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Recovery of Phosphorus forRecyclingKaj Thomsen
CERE, Center for Energy Ressources Engineering
DTU, Technical University of DenmarkLyngby, Denmark
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June 27, 2012Recovery of Phosphorus for Recycling2 DTU Chemical Engineering,
Technical University of Denmark
Importance of phosphorus
Phosphorus is found in every cell of all living beings(ADP/ATP, DNA, bone)
Phosphorus can not be replaced by another compound, itis a non-renewable resource
Phosphorus is one of the most abundant elements in theearths crust
The known reserves of high concentration phosphate rockare being depleted
Lack of phosphorus will cause increase in food prices,food shortages, geopolitical rifts
Phosphorus has been designated as a strategic mineralresource by many countries
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June 27, 2012Recovery of Phosphorus for Recycling3 DTU Chemical Engineering,
Technical University of Denmark
Peak phosphorus
Hubbert curve by Dana Cordell and Stuart White, Sustainability,3(2011)2027-2049
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Phosphorus as a waste product
Straw and other organic material is increasingly being used for
power and heat generation
Gasification and combustion processes
Much of the phosphorus in the straw ends up in the fly ash
from the combustion Up to 90% of the fly ash is soluble, inorganic salts
The fly ash cant be deposited in land fills in the European
Union due to its solubility
The fly ash cant be used as a fertilizer due to its content ofcadmium and other heavy metals
This project was started in cooperation with the Danish
company Kommunekemi in order ot solve this waste problem
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Soluble salts in fly-ash
Flyash from straw combustion
30 mass % K2SO4 50 mass % KCl
5-10 mass % P2O5 10-15 mass % insoluble
Flyash from sewage sludge or manure combustion
Rich in P2O5
Both contain various metals and other impurities besidesfertilizer material
Fluoride Aluminum
Iron(III)
Copper(II)
Cadmium (10-15 ppm)
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Benefits of recycling phosphorus
The rate of consumption of the limited sources of
phosphate rock in the world can be reduced
The environment benefits from reduced eutrophication
Money and energy is saved on the mining and import of
phosphate products
Indepedence from geopolitical tensions
Thermodynamic modeling of the relevant aqueous salt
systems is required in order to design appropriate
processes for recycling phosphorus
Process simulation
Process design
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June 27, 2012Recovery of Phosphorus for Recycling7 DTU Chemical Engineering,
Technical University of Denmark
Previous modeling of similar
systems Wang et al., Modeling phase equilibria and speciation in mixed-
solvent electrolyte systems, Fluid Phase Equilibria, 222-223(2004)11-17
System: K+, Na+, H2PO4-, HPO4
2-, H3PO4 OLI mixed solvent electrolyte model
Christensen and Thomsen, Modeling of Vapor-Liquid-SolidEquilibria in Acidic Aqueous Solutions, Ind. Eng. Chem. Res.,42(2003)4260-4268
System: K+, Na+, NH4+, Ca2+, Cl-, H2PO4
-, HPO42-, H3PO4
Extended UNIQUAC modeling did not include high pH range
Weber et al., A Solubility Model for Aqueous SolutionsContaining Sodium, Fluoride, and Phosphate Ions, Ind. Eng.Chem. Res., 39(2000)518-526
System: Na3PO4, Na2HPO4, NaF, NaOH
Pitzer model to describe phase equilibria up to 100C
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June 27, 2012Recovery of Phosphorus for Recycling8 DTU Chemical Engineering,
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Extended UNIQUAC model
Not a new model but new parameters
Thermodynamic model for solutions containing
electrolytes
