibly stemming from increased copper solubility from high DIC conditions. Operational distribution systems must carefully balance pH conditions with DIC concentrations. While pH above 8.0 can decrease solubility these conditions may cause precipitation of carbonate in the distribution piping.

55 CHAPTER 5

CONCLUSION AND RECOMMENDATIONS

Several significant findings resulted from this study:

 Based on this research, pH and DIC are significant factors in controlling copper solubility,

morphology and mineralogy. High pH and low DIC conditions are primary parameters

for reducing cuprosolvency. Systems operating in low pH ranges can expect to

experience higher solubility levels than operating in alkaline conditions. The presence of

DIC affects the internal corrosion of copper and formation of stable passivating films.

High DIC levels (50 mg/L) are predicted to increase copper solubility by an order of

magnitude, compared to low DIC conditions.

 Chloride and sulfate appear to provide some benefit of reduction soluble copper levels

at initial formation, however the effect over time is variable. Chloride and sulfate

appear most effective during aging in low pH-high DIC conditions.

 Changes in mineralogy due to the presence of chloride and sulfate were minimal. Work

from experiments confirmed high pH conditions preferentially develop tenorite, and low

pH (high DIC) conditions form malachite. This trend is also observed in operational

distribution systems. The only exception was in low pH – low DIC conditions where

copper-chloride and copper-chloride-sulfate minerals were detected.

56  Synthetically precipitated solids showed a close resemblance in structure and size to

films formed on distribution pipelines. Corroboration of morphology further validates

use of jar testing to generate solids found in distribution systems as well as

extrapolating information on aqueous conditions conducive to corrosion mineral

formation.

 The formation of connellite and langite were both unique under jar conditions utilized

for experiments. Connellite precipitated in two conditions, both in the presence of high

sulfate concentrations, which is contrary to previous work which confirms the mineral

formation occurs in high chloride environments. SEM confirmed the morphology

coincided with published mineral data. Langite was also detected, through use of SEM

images, when the XRD spectra was inconclusive.

 XRD and SEM have been shown to be complementary techniques for identifying copper

corrosion minerals associated with uniform and pitting corrosion. The use of SEM was

critical for identifying langite and confirming connellite.

Recommendations

1. Precipitation experiments should continue at lower pH conditions, varying chloride and

sulfate concentrations. It is anticipated that additional minerals, specifically associated

with pitting corrosion will precipitate under these conditions.

2. It is recommended that additional experiments be conducted at lower chloride and

sulfate conditions. Replicating conditions typically found in distribution systems may

provide additional observation on the competing role of chloride and sulfate.

3. It is recommended that chemical equilibrium modeling, using Mineql+ or Phreecq, be

considered to confirm mineral by-product precipitation.

4. More frequent sampling timelines are recommended between initial precipitation and

14 days to capture key transitions in mineral solubility and morphological phase change.

5. Future work should consider the role of anodic and cathodic corrosion inhibitors (such

as orthophosphate and zinc orthophosphate) in competition with chloride and sulfate.

58 REFERENCES

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59 Loganathan, G.V., and Lee, J. (2005). “Decision tool for optimal replacement of plumbing systems.” Civ. Eng. Environ. Syst., 22(4), 189-204.

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Schock, M.R., Lytle, D.A., and Clement, J.A. (1995). “Effect of pH, DIC, Orthophosphate, and Sulfate on Drinking Water Cuprosolvency.” EPA/600/R-95/085, USEPA, Washington, DC.

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60 APPENDIX A

WATER CHEMISTRY DATA – SOLUBILITY EXPERIMENTS

Concentration (mg/L) Age - 2- Sample ID (days) colldate Total Cu Soluble Cu CL SO4 71 1020 0 8/1/2007 21.44 2.33 966.77 203.41 71 1020 7 8/7/2007 12.43 0.92 n/d 199.26 71 1020 28 8/29/2007 12.87 0.49 n/d 209.44 71 1020 60 10/5/2007 12.08 0.12 967.51 203.29 71 2010 0 8/1/2007 18.35 2.18 211.53 1007.22 71 2010 7 8/7/2007 12.57 1.44 n/d 1001.53 71 2010 28 8/29/2007 11.68 0.92 n/d 1006.23 71 2010 60 10/5/2007 11.76 0.31 219.09 1014.39 71 2020 0 8/1/2007 2.71 0.05 n/d 194.69 71 2020 7 8/7/2007 12.18 0.77 n/d 195.91 71 2020 28 8/29/2007 12.97 0.68 n/d 200.58 71 2020 60 10/5/2007 12.96 0.41 209.95 202.77 71 8080 0 8/1/2007 18.99 1.25 772.59 814.88 71 8080 7 8/7/2007 12.95 1.07 n/d 783.87 71 8080 28 8/29/2007 12.25 0.69 n/d 845.34 71 8080 60 10/5/2007 13.74 0.45 772.41 822.39 71 CONTROL 0 8/14/2007 13.55 2.77 n/d n/d 71 CONTROL 7 8/22/2007 5.05 0.35 n/d 0.26 71 CONTROL 28 9/11/2007 0.71 0.05 n/d 1.73 75 1020 0 8/2/2007 11.41 4.24 962.83 198.32 75 1020 8 8/10/2007 8.41 0.10 n/d 200.70 75 1020 28 8/30/2007 3.40 0.08 n/d 221.65 75 1020 60 10/5/2007 11.88 0.03 785.53 206.08 75 2010 0 8/2/2007 16.91 4.44 220.83 1051.41 75 2010 8 8/10/2007 0.64 0.29 n/d 1065.45 75 2010 28 8/30/2007 1.91 0.13 n/d 1124.92 75 2010 60 10/5/2007 0.24 0.07 219.17 1072.84 n/d= Non detect

