Merge pull request #277 from ugognw/fix-salt-dict-non-h-o-heteroatom

Fix salt dict non-h/o-heteroatom

Author: rkingsbury

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.3.1] - 2025-08-18
+
+### Fixed
+
+- `Solution.get_salt_dict()`: In solutions containing polyatomic ions with a heteroatom (an atom other than `H` or `O`)
+  having a stoichiometric coefficient greater than 1 mol per mol salt , such as Fe(CN)6[-3], the method would
+  return incorrect results, possibly impacting activity coefficient calculations. This has now been fixed.  (#277, @ugognw)
+
 ## [1.3.0] - 2025-08-08
 
 ### Fixed

src/pyEQL/solution.py

@@ -1571,7 +1571,11 @@ def get_salt_dict(self, cutoff: float = 1e-6, use_totals: bool = True) -> dict[s
             # # use only the predominant species for each element
             components = {}
             for el, lst in self.get_components_by_element().items():
-                components[lst[0]] = self.get_total_amount(el, "mol").magnitude
+                component = lst[0]
+                ion = Ion.from_formula(component)
+                el_no_oxi_state = el.split("(")[0]
+                nu_el = ion.get_el_amt_dict()[el_no_oxi_state]
+                components[component] = self.get_total_amount(el, "mol").magnitude / nu_el
             # add H+ and OH-, which would otherwise be excluded
             for k in ["H[+1]", "OH[-1]"]:
                 if self.components.get(k):

tests/conftest.py

@@ -7,8 +7,8 @@
 from pyEQL.engines import EOS
 from pyEQL.salt_ion_match import Salt
 
-_CATIONS = ["Na[+1]", "Ca[+2]", "Fe[+3]", "K[+1]", "Li[+1]", "Cu[+2]", "Ba[+2]"]
-_ANIONS = ["Cl[-1]", "SO4[-2]", "PO4[-3]", "ClO[-1]", "NO3[-1]", "CO3[-2]", "MnO4[-2]"]
+_CATIONS = ["Na[+1]", "Ca[+2]", "Fe[+3]", "K[+1]", "Li[+1]", "Cu[+2]", "Ba[+2]", "NH4[+1]"]
+_ANIONS = ["Fe(CN)6[-3]", "Cl[-1]", "SO4[-2]", "PO4[-3]", "ClO[-1]", "NO3[-1]", "CO3[-2]", "MnO4[-2]"]
 _SALTS = list(product(_CATIONS[:3], _ANIONS[:3]))
 _ACIDS = [("H[+1]", anion) for anion in _ANIONS[:3]]
 _BASES = [(cation, "OH[-1]") for cation in _CATIONS[:3]]