PHREEQC-v3.8 to v-3.7 by SuixiongTay · Pull Request #3 · YitongPan1/Another-Comparison

SuixiongTay · 2026-02-11T21:19:20Z

Description

Left (red color): PHREEQC-v3.7
Right (green color): PHREEQC-v3.8

rkingsbury

Thanks both for putting this together. I assume the right side (green) is v3.8?

Anyway, I went through the diff quickly and just highlighted some differences that I noticed. In general, the right version seems to have introduced a new method of calculating viscosity, and added some parameters for that. Also, I noticed that some of the log K values for aqueous complexes like NaSO4- changed.

Interestingly, I can't seem to find NaCl(aq) anywhere in either file. The native engine with our phreeqpython wrapper predicted a little bit of NaCl ion pairing, but I just realized that's because the native version uses llnl.dat by default. If instead I use the phreeqc engine, which uses phreeqc.dat:

from pyEQL import Solution
>>> s1 = Solution({"Na+": 0.5, "Cl-": 0.5}, units="mol/L")
>>> s1 = Solution({"Na+": 0.5, "Cl-": 0.5}, engine='phreeqc')
>>> s1.equilibrate()
>>> s1.components
{'H2O(aq)': 55.34457593619076, 'Na[+1]': 21.684602829814455, 'Cl[-1]': 14.061546723432981, 'H[+1]': 1.4403500703847783e-07, 'OH[-1]': 9.196276962193604e-08, 'NaOH(aq)': 1.935707352229342e-17, 'O2(aq)': 2.038896481967645e-27, 'H2(aq)': 1.1379335332851315e-36}

Then there is no NaCl(aq)

Based on this, I don't see any reason not to use the latest (3.8, or right hand side) phreeqc.dat. I don't know the motivations behind all of the changes, but I trust the PHREEQC developers, and in any case our job in pyEQL is mainly to provide a faithful representation of PHREEQC output.

rkingsbury · 2026-02-13T14:09:03Z

+	NaCl = Cl- + Na+
+	log_k 1.57


Both versions have the same Ksp for NaCl(s)

rkingsbury · 2026-02-13T14:11:46Z

 Na+ = Na+
-	-gamma	4.0	 0.075
-	-gamma	4.08 0.082 # halite solubility
-	-dw	1.33e-9  122  1.52  3.70
-	-Vm   2.28  -4.38  -4.1  -0.586  0.09  4  0.3  52  -3.33e-3  0.566 # ref. 1
-# for calculating densities (rho) when I > 3...
-	# -Vm   2.28  -4.38  -4.1  -0.586  0.09  4  0.3  52  -3.33e-3  0.45
+	-gamma 4 0.075
+	-gamma 4.08 0.082 # halite solubility
+	-Vm 2.28 -4.38 -4.1 -0.586 0.09 4 0.3 52 -3.33e-3 0.566
+	# -Vm   2.28  -4.38  -4.1  -0.586  0.09  4  0.3  52  -3.33e-3  0.45 # for densities (rho) when I > 3.
+	-viscosity 0.1387 -8.66e-2 1.25e-2 1.45e-2 7.5e-3 1.062
+	-dw 1.33e-9 75 3.627 0 0.7037
 K+ = K+
-	-gamma	3.5	0.015
-	-dw	1.96e-9  395  2.5  21
-	-Vm  3.322  -1.473  6.534  -2.712  9.06e-2  3.5  0  29.7  0  1 # ref. 1
+	-gamma 3.5 0.015


Na+ and K+ Vm parameters look; just reorganized, dw values changes and viscosity terms were added

rkingsbury · 2026-02-13T14:12:27Z

 Cl- = Cl-
-	-gamma	3.5	  0.015
-	-gamma	3.63  0.017 # cf. pitzer.dat
-	-dw	2.03e-9  194  1.6  6.9
-	-Vm  4.465  4.801  4.325  -2.847  1.748  0  -0.331  20.16  0  1 # ref. 1
+	-gamma 3.5 0.015
+	-gamma 3.63 0.017 # cf. pitzer.dat
+	-Vm 4.465 4.801 4.325 -2.847 1.748 0 -0.331 20.16 0 1
+	-viscosity 0 0 0 0 0 0 1 # the reference solute
+	-dw 2.033e-9 216 3.16 0.2071 0.7432


Similar here; Vm same, dw modified a bit, viscosity added

rkingsbury · 2026-02-13T14:12:51Z

-Na+ + CO3-2 = NaCO3-
-	-log_k	1.27
-	-delta_h 8.91 kcal
-	-dw  1.2e-9  0  1e-10  1e-10
-	-Vm  3.89  -8.23e-4  20  -9.44  3.02  9.05e-3  3.07  0  0.0233  1 # ref. 1