61 APPENDIX A (CON’T)

Concentration (mg/L) Age - 2- Sample ID (days) colldate Total Cu Soluble Cu CL SO4 75 2020 0 8/2/2007 14.47 4.35 216.97 200.38 75 2020 8 8/10/2007 0.25 0.18 n/d 208.97 75 2020 28 8/30/2007 4.72 0.09 n/d 223.16 75 2020 60 10/5/2007 0.18 0.03 54.91 212.99 75 8080 0 8/2/2007 14.82 4.61 792.54 908.31 75 8080 8 8/10/2007 0.52 0.35 n/d 831.25 75 8080 28 8/30/2007 2.64 0.14 n/d 915.49 75 8080 60 10/5/2007 0.18 0.04 217.25 846.92 75 CONTROL 0 8/14/2007 13.78 12.19 n/d n/d 75 CONTROL 7 8/22/2007 3.87 0.21 n/d 0.12 75 CONTROL 28 9/11/2007 0.22 0.12 n/d n/d 75 CONTROL 63 10/15/2007 0.22 0.16 n/d n/d 91 1020 0 8/22/2007 13.67 2.78 952.41 197.66 91 1020 7 8/29/2007 8.25 0.02 n/d 174.04 91 1020 30 9/25/2007 11.23 0.84 n/d n/d 91 2010 0 8/22/2007 14.06 0.15 190.39 1005.48 91 2010 7 8/29/2007 10.63 0.00 n/d 993.81 91 2010 30 9/25/2007 3.21 0.03 n/d n/d 91 2020 0 8/22/2007 14.06 0.17 191.68 201.31 91 2020 7 8/29/2007 10.89 0.00 n/d 205.63 91 2020 30 9/25/2007 5.36 0.02 n/d 211.45 91 8080 0 8/22/2007 13.49 0.12 757.45 786.64 91 8080 7 8/29/2007 10.75 0.00 n/d 809.13 91 8080 30 9/25/2007 10.88 0.03 754.06 833.67 91 CONTROL 0 8/14/2007 11.53 0.11 n/d 0.14 91 CONTROL 7 8/22/2007 12.30 0.40 n/d 0.10 91 CONTROL 28 9/11/2007 9.76 0.05 n/d 1.08 91 CONTROL 63 10/15/2007 10.89 0.18 n/d n/d 91 1020 0 8/22/2007 13.67 2.78 952.41 197.66 91 1020 7 8/29/2007 8.25 0.02 n/d 174.04 91 1020 30 9/25/2007 11.23 0.84 n/d n/d 91 2010 0 8/22/2007 14.06 0.15 190.39 1005.48 91 2010 7 8/29/2007 10.63 0.00 n/d 993.81 91 2010 30 9/25/2007 3.21 0.03 n/d n/d 91 2020 0 8/22/2007 14.06 0.17 191.68 201.31 91 2020 7 8/29/2007 10.89 0.00 n/d 205.63 91 2020 30 9/25/2007 5.36 0.02 n/d 211.45 n/d= Non detect

