Negative temperature dependency of solubility of Nahcolite , pitzer.dat ?

[TobiasHogen]

Dear All,
under application of pitzer.dat I found the solubility of Nahcolite evolving negatively with temperature.
This contradicts other publications (e.g. doi: 10.1016/j.egypro.2017.03.1412).

pKS is constant, but HCO3-activity goes down with temp. due to ion interaction parameters.

For a quick check I used the code listed below.

Does somebody else also see the problem or am I totally wrong? :-)

USER_GRAPH 1
    -headings               Temp Nahcolite
    -axis_titles            "Temp [?C]" "N [MOL]" "pH [-]"
    -chart_title            "Solubility Nahcolite"
    -axis_scale x_axis      20 80 auto auto
    -axis_scale y_axis      0 auto auto auto
    -axis_scale sy_axis     5 10 auto auto
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X TC
50 GRAPH_Y MOL("Na+")
60 GRAPH_SY -LA("H+")
  -end
    -active                 true
SOLUTION 1
    temp      25
    pH        7.99
    pe        4
    redox     pe
    units     mg/l
    density   1
    C(4)      1
    Na        1
    -water    1 # kg


REACTION_TEMPERATURE 1
    25  30  35  40  45  50  55 
    60  65  70
EQUILIBRIUM_PHASES 1
    Nahcolite 0 100

[dlparkhurst]

Pitzer.dat has no temperature dependence defined for Nahcolite, only log K at 25 C.

Other databases have a delta_h or analytical expressions defined, all of which indicate as increase in solubiity with temperature. An analytical expression is used in preference to delta_H if both are defined. You will have to decide which selection is prefereable:

Tipping and Hurley:
Nahcolite           58
        NaHCO3 = Na+ + HCO3-
        log_k           -0.548
        delta_h 3.720 kcal

Core10:
Nahcolite
   NaHCO3 = HCO3- + Na+
   log_k      -0.1118
   -delta_H   17.0247      kJ/mol
#   deltafH      -226.4      kcal/mol
   -analytic   -2.2282e2 -5.9693e-2 5.4887e3 8.9744e1 8.5712e1
#   Range      0-300
   -Vm      38.62 # thermo.com.V8.R6+.tdat
#   Extrapol   Cp integration
#   Ref      73bar/kna

frezchem.dat:
Nahcolite
   NaHCO3  =  HCO3- + Na+
   -analytic   5733.307217   4.09729508   -128132.8263   -2555.137922   2939222.2   -0.002655951
   Vm 38.91

llnl.dat:
Nahcolite
        NaHCO3  =  + 1.0000 HCO3- + 1.0000 Na+
        log_k           -0.1118
   -delta_H   17.0247   kJ/mol   # Calculated enthalpy of reaction   Nahcolite
#   Enthalpy of formation:   -226.4 kcal/mol
        -analytic -2.2282e+002 -5.9693e-002 5.4887e+003 8.9744e+001 8.5712e+001
#       -Range:  0-300

sit.dat:
Nahcolite
Na(HCO3)     = 1.000Na+     + 1.000H+     + 1.000CO3-2
     log_k   -10.740     #84HAR/MOL
     delta_h  33.430     #kJ/mol       
     # Enthalpy of formation:           -949        #kJ/mol        #82VAN
     -analytic -4.88332E+0 0E+0 -1.74617E+3 0E+0 0E+0

wateq4f.dat:
Nahcolite           58
        NaHCO3 = Na+ + HCO3-
        log_k           -0.548
        delta_h 3.720 kcal

[TobiasHogen]

Dear Dr. Parkhurst,

thank you so much for your fast and helpful reply.

Best regards
Tobias