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