Presentación3 def

Study of the transport of heavy metal ions through cation-exchange membranes applied to

the treatment of industrial effluents

Manuel César Martí Calatayud

Dr. D. Valentín Pérez Herranz

Dra. Dª. Montserrat García Gabaldón

FUNDING

Ayuda predoctoral: Formación de Personal Investigador de la Universitat Politècnica de València (Ref. FPI-UPV 2010-12)

Ayuda para la realización de estancias en centros de investigación de prestigio de la Universitat Politècnica de València:

(PAID-00-12)

Proyecto del Ministerio de Economía y Competitividad: “Caracterización electroquímica de membranas cerámicas nanoestructuradas de intercambio iónico para su aplicación en reactores electroquímicos y sistemas electrodialíticos” (CTQ2012-37450-C02-01/PPQ)

Proyecto del Ministerio de Ciencia e Innovación: “Desarrollo de nuevos reactores electroquímicos basados en membranas cerámicas para la recuperación de cromo hexavalente de los efluentes de las industrias de tratamiento de superficies” (CTQ2008-06750-C02-01/PPQ)

Predoctoral funding

Projects

Programa Oficial de posgrado en Ingeniería y Producción Industrial

RESEARCH ARTICLES IN SCIENTIFIC JOURNALS

Determination of transport properties of Ni(II) through a Nafion cation-exchange membrane in chromic acid solutions.M.C. Martí-Calatayud, M. García-Gabaldón, V. Pérez-Herranz, E. OrtegaJournal of Membrane Science, 379 (2011) 449-458.

Study of the effects of the applied current regime and the concentration of chromic acid on the transport of Ni2+ ions through Nafion 117 membranes.M.C. Martí-Calatayud, M. García-Gabaldón, V. Pérez-HerranzJournal of Membrane Science, 392-393 (2012) 137-149.

Effect of the equilibria of multivalent metal sulfates on the transport through cation-exchange membranes at different current regimes.M.C. Martí-Calatayud, M. García-Gabaldón, V. Pérez-HerranzJournal of Membrane Science, 443 (2013) 181-192.

Ion transport through homogeneous and heterogeneous ion-exchange membranes in single salt and multicomponent electrolyte solutions.M.C. Martí-Calatayud, D.C. Buzzi, M. García-Gabaldón, A.M. Bernardes, J.A.S. Tenório, V. Pérez-HerranzJournal of Membrane Science, 466 (2014) 45-57.

Results related to the Doctoral Thesis

Layer-by-Layer modification of cation exchange membranes controls ion selectivity and water splitting.S. Abdu, M.C. Martí-Calatayud, J.E. Wong, M. García-Gabaldón, M. WesslingACS Applied Materials & Interfaces, 6 (2014) 1843-1854.

Research stay at Chemische Verfahrenstechnik – RWTH Aachen University (Germany)

Synthesis and electrochemical behavior of ceramic cation-exchange membranes based on zirconium phosphate.M.C. Martí-Calatayud, M. García-Gabaldón, V. Pérez-Herranz, S. Sales, S. MestreCeramics International, 39 (2013) 4045-4054.

Chronopotentiometric study of ceramic cation-exchange membranes based on zirconium phosphate in contact with nickel sulfate solutions.M.C. Martí-Calatayud, M. García-Gabaldón, V. Pérez-Herranz, S. Sales, S. MestreDesalination and Water Treatment, 51 (2013) 597-605.

Collaboration with the Instituto de Tecnología Cerámica – UJI Castelló

Collaboration with the Departamento de Ingeniería de Materiales – Universidade do Rio Grande do Sul (Brasil) Sulfuric acid recovery from acid mine drainage by means of electrodialysis.

M.C. Martí-Calatayud, D.C. Buzzi, M. García-Gabaldón, E. Ortega, A.M. Bernardes, J.A.S. Tenório, V. Pérez-HerranzDesalination, 343 (2014) 120-127.

10th European Symposium on Electrochemical Engineering, 2014, Sardinia (Italy)

65th Annual Meeting of the International Society of Electrochemistry, 2014, Lausanne (Switzerland)

IX Ibero-americal Congress on Membrane Science and Technology, 2014, Santander.

13th International Conference on Environmental Science and Technology (CEST 2013), Atenas

XXXIV Reunión bienal de la RSEQ 2013, Santander 2 contribuciones XXXIV Reunión de electroquímica de la RSEQ, 2013, València 1st International Conference on Desalination using Membrane Technology,

2013, Sitges (Spain) 63rd Annual Meeting of the International Society of Electrochemistry, 2013,

Prague (Czech Republic) VIII Simposio Internacional de Qualidade Ambiental, 2012, Porto Alegre

(Brazil) Conference on Desalination for the Environment, Clean Water and Energy,

2012, Barcelona. 13 Network of Young Membrains, 2011, Enschede (The Netherlands) 9th European Symposium on Electrochemical Engineering, 2011, Chania

(Greece) 2nd Regional Symposium on Electrochemistry, 2011, Belgrade (Serbia)

Premio en el VII Certamen València Idea 2013, sección Energía y Medio Ambiente“Desarrollo de membranas de intercambio iónico con funcionalidad óptima para su utilización en baterías de flujo redox de elevada eficiencia energética”.