Debye-Hckel term for electrostatic interactions
UNIQUAC term for short range interactions
Soave-Redlich-Kwong term for gas phase fugacities
The model is used for calculation of
Speciation equilibrium
Solid-liquid equilibrium
Vapor liquid equilibrium
Liquid-liquid equilibrium
Thermal properties
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June 27, 2012Recovery of Phosphorus for Recycling9 DTU Chemical Engineering,
Technical University of Denmark
Extended UNIQUAC modelex ex ex ex
Combinatorial Residual Extended Debye-Hckel = + +G G G G
ln - ln2
exCombinatorial i i
i ii
i i ii
zG x xq
RT x
ln
ex
Residualji i ji
i j
G = x qRT
expji ii
ji
u u
= - T
;i i i i
i i
j j j j
j j
x r x q
x r x q
2
3
4ln 1
2
EExtended Debye-Hckel
w w
Ba IAG= x M BaI BaI +
RT Ba
3/2
21/2
0
0
2 ; 1.54
A
r
eA N d Ba
kT
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June 27, 2012Recovery of Phosphorus for Recycling10 DTU Chemical Engineering,
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Extended UNIQUAC model
Relative permittivity for pure water is used for all
solutions
The effect of other species on the chemical potentials in the
solution is accounted for by interaction parameters
The hydrogen ion is given fixed parameters, includinginteraction parameters with all other species
The hydrogen ion is considered an anchor for the parameters
The properties of all other species are determined relative to
those of the hydrogen ion The temperature dependence of chemical potentials is
determined by the Gibbs-Helmholtz equation: 0 0
2
/lnat constant pressure
d G RT d K H
dT dT RT
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Model parameters and standard
state properties H2O, CO2, HF, HCl, HNO3, H3PO4
H+, Na+, K+, Ca2+, Cu2+, Cd2+, Fe3+, Al3+
F-, Cl-, SO42-, HSO4
-, NO3-, OH-, CO3
2-, HCO3-, PO4
3-, HPO42-, H2PO4
-,
AlO2-
Adjustable model parameters UNIQUAC surface area and volume parameters
Interaction parameters for each pair of species
Standard state properties
Aqueous species properties were taken from NIST/NBS tables
Temperature dependent heat capacities of aqueous speciesgiven by three-parameter expression
Pure salt properties were adjusted to the experimental data
Heat capacities of pure salts were determined by Kopps rule
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June 27, 2012Recovery of Phosphorus for Recycling12 DTU Chemical Engineering,
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Experimental data
Over 150,000 experimental data on electronic form
More than 350 solute species
Types of data include:
Activity/osmotic coefficient
Enthalpy of mixing
Heat capacity
Degree of dissociation
Gas solubility
Enthalpy of absorption/evaporation
Density
Salt solubility (Solid-liquid equilibrium)
Liquid-liquid equilibrium
Vapor-liquid equilibrium
The databank can be browsed at http://www.cere.dtu.dk/Expertise/
Electrolyte data bank will be presented in the poster session
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Determination of parameters
The adjustable parameters were determined using a modifiedMarquard routine from Harwell subroutine library and aNelder-Mead simplex routine
Sequence of parameter determination:1. Core system consisting of H+, Li+,Na+, K+, Mg2+, Ca2+, OH-, Cl-, HCl,
NO3-
, HNO3, SO42-
, HSO4-
based on ca. 27000 experimental datapoints. 23 binary and 87 ternary systems.
2. Carbonate species based on ca. 7000 experimental data
3. Phosphate species based on ca. 5000 experimental data
4. Fluorides species based on ca. 2000 experimental data
5. Aluminum species based on ca 1100 experimental data
6. Copper (II) based on ca 1500 experimental data7. Iron (III) based on ca 1900 experimental data
8. Cadmium based on ca 1000 experimental data
About 200 model parameters and 360 standard stateproperties of salts were adjusted based on these data.
