The Pennsylvania State University

The Graduate School

Intercollege Program in Environmental Pollution Control

DISSOLVED COPPER REMOVAL BY ELECTROWINNING PROCESS FROM

WASTE BRINE SOLUTION

A Thesis in

Environmental Pollution Control

by

Linlin Tang

2018 Linlin Tang

Submitted in Partial Fulfillment

of the Requirements

for the Degree of

Master of Science

May 2018

ii

The thesis of Linlin Tang was reviewed and approved by the following:

Yuefeng Xie

Professor of Environmental Engineering

Thesis Advisor

Yen-Chih Chen

Associate Professor of Environmental Engineering

David M. Swisher

Operations Engineer

Shirley Clark

Professor of Environmental Engineering

Professor-in-Charge, Master of Science in Environmental Pollution Control Program

*Signatures are on file in the Graduate School

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ABSTRACT

Copper in sewage sludge is regulated under the land application regulations by the United States

Environmental Protection Agency (USEPA) in 1994. To comply with EPA regulations, Penn State

University has been sending their sewage sludge to a landfill due to high copper concentrations for the

past 30 years. A previous study indicates that the main source of copper was the corrosion of copper in

the University’s steam heating systems. The copper in condensates were captured by the ion exchange

softening process and released into the university sanitary sewer systems through the waste brine

solution. This study focused on removing dissolved copper from synthetic water samples and actual

waste brine solutions which generated from Penn State University’s Steam Plant. To aid in copper

removal, a lab scale electrowinning process was constructed. At first, synthetic water samples were

prepared for the test had similar copper concentration as the actual waste brine solution. Various levels

(0 – 4 M) of sodium chloride were evaluated in this study. The results indicated that the concentration

of sodium chloride plays a major role in copper removal. More than 90% of copper reduction could be

achieved after three hours of reaction at an appropriate salt concentration (0.04 – 1.5 M). Several

electrochemical parameters, distance between electrodes and the voltage applied into the system, were

studied and verified. Both of them play important roles in copper removal. A significant positive

correlation existed between voltage and maximum copper reduction. Current efficiency decreases with

increasing time of electrowinning, and it is low, only 14 – 23%. Two types of internal circulation

reactors were constructed for copper electrowinning test. One has three square plate electrodes, two for

anodes, one for cathode. Another use aluminum or titanium/platinum alloy basket electrode as cathode,

anode still use graphite rod electrode. The copper remove efficiency for both reactors lower than 55%

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and some blue flocs were precipitated out. A bench scale test using batch reactor was conducted using

actual waste brine solutions collected at University East Steam Plant. Around 50% of copper reduction

achieved after three hours of reaction, which is much lower than the remove efficiency of synthetic

water. 85% of copper reduction achieved after three hours of reaction, with high initial copper

concentration (221 mg/L). High salt concentration (2.0 – 2.5M) and low copper concentration of actual

waste brine water (6.5 – 63.5 mg/L) are likely the reasons. The extracted copper did not stick to the

electrode very well, but those copper can be removed completely using a bag filter. This research will

provide us with a better understanding of the process of copper removal by electrowinning process in

wastewater treatment and assist Penn State University in complying with the rules of land application.

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TABLE OF CONTENTS

LIST OF FIGURES ............................................................................................................... vii

List of Tables ......................................................................................................................... viii

Acknowledgements .................................................................................................................. ix

Chapter 1 Introduction ............................................................................................................. 1

Chapter 2 Literature Review .................................................................................................... 4

2.1 Regulations and health Impacts ................................................................................. 4

2.2 Modern methods of removing heavy metals from aqueous solution ......................... 5

2.2.1 Chemical Precipitation .................................................................................... 5

2.2.2 Ion Exchange ................................................................................................... 7

2.2.3 Adsorption ....................................................................................................... 8

2.2.4 Membrane filtration ......................................................................................... 9

2.2.4.1 Ultrafiltration ........................................................................................ 9

2.2.4.2 Reverse Osmosis ................................................................................ 10

2.2.4.3 Nanofiltration ..................................................................................... 11

2.2.4.4 Electrodialysis .................................................................................... 11

2.2.5 Coagulation and flocculation......................................................................... 11

2.2.6 Electrochemical treatment ............................................................................. 12

2.3 Copper Removal/Recovery by Electrowinning (Electroextraction), Chemistry ...... 13

2.3.1 Conventional Electrowinning studies for copper removal ............................ 13

2.3.2 EMEW Electrowinning ................................................................................. 14

2.3.3 Chemistry for copper electrowinning ............................................................ 15

Chapter 3 Materials and Methods .......................................................................................... 17

3.1 Chemicals ................................................................................................................. 17

3.2 Electroextraction method and Apparatus ................................................................. 17

3.2.1 Batch Reactor: Graphite anode (rod) and graphite cathode (rod) ................. 17

3.2.2 Continuous Reactor: Double graphite anode (rectangle plate sheet) and Single

graphite cathode (rectangle plate sheet) ......................................................... 18

3.2.3 Internal Circulation Reactor: graphite anode (rod) and aluminum/titanium and

platinum mesh basket cathode ........................................................................ 19

3.3 Copper Analysis ....................................................................................................... 20

3.4 Free Chlorine Analysis ............................................................................................. 21

3.5 Conductivity Analysis .............................................................................................. 21

3.6 Sampling events at Harrisburg and University Park ................................................ 21

Chapter 4 Results and Discussion .......................................................................................... 23

4.1 Analysis of brine solutions ....................................................................................... 23

4.2 Electrowinning of actual waste brine solutions using the Batch Reactor ................ 26

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4.3 Synthetic Samples .................................................................................................... 28

4.3.1 Impact of salt concentration of Copper Removal .......................................... 28

4.3.2 Kinetics.......................................................................................................... 32

4.3.3 Voltage-Maximum copper reduction relationship ......................................... 34

4.3.4 Change of current efficiency with reaction time ........................................... 35

4.4 Continuous Reactors ................................................................................................ 37

4.5 Internal Circulation Reactor ..................................................................................... 40

Chapter 5 Conclusion ............................................................................................................. 42

References .............................................................................................................................. 44

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LIST OF FIGURES

Figure 3.1: The setup of Batch Reactor: Graphite anode (rod) and graphite cathode (rod). . 18

Figure 3.2: The set-up of Continuous Reactor: Double graphite anode (rectangle plate sheet)

and Single graphite cathode (rectangle plate sheet) ............................................................... 19

Figure 3.3: The set-up of Internal Circulation Reactor: graphite anode (rod) and

aluminum/titanium and platinum mesh cylinder cathode. ............................................... 20

Figure 4.1: The concentration of copper varies according to reaction time of electrowinning

process for different samples ................................................................................................. 26

Figure 4.2: Copper concentration and the current of copper deposition vs. time. The

electrolyte: 221 mg/L Cu, 2.16 M NaCl ................................................................................ 27

Figure 4.3: Effects of Brine Concentration on Copper Removal .......................................... 29

Figure 4.4: Summary of Brine Concentration Effects on Copper Removal ......................... 29

Figure 4.5: Effects of Brine Concentration on Chlorine Production ..................................... 31

Figure 4.6: Effect of lower salt concentration on maximum copper reduction ..................... 32

Figure 4.7: A semi plot of the course of copper electrowinning with four different salt

concentrations (0, 1, 2.5, 4M) ................................................................................................ 33

Figure 4.8: Effect of salt concentrations (M) on rate constants ............................................ 34

Figure 4.9: Effects of Brine Concentration on Copper Removal and Chlorine Production.