It's interesting that this complexed species seems to have been removed

rkingsbury · 2026-02-13T14:14:57Z

+Mg+2 = Mg+2
+	-gamma 5.5 0.2
+	-Vm -1.41 -8.6 11.13 -2.39 1.332 5.5 1.29 -32.9 -5.86e-3 1
+	-viscosity 0.426 0 0 1.66e-3 4.32e-3 2.461
+	-dw 0.705e-9 -4 5.569 0 1.047
+Ca+2 = Ca+2
+	-gamma 5 0.165
+	-Vm -0.3456 -7.252 6.149 -2.479 1.239 5 1.6 -57.1 -6.12e-3 1
+	-viscosity 0.359 -0.158 4.2e-2 1.5e-3 8.04e-3 2.3 # ref. 4, CaCl2 < 6 M
+	-dw 0.792e-9 34 5.411 0 1.046


Same for Mg and Ca - they are now sorted differently, Vm just reorganized, dw parameters updated and viscosity added

rkingsbury · 2026-02-13T14:16:08Z

+MEAN_GAMMAS
+CaCl2    Ca+2  1  Cl-    2
+CaSO4    Ca+2  1  SO4-2  1
+CaCO3    Ca+2  1  CO3-2  1
+Ca(OH)2  Ca+2  1  OH-    2
+MgCl2    Mg+2  1  Cl-    2
+MgSO4    Mg+2  1  SO4-2  1
+MgCO3    Mg+2  1  CO3-2  1
+Mg(OH)2  Mg+2  1  OH-    2
+NaCl     Na+   1  Cl-    1
+Na2SO4   Na+   2  SO4-2  1
+NaHCO3   Na+   1  HCO3-  1
+Na2CO3   Na+   2  CO3-2  1
+NaOH     Na+   1  OH-    1
+KCl      K+    1  Cl-    1
+K2SO4    K+    2  SO4-2  1
+HCO3     K+    1  HCO3-  1
+K2CO3    K+    2  CO3-2  1
+KOH      K+    1  OH-    1
+HCl      H+    1  Cl-    1
+H2SO4    H+    2  SO4-2  1
+HBr      H+    1  Br-    1



This seems to be a new section. I don't know exactly what it does, but assuming GAMMA is activity coefficient, I'm guessing this defines the stoichiometry for how to calculate mean ionic activity coefficient.

rkingsbury · 2026-02-13T14:17:25Z

+#    but are overwritten by the data block GAS_BINARY_PARAMETERS of this file.
 # =============================================================================================
 # The molar volumes of solids are entered with
-#                         -Vm vm cm3/mol
+#			 -Vm vm cm3/mol
 #    vm is the molar volume, cm3/mol (default), but dm3/mol and m3/mol are permitted.
 # Data for minerals' vm (= MW (g/mol) / rho (g/cm3)) are defined using rho from
 #   Deer, Howie and Zussman, The rock-forming minerals, Longman.
-#                           --------------------
+#			   --------------------
 # Temperature- and pressure-dependent volumina of aqueous species are calculated with a Redlich-
 #   type equation (cf. Redlich and Meyer, Chem. Rev. 64, 221), from parameters entered with
-#                        -Vm a1 a2 a3 a4 W a0 i1 i2 i3 i4
+#			-Vm a1 a2 a3 a4 W a0 i1 i2 i3 i4
 # The volume (cm3/mol) is
 #    Vm(T, pb, I) = 41.84 * (a1 * 0.1 + a2 * 100 / (2600 + pb)  + a3 / (T - 228) +
-#                            a4 * 1e4 / (2600 + pb) / (T - 228) - W * QBrn)
-#                   + z^2 / 2 * Av * f(I^0.5)
-#                   + (i1 + i2 / (T - 228) + i3 * (T - 228)) * I^i4
+#			    a4 * 1e4 / (2600 + pb) / (T - 228) - W * QBrn)
+#		   + z^2 / 2 * Av * f(I^0.5)
+#		   + (i1 + i2 / (T - 228) + i3 * (T - 228)) * I^i4
 #   Volumina at I = 0 are obtained using supcrt92 formulas (Johnson et al., 1992, CG 18, 899).
 #   41.84 transforms cal/bar/mol into cm3/mol.
 #   pb is pressure in bar.
 #   W * QBrn is the energy of solvation, calculated from W and the pressure dependence of the Born equation,
-#     W is fitted on measured solution densities.
+#	W is fitted on measured solution densities.
 #   z is charge of the solute species.
 #   Av is the Debye-Hückel limiting slope (DH_AV in PHREEQC basic).
 #   a0 is the ion-size parameter in the extended Debye-Hückel equation:
-#     f(I^0.5) = I^0.5 / (1 + a0 * DH_B * I^0.5),
-#     a0 = -gamma x for cations, = 0 for anions.
+#	f(I^0.5) = I^0.5 / (1 + a0 * DH_B * I^0.5),
+#	a0 = -gamma	  x for cations, = 0 for anions.
 # For details, consult ref. 1.
+# =============================================================================================
+# The viscosity is calculated with a (modified) Jones-Dole equation:
+#    viscos / viscos_0 = 1 + A * Sum(0.5 z_i m_i) + fan * Sum(B_i m_i + D_i m_i n_i)
+# Parameters are for calculating the B and D terms:
+#    -viscosity 9.35e-2 -8.31e-2 2.487e-2 4.49e-4 2.01e-2 1.570    0
+#    #	   b0	  b1	  b2	 d1	  d2	 d3	tan
+#    z_i is absolute charge number, m_i is molality of i
+#    B_i = b0 + b1 exp(-b2 * tc)
+#    fan = (2 - tan V_i / V_Cl-), corrects for the volume of anions
+#    D_i = d1 * exp(-d2 tc)
+#    n_i = (I^d3 * (1 + fI) + ((z_i^2 + z_i) / 2 · m_i)^d3) / (2 + fI), fI is an ionic strength term.
+# For details, consult ref. 4.