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June 27, 2012Recovery of Phosphorus for Recycling14 DTU Chemical Engineering,
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0
10
20
30
40
50
60
70
80
90
100
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
P2O5
Na2O
H2O
H3PO4
NaOH
NaH2PO4
NaOH3H2O
NaOHH2O
NaH2PO42H2O
NaH2PO4H2O
NaH2PO4H3PO4
Na2HPO42NaH2PO42H2O
Na2HPO4NaH2PO4
Na2HPO4
Na3PO4
Na3PO4H2O
Na3PO48H2O
Na3PO46H2O
Na3PO412H2O
Na2HPO412H2O
Na2HPO47H2O
H3PO4H2O
4(Na3PO412H2O)H2O
2H3PO4 = 3H2O + P2O52H3PO4H2O = 4H2O + P2O52Na3PO4 = 3Na2O + P2O52Na2HPO412H2O = 2Na2O + P2O5 + 25H2O
Large number of phosphates
24 solids can form inthe H3PO4NaOH
H2O system
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June 27, 2012Recovery of Phosphorus for Recycling15 DTU Chemical Engineering,
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0
5
10
15
20
25
30
35
40
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
molH2O/molsalt
mol Na2O/(mol Na2O + mol P2O5)
ExperimentalExtended UNIQUACTie linesSolids composition
NaH2PO4H3PO4
NaH2PO4H2O
Na2HPO42
NaH2PO42H
2O
Na3PO412
H2O
Na2
HPO42H2
O
(4Na3PO412H2O)NaOH
Na3PO4H2O
40 C
Na2HPO4NaH2PO4
Na2HPO47H2O
NaH2PO4
NaH2PO4 Na2HPO4 Na3PO4
H3PO4
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0
10
20
30
40
50
60
70
80
90
100
100
90
80
70
60
50
40
30
20
10
0
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
Experimental
Extended UNIQUAC
P2O5
Na2O
H2O
H3PO4
NaH2PO4
NaOH3H2O
NaH2PO42H2O
NaH2PO4H2O
NaH2PO4H3PO4 Na2HPO42NaH2PO42H2O
Na3PO412H2O
Na2HPO412H2O
H3PO4H2O
4(Na3PO412H2O)NaOH
25C
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June 27, 2012Recovery of Phosphorus for Recycling17 DTU Chemical Engineering,
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0
10
20
30
40
50
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
molH2O/molsalt
mol K2O/(mol K2O + mol P2O5)
Experimental
Extended UNIQUAC
Tie linesSolids composition
0 C
H3PO4H2OKH2PO4H3PO4
KH2PO4
K2HPO
46H
2O
K3PO47H2O
KOH2H2O
K3PO4KH2PO4 K2HPO4
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0
10
20
30
40
50
60
70
80
90
100
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Ravich and Popova, 1942Platford, 1974Beremzhanov et al., 1978Makin, 1957Bel Madani et al., 1999Ravich, 1938Selva, 1947Extended UNIQUAC, this work
T= 25.0C
NaKHPO45H2O
Na2HPO47H2O
K2HPO43H2O
Na2HPO412H2O
K2HPO
Na2HP
H2O
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-2
0
2
4
6
8
10
12
14
0
10000
20000
30000
40000
50000
60000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
pH
molH2O/(molCa
O+molP2O5)
mol CaO/(mol CaO + mol P2O5)
Experimental
Extended UNIQUACTie lines
pH
25C
Ca3(PO4)2
CaHPO42H2O
Ca(H2PO4)2H2O
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-2
0
2
4
6
8
10
12
14
0
5
10
15
20
25
30
35
40
45
50
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
pH
molH2O/(molCa
O+molP2O5)
mol CaO/(mol CaO + mol P2O5)
Experimental
Extended UNIQUACTie linespH
25C
Ca(H2PO4)2H2O
CaHPO42H2O
3 0E+09
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0.0E+00
5.0E+08
1.0E+09
1.5E+09
2.0E+09
2.5E+09
3.0E+09
0 0.2 0.4 0.6 0.8 1
molH2O/molsalt
mol Fe2O3/(mol Fe2O3+ Mol P2O5)
Experimental
Extended UNIQUAC model, this work
25C
FePO42H2O
Fe2(HPO4)3H3PO46H2O
Fe(H2PO4)32H2O
0
100
200
300
400
500
600
0 0.05 0.1 0.15 0.2 0.25
molH2O/molsalt
mol Fe2O3/(mol Fe2O3+ Mol P2O5)
ExperimentalExtended UNIQUAC
25C
FePO42H2O
Fe2(HPO4)3H3PO46H2O
Fe(H2PO4)32H2O
FePO42H2O
Solubility: Ca3
(PO4
)2
> Cu3
(PO4
)2
>
AlPO4> FePO4
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0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
NaFmass%
Na3PO4, mass %
Extended UNIQUAC
Guiot (1967)
Nagorskaya and Novoselova (1935)
Morozova and Rzhechitskii (1977)
Tananaev (1941)
Morrison and Jache (1959)
Payne (1937)
Na3PO412H2O
2Na3PO4NaF19H2O
NaF0 C
Systems with data of
questionable quality