The concentration of sodium chloride was controlled at 1 M ................................................ 35

Figure 4.10: Copper concentration and the current of copper deposition vs. time. The

electrolyte: 237 mg/L Cu, 0.08 M NaCl ................................................................................ 36

Figure 4.11: The concentration of copper varies according to reaction time of

electrowinning process with different flow rate ..................................................................... 38

Figure 4.12: Maximum copper reduction of copper after applying electrowinning with

different flow rates ................................................................................................................. 39

Figure 4.13: Current varies according to reaction time of electrowinning process with

different flow rate................................................................................................................... 40

Figure 4.14: The concentration of copper varies according to reaction time of

electrowinning process with different flow rate. The data label means percentage of copper

reduction ................................................................................................................................ 41

viii

LIST OF TABLES

Table 4.1: System operation parameters of PSU East Steam Plant ...................................... 23

Table 4.2: Electrical Conductivity of Sodium Chloride NaCl . ............................................. 23

Table 4.3: Salt concentration result of waste brine solution from East Steam Plant, University

Park, when samples were collected on Dec 6th, 2017 .......................................................... 24

Table 4.4: Salt concentration result of waste brine solution from East Steam Plant, University

Park, when samples were collected on Jan. 22nd, 2018 ......................................................... 24

Table 4.5: Copper concentration of waste brine solution from slow rinse and fast rinse stage,

samples were collected from East Steam Plant, University Park on Dec 6th, 2017 .............. 25

Table 4.6: Copper concentration of waste brine solution from slow rinse and fast rinse stage,

samples were collected from East Steam Plant, University Park on Jan. 22nd, 2018 ............ 25

Table 4.8: Summary of rate constant for different salt concentrations. ................................ 34

Table 4.9: Estimated Current Efficiency (V = 2.5V) ............................................................ 37

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ACKNOWLEDGEMENTS

This study is made possible by The Pennsylvania State University Physical Plant under project 30J80.

The author would like to acknowledge the technical assistance from David M. Swisher of Wastewater

Treatment Plant, and all the operators at the East Steam Plant, The Pennsylvania State University. The

author would also like to thank the help of sample collection from visiting scholar, Fuyang Jiang who

is in Dr. Yuefeng Xie’s research group.

I would also like to thank my research advisor Dr. Yuefeng Xie for his outstanding guidance and support

through out my thesis project and I would like to express my appreciation to my academic advisor Dr.

Yen-Chih Chen for his guidance and support.

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Chapter 1

Introduction

Since 1987, Pennsylvania State University has been sending their sewage sludge to a landfill because

of high copper concentrations. Our recent study indicated that the main source of copper in the sludge

was the corrosion of copper and copper alloys in the University’s steam heating system. The copper in

condensates were captured by the ion exchange softening process at the steam plants and released into

the university sanitary sewer systems through the waste brine solution. In 2016, researchers collected

14 samples at various backwash cycles for the copper test. During the water backwash stage, the copper

that is in particulate form can be backwashed out by the hydraulic force. After brine solution was

injected, the copper concentration increased threefold. This increase is likely due to the ion exchange

regeneration by the brine solution. During slow rinse stage, the copper concentration was further

increased, and it was quickly reduced during fast rinse. The analytical results indicated that 87% of total

copper in the softener regeneration wastewater are in dissolved form, while13% of total copper are

particulate copper. Particulate copper can be easily removed by sedimentation or filtration. The bag

filter prior to the ion exchange vessel can only remove approximately 2.2% of copper discharged by the

steam operation and is not an effective process for copper removal. The Limit of copper concentration

is regulated at 1,500 mg/kg, dry weight under the Pollutant Limits for the land Application of Sewage

Sludge (USEPA,1994). Therefore, it is critical to develop cost-effective methods to reduce/remove

copper from waste brine solutions.

Electrochemical methods are generally used in the wastewater industry to remove heavy metals.

Electrowinning is also one of the best available technologies for dissolved copper removal. Because it

2

has high remove efficiency without further treatment. Several sources have shown that copper can be

removed by electrowinning process from different kinds of water system, such as acid mine drainage

(Gorgievski et al., 2009), dilute cyanide solution (Lu et al., 2001), or simulated wastewater which

contain some other heavy metals, such as nickel and chromium. (Hunsom, et al., 2004; Grimshaw et al.,

2011). However, there is no study focused on copper electrowinning from waste brine solutions.

Since 2014, our group started performing some studies on the high copper concentration problem in

wastewater treatment plant’s sludge. They investigated copper is likely discharged into the sewer

system as waste brine solutions. The present research will evaluate the electrowinning process to

remove dissolved copper in the waste brine solution. The results from this research will provide a better

understanding of copper removal by electrowinning process, which will benefit Penn State University’s

steam plants by removing copper from their waste brine solutions as well as complying with the

regulation of copper limit for Land Application of Sewage Sludge. (USEPA, 1994)

The objective of the proposed research was to investigate electrowinning process as a potential

technology for dissolved copper removal and recovery from waste brine solutions (synthetic water

sample and actual water sample). The specific approaches were:

1. Concentration of Sodium Chloride: To verify the impact of salt concentration between voltage and

copper reduction during the electrowinning process. The salt concentrations of synthetic water samples

were determined by balance and calculations; the salt concentrations of real waste brine solutions were

determined by conductivity tests.

2. Voltage: To verify the relationship between voltage and copper reduction, different voltages were

applied to electrochemical reactor. The voltage through out the electrochemical cell is controlled by the

3

Aglient technologies U8002A power supply, DC, Bench, 30V, 150W.

3. Current efficiency: Current efficiency is estimated by copper reduction and current through out the

electrochemical reactor.

4

Chapter 2

Literature Review

2.1 Regulations and health Impacts

Copper is a reddish metal which occurs naturally in water, soil, sediment, and rock at low levels. In

December, 1994, U.S. EPA published a guide for land appliers about the requirements for use or disposal

of Sewage Sludge based on the Federal Standards. As seen in this guide, the Monthly Average copper

concentration can’t exceed 1,500 mg/kg, dry weight, and the ceiling concentration of copper is 4,300

mg/kg, dry weight (EPA,1994). In 1991, U.S. EPA published a regulation to control lead and copper in

drinking water. The regulation is named as the Lead and Copper Rule, so it also known as the LCR. If

copper concentrations exceed an action level 1.3 ppm (1.3 mg/L), the system must inform the public

about steps’ information and they should take to protect their health at once (EPA, 2000). The

Occupational Safety and Health Administration (OSHA) has set a regulation for copper fumes (0.1

mg/m3) and mists (1.0 mg/m3) which are aerosols of soluble copper.

When copper is released into water, the copper will dissolve and be carried in surface waters either as

free copper or in the form of copper compounds, copper bound to particles and suspended in the water

as well. Even though copper binds strongly to suspended particles and sediments, there is still evidence

to prove that some water-soluble copper enter the groundwater. Eventually, copper enters water and

collect in the sediments of rivers, lakes, and estuaries.

Copper can enter our body when we eat food or drink water. Copper can also enter our body by breathing

air or dust which contains copper. Copper can be found at high concentrations in filter feeders such as

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oysters and mussels. Our bodies are very good at blocking high levels of copper from entering the blood

stream (ASTDR, 2002).

Although copper is necessary for good health, high doses can be harmful. Long time exposure to copper

dust can irritate our eyes, nose, and mouth, and will cause headaches, dizziness, nausea, and diarrhea.

If we drink water that contains higher than normal levels of copper it will cause vomiting, stomach

cramps, nausea or diarrhea.

2.2 Methods of removing heavy metals from aqueous solution

There are seven methods that are commonly used to treat heavy metal in wastewater: chemical

precipitation, ion-exchange, adsorption, membrane filtration, coagulation-flocculation, flotation and

electrochemical methods.

2.2.1. Chemical Precipitation

Chemical precipitation is an effective way and most widely used in industries. It is relatively easy and

cheap to operate. In precipitation process, chemicals react with heavy metal ions to form precipitates.

Those insoluble precipitates can be separated from the water by sedimentation or filtration processes.

Finally, the treated water can be reused or appropriately discharged. Hydroxide precipitation and sulfide

precipitation are conventional chemical precipitation processes.

Hydroxide precipitation is the most widely used chemical precipitation technique. The cost of this

technique is relatively low and pH control is also relatively easy. When the pH range is 8.0-11.0, the

various metal hydroxides are minimized. The formed metal hydroxides can be removed by flocculation

and sedimentation. Hydroxide precipitation process using Ca(OH)2 and NaOH in removing Cu(II) from

6

wastewater was evaluated by Mirbagheri and Hosseini (2005).

