Journal of Physics Conference Series

OPEN ACCESS

Carbonation of residual brines produced byammonia-soda processTo cite this article I V Filippova et al 2013 J Phys Conf Ser 416 012014

View the article online for updates and enhancements

You may also likeCarbonation Resistance of Concrete withFly Ash as Fine AggregateD Zhang M Mao Q Yang et al

-

Research on Concrete Carbonation DepthPrediction Algorithm Based on BP-ARXuehua Yang Junqi Yu Zhenping Donget al

-

Prediction model for carbonation depth ofconcrete subjected to freezing-thawingcyclesQian Hui Xiao Qiang Li Xiao Guan et al

-

Recent citationsSalt effect on gas dispersion in flotationcolumn ndash Bubble size as a function ofturbulent intensityLO Filippov et al

-

This content was downloaded from IP address 21910037233 on 19122021 at 0314

Carbonation of residual brines produced by ammonia-soda process

I V Filippova P Piriou L O Filippov J Yvon M Grandjean Laboratoire Environnement Mineacuteralurgie UMR 7569 CNRS-Nancy-Universiteacute France

innafilippovauniv-lorrainefr

Abstract This work deals with the carbonation of residual brines produced during the manufacture of soda ash to avoid the unsuitable phase transformation during the land storage The study resulted in a demonstration pilot which showed the feasibility of such an approach and the possibility of his extension to an industrial scale Carbonation of the residual brines is a promising process as it entirely transforms Ca(OH)2 ldquoCaOHClrdquo and CSH into calcite avoids the further phase evolution allows to obtain a neutral pH which considerably reduce the land storage impact on environment and shorten by around 10 the global CO2 emission of the ammonia-soda process

1 Introduction Nowadays accelerated carbonation begins to be used for the treatment of wastes and contaminated soils and for the sequestration of CO2 [1 2] the most important greenhouse gas whose atmospheric concentration has been raising from 280 ppm to 380 ppm since the beginning of the industrial era This kind of mineral sequestration of CO2 is adapted to modern carbon management whose main ideas are the capture and sequestration of CO2 the increase of efficiency of energy conversion and the use of low carbon or carbon free energy sources [3] Thus carbonation of the residues of the ammonia-soda process which makes them passive and avoids further phases transformation is a modern and promising way of dealing with such hazardous for environment materials mainly through chloride leaching [4]

Previous studies have already shown the possibility of using these residual materials to produce calcium-magnesium phosphates cosmetic chalk andor gypsum of standard value Some authors also suggested the use of these residues for the neutralization of combustion gases [5-6] Same authors focussed on the optimal parameters for the precipitation of calcium sulphate and performed a simple economic study of their process to show the feasibility of such an approach [7] Recently CO2 sequestration in different brine solutions has been studied For example carbonation of brine solutions containing fly ashes from coal combustion have been proved to have a great potential for CO2 sequestration [8-9]

The objectives of this study are to determine the phases present in the residual brines which are sensitive to carbonation to obtain a magnitude order of carbonation of theses phases to assess the decrease of CO2 emissions of the overall ammonia-soda process and to highlight the limits of this process

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

Published under licence by IOP Publishing Ltd 1

2 Material and methods Carbonation reactions were carried out in a Pyrex reactor with a 1900 mL volume capacity at a constant temperature of 55degC which corresponds to the temperature of the residual brines getting out of the ammonia-soda process factory Gas injected by bubbling contained 15 of CO2 and 85 of air corresponding to the composition of the gas at the outlet of the boiler The mixture was continuously stirred for a better bubble dispersion and to prevent sedimentation of particles however it must be noted that in industrial conditions the possible use of a counterndashcurrent bubbling column avoids using a stirring device Indeed in a continuous reactor the large amount of gas injected is sufficient to ensure an efficient mixing of the brines When pH is considered as stable 250 mL of the mixture are sampled and then filtrated at 045 microm in a Teflon Millipore compressed air system The liquid phases are acidified whereas the solid phases are frozen and freeze-dried to withdraw the free water Crystalline phases present in the solids are determined by X-Ray Diffraction (XRD) using a Bruker D8 Advance diffractometer equipped with a Co-Kα1 computed monochromatic source (1789Aring) at 35 kV and 45 mA with a linear Lynx-Eye detector at 0035deg by 2 theta step from 3deg to 64deg and a 3 seconds counting time Presence of sulphate hydrated silicate or carbonate phases are determined by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) using a Bruker IFS 55 equipped with a large band (600-5500 cm-1) mercury-cadmium telluride (MCT) detector cooled to 77 K Fine chemical analysis of Cd Cr Mn Ni and Pb concentrations in the liquid phases are performed using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS VARIAN 820-MS)

3 Results and discussion

31 Order of carbonation After filtration and freeze-drying of a sample the composition of residual brine was deduced from associating XRD and DRIFTS results XRD shows the presence of portlandite and calcium hydroxychloride CaOHCl The vibrations at 3644 cm-1 3698 cm-1 and 3570 cm-1 in the DRIFTS spectra are assigned to the hydroxyl stretching vibration in Ca(OH)2 Mg(OH)2 and CaOHCl respectively (figure 1) The large band at 966 cm-1 corresponds to the vibration of Si-O in the C-S-H and the large band centred on 1430 cm-1 to the C-O elongations in carbonates Other bands are diverse overtones deformations or combinations of the same groups

0

02

04

06

08

1

12

60010001400180022002600300034003800Wavenumber (cm-1)

Abs

orba

nce

Uni

t

3698

36443570

966

Figure 1 Diffuse reflectance FT-IR spectrum of solid phase from initial brines

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

2

At carbonation pH (close to 6) all peaks characterising the presence of these minerals have disappeared (figure 2) However these mineral phases are not directly carbonated In fact CO2 must first be solvated hydrated and ionised giving carbonate ion CO3

2 (-reaction 1) which reacts with free Ca2+ according to reaction (2)

CO2 (g) + H2O = CO32-

(aq) + 2 H+ (1) Ca2+

(aq) + CO32-

(aq) = CaCO3 (s) (2) These two reactions displace the solid-solution equilibria of Ca(OH)2 Mg(OH)2 CaOHCl and CSH

(reactions (3) ndash (5)) due to the consumption of free Ca2+ and to the slow disappearance of OH- ions when pH decreases Indeed the appearance of CO3

2- in water comes along with the appearance of two H+ according to reaction (1) This reaction explains why the pH tends to decrease when CO2 is injected in the reactor