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0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 2 4 6 8 10 12 14
NaF
mass%
Na3PO4, mass %
Extended UNIQUAC
Roslyakova et al. (1979)
Foote and Schairer (1930)
Herting (1996)
Clark (1919)
Carter (1928)
Na3PO412H2O
2Na3PO4NaF19H2O
NaF
25 C
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0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
0.0030
0.0035
0.0040
0.0045
0 10 20 30 40 50 60 70 80
Mass
%CaF2
Temperature C
Extended UNIQUAC
Experimental
CaF2
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Potassium salts with low
solubility
0
5
10
15
20
25
30
0 2 4 6 8
Wt%A
l2(SO4)3
Wt % K2SO4
Extended UNIQUAC this work
Ts'ai et al., 1936
0C
KAl(SO4)212H2O
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0
5
10
15
20
25
30
35
0 10 20 30 40 50 60 70
Wt%
Al(OH)3
wt % KOH
Extended UNIQUAC, this work
Du et al., 200540C
2KOHAl2O32H2O
Al(OH)3
Aluminate ion, AlO2-
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
8.5 9 9.5 10 10.5 11
A
lO2-fraction
pH
Al3+
AlO2-
Al3++4OH-AlO2-+2H2O
Standard state properties for AlO2-
fG, kJ/mol fH, kJ/mol
NIST -830.9 -930.9
This work -734.0 -923.0
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Salting in of CaSO4by AlCl3
0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Wt%A
lCl3
Wt % CaSO4
Extended UNIQUAC, this work
Li and Demopoulos, 2006
50C
AlCl36H2O
CaSO4
CaSO42H2O
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0
200
400
600
800
1000
1200
0 0.2 0.4 0.6 0.8 1
Vaporpressure,kPa
HF mol fraction
Pxy diagram for HF-H2O at 100C
Extended UNIQUAC
Experimental
50
60
70
80
90
100
110
120
0 0.2 0.4 0.6 0.8 1
Vaporpress
ure,kPa
HF mol fraction
Pxy diagram for HF-H2O at 100C
Extended UNIQUAC
Experimental
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Model implementation
The model is implemented in a dynamic link library (DLL-
file)
Multi-phase flash algorithm
The program can be called from programs that have a Visual Basic
interface such as Microsoft Excel Simulations can be carried out directly in Excel
The excel sheet can be used as an interface to Aspen Plus
The model can be implemented as a user model in Aspen Plus
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Conclusion
Phosphate is essential to life on earth no substitutes
Recycling of phosphate is extremely important due to limitedressources.
Thermodynamic modeling of phase behaviour in systemscontaining phosphate enable us to design processes for
producing food grade phosphate from waste such as sewagesludge
Modelling with current activity coefficient models only possible withthe use of good quality experimental data
Experimental data for solubility in many systems representingphosphate and its impurities are of low quality
New experimental measurements of solubility and otherproperties of these systems are required to improve themodeling
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Acknowledgment
This project was supported by a grant from ForskEL
projekt nr. 2008-1-0111 Working up phosphate from
ashes
The project was carried out in cooperation with
Kommunekemi as, Denmark
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Thank you for your attention
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0
0.05
0.1
0.15
0.2
0 10 20 30 40 50 60
CaSO4solubili
ty,mol/kgwater
H3PO4 mol/kg water
Experimental, CaSO4
Experimental, CaSO4H2O
Experimental, CaSO42H2O
Extended UNIQUAC
80 C
CaSO4
CaSO4H2O
CaSO42H2O
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-60
-40
-20
0
20
40
0 20 40 60 80 100
Tem
peratureC
Mass % H3PO4
Experimental
Extended UNIQUAC
H3PO4H2O
H3PO4
Ice
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0
1
2
3
4
5
6
0 10 20 30 40 50 60
FeF3
KF
T= 25.0C
Weight%
FeF33H2O
FeF32KFH2O
KF2H2OFeF33KF3H2O
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80 90 100 110 120
saltfraction
Calculated
Experimental
Temperature, CCuSO4
Na2SO4
CuSO4Na2SO42H2O
CuSO45H2O
Na2SO410H2O
Na2SO4
CuSO43H2O