There are also some limitations for copper removal when using hydroxide precipitation processes.

Firstly, copper(II) hydroxide is mildly amphoteric. If there are some other metals also present in

wastewater, it will be specific when using hydroxide precipitation. Since ideal pH for one metal may

put another metal back into treated water. Secondly, hydroxide precipitation will generate large volumes

of relatively low-density sludge, which can present dewatering and disposal problems. Thirdly, if there

are some complexing agents present in the wastewater, they will inhibit metal hydroxide precipitation.

Sulfide precipitation is another effective process for the treatment of toxic heavy metals ions. The

primary advantages of using sulfides is that the solubility of metal sulfide precipitates is lower than

hydroxide precipitates and sulfide precipitates are not amphoteric. Therefore, the sulfide precipitation

process can achieve a high degree of metal removal over a broader pH range when compared to

hydroxide precipitation. There also is a limit for this process, as metal sulfide precipitation tends to

form colloidal precipitates, which are difficult to separate using filtration or settling processes.

Chemical precipitation has shown success when combined with other methods. Gonzalez-Munoz et al.

(2006) studied sulfide precipitation to reuse and recover heavy metal ions and nanofiltration was

employed as a second step. Results indicated sulfide precipitation can reduce the metal content

successfully, and nanofiltration yielded solutions that can be directly reused in the plant. Chemical

precipitation can also be combined with ion-exchange treatments.

As conventional precipitation process has many limitations, many companies tried to use chelat on to

precipitate heavy metals from wastewater or other aqueous systems. Fu et al. (2006, 2007) employed

dithiocarbamate-type supramolecular heavy metal precipitants to treat complex heavy metal wastewater.

7

The precipitants are N,N”-bis-(dithiocarboxy) poperazine (BDP) and 1,3,5-

hexahydrotriazinedithiocarbamate (HTDC).

The xanthate process has also been found as an effective method to remove heavy metal from

contaminated water. Chang et. al. (2002) employed potassium ethyl xanthate in removing copper ions

from wastewater. The results of this study showed that ethyl xanthate is able to remove copper in

wastewater over a wide copper concentration range (50, 100, 500 and 1000 mg/L) to the Taiwan EPA’s

Effluent regulation (3 mg/L). Xu and Zhang (2006) developed a new organic heavy metal chelator

which is dipropyl dithiophosphate. This chelator was used to remove mercury, cadmium, copper, and

lead (200 mg/L) at pH 3-6. The removal efficiency can achieve 99.9%. The final concentration of metal

ions is 0.05, 0.1, 0.5 and less than 1 mg/L, respectively.

2.2.2. Ion Exchange

Ion exchange has a lot of advantages, such as high removal efficiency, fast kinetics, and treatment

capacity. (Kang et al., 2004) Ion exchange resin has the specific ability to exchange its cations with the

metal ions that are present in the wastewater. Both synthetic or natural solid resins have this specific

ability. The most common cation exchangers are strongly acidic resins and weakly acidic resins. The

strongly acidic resins with sulfonic acid groups (-SO3H), weakly acidic resins with carboxylic acid

groups (-COOH), hydrogen ions in those two groups can serve as exchangeable ions with metal cations.

The uptake of heavy metal ions by ion-exchange resins is affected by several variables, such as initial

metal concentration, temperature, pH, and contact time (Gode and Pehlivan, 2006). Ionic charge also

plays an important role, as higher ionic charge ion exchange resin will adsorb faster. In addition to

synthetic resins, natural zeolites and naturally occurring silicate minerals have also been widely used

8

for heavy metal removal from aqueous solutions because of their high abundance and low cost. Zeolites

are limited at present compared with synthetic resins. The application of zeolites is limited to the lab

scale. There are a lot work needed until the application of zeolites at an industrial scale.

2.2.3. Adsorption

At present, adsorption is recognized as an effective and economic method for heavy metal wastewater

treatment. The adsorption process offers flexibility in design and operation and in many cases will

produce high-quality treated effluent. Adsorption has another advantage, in that, adsorption is reversible.

There are four types of adsorbents: activated carbon adsorbents, carbon nanotubes adsorbents, low-cost

adsorbents, and bio-adsorbents. Activated carbon (AC) adsorbents’ usefulness derives mainly from its

large micropore volumes and the resulting high surface area. Carbon nanotubes (CNTs) as relatively

new adsorbents, and it has been proven to have great potential for removing heavy metal ions. For

example, Li et al., 2010 used CNTs immobilized by calcium alginate as adsorbents for removing copper

ions, and maximum sorption capacities of copper is 67.7 mg/g, when pH = 5 and temperature is equal

to 25℃. Although activated carbon has been the most used adsorbent, the price of AC is relatively high,

so more and more researchers are trying to find low-cost and easily available adsorbents to remove

heavy metals. Those researchers found agricultural wastes, industrial byproducts and natural substances

all can be used as adsorbents. Agoubordea and Navia (2009) reported copper can be removed by brine

sediments from aqueous solution, and the maximum adsorption capacity was found to be 4.69, 2.31,

and 4.33 mg/g for copper, using an adsorbent/solution ratio of 1/40. Apiratikul and Pavasant, 2008

illustrated typical biosorbents can be derived from three sources as follows: (1) non-living biomass such

as bark, lignin, shrimp, krill, squid, crab shell, etc.; (2) algal biomass; (3) microbial biomass, e.g.

9

bacteria, fungi and yeast. There is a renewable natural biomass founded by some researchers, which is

algae. Several advantages in applying algae as biosorbent include the wide availability, low cost, high

metal sorption capacity and reasonably regular quality. Ajjabi and Chouba (2009) investigated Cu2+ can

be removed by dried marine green macroalga (C.linum). At biosorbent dosage (20 g/L) and initial

solution pH of 5, the dired alga produced maximum Cu2+ 1.46 mmol/g (104.14 mg/g).

2.2.4 Membrane filtration

Recently, membrane technologies have been used to remove metals from wastewater. The common

membrane processes that used are ultrafiltration, nanofiltration, reverse osmosis and electrodialysis (Fu

and Wang, 2011).

2.2.4.1 Ultrafiltration

Ultrafiltration (UF) is normally working at low transmembrane pressures to remove dissolved and

colloidal material. The pore sizes of UF membranes are larger than the dissolved metal ions in the form

as low molecular weight complexes or in the form of hydrated ions and could easily pass through

Ultrafiltration membranes. In order to get high removal efficiency of metal ions, two kinds of

ultrafiltration membranes were proposed, one is miceller enhanced ultrafiltration (MEUF) another is

polymer enhanced ultrafiltration (PEUF). MEUF was first proposed to remove multivalent metal ions

and dissolved organic compounds from aqueous streams (Landaburu-Aguirre et al., 2009). Metal

removal efficiency by MEUF depends on the membrane characteristics, concentration of metals and

surfactants, ionic strength, pH of solution and parameters of membrane operation. Sampera et al. (2009)

used MEUF to remove Cd2+, Cu2+, Ni2+, Pb2+ and Zn2+ from synthetic water using two anionic

surfactants: sodium dodecyl sulfate (SDS) and linear alkylbenzene sulfonate (LAS) in a lab-scale

10

membrane system. LAS is quite effective at removing heavy metals from aqueous solution. To remove

90% of metal ions, LAS concentrations as low as 1 mM, which is lower than those obtained for SDS at

9 mM concentration.

PEUF also has been proposed to separate a great variety of metal ions from aqueous streams. PEUF

uses water-soluble polymers to react with metal ions and form a high molecular complex that is larger

than the molecular weight cut-off of the membrane. The high-molecular complex will be retained when

they are pumped through the UF membrane. Based on previous PEUF studies, finding suitable polymers

to achieve complexation with achieve complexation with metal ions is the main concern of membrane

choice. Common complexing agents used in PEUF are polyethyleneimine (PEI) (Molinari et al., 2008),

carboxy methyl cellulose (Barakat and Schmidt, 2010) and Poly(acrylic acid) sodium (Camarilloa et al.,

2010). There are a lot of advantages of PEUF, such as high binding selectivity, and highly concentrated

metal concentrates for reuse and so on.