Ca(OH)2 = Ca2+ + 2 OH- (3) CaOHCl = Ca2+ + OH- + Cl- (4) Mg(OH)2 = Mg2+ + 2 OH- (5) x CaO ndash y SiO2 ndash z H2O = x CaO +y Si(OH)4 + (z-2y) H2O (6) The solubilization of the C-S-H (reaction (6)) is a two-step reaction Indeed CO3

2- reacts with free Ca2+ (reaction (2)) modifying the equilibrium between sequestered CaO and solubilized CaO that is Ca(OH)2 (reaction (3)) It cannot be accepted that C-S-H are directly carbonated They are dissolved due to an equilibrium between CaO contained in C-S-H and free Ca2+ continuously consumed by carbonation

0010203040506070809

1

30003250350037504000Wavenumber (cm-1)

Abs

orba

nce

Uni

t

(a)

3698

3570

3640

03

04

05

06

07

08

09

600800100012001400Wavenumber (cm-1)

Abs

orba

nce

Uni

t

(b)

966

Figure 2 Evolution of diffuse reflectance infrared spectra of residual brines with pH Due to kinetics and solubility products an order of carbonation of phases was obtained CaOHCl

which crystallizes [1a] at the surface of Ca(OH)2 first disappears followed by Ca(OH)2 whose dissolution is relatively quick due to the facts that both Ca2+ and OH- are consumed by carbonation C-S-H then disappear after its slow but complete dissolution releasing colloidal silica in the brine (reaction (6)) whose dissolution is favoured by the alkaline pH Mg(OH)2 finally disappears from the mixture when pH is low enough to ensure the total solubilization of brucite [4]

32 Less CO2 emission for the ammonia-soda process Using the BAT (Best Available Techniques) document of the IPPC (Integrated Pollution Prevention and Control) directive [10] the ammonia-soda process has been schematized in 12 steps with the software BILCO reg [1] This model has been intentionally designed for the production of one ton of sodium carbonate Na2CO3 so that the values of the flow-rates of the wastes (CO2 and brines) are now given per ton of Na2CO3 produced Thus the production of one ton of Na2CO3 comes along with the emission of 351 kg of CO2 [1] The CO2 consumption for the carbonation of the residual brines

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

3

depends on the value of the pH at the end of the carbonation For a final value of pH 7 the consumption of CO2 is around 35 kg per ton of produced Na2CO3 then with a 10 decrease of the CO2 emission from the ammonia-soda process For a worldwide annual production of 60 Mt of Na2CO3 this process would allow the sequestration of 21 Mt of CO2

33 Further phase transformation avoided Residual brines contain mix layered double hydroxides (LDH) of Ca2+ and Al3+ such as hydrocalumite [Ca2Al(OH)6][Cl1-xOHx]3H2O During landfield storage these LDH lead to the formation of expansible phases such as ettringite which shorten the designed life-time of tailing dumps [12] Furthermore these expansible phases are also responsible for the creation of a lens in the middle of the tailing dumps which prevents them from the complete leaching of chloride [12] The vertical zonality model of phase evolution in dump proposed in [12] reveals the essential role played by Al (and Mg) in the blocking of the maturation of the solids resulting from the effluent decantation and contact with the air In the case of a waste disposal processed by a simple decantation without carbonation since the kinetics of the natural carbonation controlled by the diffusion of CO2 is not fast enough the solids precipitate and free water preserve an alkaline pH buffered by the portlandite This alkaline pH will cause on one hand to continue the dissolution of residual silico-aluminous minerals contained in the brine (mullite) and on the other hand to support the alkaline mineral formation (layered double hydroxides and cancrinites) These neoformed phases by their structuring capacity (swelling and retention of water) favour the relative impermeability and will delay the carbonation of the level where they occur

Decreasing the pH causes the sequestration of aluminium in the solid phase as predicted by Pourbaixrsquo diagram of Al It can be noted that carbonation decreases the mobility of aluminium because of pH decreasing and avoids formation of layered double hydroxides

00000

02000

04000

06000

08000

10000

12000

14000

5 6 7 8 9 10 11

pH

[Al]

(mg

kg)

0307200807072008031120080511200805022009

Figure 3 Evolution of aluminium concentration in the liquid phase with pH (Evolution is given for five different dates)

34 Limits of the carbonation process The CO2 sequestration method by carbonation of industrial brines has limits Indeed when decreasing the pH two limits clearly appear which lead to the necessary incomplete carbonation of the residual brines of the ammonia-soda process

341 Heavy metals solubilization Heavy metals such as Cr Pb Mn Ni or Zn are known for their behaviours which strongly depend on the pH value Most of these heavy metals are more solubilized for acid pH than for alkaline pH Due to the decrease of the pH value it can be assumed that the carbonation leads to increase the heavy metals concentrations in the liquid phase

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

4

For the reason that liquid phase of the residual brines produced by the ammonia-soda process is then rejected in rivers oceans or lakes proceeding with the entire carbonation of the brines has to be avoided A pH value between 70 and 75 can be considered as a good choice to limit the heavy metals mobilization

000

001

002

003

004

005

006

5 6 7 8 9 10 11

pH

[Cr]

(mg

kg)

031120080511200805022009

00000

00050

00100

00150

00200

00250

00300

00350

5 6 7 8 9 10 11

pH

[Cd]

(mg

kg)

03072008070720080311200805022009

Figure 4 Evolution with pH of Cr and Cd concentration in the liquid phase at different dates

342 Calcite solubilization for acid pH In order to understand the calcite dissolution when the acidity growths the acido-basic reactions of carbon dioxide and the dissociation reaction of calcite are shown below

H2O CO2 = H+ + HCO3- (pKa1 = 637)

HCO3- = H+ + CO3

2- (pKa2 = 1032) CaCO3 = Ca2+ + CO3

2- (pKS = 872 at 55degC) Thus decreasing the pH value leads to the decrease of CO3

2- concentration which may lead to the solubilization of the calcite if the product of the concentration of Ca2+ by the concentration of CO3

2- is lower han the product of solubility of calcite at 55degC calculated with an experimentally obtained expression [11] Moreover for acid pH HCO3

- ions attack CaCO3 releasing free Ca2+ in brines as Ca(HCO3

2-) is not a solid compound modifying the equilibrium between free Ca2+ and ldquosequesteredrdquo Ca

4 Conclusion The analysis of the results leads to the three main conclusions

First phases presents in the residual brines sensitive to carbonation are identified and an magnitude order of carbonation of them is obtained by coupling infrared spectroscopy and X-ray diffraction methods Thus the first phase which disappears is CaOHCl followed by the disappearance of Ca(OH)2 at pH around 10 then C-S-H disappear for pH around 85 and finally Mg(OH)2 at pH around 75

