Saturated aqueous solutions in Potash
industry. Modeling of properties and composition
Sergei Panasiuk, Ph.D. Chief mineral process specialist
WorleyParsons Canada, Minerals & Metals
Potash – any potassium compound (KCl – most common).
Potash = “pot ashes” old method of making K2CO3 by
leaching of wood ashes, evaporating the resulting solution in
iron pots.
The first U.S patent issued in 1790 and sighed by G.
Washington. “in the making of Pot ash … by new Apparatus
and Process”.
Samuel Hopkins
“…making of Pot ash and Pearl ash by a
new Apparatus and Process”
In 1791, Government of Lower Canada
(Quebec) issued “letter of reward” to
Hopkins for his improved method.
Regarded as the first “patent” issued in
Canada.
Potassium minerals
Mineral Composition K2O, %
Chlorides:
Sylvinite KCl · NaCl mixture 28
Sylvite KCl 63
Carnalite KCl · MgCl2 · H2O 17
Kainite 4KCl · 4MgSO4 · 11H2O 19
Hanksite KCl · 9Na2SO4 · 2Na2CO3 3
Sulphates:
Polyhalite K2SO4 · 2MgSO4 · 2CaSO4 · 2H2O 16
Langeinite K2SO4 · 2MgSO4 23
Leonite K2SO4 · MgSO4 · 4H2O 26
Schoenite K2SO4 · MgSO4 · 6H2O 23
Krugite K2SO4 · MgSO4 · 4CaSO4 · 2H2O 11
Glaserite 3K2SO4 · Na2SO4 43
Syngenite K2SO4 · CaSO4 · H2O 29
Aphthitalite (K,Na)2SO4· 30
Kalinite KAl(SO4)2 · 11H2O 10
Alunite K2Al6(OH)12 · (SO4)4 11
Nitrates:
Niter KNO3 47
Mines (Canada, USA, Russia) - 96%
Evaporating ponds (USA, Jordan, Israel) - 3%
NEW
Potash deposits composition
Dead Sea
KCl·NaCl
K2SO4·2MgSO4
Seawater
KCl-NaCl mining 1000m deep
Surface mining Dead Sea
Block Flow Diagram – Potash Solution Mine
Solubility: - Flotation (salts and amines)
- U/G solution mining
- Brine evaporation
- KCl crystallization
- Brine U/G injection
Density: - U/G solution mining
- Evaporation/crystallization
- Brine U/G injection
Vapor pressure and composition: - Evaporation/crystallization
- Exhaust gas scrubbers
- Dryers
Boiling point elevation: - Evaporation/crystallization
- Dryers
KC l- NaCl - MgCl2 - H2O
METSIM(PFD KCl centrifuges)
METSIM solubility equilibrium
METSIM – Equilibrium functions
KC l- NaCl - H2O
OLI
NaCls
KCls
NaCl – KCl invariant
KC l- NaCl - H2O
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35 40
Na
Cl,
wei
gh
t %
KCl, weight %
OLI data 0C
25C
50C
75C
100C
150C
NaCl
KCl
NaCl + KCl
KC l- NaCl -H2O invariant solubility
NaCl
KCl
Solution mine
NaCl saturated
KCl depleted
KCl -NaCl
NaCl
NaCl
65 °C 55 °C
NaCl saturated
KCl saturated
1500 m depth
Solution mine
NaCl
KCl
ΔC (KCl)
Solution mine with evaporaton
NaCl
KCl
ΔC (KCl)
ΔC (NaCl) ΔCevp (KCl)
Saskatchewan solution mine
NaCl
KCl
ΔC (KCl)
ΔC (NaCl) ΔCevp (KCl)
ΔCfr (KCl)
KC l- NaCl - MgCl2 - H2O
NaCl + KCl
100 g/ L MgCl2
20 g/ L MgCl2
0 g/ L MgCl2
KC l- NaCl - CaSO4 - H2O
pH of vapor condensate
Vapor: HCl-H2O
No problems?
OLI predicts proper pH for the vapor condensate from evaporators but not for dryers.
1
MgCl2·2H2O = MgOHCl + HCl + H2O t > 135 °C
Problem 2
NaCl saturated
KCl depleted
KCl -NaCl
NaCl
NaCl
65 °C 55 °C
NaCl saturated
KCl saturated
1500 m depth
Oversaturation
Reality - >10% undersaturation for KCl
Problem 3. Complexity
Process Flow Diagrams (Dryers)
Dynamic process simulation
Conclusions:
• Potash industry requires accurate prediction of solubility in system
K-Na-Mg-Cl-SO4-H2O system
• Predictions of the brine density, boiling point elevation, viscosity,
vapor pressure and compositions are also very important
• METSIM uses polynomial functions to approximate some of the
brine parameters
• OLI is capable to predict all required brine properties in the wide
range of conditions
• OLI and METSIM predictions of the brine properties are very
similar in the narrow range of the most common potash industry
applications.
• Computer simulation of the large industrial projects requires to use
some simplifications of OLI approach