2.2.4.2 Nanofiltration

Nanofiltration is a promising technology to remove heavy metal ions from wastewater. The anofiltration

process is relatively easy to operate, has comparatively low energy consumption and a high removal

efficiency. Ku et al., 2004 used nanofiltration to remove copper from aqueous solutions using two

surfactants: anionic surfactants, sodium dodecyl sulfate (SDS) and cationic surfactants, Cetyl trimethyl

ammonium bromide (CTAB). The rejection rate of copper is strongly influenced by several factors,

including solution pH, operating pressure, concentration of anion, presence of surfactant and chelating

agent. Copper rejection was increased by increasing the operating pressure, however, when the pressure

is very high, copper rejection reached a constant point with no further increase. If there are surfactants

11

present in aqueous solution, it will be adsorbed and form a secondary filtration layer on the membrane

surface. This secondary filtration layer may influence the charge characteristics of the membrane

surface, thus increasing copper rejection. Chelating reagents will react with copper ions and form copper

chelates, which has high molecular weight and exceeds the molecular weight cut-off of the membrane,

therefore copper rejection rate was clearly increased by using chelating reagents.

2.2.4.3 Reverse Osmosis

Reverse osmosis is a technique which is able to remove a wide range of dissolved species from aqueous

solution. Copper ions were successfully removed by the reverse osmosis process, and removal

efficiency is 99.5% by using Na2EDTA (Mohsen-Nia et al., 2007).

2.2.4.4 Electrodialysis

Electrodialysis (ED) also is a membrane process for the separation of ions transported through charged

membranes from one solution to another which uses an electric field as the driving force. Most ED

processes use ion-exchange membranes, and those membranes consist of two basic types: anion-

exchange and cation-exchange membranes. Cifuentes et al. (2009) studied the effectiveness of ED for

the separation of Cu and water recovery from solutions in copper electrowinning operations. They

proved ED is a very effective process in removal of Cu from the working solution.

2.2.5 Coagulation and flocculation

Coagulation and flocculation is always followed by sedimentation and filtration in a conventional water

treatment plant. Coagulation is the destabilization of hydrophobic colloids by double layer compression,

charge neutralization, enmeshment, and interparticle bridging. Aluminum, and ferric chloride are

12

widely used in the conventional wastewater treatment process. El Samrani et al. (2008) found

coagulation of combined sewer overflow with two commercial coagulants’ combination, ferric chloride

and polyaluminum chloride (PAC) can effectively to remove heavy metals from wastewater.

Flocculation is the action of polymers to form bridges between flocs and bind the particles into large

particles, so they can be removed by filtration. Since the traditional flocculants can’t remove heavy

metals very well from wastewater directly, Heredia and MartI n (2009) reported a new commercial

tannin-based flocculant to remove Zn2+, Ni2+ and Cu2+ by coagulation-flocculation process.

2.2.6 Electrochemical treatment

Electrochemical methods mainly concerned the plating-out of metal ions on a cathode surface and can

recover metals in the elemental metal state (Fu and Wang, 2011). A few decades ago, electrochemical

waste water technologies haven’t been widely applied due to high capital cost and the expensive

electricity supply. However, because of the rigorous environmental regulation, the electrochemical

technologies are becoming more widely used. Electrocoagulation (EC), electroflotation (EF), and

electrodeposition (ED) were examined by several studies.

Jack et al. (2013) studied the performance of an EC system for removing copper. Their initial laboratory-

scale study comfirmed that copper in settlings could be reduced by up to 95%. This system was scaled

up and copper reduction of 88% was achieved at 34 W h/m3 and 96% removal was achieved at 112 W

h/m3.

Electroflotation (EF) is a process which is used to separate solid and liquid. Pollutants are floated to the

surface of a water body by tiny bubbles of hydrogen and oxygen gases that are generated from water

13

electrolysis (Fu and Wang, 2011). EF has been widely used for removing heavy metals from industrial

waste water. Belkacem et al. (2008) studied the decontamination of wastewater using EF technique with

aluminum electrodes. Their study proved that the metal removal rate reached 99%.

Electrodeposition (ED) has been prevalently applied for the recovery of metals from wastewater. It is a

“clean” technology which will not produce any permanent residues for removing heavy metal from

wastewater. Chang et al. (2009) employed ED in conjunction with ultrasound to recover copper from

EDTA-copper wastewater. They investigated that the technique can effectively remove copper, and the

removal rate of copper reached 95.6%. Electrodeposition is a technique which can provide good

reduction and produce less sludge simultaneously. Rahimi et al. (2017) developed a thermally

regenerative ammonia battery (TRAB) to remove copper from water and generate electricity. Maximum

77% removal was achieved when initial copper concentration was 0.05M when lowering the initial

copper concentration, the percentage of copper removal decreased from 51%(Ci =0.01M) to 2% (Ci

=0.002M)

2.3 Copper Removal/Recovery by Electrowinning (Electroextraction), Chemistry

2.3.1 Conventional Electrowinning studies for copper removal

Electrowinning, also called electroextraction, which is commonly used process in the smelting industry.

Electrowinning is an electrodeposition of metals process from their ores using aqueous solution also

called leach solution. In the traditional electrowinning process, a current is passed from an anode

through an aqueous solution which contains the metal, and the metal is extracted and deposited onto the

cathode.

14

In recent years, the electrowinning process is also commonly used to remove heavy metals from

different kinds of water system. Panda and Das (2000) proposed a study on copper electrowinning from

sulfate electrolyte in presence of sulfurous acid. In this study, anode material plays an important role in

electro-oxidation of Sulfur dioxide. They discovered graphite anode showed the best performance

comparing to other anodes tested.

Lu et al. (2002) established a membrane cell with graphite cathode for copper electrowinning from

dilute cyanide solution. Lu et al. discovered that copper current deposition efficiency increased with the

increasing surface area but decreases with the increasing the mole ratios of cyanide and copper.

Gorgievski et al. (2009) applied electrowinning to remove copper from acid mine drainage which

contains a small number of ferrous/ferric ions. Gorgievski et al. confirmed that copper can be removed

successfully from acid mine drainage by the direct electrowinning method, and removal rate can be

achieved above 92%. Both carbon felt or porous copper sheets are a good choice for cathode application.

The decrease of pH value is a consequence of oxygen evolution in anode reaction which increases the

acid content and results in the decrease of cell voltage.

2.3.2 EMEW Electrowinning

In 1992, “vortex” electrowinning technology was developed by EMEW clean technologies in Australia.

Conventional electrowinning places an anode and cathode into an electrolyte bath at a low flow rate or

remain still. The metal ions plated on the cathode via diffusion after a reaction. For EMEW

electrowinning technology, the electrolyte is circulated rapidly past the anode and cathode at a very

high flow rate, like a cyclone. This technique significantly enhances mass transfer of copper ions and

improves the removal efficiency of the copper.

15

The design principle of EMEW electrowinning cells is similar to the conventional electrowinning cell.

However, the flow rate of EMEW cell is very high and the electrolyte will form a “cyclone” flow. The

structure of EMEW cell is a cylinder, and a stainless-steel sheet is used as a cathode and inserted into

the body of the EMEW electrowinning cell. The electrolyte is pumped into the cell from the bottom of

the cell. Power is applied to the anode and cathode and metal will plate on the cathode.

2.3.3 Chemistry for copper electrowinning

This approach concerns electrodeposition or reduction of metal ions from an electrolyte. In

electrowinning process, a current passed between the electrodes and metal ions diffuse to the surface of

the cathode forming a surface complex on the cathode, receive electrons from the cathode, and are

reduced to the metallic state (Grimshaw et al., 2011). Lin et al. (1991) presented two competitive

processes for copper electrowinning from cupric chloride solution: complexation and dissolution

(Equation 2.1) or further reduction to metallic copper (Equation 2.2).