It must be noted that carbonation is not only interesting because of the precipitation of new mineral phases (calcium carbonate essentially) from different mineral phases (Ca(OH)2 CaOHCl C-S-H) Indeed it also deeply modifies the global equilibrium of the system leading to the decrease of mobility of elements such as aluminium which is responsible of the appearance of unsuitable phases during land-storage

However this process has two main negative aspects when pH reaches acid values This means that CO2 sequestration cannot be achieved to the maximum Indeed when pH is too low some hazardous heavy metals such as chromium and cadmium are solubilized Moreover calcite is also solubilized due to the acido-basic equilibrium of carbonate which leads to the disappearance of CO3

2- and the appearance of HCO3

- which attacks calcite

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

5

References [1] Bodeacutenan F Lassin A Hottier M Filippov L Durance M V and Piantone P 2008 Pieacutegeage et

valorisation de deacutechets alcalins par passivation au CO2 industriel Rapport final ANR-Decalco BRGMRP-56361 151 p

[2] Fernaacutendez Bertos M Simons S J R Hills C D Carey P J 2004 J Hazardous Materials B112 193

[3] Soong Y Fauth D L Howard B H Jones J R Harrison D K Goodman A L Gray M L and Frommell E A 2006 Energy Conversion and Management 47 1676

[4] Bodeacutenan F Hottier M Lassin A Filippov L and Piantone P 2008 Reducing CO2 emissions from the Solvay process by entrapment in saline waste Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P171 7 pp

[5] Kasikowski T Buczkowski R Dejewska B Peszynska-Bialczyk K Lemanowska E and Iglinski B 2004 J of Cleaner Production 12 759

[6] Kasikowski T Buczkowki R and Lemanowska E 2004 J of Environmental Management 73 339 [7] Kasikowski T Buczkowski R and Cichosz M 2008 Int J Production Economics 112 971 [8] Soong Y Goodman A L McCarthy-Jones J R Baltrus J P 2004 Energy Conversion and

Management 45 1845-1859 [9] Nyambura M G Mugera G W Felicia P L and Gathura N P 2011 J Environmental

Management 92 655 [10] CEFIC 2004 IPPC BAT reference document ndash Large volume solid inorganic chemicals family

ndash Process BREF for soda ash issue ndeg3 - httpwwwceficbefilesPublicationsESAPA_Soda_Ash_Process_BREF3pdf

[11] Dorange G Marchand A Le Guyader M 1990 Revue des sciences de lrsquoeau 3 261 [12] Filippov L O Yvon J Filippova I V Godon B Perrin P and Piantone P 2008 Characterisation

and descriptive model of saline waste evolution Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P 143 2pp

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

6

2 Material and methods Carbonation reactions were carried out in a Pyrex reactor with a 1900 mL volume capacity at a constant temperature of 55degC which corresponds to the temperature of the residual brines getting out of the ammonia-soda process factory Gas injected by bubbling contained 15 of CO2 and 85 of air corresponding to the composition of the gas at the outlet of the boiler The mixture was continuously stirred for a better bubble dispersion and to prevent sedimentation of particles however it must be noted that in industrial conditions the possible use of a counterndashcurrent bubbling column avoids using a stirring device Indeed in a continuous reactor the large amount of gas injected is sufficient to ensure an efficient mixing of the brines When pH is considered as stable 250 mL of the mixture are sampled and then filtrated at 045 microm in a Teflon Millipore compressed air system The liquid phases are acidified whereas the solid phases are frozen and freeze-dried to withdraw the free water Crystalline phases present in the solids are determined by X-Ray Diffraction (XRD) using a Bruker D8 Advance diffractometer equipped with a Co-Kα1 computed monochromatic source (1789Aring) at 35 kV and 45 mA with a linear Lynx-Eye detector at 0035deg by 2 theta step from 3deg to 64deg and a 3 seconds counting time Presence of sulphate hydrated silicate or carbonate phases are determined by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) using a Bruker IFS 55 equipped with a large band (600-5500 cm-1) mercury-cadmium telluride (MCT) detector cooled to 77 K Fine chemical analysis of Cd Cr Mn Ni and Pb concentrations in the liquid phases are performed using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS VARIAN 820-MS)

3 Results and discussion

31 Order of carbonation After filtration and freeze-drying of a sample the composition of residual brine was deduced from associating XRD and DRIFTS results XRD shows the presence of portlandite and calcium hydroxychloride CaOHCl The vibrations at 3644 cm-1 3698 cm-1 and 3570 cm-1 in the DRIFTS spectra are assigned to the hydroxyl stretching vibration in Ca(OH)2 Mg(OH)2 and CaOHCl respectively (figure 1) The large band at 966 cm-1 corresponds to the vibration of Si-O in the C-S-H and the large band centred on 1430 cm-1 to the C-O elongations in carbonates Other bands are diverse overtones deformations or combinations of the same groups

0

02

04

06

08

1

12

60010001400180022002600300034003800Wavenumber (cm-1)

Abs

orba

nce

Uni

t

3698

36443570

966

Figure 1 Diffuse reflectance FT-IR spectrum of solid phase from initial brines

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

2

At carbonation pH (close to 6) all peaks characterising the presence of these minerals have disappeared (figure 2) However these mineral phases are not directly carbonated In fact CO2 must first be solvated hydrated and ionised giving carbonate ion CO3

2 (-reaction 1) which reacts with free Ca2+ according to reaction (2)

CO2 (g) + H2O = CO32-

(aq) + 2 H+ (1) Ca2+

(aq) + CO32-

(aq) = CaCO3 (s) (2) These two reactions displace the solid-solution equilibria of Ca(OH)2 Mg(OH)2 CaOHCl and CSH

(reactions (3) ndash (5)) due to the consumption of free Ca2+ and to the slow disappearance of OH- ions when pH decreases Indeed the appearance of CO3

2- in water comes along with the appearance of two H+ according to reaction (1) This reaction explains why the pH tends to decrease when CO2 is injected in the reactor

Ca(OH)2 = Ca2+ + 2 OH- (3) CaOHCl = Ca2+ + OH- + Cl- (4) Mg(OH)2 = Mg2+ + 2 OH- (5) x CaO ndash y SiO2 ndash z H2O = x CaO +y Si(OH)4 + (z-2y) H2O (6) The solubilization of the C-S-H (reaction (6)) is a two-step reaction Indeed CO3

2- reacts with free Ca2+ (reaction (2)) modifying the equilibrium between sequestered CaO and solubilized CaO that is Ca(OH)2 (reaction (3)) It cannot be accepted that C-S-H are directly carbonated They are dissolved due to an equilibrium between CaO contained in C-S-H and free Ca2+ continuously consumed by carbonation

