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

Programa Oficial de posgrado en Ingeniería y Producción Industrial
FUNDING
Predoctoral 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)
Projects
 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)

RESEARCH ARTICLES IN SCIENTIFIC JOURNALS
Results related to the Doctoral Thesis
 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. Ortega
Journal 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-Herranz
Journal 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-Herranz
 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-
Herranz

Research stay at Chemische Verfahrenstechnik – RWTH Aachen University
(Germany)
 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. Wessling
ACS Applied Materials & Interfaces, 6 (2014) 1843-1854.
Collaboration with the Instituto de Tecnología Cerámica – UJI Castelló
 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. Mestre
Ceramics 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. Mestre
Desalination and Water Treatment, 51 (2013) 597-605.
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-Herranz
Desalination, 343 (2014) 120-127.

CONTRIBUTIONS IN CONFERENCES
 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)
AWARDS
 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”.

LIST OF CONTENTS
1. INTRODUCTION
2. OBJECTIVE
3. EXPERIMENTAL TECHNIQUES
4. RESULTS & DISCUSSION
Transport of single salt solutions
Transport of multicomponent mixtures
Mechanisms of transport at overlimiting currents
Galvanostatic electrodialysis experiments
5. CONCLUSIONS

1.1 Scope / Background
Heavy metals have high specific density (>5), and are
highly persistent. Most of them (Cr, Ni, Cd, …) are
carcinogenic.
 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. Objetive 3. Techniques Single salt
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
4. Results and discussion
1.Introduction 1

2
1.2 Electromembrane processes
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
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

3
1.3 Characteristics / Limitations
They 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
0.8
0.6
0.4
0.2
0.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Um (V)
i (mA·cm-2)
ilim
Overlimiting
current densities
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

2. Objective and structure of the Thesis
To identify and investigate the mass transfer phenomena involved in electromembrane
processes in order to optimize the treatment of industrial effluents containing heavy metals.
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
2. Objective 3. Techniques Single salt
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction 4

3. Experimental techniques
Cation-exchange membranes  NAFION 117
Properties:
 High conductivity (low electrical resistance)
 High selectivity
 High mechanical and chemical resistance (durability).
solutions
IEC (ion exchange capacity) :
0.90 meq. SO3
Multicomponent
solutions
- / g membrane
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction 5

6
A) Ion sorption experiments
B) Chronopotentiometry
Electrochemical technique used to analyze the dynamics of ion transport processes through a system
composed by a membrane and an electrolyte: Concentration polarization
2
2
ö
Sand’s equation: t p +
0 1
æ
D c z F
÷ ÷
ö çè
4 T t i
ø
ç ç
è
-
÷ø
=æ
+ +
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
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
z Dc F
+
-
( ) lim
+ +
=
T t
i
d
0
Peers’ equation:
0.8
0.6
0.4
0.2
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
0.0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Um (V)
i (mA·cm-2)
ilim
Overlimiting
region
quasi-ohmic
region
plateau

(%)
(%)
( ) (kW·h·kg-1)
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:
100
= c 0 - c
´
X(t ) t
0
c
( ) 100
= - t
nFV c c
0 ´
ò
0
t
Idt
f(t )
( )
t
M c - c
h( t )= 0
t
ò × =
U I dt
M V c X
E t
t
cell
s × × × ×
0
0
3600
(g·l-1·h-1)
C) Polarization curves: i vs. Um
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

4.1. Transport in single salt solutions
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
Monovalent metal:
Na+
Present in effluents
generated in leather
solutions
Cr(III)
tanneries
Present in acid
mine drainage
solutions
Results and d disicsucusssiioónn
Multicomponent
solutions
Mechanisms
i>ilim
Fe(III)
Galvanostatic
experiments
Ni(II), Cr(III) y Fe(III)
Present in spent baths
generated in the metal
finishing industry
5. Conclusions
4. Resultados y discusión
1.Introduction 9

10
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.0E+00 5.0E-03 1.0E-02 1.5E-02 2.0E-02 2.5E-02
[M+n] (mol/L)
cm (mmol/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
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