𝐂𝐮𝟐+ + 𝑪𝒍− + 𝒆− = 𝑪𝒖𝑪𝒍𝒂𝒅𝒔 + 𝒏𝑪𝒍− = 𝑪𝒖𝑪𝒍𝒏−(𝒏−𝟏)

Equation 2.1

𝐂𝐮𝟐+ + 𝑪𝒍− + 𝒆− = 𝑪𝒖𝑪𝒍𝒂𝒅𝒔 + 𝒆− = 𝑪𝒖𝟎 + 𝑪𝒍− Equation 2.2

Based on the equations presented by Lin et al, the chemical reaction equations for copper electrowinning

from brine water is proposed and shown in equation 2.3 and equation 2.4.

𝐇𝟐𝑶 → 𝟐𝑯+ +𝟏

𝟐𝑶𝟐 + 𝟐𝒆−

𝐂𝐮𝟐+ + 𝟐𝒆− → 𝑪𝒖

𝐂𝐮𝟐+ +𝑯𝟐𝑶 → 𝑪𝒖+ 𝟐𝑯+ +𝟏

𝟐𝑶𝟐 Equation 2.3

16

𝟐𝐂𝐥− − 𝟐𝒆− → 𝑪𝒍𝟐

𝐂𝐮𝟐+ + 𝟐𝒆− → 𝑪𝒖

𝐂𝐮𝟐+ + 𝟐𝑪𝒍− → 𝑪𝒖+ 𝑪𝒍𝟐 Equation 2.4

17

Chapter 3

Material and Methods

3.1 Chemicals

Table salt without iodide and cupric sulfate pentahydrate were used to prepare solutions for

electroplating process. Table salt was obtained from Morton salt (Chicago, IL). Cupric sulfate

pentahydrate (CAS 7758-99-8) was purchased from VWR International (Philadelphia, PA). For copper

concentration analysis, CuVer 1 Copper Reagent were used and purchased from HACH company

(Loveland, CO). The copper reagent contains 2,2-Bicinchoninate, Dipotassium and Potassium

Phosphate, Monobasic. For chlorine concentration analysis, DPD Free Chlorine Dispenser (10 mL

sample) was used and purchased from Scientific (Ft Myers, FL). Concentrated nitric acid was used to

preserve waste brine samples collected from East Steam Plant, University Park, PA.

3.2 Electrowinning Method and Apparatus

3.2.1 Batch Reactor: Graphite anode (rod) and graphite cathode (rod)

Basic electrochemical reactor is composed by a beaker (600 mL), a magnetic stir and two graphite rods,

one is anode, and the other is cathode. The volume of electrolyte is 400 mL. The graphite rods were

purchased from Eisco Scientific LLC (Rochester, NY), and have the following dimensions: length 10

cm, diameter 0.6 cm. A power supply is used in this study, which is Aglient technologies U8002A power

supply, DC, Bench, 30V, 150W. The Voltage (U) of power supply was controlled at different voltages.

The setup of this reactor is shown in Figure 3.1.

18

Figure 3.1: The setup of Batch Reactor: Graphite anode (rod) and graphite cathode (rod).

3.2.2 Continuous Reactor: Double graphite anode (rectangle plate sheet) and single graphite

cathode (rectangle plate sheet)

Continuous reactor (1) is composed of a beaker (1,000 mL), a plastic square vessel, and two pumps.

The plastic square vessel had the following dimensions: length 12.1 cm, width 8.4 cm, and height 12.4

cm. The volume of square vessel was 1260 mL. The total volume of electrolyte was 1400 mL, the

volume of electrolyte in square vessel was 600 mL and volume of electrolyte in the beaker was 800 mL.

The anodes and cathode used were graphite square sheet. 99.9% pure graphite block electrode rectangle

plate blank sheets were purchased from China. The graphite sheets had the following dimensions: length

10 cm, width 10 cm, and thickness 1 cm. A power supply was used in this study, which is Aglient

technologies U8002A power supply, DC, Bench, 30V, 150W. The Voltage (U) of power supply was

controlled at different voltage. The set-up is shown in Figure 3.2. The electrolyte was pumped into the

cell through a hole at the bottom of one side and pumped out of the cell through a hole at the top of

another side. The direction of flow was parallel to the plate electrodes. The copper concentrations of

electrolyte in the beaker were tested during the process.

Aglient Power Supply

Magnetic Stir

Anode Cathode

19

Figure 3.2: The set-up of Continuous Reactor: Double graphite anode (rectangle plate sheet) and

Single graphite cathode (rectangle plate sheet)

3.2.3 Internal Circulation Reactor: graphite anode (rod) and aluminum/titanium and platinum

mesh basket cathode

Internal circulation reactor was composed of a beaker (1,000 mL), and one pump. The volume of

electrolyte was 800 mL. The anodes used were graphite rods. The graphite electrodes were purchased

from Eisco Scientific LLC, NY. The graphite rods had the following dimensions; length 10 cm and

diameter 0.6 cm. Two different kinds of cathodes were used, aluminum sheets and titanium and platinum

mesh sheets. Those two kinds of sheets were shaped into a cylinder with the following dimensions;

Pump

Pump

Anodes

Cathode

20

length is 5 cm and diameter is 5 cm. A power supply was used in this study, which is Agilent

technologies U8002A power supply, DC, Bench, 30V, 150W. The Voltage (U) of power supply was

controlled at different voltages. The set-up is shown in Figure 3.3.

Figure 3.3: The set-up of Internal Circulation Reactor: graphite anode (rod) and aluminum/titanium

and platinum mesh basket cathode

3.3 Copper Analysis

The copper concentration of sample water was tested by USEPA Bicinchoninate Method 8506. The

detection range of copper concentration is 0.04 to 5.00 mg/L, so the samples were diluted prior to

analysis as necessary. First, prepare the blank sample cell with 10 mL of sample, clean the blank sample

cell then insert the blank into the cell holder and push zero. Second, CuVer 1 Copper Reagent powder

pillow was added to 10-mL sample water, swirl to mix. After 2-minute reaction, clean the prepared

sample cell, insert it into the cell holder and push READ. Results are shown in mg/L.

Anode

Cathode

Pump

21

3.4 Free chlorine Analysis

After every 45 minutes’ operation, the chlorine concentration of sample water was tested by USEPA

Method 8021. The detection range of chlorine concentration is 0.00 to 2.00 mg/L, so the samples were

diluted prior to analysis as necessary. First, a blank sample cell with 10 mL of sample was prepared,

clean the blank sample cell and then inserted the blank into the cell holder and pushed zero. Second,

DPD Free Chlorine Powder Pillow was added to 10-mL sample water, swirl to mix. Clean the prepared

sample cell, immediately inserted it into the cell holder and pushed READ, results are shown in mg/L.

3.5 Conductivity Analysis

The salt concentration for actual waste brine samples from East Steam Plant, University Park, PA were

analyzed by conductivity test. The conductivity was analyzed right after sample collection using HACH

51800-10 Sension5 water proof conductivity meter.

3.6 Sampling events at Harrisburg and University Park

In 2016, Dr. Malcolm Taylor coordinated the sampling of waste brine solution from various operation

cycles of ion exchange softener brine regeneration process at PSU East Steam Plant. All samples were

analyzed for copper using HACH Method 8506 (Xie et al. 2016, 2017). The samples were diluted if

copper concentration exceeded the maximum detection limit, 5.5 mg/L. The results indicated that the

total copper concentration for sub-wash, backwash, brine inject, slow rinse, fast rinse, was 36, 1.3-20.0,

22

2.9-8.0, 180-282, and 0.9, mg/L, respectively. Dissolved copper was mainly coming from the slow rinse

cycle.

Sampling waste brine solution was done twice at East Steam Plant, University Park on December 6th,

2017 and January 22nd, 2018 from various cycles of ion exchange softening process, brine inject, slow

rinse, and fast rinse (cold and hot). The conductivity was analyzed using HACH water proof

conductivity meter right after sample collection, then they were preserved by nitric acid, and pH was

controlled around 2.

23

Chapter 4

Results and Discussion

4.1 Analysis of brine solutions

Sampling of waste brine solution was done twice at East Steam Plant, University Park on December

6th, 2017 and January 22nd, 2018 from various cycles of ion exchange softening process, brine inject,

slow rinse, fast rinse (cold and fast). The conductivity was analyzed using HACH water proof

conductivity meter right after sample collection, then those samples were preserved by nitric acid and

pH was controlled around 2. System operation parameters of PSU East Steam Plant are shown in Table

4.1.