0010203040506070809

1

30003250350037504000Wavenumber (cm-1)

Abs

orba

nce

Uni

t

(a)

3698

3570

3640

03

04

05

06

07

08

09

600800100012001400Wavenumber (cm-1)

Abs

orba

nce

Uni

t

(b)

966

Figure 2 Evolution of diffuse reflectance infrared spectra of residual brines with pH Due to kinetics and solubility products an order of carbonation of phases was obtained CaOHCl

which crystallizes [1a] at the surface of Ca(OH)2 first disappears followed by Ca(OH)2 whose dissolution is relatively quick due to the facts that both Ca2+ and OH- are consumed by carbonation C-S-H then disappear after its slow but complete dissolution releasing colloidal silica in the brine (reaction (6)) whose dissolution is favoured by the alkaline pH Mg(OH)2 finally disappears from the mixture when pH is low enough to ensure the total solubilization of brucite [4]

32 Less CO2 emission for the ammonia-soda process Using the BAT (Best Available Techniques) document of the IPPC (Integrated Pollution Prevention and Control) directive [10] the ammonia-soda process has been schematized in 12 steps with the software BILCO reg [1] This model has been intentionally designed for the production of one ton of sodium carbonate Na2CO3 so that the values of the flow-rates of the wastes (CO2 and brines) are now given per ton of Na2CO3 produced Thus the production of one ton of Na2CO3 comes along with the emission of 351 kg of CO2 [1] The CO2 consumption for the carbonation of the residual brines

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

3

depends on the value of the pH at the end of the carbonation For a final value of pH 7 the consumption of CO2 is around 35 kg per ton of produced Na2CO3 then with a 10 decrease of the CO2 emission from the ammonia-soda process For a worldwide annual production of 60 Mt of Na2CO3 this process would allow the sequestration of 21 Mt of CO2

33 Further phase transformation avoided Residual brines contain mix layered double hydroxides (LDH) of Ca2+ and Al3+ such as hydrocalumite [Ca2Al(OH)6][Cl1-xOHx]3H2O During landfield storage these LDH lead to the formation of expansible phases such as ettringite which shorten the designed life-time of tailing dumps [12] Furthermore these expansible phases are also responsible for the creation of a lens in the middle of the tailing dumps which prevents them from the complete leaching of chloride [12] The vertical zonality model of phase evolution in dump proposed in [12] reveals the essential role played by Al (and Mg) in the blocking of the maturation of the solids resulting from the effluent decantation and contact with the air In the case of a waste disposal processed by a simple decantation without carbonation since the kinetics of the natural carbonation controlled by the diffusion of CO2 is not fast enough the solids precipitate and free water preserve an alkaline pH buffered by the portlandite This alkaline pH will cause on one hand to continue the dissolution of residual silico-aluminous minerals contained in the brine (mullite) and on the other hand to support the alkaline mineral formation (layered double hydroxides and cancrinites) These neoformed phases by their structuring capacity (swelling and retention of water) favour the relative impermeability and will delay the carbonation of the level where they occur

Decreasing the pH causes the sequestration of aluminium in the solid phase as predicted by Pourbaixrsquo diagram of Al It can be noted that carbonation decreases the mobility of aluminium because of pH decreasing and avoids formation of layered double hydroxides

00000

02000

04000

06000

08000

10000

12000

14000

5 6 7 8 9 10 11

pH

[Al]

(mg

kg)

0307200807072008031120080511200805022009

Figure 3 Evolution of aluminium concentration in the liquid phase with pH (Evolution is given for five different dates)

34 Limits of the carbonation process The CO2 sequestration method by carbonation of industrial brines has limits Indeed when decreasing the pH two limits clearly appear which lead to the necessary incomplete carbonation of the residual brines of the ammonia-soda process

341 Heavy metals solubilization Heavy metals such as Cr Pb Mn Ni or Zn are known for their behaviours which strongly depend on the pH value Most of these heavy metals are more solubilized for acid pH than for alkaline pH Due to the decrease of the pH value it can be assumed that the carbonation leads to increase the heavy metals concentrations in the liquid phase

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

4

For the reason that liquid phase of the residual brines produced by the ammonia-soda process is then rejected in rivers oceans or lakes proceeding with the entire carbonation of the brines has to be avoided A pH value between 70 and 75 can be considered as a good choice to limit the heavy metals mobilization

000

001

002

003

004

005

006

5 6 7 8 9 10 11

pH

[Cr]

(mg

kg)

031120080511200805022009

00000

00050

00100

00150

00200

00250

00300

00350

5 6 7 8 9 10 11

pH

[Cd]

(mg

kg)

03072008070720080311200805022009

Figure 4 Evolution with pH of Cr and Cd concentration in the liquid phase at different dates

342 Calcite solubilization for acid pH In order to understand the calcite dissolution when the acidity growths the acido-basic reactions of carbon dioxide and the dissociation reaction of calcite are shown below

H2O CO2 = H+ + HCO3- (pKa1 = 637)

HCO3- = H+ + CO3

2- (pKa2 = 1032) CaCO3 = Ca2+ + CO3

2- (pKS = 872 at 55degC) Thus decreasing the pH value leads to the decrease of CO3

2- concentration which may lead to the solubilization of the calcite if the product of the concentration of Ca2+ by the concentration of CO3

2- is lower han the product of solubility of calcite at 55degC calculated with an experimentally obtained expression [11] Moreover for acid pH HCO3

- ions attack CaCO3 releasing free Ca2+ in brines as Ca(HCO3

2-) is not a solid compound modifying the equilibrium between free Ca2+ and ldquosequesteredrdquo Ca

4 Conclusion The analysis of the results leads to the three main conclusions

First phases presents in the residual brines sensitive to carbonation are identified and an magnitude order of carbonation of them is obtained by coupling infrared spectroscopy and X-ray diffraction methods Thus the first phase which disappears is CaOHCl followed by the disappearance of Ca(OH)2 at pH around 10 then C-S-H disappear for pH around 85 and finally Mg(OH)2 at pH around 75

It must be noted that carbonation is not only interesting because of the precipitation of new mineral phases (calcium carbonate essentially) from different mineral phases (Ca(OH)2 CaOHCl C-S-H) Indeed it also deeply modifies the global equilibrium of the system leading to the decrease of mobility of elements such as aluminium which is responsible of the appearance of unsuitable phases during land-storage