CONTRIBUTIONS IN CONFERENCES

AWARDS

LIST OF CONTENTS

Transport of single salt solutions

Transport of multicomponent mixtures

Mechanisms of transport at overlimiting currents

Galvanostatic electrodialysis experiments

3. EXPERIMENTAL TECHNIQUES

2. OBJECTIVE

5. CONCLUSIONS

1. INTRODUCTION

4. RESULTS & DISCUSSION

2. Objetive 3. Techniques Single saltsolutions

Multicomponentsolutions

Mechanismsi>ilim

Galvanostaticexperiments

5. Conclusions4. Results and discussion

1.Introduction 1

Heavy metals have high specific density (>5), and are highly persistent. Most of them (Cr, Ni, Cd, …) are carcinogenic.

1.1 Scope / Background

Effects on the environment Effects on the human health

They have multitude of applications. Their extraction, use and price are continuously growing.

Effects on the economy. Unsustainable growth. Geopolitical problems.

Metals imports

Mineral depletion

2

1.2 Electromembrane processes

Fixed membrane ion Counterion

Coion

-

-

-

-

-

+

+

+

+

+

+ -M+n

X-y

M+n

X-y

X-y

M+n

AEM CEM

An

od

e

Cat

ho

de

The presence of heavy metals in natural watercourses is mainly consequence of mining activities and due to the discharge of industrial effluents.

Electromembrane processes, such as electrodialysis, represent a sustainable alternative for the treatment of these effluents, since they allow the selective recovery and reuse of valuable metals.

They permit the separation of ions from aqueous solutions by using:

Driving force: an electric field

Selective barriers: ion-exchange membranes

Principle of electromembrane

processes

Structure of a cation-exchange membrane



Mechanismsi>ilim



1.Introduction

3

1.3 Characteristics / LimitationsThey are selective processes which allow the separation of cationic and anionic species.

The addition of reagents is not required.

Continuous and modular processes (stacks)

Membrane fouling.

Concentration polarization phenomena: The mass transfer becomes limited with the increase in the driving force

Desalted solution

Brine

Feed solution

An

od

e

Cat

hod

e

AEM AEM AEM AEMCEM CEM CEMCEM AlkaliAcid

0.0

0.2

0.4

0.6

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Um (V)

i (m

A·c

m-2

)

ilim

Overlimiting current densities



Mechanismsi>ilim



1.Introduction

LIST OF CONTENTS






2. OBJECTIVE

5. CONCLUSIONS

1. INTRODUCTION


2. Objective3. Techniques Single saltsolutions


Mechanismsi>ilim



1.Introduction 4

2. Objective and structure of the Thesis

Identificar e investigar los fenómenos de transferencia de materia implicados en procesos electroquímicos de membrana con el fin de optimizar el tratamiento de efluentes industriales que contienen metales pesados

To identify and investigate the mass transfer phenomena involved in electromembrane processes in order to optimize the treatment of industrial effluents containing heavy metals.

Ch. 4.1. Transport in single salt solutions

Ch. 4.2. Transport in mixture solutions

Monovalent ions Multivalent ionsIon competition between H+ and

M+n ions

Ion competition between M+ and M+n ions (n>1)

Ion uptakeElectrical resistance

SelectivityMass transfer phenomena

Ch. 4.3. Evaluation of the mechanisms of overlimiting current

Ch. 4.4. Galvanostatic experiments at different current regimes

Comparison:Transport of monovalent ions vs.

Transport of multivalent ions

Generation of new current carriers

Coupled convection

Effect of current regime

Effect of electrolyte

composition

Comparison:Transport of single salt solutions vs.

Transport of mixture solutions

Ch. 5. Conclusions

Ch. 1. Introduction

Ch. 2. Objectives and scope

Ch. 3. Methodology and experimental techniques







LIST OF CONTENTS






2. OBJECTIVE

5. CONCLUSIONS

1. INTRODUCTION




Mechanismsi>ilim



1.Introduction 5

3. Experimental techniques

Cation-exchange membranes NAFION 117Properties:

High conductivity (low electrical resistance) High selectivity

High mechanical and chemical resistance (durability).

IEC (ion exchange capacity) : 0.90 meq. SO3

- / g membrane

6

B) ChronopotentiometryElectrochemical technique used to analyze the dynamics of ion transport processes through a system composed by a membrane and an electrolyte: Concentration polarization

AEM CEM

+ -H+

X-yH+ M+n

H+

M+n

M0

Um

OH-

OH-

OH-X-y

H2O

H2O

Application of current pulses Concentration polarization Chronopotentiograms

CEM

Um

i<ilim

i>ilim

i≈ilim

Electric double layer

DBL

Bulk electrolyte

c0 c0

t (s)

Um

(V

) i ≈ ilim

i < ilim

i > ilim

t (s)

i (m

A·c

m-2

)

i ≈ ilim

i < ilim

i > ilim

DBL

A) Ion sorption experiments


2

2

0 1

4 itT

FzcD

Sand’s equation:



Mechanismsi>ilim



1.Introduction

7

C) Polarization curves: i vs. Um

They provide an idea about the membrane behavior at different current regimes:

1. Quasi-ohmic region:linear dependence between i and Um

2. Plateau region:mass transfer limitations

3. Region of overlimiting currents:The transfer of current carriers toward the membrane surface is activated

)(lim

tT

FDczi

0Peers’

equation:


B) Chronopotentiometry




Mechanismsi>ilim



1.Introduction

0.0

0.2

0.4

0.6

0.8

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Um (V)

i (m

A·c

m-2

)

ilim

Overlimiting region

quasi-ohmic region

plateau

8

D) Galvanostatic experiments in 3-compartment electrochemical cell Parameters to evaluate the

efficiency in the mass transfer and energy usage in an electromembrane reactor:

AEM CEM

+ -H+

X-yH+ M+n

H+

M+n

M0

Ucell

OH-

OH-

OH-X-y

H2O

H2O

1000

0 c

cctX t)(

100

0

0

tt

dtI

ccnFVt)(

t

ccMt t 0)(

XcVM

dtIUtE

tcell

s

0

0

3600)( (kW·h·kg-1)

(g·l-1·h-1)

(%)

(%)


C) Polarization curves: i vs. Um

B) Chronopotentiometry




Mechanismsi>ilim



1.Introduction

LIST OF CONTENTS






2. OBJECTIVE

5. CONCLUSIONS

1. INTRODUCTION




Mechanismsi>ilim


5. Conclusions4. Resultados y discusión

1.Introduction 9

4. Results and discussion

4.1. Transport in single salt solutions

Monovalent metal:

Na+

4. Resultados y discusión4. Results and discussion

Tabla 1. Electrolyte compositions used for the experiments conducted with single salt solutions.

[M+n] Na2SO4 NiSO4 Cr2(SO4)3 Fe2(SO4)3

10-3M 5·10-4M 10-3M 5·10-4M 5·10-4M

5·10-3M 2.5·10-3M 5·10-3M 2.5·10-3M 2.5·10-3M

10-2M 5·10-3M 10-2M 5·10-3M 5·10-3M

2·10-2M 10-2M 2·10-2M 10-2M 10-2M

Ni(II), Cr(III) y Fe(III)Present in spent

baths generated in the metal finishing

industry

Cr(III)Present in effluents

generated in leather tanneries

Fe(III)Present in acid mine drainage solutions

10

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0E+00 5.0E-03 1.0E-02 1.5E-02 2.0E-02 2.5E-02

[M+n] (mol/L)

c m (

mm

ol/g

)

Na(I)

Ni(II)

Fe(III)

Cr(III)

Ni2

+

Cr3

+

Fe3

+

10-3M

5·10-

3M

10-2M

2·10-

2M

The membrane becomes saturated in counterions




Mechanismsi>ilim



1.Introduction4. Resultados y discusión4. Results and discussion

11

Na2SO4

5·10-4M

2.5·10-3M

5·10-3M

10-2M

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 200 300 400 500

t (s)

Um

(V

)

0.028 mA·cm-2

0.014 mA·cm-2

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 200 300 400 500

t (s)

Um

(V

)

0.044 mA·cm-2

0.028 mA·cm-2

0.014 mA·cm-2

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 200 300 400 500

t (s)

Um

(V

)0.051 mA·cm-2

0.044 mA·cm-2

0.028 mA·cm-2

0.014 mA·cm-2

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0 100 200 300 400 500

t (s)

Um

(V

)

0.054 mA·cm-2

0.051 mA·cm-2

0.044 mA·cm-2

0.028 mA·cm-2

0.014 mA·cm-2

0.00

0.15

0.30

0.45

0.60

0.75

0 100 200 300 400 500

t (s)

Um

(V

)

0.055 mA·cm-2

0.00

0.15

0.30

0.45

0.60

0.75

0 100 200 300 400 500

t (s)

Um

(V

)0.059 mA·cm-2

0.055 mA·cm-2

0.00

0.15

0.30

0.45

0.60

0.75

0 100 200 300 400 500

t (s)

Um

(V

)

0.071 mA·cm-2

0.059 mA·cm-2

0.055 mA·cm-2

0.00

0.15

0.30

0.45

0.60

0.75

0 100 200 300 400 500

t (s)

Um

(V

)

0.085 mA·cm-2

0.071 mA·cm-2

0.059 mA·cm-2

0.055 mA·cm-2

0.00

0.15

0.30

0.45

0.60

0.75

0 100 200 300 400 500

t (s)

Um

(V

)

0.113 mA·cm-2

0.085 mA·cm-2

0.071 mA·cm-2

0.059 mA·cm-2

0.055 mA·cm-2

i < ilimi > ilim




Mechanismsi>ilim




12

y1 = 7.252x - 7.405

R2 = 0.999y2 = 5.132x + 3.209

R2 = 0.994

y3 = 4.717x - 5.445

R2 = 0.995

y4 = 3.058x - 0.815

R2 = 0.990

0

20

40

60

80

100

120

0 5 10 15 20 25

(c0/I)2 (mol/L·A)2

(s

)