11
Na2SO4
5·10-4M
2.5·10-3M
5·10-3M
10-2M
0.75
0.30
0.75
0.25
0.60
0.20
0.45
0.15
0.30
0.10
0.05
0.044 mA·cm-2
t (s)
Um (V)
0.028 mA·cm-2
0.014 mA·cm-2
0.051 mA·cm-2
0.054 mA·cm-2
0.00
0.055 mA·2
0 100 200 300 400 500
0.15
0.059 mA·cm-2
0.055 mA·cm-2
t
0.071 mA·cm-2
0.085 mA·cm-2
0.113 mA·cm-2
i < ilim
> 4.1. Transport in single salt solutions
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

12
æ
t p +
ö çè
D c z F
ö
÷ ÷
Sand’s equation: 2
1.0
Indicates the fraction of current associated with the transport of a specific
ion with respect to the total current passed through the membrane
 Agreement with the Sand’s eq.
y1 = 7.252x - 7.405
R2 = 0.999
y2 = 5.132x + 3.209
R2 = 0.994
y3 = 4.717x - 5.445
R2 = 0.995
y4 = 3.058x - 0.815
R2 = 0.990
120
100
80
60
40
20
0
0 5 10 15 20 25
(c0/I)2 (mol/L·A)2
t (s)
10-2M Na2SO4
5·10-3M Na2SO4
2.5·10-3M Na2SO4
5·10-4M Na2SO4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
4.E-02
3.E-02
2.E-02
1.E-02
0.8
 Calculation of the transition time
0.6
0.4
0.2
0 100 200 300 400
t (s)
Um (V)
0.E+00
DUm/Dt
0.99 mA·cm-2
0.71 mA·cm-2
0.62 mA·cm-2
0.58 mA·cm-2
2
0 1
4 T t i
ø
ç ç
è
-
÷ø
=æ
+ +
T+
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
44.. RReessuullttas daonsd d disicsucusssiioónn
0.0
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
0.8
0.6
0.4
0.2
0.0
0.015
0.010
0.005
1.346 mA·cm-2
1.133 mA·cm-2
0.992 mA·cm-2
0.878 mA·cm-2
0 100 200 300 400
t (s)
Um (V)
0.000
DUm/Dt
0.538 mA·cm-2
t1
t1
t1
t2
t2
t2
Cr2(SO4)3
2.5·10-3M
Multiple transition times
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

14
CrSO4
+
Cr3+
pHeq
pH ai
CrOH2+
Speciation diagram of 2.5·10-3M Cr2(SO4)3
1.0
0.8
0.6
0.4
0.2
0.0
Cr(OH)2
+
0 1 2 3 4 5 6 7
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

Plateau in the
relaxation of Um
15
NiSO4 ilim (mA·cm-2)
10-2M 0.85
1.0
0.8
0.6
0.4
0.2
0.0
2.27 mA·cm-2
1.56 mA·cm-2
1.70 mA·cm-2
0 100 200 300 400 500
t (s)
Um (V)
0.99 mA·cm-2
0.57 mA·cm-2
1.98 mA·cm-2
Fe2(SO4)3 ilim (mA·cm-2)
10-2M 7.08
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
0.4
Um (V)
5. Conclusions
5
4
3
2
1
1.Introduction
Formation of
precipitates
Plateau in the
relaxation of Um
0
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
Formation of
precipitates
0.0
300 t (s) 350

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)
16
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
1.E-07
1.E-08
1.E-09
pH
0 2 4 6 8 10 12 14
s (mol/L)
pHeq pHeq
NiSO4 2·10-2M
Cr2(SO4)3 10-2 M
Fe2(SO4)3 10-2 M
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

17
300
250
200
150
100
50
0
1.2
1.0
0.8
0.6
0.4
0.2
0.0E+00 5.0E-03 1.0E-02 1.5E-02 2.0E-02 2.5E-02
[Na(I)] (mol/L)
R1 (W·cm2)
0.0
ilim (mA·cm-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.
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
0.8
0.6
0.4
0.2
1.Introduction
0.0
0.0 0.2 0.4 0.6 0.8 1.0
Um (V)
i (mA·cm-2)
2.5·10-3M Na2SO4
5·10-4M Na2SO4
1/R1
ilim
Quasi-ohmic
region
Plateau
Overlimiting
region

18
2.0
1.5
1.0
0.5
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Um (V)
i (mA·cm-2)
ilim1
2.5·10-3M Cr2(SO4)3
5·10-4M Cr2(SO4)3
ilim2
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