However this process has two main negative aspects when pH reaches acid values This means that CO2 sequestration cannot be achieved to the maximum Indeed when pH is too low some hazardous heavy metals such as chromium and cadmium are solubilized Moreover calcite is also solubilized due to the acido-basic equilibrium of carbonate which leads to the disappearance of CO3

2- and the appearance of HCO3

- which attacks calcite

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

5

References [1] Bodeacutenan F Lassin A Hottier M Filippov L Durance M V and Piantone P 2008 Pieacutegeage et

valorisation de deacutechets alcalins par passivation au CO2 industriel Rapport final ANR-Decalco BRGMRP-56361 151 p

[2] Fernaacutendez Bertos M Simons S J R Hills C D Carey P J 2004 J Hazardous Materials B112 193

[3] Soong Y Fauth D L Howard B H Jones J R Harrison D K Goodman A L Gray M L and Frommell E A 2006 Energy Conversion and Management 47 1676

[4] Bodeacutenan F Hottier M Lassin A Filippov L and Piantone P 2008 Reducing CO2 emissions from the Solvay process by entrapment in saline waste Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P171 7 pp

[5] Kasikowski T Buczkowski R Dejewska B Peszynska-Bialczyk K Lemanowska E and Iglinski B 2004 J of Cleaner Production 12 759

[6] Kasikowski T Buczkowki R and Lemanowska E 2004 J of Environmental Management 73 339 [7] Kasikowski T Buczkowski R and Cichosz M 2008 Int J Production Economics 112 971 [8] Soong Y Goodman A L McCarthy-Jones J R Baltrus J P 2004 Energy Conversion and

Management 45 1845-1859 [9] Nyambura M G Mugera G W Felicia P L and Gathura N P 2011 J Environmental

Management 92 655 [10] CEFIC 2004 IPPC BAT reference document ndash Large volume solid inorganic chemicals family

ndash Process BREF for soda ash issue ndeg3 - httpwwwceficbefilesPublicationsESAPA_Soda_Ash_Process_BREF3pdf

[11] Dorange G Marchand A Le Guyader M 1990 Revue des sciences de lrsquoeau 3 261 [12] Filippov L O Yvon J Filippova I V Godon B Perrin P and Piantone P 2008 Characterisation

and descriptive model of saline waste evolution Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P 143 2pp

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

6

At carbonation pH (close to 6) all peaks characterising the presence of these minerals have disappeared (figure 2) However these mineral phases are not directly carbonated In fact CO2 must first be solvated hydrated and ionised giving carbonate ion CO3

2 (-reaction 1) which reacts with free Ca2+ according to reaction (2)

CO2 (g) + H2O = CO32-

(aq) + 2 H+ (1) Ca2+

(aq) + CO32-

(aq) = CaCO3 (s) (2) These two reactions displace the solid-solution equilibria of Ca(OH)2 Mg(OH)2 CaOHCl and CSH

(reactions (3) ndash (5)) due to the consumption of free Ca2+ and to the slow disappearance of OH- ions when pH decreases Indeed the appearance of CO3

2- in water comes along with the appearance of two H+ according to reaction (1) This reaction explains why the pH tends to decrease when CO2 is injected in the reactor

Ca(OH)2 = Ca2+ + 2 OH- (3) CaOHCl = Ca2+ + OH- + Cl- (4) Mg(OH)2 = Mg2+ + 2 OH- (5) x CaO ndash y SiO2 ndash z H2O = x CaO +y Si(OH)4 + (z-2y) H2O (6) The solubilization of the C-S-H (reaction (6)) is a two-step reaction Indeed CO3

2- reacts with free Ca2+ (reaction (2)) modifying the equilibrium between sequestered CaO and solubilized CaO that is Ca(OH)2 (reaction (3)) It cannot be accepted that C-S-H are directly carbonated They are dissolved due to an equilibrium between CaO contained in C-S-H and free Ca2+ continuously consumed by carbonation

0010203040506070809

1

30003250350037504000Wavenumber (cm-1)

Abs

orba

nce

Uni

t

(a)

3698

3570

3640

03

04

05

06

07

08

09

600800100012001400Wavenumber (cm-1)

Abs

orba

nce

Uni

t

(b)

966

Figure 2 Evolution of diffuse reflectance infrared spectra of residual brines with pH Due to kinetics and solubility products an order of carbonation of phases was obtained CaOHCl

which crystallizes [1a] at the surface of Ca(OH)2 first disappears followed by Ca(OH)2 whose dissolution is relatively quick due to the facts that both Ca2+ and OH- are consumed by carbonation C-S-H then disappear after its slow but complete dissolution releasing colloidal silica in the brine (reaction (6)) whose dissolution is favoured by the alkaline pH Mg(OH)2 finally disappears from the mixture when pH is low enough to ensure the total solubilization of brucite [4]

32 Less CO2 emission for the ammonia-soda process Using the BAT (Best Available Techniques) document of the IPPC (Integrated Pollution Prevention and Control) directive [10] the ammonia-soda process has been schematized in 12 steps with the software BILCO reg [1] This model has been intentionally designed for the production of one ton of sodium carbonate Na2CO3 so that the values of the flow-rates of the wastes (CO2 and brines) are now given per ton of Na2CO3 produced Thus the production of one ton of Na2CO3 comes along with the emission of 351 kg of CO2 [1] The CO2 consumption for the carbonation of the residual brines

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

3

depends on the value of the pH at the end of the carbonation For a final value of pH 7 the consumption of CO2 is around 35 kg per ton of produced Na2CO3 then with a 10 decrease of the CO2 emission from the ammonia-soda process For a worldwide annual production of 60 Mt of Na2CO3 this process would allow the sequestration of 21 Mt of CO2

33 Further phase transformation avoided Residual brines contain mix layered double hydroxides (LDH) of Ca2+ and Al3+ such as hydrocalumite [Ca2Al(OH)6][Cl1-xOHx]3H2O During landfield storage these LDH lead to the formation of expansible phases such as ettringite which shorten the designed life-time of tailing dumps [12] Furthermore these expansible phases are also responsible for the creation of a lens in the middle of the tailing dumps which prevents them from the complete leaching of chloride [12] The vertical zonality model of phase evolution in dump proposed in [12] reveals the essential role played by Al (and Mg) in the blocking of the maturation of the solids resulting from the effluent decantation and contact with the air In the case of a waste disposal processed by a simple decantation without carbonation since the kinetics of the natural carbonation controlled by the diffusion of CO2 is not fast enough the solids precipitate and free water preserve an alkaline pH buffered by the portlandite This alkaline pH will cause on one hand to continue the dissolution of residual silico-aluminous minerals contained in the brine (mullite) and on the other hand to support the alkaline mineral formation (layered double hydroxides and cancrinites) These neoformed phases by their structuring capacity (swelling and retention of water) favour the relative impermeability and will delay the carbonation of the level where they occur