10-2M Na2SO4

5·10-3M Na2SO4

2.5·10-3M Na2SO4

5·10-4M Na2SO4

Agreement with the

Sand’s eq.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 100 200 300 400

t (s)

Um

(V

)

0.E+00

1.E-02

2.E-02

3.E-02

4.E-02

DU

m/D

t

0.99 mA·cm-2

0.71 mA·cm-2

0.62 mA·cm-2

0.58 mA·cm-2

Calculation of the

transition time

Indicates the fraction of current associated with the transport of a specific ion with respect to the total current passed through the membrane

Sand’s equation: 2

2

0 1

4 itT

FzcD

T+




Mechanismsi>ilim




0.0

0.2

0.4

0.6

0.8

1.0

0.0E+00 5.0E-03 1.0E-02 1.5E-02 2.0E-02 2.5E-02

[M+n] (mol/L)

T+

Na+

Ni2+

13

0.0

0.2

0.4

0.6

0.8

0 100 200 300 400

t (s)

Um

(V

)

0.000

0.005

0.010

0.015

DU

m/D

t

0.538 mA·cm-2

0.0

0.2

0.4

0.6

0.8

0 100 200 300 400

t (s)

Um

(V

)

0.000

0.005

0.010

0.015

DU

m/D

t

0.878 mA·cm-2

0.538 mA·cm-2

0.0

0.2

0.4

0.6

0.8

0 100 200 300 400

t (s)

Um

(V

)

0.000

0.005

0.010

0.015

DU

m/D

t0.992 mA·cm-2

0.878 mA·cm-2

0.538 mA·cm-2

0.0

0.2

0.4

0.6

0.8

0 100 200 300 400

t (s)

Um

(V

)

0.000

0.005

0.010

0.015

DU

m/D

t

1.133 mA·cm-2

0.992 mA·cm-2

0.878 mA·cm-2

0.538 mA·cm-2

0.0

0.2

0.4

0.6

0.8

0 100 200 300 400

t (s)

Um

(V

)

0.000

0.005

0.010

0.015

DU

m/D

t

1.346 mA·cm-2

1.133 mA·cm-2

0.992 mA·cm-2

1

1

1

2

2

2

0.878 mA·cm-2

0.538 mA·cm-2Multiple transition times

Cr2(SO4)3

2.5·10-3M




Mechanismsi>ilim




14

Speciation diagram of 2.5·10-3M Cr2(SO4)3

0.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4 5 6 7

pH

ai

CrSO4+

Cr(OH)2+

CrOH2+Cr3+

pHeq




Mechanismsi>ilim




15

NiSO4

ilim (mA·cm-2)

10-2M 0.85

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500

t (s)

Um

(V

)

0.99 mA·cm-2

0.57 mA·cm-2

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500

t (s)

Um

(V

)

0.99 mA·cm-2

0.57 mA·cm-2

1.56 mA·cm-2

1.70 mA·cm-2

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500

t (s)

Um

(V

)

2.27 mA·cm-2

1.98 mA·cm-2

0.99 mA·cm-2

0.57 mA·cm-2

1.56 mA·cm-2

1.70 mA·cm-2

0

1

2

3

4

5

0 100 200 300 400 500

t (s)

Um

(V

)

7.08 mA·cm-2

5.67 mA·cm-2

Fe2(SO4)3

ilim (mA·cm-2)

10-2M 7.08




Mechanismsi>ilim




0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500

t (s)

Um

(V

)

2.27 mA·cm-2

1.98 mA·cm-2

0.99 mA·cm-2

0.57 mA·cm-2

1.56 mA·cm-2

1.70 mA·cm-2

Formation of precipitates

Plateau in the relaxation of Um

0

1

2

3

4

5

0 100 200 300 400 500

t (s)

Um

(V

)

7.79 mA·cm-2

7.37 mA·cm-2

7.08 mA·cm-2

5.67 mA·cm-2


0

1

2

3

4

5

0 100 200 300 400 500

t (s)

Um

(V

)

7.79 mA·cm-2

7.37 mA·cm-2

7.08 mA·cm-2

5.67 mA·cm-2

0.0

0.4

300 350t (s)

Um

(V

)



16

The formation of precipitates is due to pH changes in the vicinities of the membrane

The difference between pHeq - pH↓ is low for the solutions of Fe(III)

The difference between pHeq - pH↓ is higher in the case of Cr(III)


1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 2 4 6 8 10 12 14

pH

s (m

ol/L

)

NiSO4 2·10-2M

Cr2(SO4)3 10-2 M

Fe2(SO4)3 10-2 M

pHeq pHeq



Mechanismsi>ilim




17

0

50

100

150

200

250

300

0.0E+00 5.0E-03 1.0E-02 1.5E-02 2.0E-02 2.5E-02

[Na(I)] (mol/L)

R1 (W

·cm

2)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

i lim

(m

A·c

m-2

)

3 regions of membrane

behavior:

Quasi-ohmic regime

Plateau ilim

Region of overlimiting currents

Good agreement with the Peers’

equation

R1 decreases with the electrolyte concentration.