4.2. Transport in multicomponent mixture solutions
NiSO4
CrO3 + H2O  H2CrO4 ↔ 2H+ + CrO4
100%
75%
50%
25%
Fraction of membrane
fixed charges
0M CrO3
10-3M CrO3
10-2M CrO3 0%
0.00E+00 2.50E-03 5.00E-03 7.50E-03 1.00E-02 1.25E-02
[Ni(II)] (mol/L)
solutions
5·10-4M NiSO4
5·10-4M NiSO4
5·10-3M NiSO4
5·10-3M NiSO4
5·10-3M NiSO4
10-3M NiSO4
10-3M NiSO4
10-3M NiSO4
10-2M NiSO4
10-2M NiSO4
10-2M NiSO4
10-3M CrO3 10-2M CrO3 0M CrO3
5·10-4M NiSO4
2-
Multicomponent
solutions
Baths from the metal finishing industry:
Mechanisms
i>ilim
H+ vs. Ni2+
Acid mine drainage solutions:
Na+ vs. Fe(III)
Electrolyte composition
Galvanostatic
experiments
5. Conclusions
0.5
0.4
0.3
0.2
0.1
0.0
cm (mmol/g)
H+
Ni2+
1.Introduction 19

4.2. Transport in multicomponent mixture solutions Baths from the metal finishing industry:
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+
1.2
1.0
0.8
0.6
0.4
0.2
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
0.0
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
Formation of
precipitates
Plateau in the
relaxation of Um

Baths from the metal finishing industry:
21
H+ vs. Ni2+ 4.2. Transport in multicomponent mixture solutions
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
0.8
0.6
0.4
0.2
With 10-2M CrO3 solutions the
formation of precipitates did
not occur. 0.0
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
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

22
H+ vs. Ni2+
1.0E+00
1.0E-01
1.0E-02
1.0E-03
1.0E-04
1.0E-05
1.0E-06
Increasing current densities
solutions
pH
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
1.0E-07
0 2 4 6 8 10 12 14
s (mol/L)
The formation of
precipitates starts
pHeq
10-2M CrO3 pHeq
10-3M CrO3
pHeq
0M CrO3

23
1.0
0.8
0.6
0.4
0.2
0.0
16
14
12
10
8
6
4
2
0.00E+00 2.50E-03 5.00E-03 7.50E-03 1.00E-02 1.25E-02
[Ni(II)] (mol/L)
2+
TNi
0M CrO3
10-3M CrO3
10-2M CrO3
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Um (V)
i (mA·cm-2)
10-2M NiSO4
5·10-3M NiSO4
10-3M NiSO4
5·10-4M NiSO4
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Um (V)
i (mA·cm-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
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

24
4.2. Transport in multicomponent mixture solutions Acid mine drainage solutions:
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
100%
75%
50%
25%
0%
Electrolyte composition
Fraction of membrane
fixed charges
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+
Na+ vs. Fe(III)
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

25
Fe2(SO4)3 Na2SO4
2·10-2M
0M
10-2M
2·10-2M
0.15
3.0
0.10
2.0
0.05
1.0
0.00
Na+ vs. Fe(III)
formation of Fe(OH)3
precipitates
0 100 200 300 400 500
t (s)
Um (V)
8.50 mA·cm-2
5.67 mA·cm-2
11.33 mA·cm-2
14.16 mA·cm-2
17.00 mA·cm-2
i < ilim
> 2. Objective 3. Techniques Single salt
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
0.0
0 100 200 t (s) 300 400 500
Um (V)
17.28 mA·cm-2
17.14 mA·cm-2
t t
17.56 mA·cm-2
depletion of
Fe3+ ions

Change in electrical resistance
ilim associated with the
26
depletion of Na+
18
15
12
9
6
3
0
20
15
10
5
0
0.0 0.1 0.2
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Um (V)
i (mA·cm-2)
0.02M Fe2(SO4)3
0.02M Fe2(SO4)3 + 0.01M Na2SO4
0.02M Fe2(SO4)3 + 0.02M Na2SO4
Um (V)
i (mA·cm-2)
1/R1
1/R2
1/R1
1/R2
0.02M Fe2(SO4)3
ilim1
ilim2
Na+ vs. Fe(III)
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