Decreasing the pH causes the sequestration of aluminium in the solid phase as predicted by Pourbaixrsquo diagram of Al It can be noted that carbonation decreases the mobility of aluminium because of pH decreasing and avoids formation of layered double hydroxides

00000

02000

04000

06000

08000

10000

12000

14000

5 6 7 8 9 10 11

pH

[Al]

(mg

kg)

0307200807072008031120080511200805022009

Figure 3 Evolution of aluminium concentration in the liquid phase with pH (Evolution is given for five different dates)

34 Limits of the carbonation process The CO2 sequestration method by carbonation of industrial brines has limits Indeed when decreasing the pH two limits clearly appear which lead to the necessary incomplete carbonation of the residual brines of the ammonia-soda process

341 Heavy metals solubilization Heavy metals such as Cr Pb Mn Ni or Zn are known for their behaviours which strongly depend on the pH value Most of these heavy metals are more solubilized for acid pH than for alkaline pH Due to the decrease of the pH value it can be assumed that the carbonation leads to increase the heavy metals concentrations in the liquid phase

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

4

For the reason that liquid phase of the residual brines produced by the ammonia-soda process is then rejected in rivers oceans or lakes proceeding with the entire carbonation of the brines has to be avoided A pH value between 70 and 75 can be considered as a good choice to limit the heavy metals mobilization

000

001

002

003

004

005

006

5 6 7 8 9 10 11

pH

[Cr]

(mg

kg)

031120080511200805022009

00000

00050

00100

00150

00200

00250

00300

00350

5 6 7 8 9 10 11

pH

[Cd]

(mg

kg)

03072008070720080311200805022009

Figure 4 Evolution with pH of Cr and Cd concentration in the liquid phase at different dates

342 Calcite solubilization for acid pH In order to understand the calcite dissolution when the acidity growths the acido-basic reactions of carbon dioxide and the dissociation reaction of calcite are shown below

H2O CO2 = H+ + HCO3- (pKa1 = 637)

HCO3- = H+ + CO3

2- (pKa2 = 1032) CaCO3 = Ca2+ + CO3

2- (pKS = 872 at 55degC) Thus decreasing the pH value leads to the decrease of CO3

2- concentration which may lead to the solubilization of the calcite if the product of the concentration of Ca2+ by the concentration of CO3

2- is lower han the product of solubility of calcite at 55degC calculated with an experimentally obtained expression [11] Moreover for acid pH HCO3

- ions attack CaCO3 releasing free Ca2+ in brines as Ca(HCO3

2-) is not a solid compound modifying the equilibrium between free Ca2+ and ldquosequesteredrdquo Ca

4 Conclusion The analysis of the results leads to the three main conclusions

First phases presents in the residual brines sensitive to carbonation are identified and an magnitude order of carbonation of them is obtained by coupling infrared spectroscopy and X-ray diffraction methods Thus the first phase which disappears is CaOHCl followed by the disappearance of Ca(OH)2 at pH around 10 then C-S-H disappear for pH around 85 and finally Mg(OH)2 at pH around 75

It must be noted that carbonation is not only interesting because of the precipitation of new mineral phases (calcium carbonate essentially) from different mineral phases (Ca(OH)2 CaOHCl C-S-H) Indeed it also deeply modifies the global equilibrium of the system leading to the decrease of mobility of elements such as aluminium which is responsible of the appearance of unsuitable phases during land-storage

However this process has two main negative aspects when pH reaches acid values This means that CO2 sequestration cannot be achieved to the maximum Indeed when pH is too low some hazardous heavy metals such as chromium and cadmium are solubilized Moreover calcite is also solubilized due to the acido-basic equilibrium of carbonate which leads to the disappearance of CO3

2- and the appearance of HCO3

- which attacks calcite

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

5

References [1] Bodeacutenan F Lassin A Hottier M Filippov L Durance M V and Piantone P 2008 Pieacutegeage et

valorisation de deacutechets alcalins par passivation au CO2 industriel Rapport final ANR-Decalco BRGMRP-56361 151 p

[2] Fernaacutendez Bertos M Simons S J R Hills C D Carey P J 2004 J Hazardous Materials B112 193

[3] Soong Y Fauth D L Howard B H Jones J R Harrison D K Goodman A L Gray M L and Frommell E A 2006 Energy Conversion and Management 47 1676

[4] Bodeacutenan F Hottier M Lassin A Filippov L and Piantone P 2008 Reducing CO2 emissions from the Solvay process by entrapment in saline waste Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P171 7 pp

[5] Kasikowski T Buczkowski R Dejewska B Peszynska-Bialczyk K Lemanowska E and Iglinski B 2004 J of Cleaner Production 12 759

[6] Kasikowski T Buczkowki R and Lemanowska E 2004 J of Environmental Management 73 339 [7] Kasikowski T Buczkowski R and Cichosz M 2008 Int J Production Economics 112 971 [8] Soong Y Goodman A L McCarthy-Jones J R Baltrus J P 2004 Energy Conversion and

Management 45 1845-1859 [9] Nyambura M G Mugera G W Felicia P L and Gathura N P 2011 J Environmental

Management 92 655 [10] CEFIC 2004 IPPC BAT reference document ndash Large volume solid inorganic chemicals family

ndash Process BREF for soda ash issue ndeg3 - httpwwwceficbefilesPublicationsESAPA_Soda_Ash_Process_BREF3pdf

[11] Dorange G Marchand A Le Guyader M 1990 Revue des sciences de lrsquoeau 3 261 [12] Filippov L O Yvon J Filippova I V Godon B Perrin P and Piantone P 2008 Characterisation

and descriptive model of saline waste evolution Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P 143 2pp

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

6

depends on the value of the pH at the end of the carbonation For a final value of pH 7 the consumption of CO2 is around 35 kg per ton of produced Na2CO3 then with a 10 decrease of the CO2 emission from the ammonia-soda process For a worldwide annual production of 60 Mt of Na2CO3 this process would allow the sequestration of 21 Mt of CO2