Table 4.1: Backwash operating procedure of PSU East Steam Plant

Stage Duration (min) Cum. Time (min) Flow (gpm)

Sub-wash 5 5 35

Backwash 30 35 35

Brine Inject 25 60 4

Slow rinse 40 100 8

Fast rinse 10 110 35

Fast rinse hot 10 120 35

Both conductivity test and copper concentration test were done for all of the samples collected.

Salt concentrations were estimated by the relationship between conductivity which shown in Table 4.2,

while results for Dec. 6th, 2017 and Jan. 22nd, 2018 are shown in Table 4.3 and 4.4.

Table 4.2: Electrical Conductivity of Sodium Chloride NaCl (Haynes, W. M., 2009)

Concentration (mass percent) 0.5% 1% 2% 5% 10% 15% 20% 25%

Molar concentration (M) 0.09 0.17 0.34 0.86 1.70 2.57 3.42 4.28

Conductivity (mS/cm) 8.2 16.0 30.2 70.1 126 171 204 222

The salt concentration of brine inject solution is 3.91- 4.40 M, and the average salt concentration for

slow rinse is 1.98 - 2.13 M.

24

Table 4.3: Salt concentration result of waste brine solution from East Steam Plant, University Park,

when samples were collected on Dec 6th, 2017

Sample Temperature (degree C) Conductivity (mS/cm)

Estimated Salt

Concentration (M)

Brine Inject 24.5 234 4.40

Slow Rinse 0 min 19.5 140 1.98

5 min 19.4 142 2.02

10 min 20.2 145 2.07

15 min 20.1 150 2.16

20 min 20.3 152 2.19

25 min 20.5 152 2.20

30 min 20.3 163 2.42

35 min 20.2 156 2.28

40 min 20.1 135 1.86

Fast Rinse (Cold)

5 min 20.1 87 1.11

Fast Rinse (Hot)

5 min 16.1 1.27 0.01

Table 4.4: Salt concentration result of waste brine solution from East Steam Plant, University Park,

when samples were collected on Jan. 22nd, 2018

Sample Temperature (degree C) Conductivity (mS/cm)

Estimated Salt

Concentration (M)

Brine Inject solution 12.5 214 3.91

Brine Inject 5 min 15.8 34.8 0.40

Brine Inject 10 min 16.2 77.6 0.97

Brine Inject 20 min 16.4 166 2.47

Slow Rinse 0 min 17.1 136 1.89

5 min 18.7 137 1.90

10 min 17.8 143 2.03

15 min 18.6 148 2.13

20 min 19.8 149 2.14

25 min 18.3 152 2.21

30 min 18.7 150 2.17

35 min 19.1 150 2.17

40 min 19.0 85.1 1.09

Fast Rinse (Cold) 5 min 13.3 34.9 0.40

Fast Rinse (Hot) 5 min 19.0 0.8 0.01

25

The dissolved copper concentration results are shown in Table 4.5 and Table 4.6 for Dec. 6th, 2017

and Jan. 22nd, 2018, respectively. The copper concentrations during slow rinse for Dec. 6th, 2017 and

Jan. 22nd, 2018 are 14.3 – 61.0 mg/L and 7.3 – 34.7 mg/L, which are much lower than the copper

concentration of samples collected by Dr. Malcolm Taylor on Dec 20, 2016 (180-282 mg/L).

Table 4.5 Dissolved copper concentration of waste brine solution from slow rinse and fast rinse stage,

samples were collected from East Steam Plant, University Park on Dec 6th, 2017

Sample Dissolved opper concentration

Slow Rinse First Test (mg/L) Second Test (mg/L) Average Value (mg/L)

0 58.5 63.5 61.0

5 57.5 61.5 59.5

10 52.5 55.5 54.0

15 45.0 46.0 45.5

20 40.0 40.5 40.3

25 36.5 37.5 37.0

30 33.0 33.0 33.0

35 30.5 23.0 26.8

40 15.0 13.5 14.3

Fast Rinse (Cold) 4.7 5.0 4.9

Fast Rinse (Hot) 1.2 1.5 1.4

Table 4.6: Dissolved copper concentration of waste brine solution from slow rinse and fast rinse stage,

samples were collected from East Steam Plant, University Park on Jan 22nd , 2018

Sample

Copper concentration

First Test (mg/L) Second Test (mg/L) Average Value (mg/L)

Brine Inject 20 min 33.3 41.3 Slow Rinse

0 32.2 37.2 34.7

5 25.5 29.5 27.5

10 28.5 31.5 30.0

15 26.5 27.5 27.0

20 20.5 21.0 20.8

25 19.5 20.5 20.0

30 15.5 15.5 15.5

35 11.5 8.5 10.0

40 8.0 6.5 7.3

Fast Rinse (Cold) - 5.0 5.0

Fast Rinse (Hot) - 1.5 1.5

26

4.2 Electrowinning of actual waste brine solutions using the Batch Reactor

Copper electrowinning test were done by using two samples collected during slow rinse cycle (10

min and 25 min) in East Steam Plant on Dec. 6th, 2017. The setup for the electrowinning process is

followed by Figure 3.1. The distance between two electrodes were controlled at 1 cm.

The salt concentration for these two samples is around 2.15 M. After three hours’ reaction, the

percent removal is 46.5% and 61.6%, respectively. In order to analyze the influence of other contents

and nitric acid in waste brine solution on copper electrowinning, two simulated sample of brine solution

with similar initial copper concentration (70 mg/L) and salt concentrations (2.15 M) was prepared for

the test. These two samples, one is added nitric acid, one isn’t added any nitric acid. As seen in Figure

4.1, after three hours of reaction, 69.9% of dissolved copper was extracted from the simulated brine

solution (with nitric acid), 72% of dissolved copper was extracted from the simulated brine solution

(without nitric acid). Based on the results, other content and nitric acid in the waste brine solution didn’t

play an important role in copper electrowinning process.

0

10

20

30

40

50

60

70

80

0 50 100 150 200

Dis

solv

ed C

op

per

Co

nce

ntr

atio

n (

mg/L

)

Reaction time (min)

Slow rinse 10 min

Slow rinse 25 min

Simulated water sample (with nitric acid)

Simulated water sanple (without nitric acid)

27

Figure 4.1: The concentration of copper varies according to reaction time of electrowinning process for

different samples. (Salt concentration for four samples: ~ 2.15 M)

Lower initial copper concentration is likely a reason for lower removal efficiency. To prove this

hypothesis, 0.175 g copper sulfate was spiked to actual waste brine sample (slow rinse 15 minutes) to

control the initial copper concentration at 221 mg/L which is similar to the copper concentration of

samples collected in December, 2016. After three hours of electrowinning, 85% removal of copper was

achieved, which means at the same condition, an increase in initial copper concentration could increase

the copper removal efficiency. The results of copper concentration verses time are shown in Figure 4.2.

The removal efficiency of this sample is very similar to the simulated water sample when at similar salt

concentration. Based on this, initial copper concentration is an important factor of copper removal

efficiency.

Figure 4.2: Copper concentration vs. time. The electrolyte: 221 mg/L Cu, 2.16 M NaCl.

28

4.3 Electrowinning of synthetic samples using the Batch Reactor

4.3.1 Impact of salt concentration on Copper Removal

Since the copper was discharged through waste brine solution, the effects of sodium concentration

on copper removal was investigated. Four simulated waste brine water samples were prepared with

different concentration of sodium chloride, 0, 1M, 2.5M, 4M (saturated point of sodium chloride) and

constant concentration of copper sulfate pentahydrate (Cu2+ = 250 mg/L). Those four simulated water

samples were treated using batch reactor, the set up as shown in Figure 3.1. The area of each electrode

immersed in the solution was 15.072 cm2, and the distance between anode and cathode was controlled

at 2 cm.

