KCl Phase Data

[RanjeevB]

Hi Everyone!

I was trying to model the precipitation of Salts like Halite ( NaCl) and Sylvite (KCl) I was wondering what database (or do i have to define it as a new phase) is best for Precipitation of KCl since in my current model using the Pitzer database, there is no precipitation of KCl only NaCl.

Thank You in advance! for the help.

[dlparkhurst]

Sylvite is in the pitzer.dat database and will precipitate if it is included in EQUILIBRIUM_PHASES and it becomes supersaturated.

[RanjeevB]

Yes, I agree, but its the same with the Pitzer database?
Would precipitation also depend on the number of moles of Na, K?

I have attached my code for reference.

Thank you Kindly .

Code: [Select]

Database C:\phreeqc\database\PITZER.DAT


# Phase defintion

Phases
Brucite
      Mg(OH)2  = Mg++ + 2 OH-
log_k    -10.88
-delta_H 4.85   kcal/mol
Vm 24.6
Magnesite
 MgCO3 = CO3-2 + Mg+2
-log_k -7.8
-delta_h -7.048 kcal
-analytic 7.267 -0.033918 -1476.604
-Vm 28.018

Calcium_Hydroxide  # Reardon, 1990
Ca(OH)2 = Ca+2 + 2 OH-
  -log_k -5.19
  -Vm 33.1
 
END

solution 1 1st stage RO brine
-units mg/L
-temp 20.0
pH  7.4
Si 48.2
Ca 703.3
Mg 2105.5 
K 619.9
Na 17760.9
Alkalinity 202.6 as HCO3
Br 146
Cl 32510
F 0.617
N 2.85
P 0.27
S(6) 4630
Al 0.003
Ba 0.194
Sr 20.3
Li 0.198
B 6.31
END


solution 11 2nd stage RO brine
-units mg/L
-temp 20.0
pH  7.6
Si 49.1
Ca 956.5
Mg 2760.4
K 824.9
Na 21070.0
Alkalinity 265.25 as HCO3
Br 152
Cl 39645
F 0.898
N 6.65
P 0.15
S(6) 5593
Al 0.004
Ba 0.09
Sr 27.1
Li 0.329
B 8.63
END




use solution 1
reaction 1
HCl 1
0.004 moles
Equilibrium_Phases 1
CO2(g) -3.4
Save solution 2
END





Use solution 2
reaction 2
NaOH 1
0.2 moles
Equilibrium_Phases 2
Brucite 0 0
Calcium_Hydroxide 0 0
Magnesite 0 0
Calcite 0 0
Dolomite 0 0
Chrysotile 0 0
Talc 0 0
Barite 0 0
Sepiolite 0 0
Quartz 0 0
# Chlorite(14A) 0 0
# Strontianite 0 0   
# K-feldspar  0 0 ** Not in Pitzer database
# K-mica 0 0 **
# Hydroxyapatite 0 0 **
Save solution 3
END


Use solution 3
reaction 3
CaCl2 1
0.033 moles in 1 steps
save solution 4
END



Use solution 4
Reaction_Temperature 1
70
Reaction 4
H2O -1
46 moles
Equilibrium_Phases 3
Gypsum 0 0
Halite 0 0
Sylvite 0 0
Anhydrite 0 0
Barite 0 0
Aragonite 0 0
Calcite 0 0
Brucite 0 0
Calcium_Hydroxide 0 0
Magnesite 0 0
Dolomite 0 0
Quartz 0 0
save solution 5
END



Use solution 5
Use reaction_temperature 1
Reaction 5
H2O -1
9 in 18 Steps
Equilibrium_Phases 4
Halite 0 0
Sylvite 0 0
Save solution 6
User_graph 1
-chart_title " Extent of evaporation to extract Salt -1  "
-axis_titles "Volume of water Evaporated  (ml) " "moles"
-headings "Volume_Remaining(ml)" "NaCl" "KCl"
-start
10 vol_rW= 0.198*.998  # volume fo water remaining after gypsum extraction in l
20 graph_x (vol_rW-tot("water")*0.998)*1000 # in ml - vol of water remaining after further evaporation
30 graph_y EQUI_DELTA("Halite") EQUI_DELTA("Sylvite")
-end
END

User_graph 1
-detach
end

Use solution 5
use reaction_temperature 1
use Equilibrium_Phases 4
use reaction 5
user_graph 2
-chart_title " Extent of evaporation to extract Salt -2  "
-axis_titles "Volume of water Evaporated  (ml) " "Efficiency(%)"
-headings "Volume_Remaining(ml)" "NaCl_EXTEFF" "Na_Removal_EFF" "Cl_Removal_EFF"
-start
10 vol_rW= 0.198  # volume fo water remaining after gypsum extraction in l after step 6
20 graph_x (vol_rW-tot("water")*0.998)*1000 # in ml vol of water evaporated
40 Nai= 1.021e+00 # only mass initial Na present after CaCl2 dosage
50 Cli= 1.044e+00  # only mass initial Cl present after CaCl2 dosage
60 NaCl_ExtEff= EQUI_DELTA("Halite")*100/Nai
70 Na_Removal_EFF= (Nai-totmole("Na"))*100/Nai
80 Cl_Removal_EFF = (Cli-totmole("Cl"))*100/Cli
90 graph_y  NaCl_ExtEff Na_Removal_EFF Cl_Removal_EFF
-end
END



[dlparkhurst]

Yes, the precipitation of halite and sylvite in an evaporation sequence will depend on the initial moles of K, Na, and Cl. It will also depend on the concentrations of other solutes, which affect the ionic strength, activity coefficients, and minerals that precipitate.

Your example has a lot of steps that I don't want to work through. Here is an example where sylvite precipitates a couple evaporation steps before halite. For seawater, halite precipitates before sylvite. There is a Black Sea evaporation example in the manual. Any potential sequence is strongly dependent on starting conditions and the treatments that you are applying to your RO brine.

Code: [Select]

SOLUTION
-units mol/kgw
Na 1
K 1
Cl 2
END
USE solution 1
EQUILIBRIUM_PHASES
Halite 0 0
Sylvite 0 0
REACTION 1
H2O 1
-55.4 in 20 steps
USER_GRAPH 1
    -headings               f Halite Sylvite
    -axis_titles            "Concentration factor" "Moles" ""
    -axis_scale x_axis      auto auto auto auto log
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X 1 / TOT("Water")
20 GRAPH_Y EQUI("Halite"), EQUI("Sylvite")
30 END
  -end
    -active                 true
END


[RanjeevB]

I understand now.

Thank you so much for clarifying my doubt.
Much Appreciated!

Have a nice day/evening ahead.