Adsorption of fluoride on iron hydroxides/oxides · 2016. 10. 17. · Adsorption of fluoride • Proposed mechanism – Ligand exchange* • Important factors – pH – Surface area

Adsorption of fluoride on

iron hydroxides/oxides

Ina Beate Jenssen

HYDROMET project meeting

October 5th, 2016

Porsgrunn

2

Outline

• Adsorption of fluoride

• Initial experiments

– Preparation of ferric hydroxides

• Fluoride adsorption

– Effect of pH, adsorbent, surface area, and temperature

• BET surface area

• Summary of results

• Hydromet in education at NTNU

• Further work

3

Adsorption of fluoride

• Results from SINTEF – even distribution of fluoride on theprecipitate– Adsorption?

• Literature research– Iron hydroxides as adsorbent for fluoride in water treatment*

• Adsorption (IUPAC definition):– Increase in the concentration of a substance at the interface of a

condensed and a liquid or gaseous layer owing to the operation of surface forces.

– Physisorption

– Chemisorption

*Mohapatra, M., Anand, S., Mishra, B. K., Giles, D. E., & Singh, P. (2009). Review of fluoride removal from drinking water. Journal of Environmental Management, 91(1), 67-77.

4

Adsorption of fluoride

• Proposed mechanism

– Ligand exchange*

• Important factors

– pH

– Surface area

– Competing anions

– Fe(II)/Fe(III) ratio

– Temperature

*Ding, X. (2012). Identity of Fluoride and Phosphate-Binding Sites at FeOOH Surfaces.

5

Initial experiments – effect of pH

• From the literature:

Kumar, E., Bhatnagar, A., Ji, M., Jung, W., Lee, S.-H., Kim, S.-J., . . . Jeon, B.-H. (2009). Defluoridationfrom aqueous solutions by granular ferric hydroxide(GFH). Water research, 43(2), 490-498.

Tang, Y., Wang, J., & Gao, N. (2010). Characteristics and model studies for fluoride and arsenic adsorption on goethite. Journal of Environmental Sciences, 22(11), 1689-1694.

6

Initial experiments – preparation of

ferric hydroxides• Goethite

– 1 M Fe(NO3)3

– 5 M NaOH

– pH 12, 80 °C, 3 days

SEM picture of goethite crystals

XRD diagram of goethite

7

Initial experiments – preparation of

ferric hydroxides

• Ferrihydrite (2-line)

– 1 M Fe(NO3)3

– 1 M NaOH added until pH 7

SEM picture of ferrihydrite

XRD diagram of ferrihydrite

8

"Felleslab" experiment

• 3rd year students in chemical engineering and

biotechnology master program

“Separation of fluoride – adsorption of fluoride

on iron hydroxides”

• Study effect of pH, adsorbent and temperature

– Ferrihydrite, goethite, Al(OH)3

– 10 groups

– pH range 2 - 10, temperatures 25, 50 and 80 C

– Each group: 3 pH values, 1 temperature

9

Effect of pH

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

0 2 4 6 8 10

mg

F ad

sorb

ed /

g a

dso

rben

t

pH

T=80 °C Goethite

Stronglydecreasingadsorption withincreasing pH

10

Effect of adsorbent –

mg F adsorbed /g adsorbent

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

0 2 4 6 8 10

mg

F ad

sorb

ed /

g a

dso

rben

t

pH

T=80 °C Goethite

T=80 °C Ferrihydrite

Not taking surfacearea into account, goethite and ferrihydrite equallygood at low pH, ferrihydrite better at higher pH

11

Effect of adsorbent –

mg F adsorbed / m2

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0 2 4 6 8 10

mg

F ad

sorb

ed /

m2

pH

T=80 °C Goethite


Taking surface area into account, goethiteis the best adsorbent

12

Effect of temperature

0

0,002

0,004

0,006

0,008

0,01

0,012

0,014

0,016

0,018

0 2 4 6 8

mg

F ad

sorb

ed /

m2

pH




No significantdifferences in adsorption at different temperatures

13

Effect of pH, adsorbent and

temperature

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

0 2 4 6 8 10

mg

F ad

sorb

ed /

g a

dso

rben

t

pH

T=25 °C Goethite

T=50 °C Goethite

T=80 °C Goethite




• Surface area not taken into account

14

Effect of pH, adsorbent and

temperature

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

0 2 4 6 8 10

mg

F ad

sorb

ed /

m2

pH

T=25 °C Goethite

T=50 °C Goethite

T=80 °C Goethite




• Surface area taken into account

15

• Goethite is more affected by pH than ferrihydrite

• Adsorption capacity (mg/m2) higher for goethite

than ferrihydrite

• Type of surface area matters!