As shown in Figure 4.3, the concentration of sodium chloride greatly impacts the copper removal

with electrowinning. Without sodium chloride addition (sodium chloride concentration at 0 M), the

electrical conductivity of this solution is very low, which gave a poor removal of copper. Increasing the

concentration of sodium chloride to 1.0 M and 2.5 M, the copper removal increased to 94% and 89%,

respectively. Further increasing brine solution to 4 M resulted in the lowest copper removal, at 26%.

In order to determine appropriate range of salt concentration for copper electroextraction, we did

nine concentrations between zero and saturated point of sodium chloride. The result of maximum copper

reduction for different salt concentration appears in Figure 4.4.

29

Figure 4.3: Effects of Brine Concentration on Copper Removal.

Figure 4.4: Summary of Brine Concentration Effects on Copper Removal. The error bar represents 2

standard deviations.

0

50

100

150

200

250

300

0 45 90 135 180

Co

pp

er c

on

cen

trat

ion (

mg/L

)

Time (min)

0 M

1 M

2.5 M

4 M

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3 3.5 4

Max

imum

Red

uct

ion (

%)

NaCl Concentration

30

Based on the results which presented in Figure 4.4, when the concentration was between 0.5 – 1.5

M, more than 90% copper reduction was achieved after a three-hour reaction. If the salt concentration

is out of this range, the maximum copper reduction is below 60% after a three-hour reaction. After three

hours’ reaction, there are some dark red particles attached to cathode, but those particles can’t attach to

electrode very well, when the electrode was taken out from water, those particles will drop down to the

water. The observations of color change are different with different salt concentration. When the

concentration of sodium chloride is below 1 M, the color change of solution during the process is from

light blue to clear and colorless. However, when the concentration of sodium chloride is above 1 M, the

color of water sample is from cloudy and blue-green to cloudy and dark yellow. Copper concentrations

for each of four simulated waste brine water samples over the course of three hours’ electrowinning

process are presented in Figure 4.3. The reason that has caused these different color observation is when

salt concentration increases, the following reaction will happen.

CuSO4 + 4NaCl ⇄ Na2[CuCl4] + Na2SO4

There is a coordination bond between the chlorine ion and the copper ion. The color of CuCl42- is

yellow, and the resulting green color is because it still has some Cu2+ ion. The color of Cu2+ ion is blue,

the combination of yellow and blue is green. When Cu2+ ions in the solution were extracted completely,

the color turned to yellow. When chlorine presented in the solution, the color was yellow. Therefore,

yellow color of the solution should be the result of the combination of CuCl42- and Cl2.

The concentration of chlorine was tested after three hours’ reaction, results are shown in Figure

4.5. As seen in Figure 4.5, when salt concentration was less than 2.5 M, the maximum chlorine

concentration was obviously increasing, and salt concentration was more than 2.5 M and below 4 M,

31

the maximum chlorine concentration was decreasing. Discharge of the treated waste brine solution with

chlorine levels up to 90 mg/L is unlikely to affect the downstream wastewater treatment plant operation

because of the high dilution factor. However, this high chlorine level is a safety concern for

electrowinning operation. Proper measures should be adopted to mitigate the risk.

Figure 4.5: Effects of Brine Concentration on Chlorine Production.

Furthermore, based on the observation during the reaction, extracted copper could not stick to the

electrode very well. The copper dropped into the water when the electrode was removed from water. To

solve this problem, we decreased the salt concentration to below 0.5 M. It is well known that decrease

the distance between anode and cathode could increase current density, so the distance between anode

and cathode was controlled at 1 cm for this study.

Five different salt concentrations between 0 – 0.5 M (0.1, 0.2, 0.3, 0.4, 0.5 M) were applied in the

process. After three hours’ reaction, maximum reduction of copper with those five salt concentrations

0

15

30

45

60

75

90

0 0.5 1 1.5 2 2.5 3 3.5 4

Chlo

rine

conce

ntr

atio

n (

mg/L

)

Salt concentration (M)

32

were all above 90%. Unfortunately, the copper could not stick to the cathode either, so the salt

concentration kept reducing to 0 – 0.1 M, (0.02, 0.04, 0.06, 0.08 M), and results are seen in Figure 4.6.

Based on the observation, when the salt concentration was below 0.08 M, the copper stuck to the

cathode, and easily be removed from water. When the salt concentration was equal to 0.08 M, the

maximum copper reduction could be achieved to 98% after three hours.

Figure 4.6: Effect of lower salt concentration on maximum copper reduction.

4.3.2 Kinetics

Regarding the kinetic of copper reduction in the brine solutions, a plot of ln C versus time for

copper reduction gives a linear trace as shown in Figure 4.7. We found that the kinetic of copper

reduction occurs as a first order reaction.

0

20

40

60

80

100

120

0 0.02 0.04 0.06 0.08 0.1

Max

imum

Co

pp

er R

educt

ion (

%)

NaCl Concentration (M)

33

Figure 4.7: A semi log plot of the course of copper electrowinning with four different salt concentrations

(0, 1, 2.5, 4M)

The copper concentration could be expressed by equation 4.1, where k is the rate constant of copper

reduction. Estimated rate constants of copper electrowinning with four salt concentrations are presented

in Table 4.8.

[Cu2+]t = [Cu2+]0 ∗ 𝑒−kt

Equation 4.1

As seen in Table 4.7, rate constant is not constant for all salt concentrations. This is likely caused

by the impurity of the table salt, because table salt has some other complexes, such as calcium silicate.

However, there is linear relationship within a certain range. As seen in Figure 4.8, two linear

relationships happened in the range of 0.5 – 2 M and 2.5 – 4 M.

0

1

2

3

4

5

6

0 50 100 150 200

ln C

Time (min)

0 M

1 M

2.5 M

4 M

34

Table 4.7 Summary of rate constant for different salt concentrations

Salt concentration (M) k (1/min)

0 -0.0026

0.5 -0.0156

1 -0.0148

1.5 -0.014

2 -0.0127

2.5 -0.0091

3 -0.0065

3.5 -0.0042

4 -0.0015

Figure 4.8: Effect of salt concentrations (M) on rate constants (1/min).

4.3.3 Voltage-Maximum copper reduction relationship

In order to figure out the relationship between voltage and maximum copper reduction, four

different voltages were tested. The results of maximum copper reduction and chlorine concentration are

presented in Figure 4.9. Based on the results, a significant positive correlation exists between voltage

and maximum copper reduction. Furthermore, the larger voltage was applied, the higher chlorine

y = 0.0019x - 0.0167

y = 0.005x - 0.0216

-0.018

-0.016

-0.014

-0.012

-0.01

-0.008

-0.006

-0.004

-0.002

0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Rat

e C

onst

ant

(1/m

in)

Salt concentration (M)

35

concentrations were detected. Increasing electrowinning voltage to 2.5 V, copper reduction was over

90%, but chlorine production also reached the maximum, 80 mg/L.

Figure 4.9: Effects of Brine Concentration on Copper Removal and Chlorine Production. The

concentration of sodium chloride was controlled at 1 M.

4.3.4 Change of current efficiency with reaction time

To improve the removed efficiency of copper, graphite blank sheets were used instead of rods. The

graphite blank sheets had the following dimensions: length 10 cm, width 5 cm, and thickness 1 cm. The

distance between anode and cathode was controlled at 2 cm. 99% removal of copper was achieved after

2 hours, which meant that at the same condition, increasing the immersed electrode surface area could

increase the copper remove efficiency. The results of copper concentration and current varies with time

as seen in Figure 4.10.

0

10

20

30

40

50

60

70

80

90

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 1.5 2 2.5 3

Ch

lori

ne

Co

nce

ntr

atio

n (

mg/L

)

Max

imu

m R

edu

ctio

n (

%)

Voltage (V)

Copper reduction

Chlorine concentration

36

Figure 4.10: Copper concentration and the current of copper deposition vs. time. The electrolyte: 237

mg/L Cu, 0.08 M NaCl.

The current efficiency is defined by the ratio of the actual mass of deposited copper and that

computed according to Faraday’s Law. The actual mass of deposited copper could be expressed by

Equation 4.2. The current efficiency could be defined by Equation 4.3. (Gorgievski et al., 2009) Current

efficiency verses time, estimated values are presented in Table 4.9.