Mechanismsi>ilim




0.0

0.2

0.4

0.6

0.8

0.0 0.2 0.4 0.6 0.8 1.0

Um (V)

i (m

A·c

m-2

)

2.5·10-3M Na2SO4

5·10-4M Na2SO4

1/R1

ilim

Quasi-ohmic region

Plateau

Overlimiting region

18

0.0

0.5

1.0

1.5

2.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Um (V)

i (m

A·c

m-2

)

ilim1

2.5·10-3M Cr2(SO4)3

5·10-4M Cr2(SO4)3

ilim2




Mechanismsi>ilim




LIST OF CONTENTS






2. OBJECTIVE

5. CONCLUSIONS

1. INTRODUCTION




Mechanismsi>ilim



1.Introduction 19


4.2. Transport in multicomponent mixture solutions

Baths from the metal finishing industry:

H+ vs. Ni2+


Acid mine drainage solutions:Na+ vs. Fe(III)

CrO3 + H2O H2CrO4 ↔ 2H+ + CrO42-

NiSO4

0.0

0.1

0.2

0.3

0.4

0.5

0.00E+00 2.50E-03 5.00E-03 7.50E-03 1.00E-02 1.25E-02

[Ni(II)] (mol/L)

c m (

mm

ol/g

)

0M CrO3

10-3M CrO3

10-2M CrO30%

25%

50%

75%

100%

Electrolyte composition

Fra

ctio

n o

f m

emb

ran

efi

xed

ch

arg

es

10-3M CrO3 10-2M CrO30M CrO3

5·10

-4M

NiS

O4

5·10

-4M

NiS

O4

5·10

-4M

NiS

O4

5·10

-3M

NiS

O4

5·10

-3M

NiS

O4

5·10

-3M

NiS

O4

H+

Ni2+

10-3

M N

iSO

4

10-3

M N

iSO

4

10-3

M N

iSO

4

10-2

M N

iSO

4

10-2

M N

iSO

4

10-2

M N

iSO

4

20

CrO3 NiSO4

10-3M

5·10-4M

10-3M

5·10-3M

10-2M

10-2M

5·10-4M

10-3M

5·10-3M

10-2M

Analogous behavior to that obtained with single salt solutions of NiSO4 (without CrO3)



H+ vs. Ni2+



Mechanismsi>ilim




0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 100 200 300 400 500

t (s)

Um

(V

)

3.12 mA·cm-2

2.83 mA·cm-2

2.55 mA·cm-2

2.27 mA·cm-2

1.35 mA·cm-2

1.16 mA·cm-2



21

CrO3 NiSO4

10-3M

5·10-4M

10-3M

5·10-3M

10-2M

10-2M

5·10-4M

10-3M

5·10-3M

10-2M

With 10-2M CrO3 solutions the formation of precipitates did not occur.

0.0

0.2

0.4

0.6

0.8

0 100 200 300 400

t (s)

Um

(V

)

5.38 mA·cm-2

8.50 mA·cm-2

4.25 mA·cm-2

3.97 mA·cm-2

3.26 mA·cm-2


H+ vs. Ni2+4.2. Transport in multicomponent mixture solutions



Mechanismsi>ilim




22



H+ vs. Ni2+



Mechanismsi>ilim




1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 2 4 6 8 10 12 14pH

s (m

ol/L

)The formation of

precipitates starts

pHeq

10-2M CrO3pHeq

10-3M CrO3

pHeq

0M CrO3

Increasing current densities

23

0.0

0.2

0.4

0.6

0.8

1.0

0.00E+00 2.50E-03 5.00E-03 7.50E-03 1.00E-02 1.25E-02

[Ni(II)] (mol/L)

TN

i2+

0M CrO3

10-3M CrO3

10-2M CrO30.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Um (V)

i (m

A·c

m-2

)

10-2M NiSO4

5·10-3M NiSO4

10-3M NiSO4

5·10-4M NiSO4

0

2

4

6

8

10

12

14

16

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Um (V)

i (m

A·c

m-2

)

10-2M NiSO4

5·10-3M NiSO4

10-3M NiSO4

5·10-4M NiSO4



H+ vs. Ni2+

10-3 M CrO3

10-2 M CrO3



Mechanismsi>ilim




24

The attractive forces between the SO3

- groups and Fe3+ are higher than those with Na+

Fe2(SO4)3 Na2SO4

2·10-2M

0M

10-2M

2·10-2M

0%

25%

50%

75%

100%

Electrolyte composition

Fra

ctio

n o

f m

emb

ran

e fi

xed

ch

arg

es

0.02M Fe2(SO4)3

0.02M Fe2(SO4)3

+0.01M Na2SO4

0.02M Fe2(SO4)3

+0.02M Na2SO4

0.01M

Na2SO4

FeSO4+

Fe3+

Na+





Mechanismsi>ilim




25

Fe2(SO4)3 Na2SO4

2·10-2M

0M

10-2M

2·10-2M

0.00

0.05

0.10

0.15

0 100 200 300 400 500t (s)