• Best alternative: goethite with high surface area

16

BET surface area

• Theoretical surface areas*

– Goethite: 20 m2/g

– Ferrihydrite: 200 m2/g

• Standard pretreatment: degassing at 200 C

overnight

– Avoid humidity in the BET equipment

* Schwertmann, U. and R. M. Cornell (2007). Iron Oxides in the Laboratory, Wiley-VCH VerlagGmbH.

17

BET surface area





BET surface area (m2/g)

De-gas temperature (°C) Goethite Ferrihydrite

200 80 0.74

18

BET surface area







200 80 0.74

180 81 7.8

19

BET surface area




* Schwertmann, U. and R. M. Cornell (2007). Iron Oxides in the Laboratory, Wiley-VCH VerlagGmbH.** Weidler, Peter G. "BET sample pretreatment of synthetic ferrihydrite and its influence on the determination of surface area and porosity." Journal of Porous Materials 4.3 (1997): 165-169.



200 80 0.74

180 81 7.8

120** 35 272

20

XRD diagrams of goethite before and after BET analysis:

BeforeBET

200 C

180 C

• Pretreatment at 200 C hematite

• Pretreatment at 180 C goethite + hematite

Before BET

200 C

180 C

XRD diagrams of ferrihydrite before and after BET analysis:

21

TGA

70

75

80

85

90

95

100

105

0 100 200 300 400 500 600 700

Mas

s/%

Temperature (°C)

Ferrihydrite - TGA

BeforeTGA

After TGA

XRD diagrams of ferrihydrite before and after TGA

After TGA: Hematite!

340 CTransformation at approx. 340 C

22

Summary

• Important factors affecting the adsorption are:

– pH: adsorption capacity decreases with increasing pH

– Surface area and type of surface

• Goethite has the best adsorption properties, when taking

the surface area into account

• Temperature does not seem to have an effect

– Need to study this closer

• Surface area determination by BET is not straight

forward

• Heating and dehydration of goethite and

ferrihydrate hematite

23

Hydromet in education at NTNU

• 2 project students – specialization projects fall

2016, master thesis spring 2017

• 3rd year master students Chemical Engineering

and Biotechnology – experiment in TKP4105

Separation Technology

24

Specialization projects

Boliden“Fluoride adsorption on iron hydroxide/oxide precipitates”

• How is the supersaturation affected by Fe3+/Fe2+-ratio, pH and temperature?

• Particle size and crystalline properties

• Transformation of precipitated iron hydroxides to different phases

• Experiments performed in batch reactor

• Determination of Fe2+-concentration by UV-VIS

• XRD – type of iron hydroxide

• SEM – shape and size of particles

• BET – surface area

• Adsorption of fluoride at different pH

• Is surface area the determining factor, or is the type of surface area also important?

25

Visual MINTEQ

• Chemical equilibrium software

• Modelling and planning experiments

26

27

28

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Specialization projects

Glencore“Mechanisms and particle properties for the iron hydroxide/oxide precipitation at Glencore Nikkelverk”

• Ferrous iron from raw material is oxidised with Cl2 (g), pH is adjusted with NiCO3, and the iron precipitates as ferric hydroxide/oxide:

2 FeCl2 + Cl2 (g) + 3H2O + 3 NiCO3 (s) = 2 Fe(OH)3 (s) + 3 NiCl2 +3 CO2 (g)

• How is the supersaturation affected by Fe3+/Fe2+-ratio, pH and temperature?

• Particle size and crystalline properties

• Transformation of precipitated iron hydroxides to different phases

• Experiments performed in batch reactor• Will not use Cl2 (g) due to HSE issues

• Determination of Fe2+-concentration by UV-VIS

• XRD – type of iron hydroxide

• SEM – shape and size of particles

30

Further work

• Effect of contact time

• Closer study of "felleslab"-experiments

• Precipitation under controlled conditions

– Which factors determines size and surface area?

• Ratio of Fe(II)/Fe(III)

– Effect on precipitation and adsorption

• Adsorption mechanism

• Experiments with Boliden’s conditions

31

Thank you for your attention!

Documents

Adsorption of fluoride on iron hydroxides/oxides · 2016. 10. 17. · Adsorption of fluoride • Proposed mechanism – Ligand exchange* • Important factors – pH – Surface area