𝑚 = [𝐶𝑖 − 𝐶(𝑡)] ∗ 𝑉

Equation 4.2

ƞ𝑒 =[𝐶𝑖 − 𝐶(𝑡)] ∗ 𝑉𝑧𝐹

𝐼𝑡𝑀

Equation 4.3

Where 𝐶𝑖 is the initial copper concentration (mg L-1); 𝐶(𝑡) is copper concentration at different

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0

50

100

150

200

250

0 30 60 90 120

Cu

rren

t (A

)

Co

pp

er C

on

cen

trat

ion

(m

g/L

)

Reaction time (min)

Copper Concentration

Current

37

reaction time (mg L-1); 𝑉 is the volume of electrolyte (L). 𝑧 is the number of exchanged electrons in

the reaction; 𝐹 is the Faraday’s constant (96485 A s mol−1); 𝐼 is the current (A); (Gorgievski et al.,

2009) 𝑀 is the molecular weight of copper (63.5 g mol−1). The volume of electrolyte is 0.4 L.

Table 4.9: Estimated Current Efficiency (V = 2.5V)

Reaction time (min) Copper Concentration (mg/L) Current (A) Current Efficiency (%)

0 237 0.14 0

30 141 0.11 23.4

60 51 0.11 22.7

90 15 0.11 18.1

120 2.9 0.11 14.3

As seen in table 4.9, the current efficiency rapidly increased in first hour, because the copper

concentration is rapidly decreased during this period, the increase of current efficiency leveled off after

60 minutes.

4.4 Continuous Reactor

In actual application, water flow is used instead of stirring. The set-up of the continuous reactor

was followed by Figure 3.2. Five different flow rates were applied for the continuous reactor. In order

to increase the removal efficiency of copper, graphite sheets were used instead of graphite rods for the

continuous reactor. The surface area of each electrode immersed in the solution is 170 cm2, which is

more than ten times of the rod electrodes. Applied voltage was controlled at 2.5 V, and the salt

concentration of electrolyte was 1 M. The hypothesis of this study is to improve the removal efficiency

of copper by increasing the surface area of the electrode immersed in the solution. However, the results

of the experiment contradict the original hypothesis.

At the start of this study, flow rate was controlled at 10 mL/min. There was not a significant change

38

in copper concentration for the first three-hour reaction, so reaction time was extended to five hours.

During the reaction, some light blue floccules were attached to both sides of the cathode instead of red

particles and maximum copper reduction was significantly lower than expected. In order to figure out

the reason, a new hypothesis was established. The increase in the flow rate had an effect on copper

removal efficiency. The results showed the concentration of copper kept decreasing over a longer time

of electrowinning. The maximum copper reduction increased by increasing the flow rate from 10

mL/min to 20 mL/min. However, the maximum copper reduction decreased as the flow rate further

increased. Based on the observation and results, flow rate plays a major role in copper removal in the

electrowinning process. Copper concentrations for five flow rates over the course of five hours’

electrowinning process are presented in Figure 4.11 and the result of maximum copper reduction with

different flow rates for five hours’ electrowinning process are presented in Figure 4.12.

Figure 4.11: The concentration of copper varies according to reaction time of electrowinning process

with different flow rate. (Applied voltage: 2.5 V, Salt concentration: 1 M.)

0

50

100

150

200

250

300

0 50 100 150 200 250 300 350

Cop

per

Co

nce

ntr

atin

o (

mg/L

)

Time (min)

10 mL/min

20 mL/min

30 mL/min

40 mL/min

50 mL/min

39

Figure 4.12: Maximum copper reduction of copper after applying electrowinning with different flow

rates.

As seen in Figure 4.12, 80% percent copper reduction was achieved after five hours, when flow rate

was controlled at 20 mL/min. However, the maximum copper reduction decreased with the further

increase of the flow rate. This phenomenon was probably caused by the flocs, which was produced

during the reaction. When the flow rate was further increased, some yellow flocs were precipitated

out, and the current through out the reactor decreased during the reaction. Current real-time-

monitoring data are presented in Figure 4.13. As seen in Figure 4.13, when the flow rate was

controlled at 10 mL/min and 20 mL/min, current increased during the reaction and then current kept

constant. However, when the flow rate was controlled above 20 mL/min, current decreased during the

reaction.

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60

Max

imum

Copper

Red

uct

ion (

%)

Flow Rate (mL/min)

40

Figure 4.13: Current varies according to reaction time of electrowinning process with different flow

rate.

4.5 Internal Circulation Reactor

Based on the previous study for basic reactor and continuous reactor, we found that deposited

copper could not stick to the graphite rods very well, to let extracted copper well stick to the cathode

for removing it from water easily. Furthermore, in order to figure out whether the material of the cathode

plays an important role in the strength of adhesive, Aluminum or Ti/Pt alloy mesh cylinder were applied

as the cathode. Previous study indicated 20 mL/min is a proper flow rate, so the flow rate was

controlled at 20 mL /min for this study. The electrochemical flow reactor with cylinder cathode is

followed by Figure 3.3. As shown in Figure 4.13 the maximum copper reduction after five hours’

reaction with aluminum cathode and Ti/Pt alloy cathode is 18.2% and 39.2%, respectively. The removal

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 50 100 150 200 250 300

Cu

rren

t (A

)

Time (min)

10 mL/min

20 mL/min

30 mL/min

40 mL/min

50 mL/min

41

efficiency was much lower than expected, and there were some light blue flocs appeared instead of red

particles. After 48 hours’ reaction, the copper reduction is 93.3% and 96.4%, respectively. Based on the

results, the flow reactor with aluminum and Ti/Pt alloy cylinder cathode is not an effective plan because

of its longer reaction time and it produced a large number of blue flocs that needed further treatment.

Figure 4.14: The concentration of copper varies according to reaction time of electrowinning process

with different cathode. The data label means percentage of copper reduction.

18.2%

74%93.3%

39.2%

54.6%

96.4%0

50

100

150

200

250

0 5 10 15 20 25 30 35 40 45 50

Copper

Con

cen

trat

ion

(m

g/L

)

Reaction time (h)

Aluminum Cylinder

Ti/Pt Cylinder

42

Chapter 5

Conclusion

For the studies of synthetic water samples, the salt concentration substantially impacted copper

removal efficiency. Over 90% copper reduction was achieved after three hours’ reaction with

appropriate salt concentration (0.04 M – 1.5 M). When salt concentration was below 0.1 M, the

extracted copper stuck on the cathode and could be directly taken out from the water. However, when

salt concentration was larger than 0.1 M, the copper dropped into the water when the electrodes were

taken out from water, but the copper can be completely removed by using a bag filter. Chlorine was

detected during the copper electrowinning process, with the highest concentration at 89 mg/L. The

reaction of copper electrowinning can be modeled as a first order reaction.

Analysis of the relationship between voltage and copper reduction was conducted as well. The

results indicated a significant positive correlation exists between voltage and maximum copper

reduction. Furthermore, the higher voltage applied, the higher chlorine concentrations were detected.

The longer time of electrowinning, the lower value of the current efficiency was get. It was only 14.3%

after three hours of reaction. Further studies need to be conducted to improve current efficiency.

For the studies of actual water samples, 85% copper reduction was achieved after three hours’

reaction when initial copper concentration was at 221 mg/L. However, when the initial copper

concentration was below 100 mg/L, the copper removal efficiency was reduced to 50% - 70%. High

salt concentration and low copper concentration are likely the reasons of low copper removal

efficiency of the actual samples. More sampling and tests need to be conducted on actual samples.

The tests of continuous reactor and internal circulation reactor were also conducted on synthetic

43

water samples. Five different flow rates were evaluated. The highest copper reduction was achieved

after five hours’ reaction when the flow rate was controlled at 20 mL/min. However, some light blue

floccules appeared instead of red particles and stuck to the cathode. To eliminate these floccules further

treatment, such as sedimentation and filtration, is required. To investigate the reason why the blue

floccules appeared, further studies need to be conducted on the design and operation of continuous

reactors and internal circulation reactors.

44

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