33 Further phase transformation avoided Residual brines contain mix layered double hydroxides (LDH) of Ca2+ and Al3+ such as hydrocalumite [Ca2Al(OH)6][Cl1-xOHx]3H2O During landfield storage these LDH lead to the formation of expansible phases such as ettringite which shorten the designed life-time of tailing dumps [12] Furthermore these expansible phases are also responsible for the creation of a lens in the middle of the tailing dumps which prevents them from the complete leaching of chloride [12] The vertical zonality model of phase evolution in dump proposed in [12] reveals the essential role played by Al (and Mg) in the blocking of the maturation of the solids resulting from the effluent decantation and contact with the air In the case of a waste disposal processed by a simple decantation without carbonation since the kinetics of the natural carbonation controlled by the diffusion of CO2 is not fast enough the solids precipitate and free water preserve an alkaline pH buffered by the portlandite This alkaline pH will cause on one hand to continue the dissolution of residual silico-aluminous minerals contained in the brine (mullite) and on the other hand to support the alkaline mineral formation (layered double hydroxides and cancrinites) These neoformed phases by their structuring capacity (swelling and retention of water) favour the relative impermeability and will delay the carbonation of the level where they occur

Decreasing the pH causes the sequestration of aluminium in the solid phase as predicted by Pourbaixrsquo diagram of Al It can be noted that carbonation decreases the mobility of aluminium because of pH decreasing and avoids formation of layered double hydroxides

00000

02000

04000

06000

08000

10000

12000

14000

5 6 7 8 9 10 11

pH

[Al]

(mg

kg)

0307200807072008031120080511200805022009

Figure 3 Evolution of aluminium concentration in the liquid phase with pH (Evolution is given for five different dates)

34 Limits of the carbonation process The CO2 sequestration method by carbonation of industrial brines has limits Indeed when decreasing the pH two limits clearly appear which lead to the necessary incomplete carbonation of the residual brines of the ammonia-soda process

341 Heavy metals solubilization Heavy metals such as Cr Pb Mn Ni or Zn are known for their behaviours which strongly depend on the pH value Most of these heavy metals are more solubilized for acid pH than for alkaline pH Due to the decrease of the pH value it can be assumed that the carbonation leads to increase the heavy metals concentrations in the liquid phase

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

4

For the reason that liquid phase of the residual brines produced by the ammonia-soda process is then rejected in rivers oceans or lakes proceeding with the entire carbonation of the brines has to be avoided A pH value between 70 and 75 can be considered as a good choice to limit the heavy metals mobilization

000

001

002

003

004

005

006

5 6 7 8 9 10 11

pH

[Cr]

(mg

kg)

031120080511200805022009

00000

00050

00100

00150

00200

00250

00300

00350

5 6 7 8 9 10 11

pH

[Cd]

(mg

kg)

03072008070720080311200805022009

Figure 4 Evolution with pH of Cr and Cd concentration in the liquid phase at different dates

342 Calcite solubilization for acid pH In order to understand the calcite dissolution when the acidity growths the acido-basic reactions of carbon dioxide and the dissociation reaction of calcite are shown below

H2O CO2 = H+ + HCO3- (pKa1 = 637)

HCO3- = H+ + CO3

2- (pKa2 = 1032) CaCO3 = Ca2+ + CO3

2- (pKS = 872 at 55degC) Thus decreasing the pH value leads to the decrease of CO3

2- concentration which may lead to the solubilization of the calcite if the product of the concentration of Ca2+ by the concentration of CO3

2- is lower han the product of solubility of calcite at 55degC calculated with an experimentally obtained expression [11] Moreover for acid pH HCO3

- ions attack CaCO3 releasing free Ca2+ in brines as Ca(HCO3

2-) is not a solid compound modifying the equilibrium between free Ca2+ and ldquosequesteredrdquo Ca

4 Conclusion The analysis of the results leads to the three main conclusions

First phases presents in the residual brines sensitive to carbonation are identified and an magnitude order of carbonation of them is obtained by coupling infrared spectroscopy and X-ray diffraction methods Thus the first phase which disappears is CaOHCl followed by the disappearance of Ca(OH)2 at pH around 10 then C-S-H disappear for pH around 85 and finally Mg(OH)2 at pH around 75

It must be noted that carbonation is not only interesting because of the precipitation of new mineral phases (calcium carbonate essentially) from different mineral phases (Ca(OH)2 CaOHCl C-S-H) Indeed it also deeply modifies the global equilibrium of the system leading to the decrease of mobility of elements such as aluminium which is responsible of the appearance of unsuitable phases during land-storage

However this process has two main negative aspects when pH reaches acid values This means that CO2 sequestration cannot be achieved to the maximum Indeed when pH is too low some hazardous heavy metals such as chromium and cadmium are solubilized Moreover calcite is also solubilized due to the acido-basic equilibrium of carbonate which leads to the disappearance of CO3

2- and the appearance of HCO3

- which attacks calcite

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

5

References [1] Bodeacutenan F Lassin A Hottier M Filippov L Durance M V and Piantone P 2008 Pieacutegeage et

valorisation de deacutechets alcalins par passivation au CO2 industriel Rapport final ANR-Decalco BRGMRP-56361 151 p

[2] Fernaacutendez Bertos M Simons S J R Hills C D Carey P J 2004 J Hazardous Materials B112 193

[3] Soong Y Fauth D L Howard B H Jones J R Harrison D K Goodman A L Gray M L and Frommell E A 2006 Energy Conversion and Management 47 1676

[4] Bodeacutenan F Hottier M Lassin A Filippov L and Piantone P 2008 Reducing CO2 emissions from the Solvay process by entrapment in saline waste Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P171 7 pp

[5] Kasikowski T Buczkowski R Dejewska B Peszynska-Bialczyk K Lemanowska E and Iglinski B 2004 J of Cleaner Production 12 759

[6] Kasikowski T Buczkowki R and Lemanowska E 2004 J of Environmental Management 73 339 [7] Kasikowski T Buczkowski R and Cichosz M 2008 Int J Production Economics 112 971 [8] Soong Y Goodman A L McCarthy-Jones J R Baltrus J P 2004 Energy Conversion and

Management 45 1845-1859 [9] Nyambura M G Mugera G W Felicia P L and Gathura N P 2011 J Environmental

Management 92 655 [10] CEFIC 2004 IPPC BAT reference document ndash Large volume solid inorganic chemicals family

ndash Process BREF for soda ash issue ndeg3 - httpwwwceficbefilesPublicationsESAPA_Soda_Ash_Process_BREF3pdf

[11] Dorange G Marchand A Le Guyader M 1990 Revue des sciences de lrsquoeau 3 261 [12] Filippov L O Yvon J Filippova I V Godon B Perrin P and Piantone P 2008 Characterisation

and descriptive model of saline waste evolution Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P 143 2pp

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

6

For the reason that liquid phase of the residual brines produced by the ammonia-soda process is then rejected in rivers oceans or lakes proceeding with the entire carbonation of the brines has to be avoided A pH value between 70 and 75 can be considered as a good choice to limit the heavy metals mobilization