62 APPENDIX A (CON’T)

Concentration (mg/L) Age - 2- Sample ID (days) colldate Total Cu Soluble Cu CL SO4 91 1020 0 8/22/2007 13.67 2.78 952.41 197.66 91 1020 7 8/29/2007 8.25 0.02 n/d 174.04 91 1020 30 9/25/2007 11.23 0.84 n/d n/d 91 2010 0 8/22/2007 14.06 0.15 190.39 1005.48 91 2010 7 8/29/2007 10.63 0.00 n/d 993.81 91 2010 30 9/25/2007 3.21 0.03 n/d n/d 91 2020 0 8/22/2007 14.06 0.17 191.68 201.31 91 2020 7 8/29/2007 10.89 0.00 n/d 205.63 91 2020 30 9/25/2007 5.36 0.02 n/d 211.45 91 8080 0 8/22/2007 13.49 0.12 757.45 786.64 91 8080 7 8/29/2007 10.75 0.00 n/d 809.13 91 8080 30 9/25/2007 10.88 0.03 754.06 833.67 91 CONTROL 0 8/14/2007 11.53 0.11 n/d 0.14 91 CONTROL 7 8/22/2007 12.30 0.40 n/d 0.10 91 CONTROL 28 9/11/2007 9.76 0.05 n/d 1.08 91 CONTROL 63 10/15/2007 10.89 0.18 n/d n/d 95 1020 0 8/23/2007 11.57 0.61 190.45 893.74 95 1020 7 8/30/2007 11.92 0.50 n/d 1073.89 95 1020 29 9/25/2007 1.67 0.03 189.46 1032.10 95 2010 0 8/23/2007 14.17 0.59 191.57 1010.25 95 2010 7 8/30/2007 12.46 0.52 n/d 1092.74 95 2010 29 9/25/2007 0.80 0.03 189.59 1071.21 95 2020 0 8/22/2007 13.66 0.64 189.91 201.33 95 2020 7 8/29/2007 12.37 0.46 n/d 203.27 95 2020 30 9/25/2007 1.28 0.03 191.38 210.28 95 8080 0 8/22/2007 12.05 0.66 746.09 794.78 95 8080 7 8/29/2007 11.71 0.45 n/d 781.83 95 8080 30 9/25/2007 11.64 0.04 741.02 823.40 95 CONTROL 0 8/15/2007 9.57 1.21 n/d n/d 95 CONTROL 7 8/22/2007 0.54 0.38 n/d 0.12 95 CONTROL 28 9/11/2007 8.94 0.03 n/d 0.69 95 CONTROL 63 10/15/2007 8.70 0.03 n/d n/d n/d = Non detect

63 APPENDIX B

pH DATA – SOLIDS EXPERIMENTS

pH ID 0 7 14 21 28 35 42 60 90 std dev 71-1020 7.01 6.85 6.81 6.86 7.01 - 6.74 7.11 7.37 0.20 71-2010 6.93 6.97 6.88 6.80 6.95 6.94 - 7.12 7.25 0.14 71-2020 7.08 6.95 7.52 7.01 7.06 - 6.91 7.26 7.53 0.25 71-8080 6.93 6.80 6.75 7.04 6.79 6.90 - 7.00 7.20 0.15 75-1020 7.96 7.95 8.06 8.09 8.09 8.17 8.11 8.11 8.23 0.09 75-2010 7.02 7.05 7.12 7.19 7.22 7.35 7.42 7.37 7.68 0.21 75-2020 7.02 7.60 7.23 7.21 7.42 7.32 7.46 7.58 7.84 0.25 75-8080 7.06 7.15 7.42 7.45 7.32 7.42 7.44 7.50 7.71 0.19 91-1020 8.91 8.09 8.11 8.03 8.09 8.00 8.11 7.91 7.94 0.30 91-2010 8.91 8.39 8.34 8.28 8.34 8.25 8.24 8.20 8.13 0.23 91-2020 8.91 8.40 - 7.85 7.86 - - 7.85 7.83 0.45 91-8080 8.90 8.29 8.40 8.29 8.36 8.25 8.30 8.19 8.10 0.23 95-1020 8.91 8.85 8.83 8.86 8.72 8.81 8.73 8.70 8.74 0.07 95-2010 8.91 8.92 8.91 8.90 8.92 8.79 8.83 8.79 8.93 0.06 95-2020 8.91 8.92 8.90 8.90 8.89 8.71 8.80 8.75 8.89 0.08 95-8080 8.91 8.92 8.93 8.90 8.86 8.69 8.80 8.76 8.90 0.08