Um

(V

)

8.50 mA·cm-2

5.67 mA·cm-2

0.00

0.05

0.10

0.15

0 100 200 300 400 500t (s)

Um

(V

)

11.33 mA·cm-2

8.50 mA·cm-2

5.67 mA·cm-2

0.00

0.05

0.10

0.15

0 100 200 300 400 500t (s)

Um

(V

)14.16 mA·cm-2

11.33 mA·cm-2

8.50 mA·cm-2

5.67 mA·cm-2

0.00

0.05

0.10

0.15

0 100 200 300 400 500t (s)

Um

(V

)

17.00 mA·cm-2

14.16 mA·cm-2

11.33 mA·cm-2

8.50 mA·cm-2

5.67 mA·cm-2

i < ilimi > ilim





Mechanismsi>ilim




0.0

1.0

2.0

3.0

0 100 200 300 400 500t (s)

Um

(V

)

17.28 mA·cm-2

17.14 mA·cm-2

depletion of

Fe3+ ions

0.0

1.0

2.0

3.0

0 100 200 300 400 500t (s)

Um

(V

)

17.56 mA·cm-2

17.28 mA·cm-2

17.14 mA·cm-2

depletion of

Fe3+ ions

formation of Fe(OH)3

precipitates

26

Change in electrical resistance

ilim associated with the depletion of Na+

0

3

6

9

12

15

18

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Um (V)

i (m

A·c

m-2

)

0.02M Fe2(SO4)3

0.02M Fe2(SO4)3 + 0.01M Na2SO4

0.02M Fe2(SO4)3 + 0.02M Na2SO4

0

5

10

15

20

0.0 0.1 0.2

Um (V)

i (m

A·c

m-2

)

1/R1

1/R2

1/R1

1/R2

0.02M Fe2(SO4)3

ilim1

ilim2





Mechanismsi>ilim




27

Table 6. Diffusion coefficients and ionic conductivities at infinite dilution for various species present in solutions of Fe2(SO4)3 +

Na2SO4.

Di (m2·s-1) i (mS·m2·mol-1)

Na+ 1.334 5.01

Fe3+ 0.604 20.40

SO42- 1.065 16.00

FeSO4+ 0.201 0.76

Fe3+

FeSO4+

Fe3+SO42-

SO42-

Reaction layerformed next to

the ion-exchange membrane

ion-exchange membrane





Mechanismsi>ilim




LIST OF CONTENTS






2. OBJECTIVE

5. CONCLUSIONS

1. INTRODUCTION




Mechanismsi>ilim



1.Introduction 28

Investigate the origin of the overlimiting currents

Evaluate the role of heavy metals and electrolyte composition on the overlimiting currents


4.3. Mechanisms of overlimiting current transfer

Transmembrane pressure, DP

Pe

rme

ate

flu

x,

J

Jlim

Transmembrane voltage drop, Um

Cu

rre

nt

de

ns

ity

, i

ilim

Overlimiting current

densities

Water splittingCurrent-induced

convection

Generation of new current carriers

(H+ and OH-)Exaltation effect

Gravitationalconvection

Electroconvection

Overlimiting current transfer

29

Water splittingGravitational convection

Mass transfer driven by density differences within the fluid:

Bulk solution membrane depleting surface (reduction of the thickness of the diffusion boundary layer)

H2O H⇄ + + OH-

Exaltation effect

AH + H2O ⇄ A- + H3O+

A- + H2O ⇄ AH + OH-

Protons are transferred through the CEMHidroxyls remain in the diffusion boundary layer

Electroconvection

Hydrodynamic instabilities generated due to the coexistence of intense electric fields with very diluted electrolytes

Vortex generation Distortion of the diffusion boundary layer

R. Kwak, G. Guan, W.K. Peng, J. Han, Desalination 308 (2013) 138-146

0 100 200 300t (s)

Um

(V

)

Decrease of the thickness of the

diffusion boundary layer

Maximum in Um




Mechanismsi>ilim




0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

0 100 200 300t (s)

Um

(V

)

30

Water dissociation

NiSO4

10-3M

5·10-3M

10-2M

2·10-2M

NiSO4

10-3M

5·10-3M

10-2M

2·10-2M

H+OH-

Cation-exchange membrane

-+

-----------

+

+

+

+

+

+

+

+

+

+

+

Metal hydroxide

Electric field




Mechanismsi>ilim




0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0.0 0.2 0.4 0.6 0.8 1.0

Um (V)

i (m

A·c

m-2

)

0

1

2

3

4

5

6

7

8

9

10

pH

pHcathode

pHanode

pHcentral

overlimiting region due to convective

phenomena

0

1

2

3

4

5

6

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Um (V)

i (m

A·c

m-2

)

0

1

2

3

4

5

6

7

8

9

10

pH

pHcathode

pHanode

pHcentral

catalyzed water splitting

overlimiting region due to enhanced

water splitting

31

Fe(OH)3 precipitates are more dense, they are formed inside the membrane.

Transport blockage

Ni(OH)2 precipitates are not compact, at the membrane surface.

