How carbon-chains may help mitigate mineral scaling
T. Rabizadeh, C. L. Peacock, L.G. Benning
Cohen Geochemistry, School of Earth and Environment, University of Leeds, UK
Introduction:
50mM CaSO4
Pure:
Additive: Pure+ (1-20ppm)
Citric acid
Maleic acid
Tartaric acid
2+
Ca
PESA
SO
Scale formation:
•Costly phenomenon for water and other fluid
processing systems
•Affects process efficiency (i.e., clogging up industrial
components (Fig. 1) and slowing down water-flow) [1-3].
common in heat exchanger or desalination
3 phases: bassanite, gypsum, anhydrite
CaSO4.0.5H2O
Calcium sulfate
Green inhibitors
CaSO4.2H2O
Experimental Procedures:
4
2-
±
Additives
SEM
pH 3-7
T= 21˚C
Fig. 1. Mineral scaling
reduces fluid flow
UV-VIS to measure
formation pathway is not well understood
But CaSO4 phases are useful minerals:
- medical applications (splints)
- construction industry (plaster)
- sculptures
- reduce scaling
- biodegradable(no eutrophication; Fig. 2)
- are effective at low concentrations
Aim of Research:
Additives
citric acid
Fig.2. Industrial P and N
containing additives
cause eutrophication
particles
•Turbidity
•Induction time
•Reaction kinetics
CaSO4
XRD
maleic acid
tartaric acid
Table. 1. Dissociation constants of additives used
Additive
PKa1
PKa2
PKa3
citric acid
3.13
4.76
6.40
maleic acid
1.92
6.23
tartaric acid
3.03
4.34
PESA
4.68
4.92
-
• Understanding the nucleation and growth kinetics as well as the mechanisms of
calcium sulfate formation
• Investigating the role + effects of green additives with different carbon-chain lengths
Results
H2C1-
H3C
HC2-
polyepoxysuccinic acid
(PESA)
C3-
100
*
see
Figs.
see
Figs.
6,7
6,7
*
*
see Figs. 12,13
see Figs. 12,13
60
6min
6min
9min
9min
Inductiontime
time
Induction
17min
17min
23min
23min
40
80
Turbidity (%)
80
**
see Fig.
Fig. 99
see
pure CaSO4
20ppm Tartaric acid
20ppm Maleic acid
Induction time= 23min
Induction time= 23min
60
20ppm citric acid pH 4
16
20ppm Citric acid pH 7
5ppm PESA pH 7
Inductiontime=
time=80min
80min
Induction
20
20
citric acid structure at pH 7
20ppm citric acid pH 7
18
40
20ppm Citric acid
20
citric acid structure at pH 4
Turbidity (%)
100
Turbidity (%)
Vacuum
filtration
14
12
10
8
6
4
2
see Figs. 10,11
see Figs. 10,11
*
*
0
0
25
50
75
Induction time
0
0
100
125
150
175
200
225
250
0
50
100
150
Time (min)
Fig. 3. The effect of various carboxylic acids on the
precipitation of calcium sulfates.
200
250
Time (min)
300
350
400
0
450
Fig. 4. Comparison between the effect of 20 ppm citric acid
and 5 ppm PESA on calcium sulfate precipitation.
10
20
30
40
50
Time (min)
Fig. 5. How the pH dependent citric acid speciation is affecting the inhibition
performance in the calcium sulfate system
Li et al., 2007 [4]
10µm
Fig. 6. Photomicrograph of gypsum
needles formed without additives
Fig. 7. XRD pattern of precipitates from the additive
free system after 75min
Fig. 8. Schematic of likely sorption of
carboxylic group on gypsum growth site
The small platy gypsum crystals can easily pass
through membranes without clogging them. They
also stick less to surfaces.
10µm
Fig. 9. Photomicrograph of gypsum crystals
in the system with 5ppm PESA and pH 7
after 400min
Bassanite
Gypsum
3µm
Fig. 10. SEM image of gypsum and
bassanite formed at pH 7 with 20ppm citric
acid after 28min
10µm
Fig. 11. XRD pattern of precipitates from system with
20ppm citric acid and pH 7 after 28min
Fig. 12. XRD pattern of precipitates from system with
20ppm citric acid and pH 7 after 200min
Fig. 13. Photomicrograph of gypsum plates
in system with 20ppm citric acid and pH 7
after 200min
Summary and Implications:
(1) Carboxylic acids (citric, maleic, tartaric) and PESA all increase the induction time of CaSO4 formation (Fig. 3 and 4) and are thus adequate inhibitors.
(2) The increase in induction time depends on solution pH and carbon-chain length of the additive.
(3) The polymeric nature of PESA (more functional groups), delays the CaSO4 formation more than the citric acid which has just 3 functional groups (Fig. 4, 5) and is a better green additive.
(4) Citric acid stabilize bassanite as a precursor for gypsum formation; [5] PESA and citric acid also act as a shape modifier (Fig 9, 10 and 13) in that they change the bassanite and gypsum
morphologies to more isometric nanoparticles (bassanite) and platelets (gypsum) respectively.
Acknowledgements:
• This project has received funding from the European Union’s Seventh Framework
Programme (Marie Curie, MINSC ITN) for research, technological development and
demonstration under grant agreement no. 290040.
References:
[1] Prisciandaro, M., et al., (2005) The Canadian Journal of Chemical Engineering, 83, 586-592
[2] Moghadasi, J., et al (2006) Developments in Chemical Engineering and Mineral Processing, 14, 545-566
[3] Rabizadeh et al (2014) Mineralogical Magazine (in review)
[4] Li, J., et al., (2007), Materials letters, 61(3), 872-876