These are useful details for explaining how molar volume and viscosity are calculated. The viscosity eq. appears to be new (ref 4)

rkingsbury · 2026-02-13T14:17:59Z

 Na+ + HCO3- = NaHCO3
-	-log_k  -0.25
-	-delta_h  -1 kcal
+	-log_k -0.06; -delta_h 21 kJ
+	-gamma 0 0.2
+	-Vm 7.95 0 0 0 0.609
+	-viscosity -4e-2 -2.717 1.67e-5
 	-dw 6.73e-10
-	-Vm  0.431 # ref. 1
 Na+ + SO4-2 = NaSO4-
-	-log_k	0.7
-	-delta_h 1.120	kcal
-	-gamma	5.4	0
-	-dw  1.33e-9  0  0.57  1e-10
-	-Vm  1e-5  16.4  -0.0678  -1.05  4.14  0  6.86  0  0.0242  0.53 # ref. 1
+	-gamma 5.5 0
+	-log_k 0.6; -delta_h -14.4 kJ
+	-analytical_expression 255.903 0.10057 0 -1.11138e2 -8.5983e5 # mirabilite/thenardite solubilities, 0 - 200 oC
+	-Vm 1.99 -10.78 21.88 -12.7 1.601 5 32.38 501 1.565e-2 0.2325
+	-viscosity 0.2 -5.93e-2 -4e-4 8.46e-3 1.78e-3 2.308 -0.208
+	-dw 1.13e-9 -23 8.5 0.392 0.521


log K for both of these aqueous complexes has changed

rkingsbury · 2026-02-13T14:19:04Z

+	-Vm 2.7483 -1.0708 6.1709 -2.7347 -.03 # supcrt
+K+ + HCO3- = KHCO3
+	-log_k -0.35;  -delta_h 12 kJ
+	-gamma 0 9.4e-3
+	-Vm 9.48 0 0 0 -0.542
+	-viscosity 0.7 -1.289 9e-2
 K+ + SO4-2 = KSO4-
-	-log_k	0.85
-	-delta_h 2.250	kcal
-	-analytical  3.106  0.0  -673.6
-	-gamma	5.4	0
-	-dw  1.5e-9  0  1e-10  1e10
-	-Vm  6.8  7.06 3.0   -2.07  1.1  0  0  0  0  1 # ref. 1
+	-gamma 5.4 0.19
+	-log_k 0.6; -delta_h -10.4 kJ
+	-analytical_expression -3.0246 9.986e-3 0 0 1.093e5 # arcanite solubility, 0 - 200 oC
+	-Vm 13.48 -18.03 61.74 -19.6 2.046 5.4 -17.32 0 0.1522 1.919
+	-viscosity -1 1.06 1e-4 -0.464 3.78e-2 0.539 -0.69
+	-dw 0.9e-9 63 8.48 0 1.8


rkingsbury · 2026-02-13T14:19:59Z

+	-dw 5.13e-9
+H+ + Cl- = HCl
+	-log_k -0.5
+	-analytical_expression 0.334 -2.684e-3 1.015 # from Pitzer.dat, up to 15 M HCl, 0 - 50°C
+	-gamma 0 0.4256
+	-viscosity 0.921 -0.765 8.32e-3 8.25e-4 2.53e-3 4.223


Here we have HCl(aq) complex, which I don't see in the older (left) version

phreeqc3.8to3.7

34de607

SuixiongTay changed the title ~~phreeqc3.8to3.7~~ PHREEQC-v3.8 to v-3.7 Feb 11, 2026

rkingsbury reviewed Feb 13, 2026

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SuixiongTay commented Feb 11, 2026 •

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