Add the to_phreeqc() method

src/pyEQL/solution.py

@@ -2699,3 +2699,33 @@ def add_solvent(self, formula: str, amount: str):  # pragma: no cover
         mw = self.get_property(formula, "molecular_weight")
         target_mol = quantity.to("moles", "chem", mw=mw, volume=self.volume, solvent_mass=self.solvent_mass)
         self.components[formula] = target_mol.to("moles").magnitude
+
+    def to_phreeqc(self, units: str = "mol/L", charge_balance: bool = "False") -> str:
+        """Generate a PHREEQC input string representing the Solution.
+
+        Returns:
+            A string that can be used as part of a PHREEQC input file to define
+            the solution.
+        """
+        lines = ["SOLUTION 0"]
+        lines.append(f" temp {self.temperature.to('degC').magnitude:.2f}")
+        if charge_balance == "True":
+            lines.append(f" pH {self.pH:.2f} charge")
+        else:
+            lines.append(f" pH {self.pH:.2f}")
+        lines.append(f" pe {self.pE:.2f}")
+        lines.append(f" units {units}")
+        for solute, amount in self.components.items():
+            amount = self.get_amount(solute, units).magnitude
+            if solute in ["H2O(aq)", "H[+1]", "OH[-1]"]:
+                continue
+            k = standardize_formula(solute)
+            spl = k.split("[")
+            el = spl[0]
+            chg = spl[1].split("]")[0]
+            if chg[-1] == "1":
+                chg = chg[0]
+            k = el + chg
+            lines.append(f" {k} {amount:.6e}")
+        lines.append("END")
+        return "\n".join(lines)