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) li (mS·m2·mol-1)
Na+ 1.334 5.01
Fe3+ 0.604 20.40
SO2- 1.065 16.00
4
FeSO4
+ 0.201 0.76
Na+ vs. Fe(III)
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

4.3. Mechanisms of overlimiting current transfer
Transmembrane pressure, DP
Investigate the origin of the overlimiting currents
Overlimiting
current
densities
Transmembrane voltage drop, Um
Current density, i
ilim
Evaluate the role of heavy metals and electrolyte composition on the overlimiting currents
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
Permeate flux, J
Jlim
1.Introduction 28

29
GWraatveitra stpiolitntainl cgonvection
H2O ⇄ H+ + OH-Exaltation
Mass transfer driven by density differences within the fluid:
Bulk solution  membrane depleting surface (reduction of the
thickness of the diffusion boundary layer)
0 100 200 300
Maximum in Um
Decrease of the
thickness of the
diffusion boundary layer
effect
AH + H2O ⇄ A- + H3O+
A- + H2O ⇄ AH + OH-Protons
are transferred
through the CEM
Hidroxyls 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
0 100 200 300
t (s)
Um (V)
R. Kwak, G. Guan, W.K. Peng, J. Han, Desalination 308 (2013) 138-146
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
t (s)
Um (V)
0 100 200 300
t (s)
Um (V)

10
9
8
7
6
5
4
3
2
1
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
solutions
10
9
8
7
6
5
4
3
2
1
Multicomponent
solutions
pHcentral
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
6
5
4
3
2
1
1.Introduction
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.0 0.2 0.4 0.6 0.8 1.0
Um (V)
i (mA·cm-2)
0
pH
pHcathode
pHanode
pHcentral
overlimiting region
due to convective
phenomena
0
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Um (V)
i (mA·cm-2)
0
pH
pHcathode
pHanode
catalyzed water
splitting
overlimiting region
due to enhanced
water splitting

0 0.5 1 1.5 2
31
Ni(OH)2 precipitates are not compact, at the
membrane surface.
Transport of OH- and H+
Fe(OH)3 precipitates are more dense, they
are formed inside the membrane.
Transport blockage
solutions
3
2
1
0
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
Um (V)
i/ilim
Catalyzed water
splitting
Formation of a blocking
layer of precipitates

32
Convective phenomena
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.40 mA·cm-2
overlimiting
instabilities
0.99 mA·cm-2
0 100 200 300 400
t (s)
Um (V)
0.32 mA·cm-2
0.85 mA·cm-2
1.28 mA·cm-2
0.64 mA·cm-2
0.60 mA·cm-2
intensification
of concentration
polarization
1.0
0.8
0.6
0.4
0.2
0.0
coupled gravitational convection
and electroconvection
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
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
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

33
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0 100 200 300
t (s)
Um (V)
increasing current
densities
NiSO4 CrO3
5·10-4M 10-3M
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

34
Convective phenomena favor the transport of ions at i>ilim: they imply a reduction in lplateau
3.0
2.5
2.0
1.5
1.0
0.5
0.0
l[M+n] plateau [H lplateau +]
2.5·10-3M Cr2(SO4)3
10-2M Cr2(SO4)3
0.0 0.2 0.4 0.6 0.8 1.0
Um (V)
i/ilim
lplateau1
lplateau2
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0 0.2 0.4 0.6 0.8 1 1.2
Um (V)
i/ilim
0M CrO3
10-3M CrO3
10-2M CrO3
lplateau1
lplateau2
lplateau3
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

35
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.000 0.005 0.010 0.015 0.020 0.025
[M+n] (mol/L)
lplateau (V)
Na(I)
Ni(II)
Fe(III)
Cr(III)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.000 0.002 0.004 0.006 0.008 0.010 0.012
Ni(II) (mol/L)
lplateau (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.
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

4.4. Galvanostatic electrodialysis experiments
Table 7. Compositions tested and applied current densities selected for conducting the galvanostatic
[NiSO4] [CrO3] ilim (mA·cm-2) Applied current densities
10-3M
0 M 0.064
10-3M 0.255 75%·ilim 100%·ilim 125%·ilim
10-2M 3.260 75%·ilim 100%·ilim 125%·ilim
10-2M
0M 0.850
10-3M 1.130 75%·ilim 100%·ilim 125%·ilim
10-2M 4.240 75%·ilim 100%·ilim 125%·ilim
Effect of CrO3
Effect of CrO3
and i
solutions
Evaluate the membrane selectivity in
long-term experiments
Evaluate the effect of the applied current
density in long-term experiments
Objetives
electrodialysis experiments.
75%·ilim
(10-3M NiSO4)
75%·ilim 100%·ilim 125%·ilim
75%·ilim
(10-2M NiSO4)
75%·ilim 100%·ilim 125%·ilim
Effect of the range of
applied current
Multicomponent
solutions
density
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction 36