Transport of OH- and H+




Mechanismsi>ilim




0

1

2

3

0 0.5 1 1.5 2

Um (V)

i/ilim

Catalyzed water splitting

Formation of a blocking layer of precipitates

32

Convective phenomena

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0 100 200 300 400

t (s)

Um

(V

)

0.32 mA·cm-2

0.40 mA·cm-2

0.85 mA·cm-2

0.99 mA·cm-2

1.28 mA·cm-2

0.64 mA·cm-2

0.60 mA·cm-2

overlimiting instabilities

intensification of concentration

polarization

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400

t (s)

Um

(V

)

5.10 mA·cm-2

4.53 mA·cm-2

3.12 mA·cm-2

2.69 mA·cm-2

2.34 mA·cm-2

2.13 mA·cm-2

coupled gravitational convection and electroconvection

Cr2(SO4)3

5·10-4M

2.5·10-3M

5·10-3M

10-2M

Cr2(SO4)3

5·10-4M

2.5·10-3M

5·10-3M

10-2M




Mechanismsi>ilim




33

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 100 200 300

t (s)

Um

(V

)

increasing current densities

NiSO4 CrO3

5·10-4M 10-3M




Mechanismsi>ilim




34

Convective phenomena favor the transport of ions at i>ilim: they imply a reduction in lplateau

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.2 0.4 0.6 0.8 1.0

Um (V)

i/ilim

lplateau1

lplateau2

2.5·10-3M Cr2(SO4)3

10-2M Cr2(SO4)3

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 0.2 0.4 0.6 0.8 1 1.2

Um (V)

i/ilim

0M CrO3

10-3M CrO3

10-2M CrO3

lplateau1lplateau2

lplateau3

lplateau[M+n] lplateau[H+]




Mechanismsi>ilim




35

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.000 0.005 0.010 0.015 0.020 0.025

[M+n] (mol/L)

l pla

teau

(V

)

Na(I)Ni(II)Fe(III)Cr(III)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.000 0.002 0.004 0.006 0.008 0.010 0.012

Ni(II) (mol/L)

l pla

tea

u (

V)

0M CrO3

10-3M CrO3

10-2M CrO3

Gravitational convection is favored at high concentrations of heavy metals.

The height of electroconvective vortices increases with the size of the involved cations.

The Grotthuss mechanism of H+ ions does not involve the distortion of the diffusion boundary layer.




Mechanismsi>ilim




LIST OF CONTENTS






2. OBJECTIVE

5. CONCLUSIONS

1. INTRODUCTION


2. Objective3. Techniques Single salt solutions


Mechanismsi>ilim



1.Introduction 36


4.4. Galvanostatic electrodialysis experiments

Effect of CrO3


Evaluate the membrane selectivity in long-term experimentsEvaluate the effect of the applied current density in long-term experiments

Objetives

Table 7. Compositions tested and applied current densities selected for conducting the galvanostatic electrodialysis experiments.

[NiSO4] [CrO3]ilim (mA·cm-

2)Applied current densities

10-3M

0 M 0.064

75%·ilim

(10-3M NiSO4)

75%·ilim

100%·ilim125%·il

im

10-3M 0.25575%·ili

m

100%·ilim125%·il

im

10-2M 3.26075%·ili

m

100%·ilim125%·il

im

10-2M

0M 0.850

75%·ilim (10-2M NiSO4)

75%·ilim

100%·ilim125%·il

im

10-3M 1.13075%·ili

m

100%·ilim125%·il

im

10-2M 4.24075%·ili

m

100%·ilim125%·il

im

Effect of CrO3 and i

Effect of the range of

applied current density

37


i = 0.048 mA·cm-2

Effect of CrO3

0

10

20

30

40

50

0 1 2 3 4 5 6 7

t (h)

X (

%)

0M CrO3

10-3M CrO3

10-2M CrO3

0

20

40

60

80

100

0 1 2 3 4 5 6 7

t (h)

(%

)

0 M CrO3

10-3 M CrO3

10-2 M CrO3

NiSO4 CrO3

10-3M

0M

10-3M

10-2M

Effect of CrO3 and i

0

20

40

60

80

100

0 1 2 3 4 5 6 7t (h)

X (

%)

0M CrO3

10-3M CrO3

10-2M CrO3

0

10

20

30

40

50

0 1 2 3 4 5 6 7t (h)

(%

)

0M CrO3

10-3M CrO3

10-2M CrO3

NiSO4 CrO3 75%·ilim

10-2M

0M0.64 mA·cm-

2

10-3M0.85 mA·cm-

2

10-2M3.18 mA·cm-

2



Mechanismsi>ilim




38

Ni2+ transport is improved

General improvement in all parameters

0

20

40

60

80

100

0 1 2 3 4 5 6 7

t (h)

X (

%)

125% ilim100% ilim 75% ilim

10

14

18

22

26

0 1 2 3 4 5 6 7

t (h)

Uce

ll (

V)


Development of concentration polarization

Onset of electroconvection

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7

t (h)

(%

)


0

20

40

60

80

100

0 1 2 3 4 5 6 7

t (h)