64 APPENDIX C

COLOR LOG OF PRECIPITATED MINERALS

APPENDIX D

XRD SPECTRA

D.1: 71-1020 / 28 Days ...... 76 D.2: 71-1020 / 60 Days ...... 77 D.3: 71-1020 / 90 Days ...... 78 D.4: 71-2010 / 28 Days ...... 79 D.5: 71-2010 / 60 Days ...... 80 D.6: 71-2010 / 90 Days ...... 81 D.7: 71-2020 / 28 Days ...... 82 D.8: 71-2020 / 60 Days ...... 83 D.9: 71-8080 / 28 Days ...... 84 D.10: 71-8080 / 60 Days ...... 85 D.11: 75-1020 / 28 Days ...... 86 D.12: 75-1020 / 60 Days ...... 87 D.13: 75-1020 / 90 Days ...... 88 D.14: 75-2010 / 28 Days ...... 89 D.15: 75-2010 / 60 Days ...... 90 D.16: 75-2010 / 90 Days ...... 91 D.17: 75-2020 / 0 Days ...... 92 D.18: 75-2020/ 60 Days ...... 93 D.19: 75-2020 / 90 Days ...... 94 D.20 75-8080 / 28 Days ...... 95 D.21: 75-8080 / 60 Days ...... 96 D.22: 75-8080 / 90 Days ...... 97 D.23: 91-1020 / 28 Days ...... 98

74 D.24: 91-1020 / 60 Days ...... 99 D.25: 91-1020 / 90 Days ...... 100 D.26: 91-2010 / 28 Days ...... 101 D.27: 91-2010 / 60 Days ...... 102 D.28: 91-2010 / 90 Days ...... 103 D.29: 91-2020 / 60 Days ...... 104 D.30: 91-8080 / 28 Days ...... 105 D.31: 91-8080 / 60 Days ...... 106 D.32: 91-8080 / 90 Days ...... 107 D.33: 95-1020 / 28 Days ...... 108 D.34: 95-1020 / 60 Days ...... 109 D.35: 95-1020 / 90 Days ...... 110 D.36: 95-2010 / 60 Days ...... 111 D.37: 95-2010 / 90 Days ...... 112 D.38: 95-2020 / 28 Days ...... 113 D.39: 95-2020 / 60 Days ...... 114 D.40: 95-2020 / 90 Days ...... 115 D.41: 95-8080 / 28 Days ...... 116 D.42: 95-8080 / 60 Days ...... 117 D.43: 95-8080 / 90 Days ...... 118

D.1: 71-1020 / 28 Days

D.2: 71-1020 / 60 Days

D.3: 71-1020 / 90 Days

D.4: 71-2010 / 28 Days

D.5: 71-2010 / 60 Days

D.6: 71-2010 / 90 Days

D.7: 71-2020 / 28 Days

D.8: 71-2020 / 60 Days

D.9: 71-8080 / 28 Days

D.10: 71-8080 / 60 Days

D.11: 75-1020 / 28 Days

D.12: 75-1020 / 60 Days

D.13: 75-1020 / 90 Days

D.14: 75-2010 / 28 Days

D.15: 75-2010 / 60 Days

D.16: 75-2010 / 90 Days

D.17: 75-2020 / 0 Days

D.18: 75-2020/ 60 Days

D.19: 75-2020 / 90 Days

D.20 75-8080 / 28 Days

D.21: 75-8080 / 60 Days

D.22: 75-8080 / 90 Days

D.23: 91-1020 / 28 Days

D.24: 91-1020 / 60 Days

D.25: 91-1020 / 90 Days

100

D.26: 91-2010 / 28 Days

101

D.27: 91-2010 / 60 Days

102

D.28: 91-2010 / 90 Days

103

D.29: 91-2020 / 60 Days

104

D.30: 91-8080 / 28 Days

105

D.31: 91-8080 / 60 Days

106

D.32: 91-8080 / 90 Days

107

D.33: 95-1020 / 28 Days

108

D.34: 95-1020 / 60 Days

109

D.35: 95-1020 / 90 Days

110

D.36: 95-2010 / 60 Days

111

D.37: 95-2010 / 90 Days

112

D.38: 95-2020 / 28 Days

113

D.39: 95-2020 / 60 Days

114

D.40: 95-2020 / 90 Days

115

D.41: 95-8080 / 28 Days

116

D.42: 95-8080 / 60 Days

117

D.43: 95-8080 / 90 Days

118

APPENDIX E

SELECTED SEM IMAGES

119

E.1: Connellite, ID: 71-1020 (7 days)

E.2: Connellite, ID: 71-8080 (28 days)

120

E.3 –Langite, ID: 71-2010 (28 days)

E.4 –Unidentified Mineral , ID: 71-2020 (28 days)

121

E.5 –Malachite, ID: 75-1020 (21 days)

E.6 –Malachite, ID: 75-1020 (28 days)

122

E.7 – Malachite, ID: 75-2020 (28 days)

E.8 – Malachite, ID: 75-8080 (28 days)

123

E.9 – Tenorite, ID: 91-1020 (28 days)

E.10 – Tenorite, ID: 91-2020 (28 days)

124

E.11– Tenorite, ID: 95-1020 (28 days)

E.12– Tenorite, ID: 95-2010 (28 days)

125

E.13– Tenorite, ID: 95-8080 (21 days)

126