37
Effect of CrO3
i = 0.048 mA·cm-2
50
40
30
20
10
0
0 1 2 3 4 5 6 7
t (h)
X (%)
0M CrO3
10-3M CrO3
10-2M CrO3
100
80
60
40
20
0
0 1 2 3 4 5 6 7
t (h)
f (%)
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
100
80
60
40
20
0
0 1 2 3 4 5 6 7
t (h)
X (%)
0M CrO3
10-3M CrO3
10-2M CrO3
50
40
30
20
10
0
0 1 2 3 4 5 6 7
t (h)
f (%)
0M CrO3
10-3M CrO3
10-2M CrO3
NiSO4 CrO3 75%·ilim
10-2M
0M 0.64 mA·cm-2
10-3M 0.85 mA·cm-2
10-2M 3.18 mA·cm-2
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

38
Ni2+ transport is improved
General improvement in all
parameters
100
80
60
40
20
0
0 1 2 3 4 5 6 7
t (h)
X (%)
125% ilim
100% ilim
75% ilim
Effect of the range of applied
26
22
18
14
10
0 1 2 3 4 5 6 7
t (h)
Ucell (V)
125% ilim
100% ilim
75% ilim
Development of
concentration polarization
Onset of
electroconvection
70
60
50
40
30
20
10
0
0 1 2 3 4 5 6 7
t (h)
f (%)
125% ilim
100% ilim
75% ilim
100
80
60
40
20
0
0 1 2 3 4 5 6 7
t (h)
Es (kW·h/kg)
125% ilim
100% ilim
75% ilim
NiSO4 CrO3 iaplicada
10-2M 0M
75%·ilim
100%·ilim
125%·ilim
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
currents

39
Ni2+ transport is improved
The energy consumption increases
100
80
60
40
20
0
0 1 2 3 4 5 6 7
t (h)
X (%)
125% ilim
100% ilim
75% ilim
40
35
30
25
20
15
10
5
0 1 2 3 4 5 6 7
t (h)
Ucell (V)
125% ilim
100% ilim
75% ilim
35
30
25
20
15
10
5
0
0 1 2 3 4 5 6 7
t (h)
f (%)
125% ilim
100% ilim
75% ilim
120
100
80
60
40
20
0
0 1 2 3 4 5 6 7
t (h)
Es (kW·h/kg)
125% ilim
100% ilim
75% ilim
NiSO4 CrO3 iaplicada
10-3M 10-3M
75%·ilim
100%·ilim
125%·ilim
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
currents

40
currents
70
60
50
40
30
20
10
100% ilim
solutions
100% ilim
75% ilim
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction
0
0 0.1 0.2 0.3 0.4 0.5 0.6
lplateau (V)
f (%)
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
125% ilim
125% ilim
125% ilim
75% i 125% ilim lim
75% ilim
75% ilim
125% ilim
75% ilim
100% ilim

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
 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.
solutions
Results and discussi0n
Multicomponent
solutions
Mechanisms
i>ilim
+, CrSO4
+, etc.)
Galvanostatic
experiments
5. Conclusions
1.Introduction 41

42
5. Conclusions
Multicomponent solutions
 When immersed in mixtures of NiSOand CrO, the membrane fixed charges are preferentially balanced
4 3with 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 CrOcompete with the Ni2+ ions for the
3 transport through the membranes.
 The transport number of Ni2+ through the membrane is significantly high in single salt solutions of
NiSO, reaching values around 0.9. In the mixture solutions, the T2+ decreases for increasing
4Ni
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
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

43
5. Conclusions
Mechanisms 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.
Electrochemical
techniques
Galvanostatic
experiments
solutions
Multicomponent
solutions
Mechanisms
i>ilim
Galvanostatic
experiments
5. Conclusions
1.Introduction

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