Es

(kW

·h/k

g)


NiSO4 CrO3 iaplicada

10-2M 0M

75%·ilim

100%·ilim

125%·ilim




Mechanismsi>ilim




Effect of the range of applied currents

39

Ni2+ transport is improved

The energy consumption increases

0

20

40

60

80

100

0 1 2 3 4 5 6 7

t (h)X

(%

)


5

10

15

20

25

30

35

40

0 1 2 3 4 5 6 7

t (h)

Uce

ll (

V)


0

5

10

15

20

25

30

35

0 1 2 3 4 5 6 7

t (h)

(%

)


0

20

40

60

80

100

120

0 1 2 3 4 5 6 7

t (h)

Es

(kW

·h/k

g)


NiSO4 CrO3 iaplicada

10-3M 10-3M

75%·ilim

100%·ilim

125%·ilim




Mechanismsi>ilim





40





Mechanismsi>ilim




0

10

20

30

40

50

60

70

0 0.1 0.2 0.3 0.4 0.5 0.6

lplateau (V)

%

10-3M NiSO4

10-2M NiSO4

10-3M NiSO4 + 10-3M CrO3

10-2M NiSO4 + 10-3M CrO3

10-2M NiSO4 + 10-2M CrO3

100% ilim

100% ilim

100% ilim

100% ilim

125% ilim

125% ilim

125% ilim

125% ilim 75% ilim

75% ilim

75% ilim

75% ilim

125% ilim

75% ilim

100% ilim

LIST OF CONTENTS






2. OBJECTIVE

5. CONCLUSIONS

1. INTRODUCTION




Mechanismsi>ilim



1.Introduction 41

5. Conclusions

Single salt solutions The membrane fixed charges become saturated in solution counterions (Na+, Ni2+, Cr3+,

Fe3+).

The chronopotentiometric curves obtained with multivalent metals show various transition times, which evidence the depletion of positively charged complex species (NiOH+, FeSO4

+, CrSO4+, etc.)

In systems with NiSO4 and Fe2(SO4)3 after surpassing the ilim the formation of precipitates could take place due to an increase of the local pH at the depleting membrane surface. This originates an increased membrane resistance and extended plateaus in the current-voltage curves.

In general, the current-voltage curves obtained show the three characteristic regions of membrane behavior. However, two ilim appear with diluted Cr2(SO4)3 solutions due to the depletion of different species.

4. Results and discussi0n

42

5. ConclusionsMulticomponent solutions

When immersed in mixtures of NiSO4 and CrO3, the membrane fixed charges are preferentially balanced with multicharged Ni2+ ions.

The chronopotentiometric and current-voltage curves obtained for the mixtures are similar to those obtained for single salt solutions. However, the H+ provided by CrO3 compete with the Ni2+ ions for the transport through the membranes.

The transport number of Ni2+ through the membrane is significantly high in single salt solutions of NiSO4, reaching values around 0.9. In the mixture solutions, the TNi

2+ decreases for increasing concentrations of CrO3.

The membrane fixed charges show a higher affinity for Fe(III) with respect to that for Na+ ions.

At low underlimiting currents the concentration of FeSO4+ ions is predominant in the

electrolyte. However, as the polarization of the membrane is intensified, they dissociate into Fe3+ and SO4

2- ions, which implies a reduction in the electrical resistance of the membrane system.

The curves obtained for mixtures of Fe2(SO4)3 and Na2SO4 denote a preferential transport of Na+ ions at low current densities, whereas the transport of Fe3+ is favored at higher currents, when the depletion of Na+ ions has already occurred.

NiSO4

+CrO3

Na2SO4

+Fe2(SO4)

3



Mechanismsi>ilim



1.Introduction4. Results and discussi0n

43

5. ConclusionsMechanisms of overlimiting current densities The dissociation of water is the main mechanism originating the overlimiting

currents when the formation of precipitates occurs at the anodic membrane surface.

Electroconvection is the main mechanism of overlimiting current densities in diluted solutions of all the metals tested. The magnitude of the oscillations in Um increases with the applied current density.

The role of gravitational convection becomes important in concentrated solutions of Cr2(SO4)3 and NiSO4. At high current densities gravitational convection and electroconvection have a synergic effect on the reduction of the electrical resistance of the membrane system.

The length of the plateau region of the current-voltage curves decreases for high concentrations of multivalent metals due to their participation on the motion of large volumes of fluid when coupled convection is initiated. On the contrary, H+ ions are transported via the Grotthuss mechanism and hamper electroconvection.

Overlimiting current densities lead to higher nickel transport rates. In terms of energy consumption, this increased transfer of Ni2+ is positive when the concentration of Ni2+ is relatively higher than that of H+ ions. On the contrary, for high concentrations of CrO3, the increased Ni2+ transfer rates are achieved at the cost of an important increase in the specific energy consumption.

Ele

ctro

chem

ical

tech

niq

ues

Galv

anost

ati

c experi

men

ts



Mechanismsi>ilim



1.Introduction4. Results and discussi0n

¡Thank you very much for your attention!

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