000

001

002

003

004

005

006

5 6 7 8 9 10 11

pH

[Cr]

(mg

kg)

031120080511200805022009

00000

00050

00100

00150

00200

00250

00300

00350

5 6 7 8 9 10 11

pH

[Cd]

(mg

kg)

03072008070720080311200805022009

Figure 4 Evolution with pH of Cr and Cd concentration in the liquid phase at different dates

342 Calcite solubilization for acid pH In order to understand the calcite dissolution when the acidity growths the acido-basic reactions of carbon dioxide and the dissociation reaction of calcite are shown below

H2O CO2 = H+ + HCO3- (pKa1 = 637)

HCO3- = H+ + CO3

2- (pKa2 = 1032) CaCO3 = Ca2+ + CO3

2- (pKS = 872 at 55degC) Thus decreasing the pH value leads to the decrease of CO3

2- concentration which may lead to the solubilization of the calcite if the product of the concentration of Ca2+ by the concentration of CO3

2- is lower han the product of solubility of calcite at 55degC calculated with an experimentally obtained expression [11] Moreover for acid pH HCO3

- ions attack CaCO3 releasing free Ca2+ in brines as Ca(HCO3

2-) is not a solid compound modifying the equilibrium between free Ca2+ and ldquosequesteredrdquo Ca

4 Conclusion The analysis of the results leads to the three main conclusions

First phases presents in the residual brines sensitive to carbonation are identified and an magnitude order of carbonation of them is obtained by coupling infrared spectroscopy and X-ray diffraction methods Thus the first phase which disappears is CaOHCl followed by the disappearance of Ca(OH)2 at pH around 10 then C-S-H disappear for pH around 85 and finally Mg(OH)2 at pH around 75

It must be noted that carbonation is not only interesting because of the precipitation of new mineral phases (calcium carbonate essentially) from different mineral phases (Ca(OH)2 CaOHCl C-S-H) Indeed it also deeply modifies the global equilibrium of the system leading to the decrease of mobility of elements such as aluminium which is responsible of the appearance of unsuitable phases during land-storage

However this process has two main negative aspects when pH reaches acid values This means that CO2 sequestration cannot be achieved to the maximum Indeed when pH is too low some hazardous heavy metals such as chromium and cadmium are solubilized Moreover calcite is also solubilized due to the acido-basic equilibrium of carbonate which leads to the disappearance of CO3

2- and the appearance of HCO3

- which attacks calcite

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

5

References [1] Bodeacutenan F Lassin A Hottier M Filippov L Durance M V and Piantone P 2008 Pieacutegeage et

valorisation de deacutechets alcalins par passivation au CO2 industriel Rapport final ANR-Decalco BRGMRP-56361 151 p

[2] Fernaacutendez Bertos M Simons S J R Hills C D Carey P J 2004 J Hazardous Materials B112 193

[3] Soong Y Fauth D L Howard B H Jones J R Harrison D K Goodman A L Gray M L and Frommell E A 2006 Energy Conversion and Management 47 1676

[4] Bodeacutenan F Hottier M Lassin A Filippov L and Piantone P 2008 Reducing CO2 emissions from the Solvay process by entrapment in saline waste Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P171 7 pp

[5] Kasikowski T Buczkowski R Dejewska B Peszynska-Bialczyk K Lemanowska E and Iglinski B 2004 J of Cleaner Production 12 759

[6] Kasikowski T Buczkowki R and Lemanowska E 2004 J of Environmental Management 73 339 [7] Kasikowski T Buczkowski R and Cichosz M 2008 Int J Production Economics 112 971 [8] Soong Y Goodman A L McCarthy-Jones J R Baltrus J P 2004 Energy Conversion and

Management 45 1845-1859 [9] Nyambura M G Mugera G W Felicia P L and Gathura N P 2011 J Environmental

Management 92 655 [10] CEFIC 2004 IPPC BAT reference document ndash Large volume solid inorganic chemicals family

ndash Process BREF for soda ash issue ndeg3 - httpwwwceficbefilesPublicationsESAPA_Soda_Ash_Process_BREF3pdf

[11] Dorange G Marchand A Le Guyader M 1990 Revue des sciences de lrsquoeau 3 261 [12] Filippov L O Yvon J Filippova I V Godon B Perrin P and Piantone P 2008 Characterisation

and descriptive model of saline waste evolution Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P 143 2pp

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

6

References [1] Bodeacutenan F Lassin A Hottier M Filippov L Durance M V and Piantone P 2008 Pieacutegeage et

valorisation de deacutechets alcalins par passivation au CO2 industriel Rapport final ANR-Decalco BRGMRP-56361 151 p

[2] Fernaacutendez Bertos M Simons S J R Hills C D Carey P J 2004 J Hazardous Materials B112 193

[3] Soong Y Fauth D L Howard B H Jones J R Harrison D K Goodman A L Gray M L and Frommell E A 2006 Energy Conversion and Management 47 1676

[4] Bodeacutenan F Hottier M Lassin A Filippov L and Piantone P 2008 Reducing CO2 emissions from the Solvay process by entrapment in saline waste Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P171 7 pp

[5] Kasikowski T Buczkowski R Dejewska B Peszynska-Bialczyk K Lemanowska E and Iglinski B 2004 J of Cleaner Production 12 759

[6] Kasikowski T Buczkowki R and Lemanowska E 2004 J of Environmental Management 73 339 [7] Kasikowski T Buczkowski R and Cichosz M 2008 Int J Production Economics 112 971 [8] Soong Y Goodman A L McCarthy-Jones J R Baltrus J P 2004 Energy Conversion and

Management 45 1845-1859 [9] Nyambura M G Mugera G W Felicia P L and Gathura N P 2011 J Environmental

Management 92 655 [10] CEFIC 2004 IPPC BAT reference document ndash Large volume solid inorganic chemicals family

ndash Process BREF for soda ash issue ndeg3 - httpwwwceficbefilesPublicationsESAPA_Soda_Ash_Process_BREF3pdf

[11] Dorange G Marchand A Le Guyader M 1990 Revue des sciences de lrsquoeau 3 261 [12] Filippov L O Yvon J Filippova I V Godon B Perrin P and Piantone P 2008 Characterisation

and descriptive model of saline waste evolution Proceed of 2nd IntConference on Engineering for Waste Valorisation WASTEENGrsquo08 Patras Greece Juin 2-5 2008 ISBN 978-960-530-101-9 P 143 2pp

NAMES10 New achievements in materials and environmental sciences IOP PublishingJournal of Physics Conference Series 416 (2013) 012014 doi1010881742-65964161012014

6