Changing solutions¶
These methods update solutions that already exist in the engine: change their composition, mix them, equilibrate them with phases, or delete them.
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Changes are additive
These methods change solution in place. If you run a change cell again, the reaction is applied again. To start over, rerun the first editor.
from phreeqpython import PhreeqPython
pp = PhreeqPython()
solution = pp.add_solution_simple({'NaCl': 2})
print('Na mmol', round(solution.total('Na'), 3), 'Cl mmol', round(solution.total('Cl'), 3))Modifying solution composition¶
add, remove, remove_fraction, and change add or take out species through a PHREEQC REACTION. change_ph and change_temperature set pH and temperature.
Adding components¶
add adds a single component. The default unit is mmol.
solution.add('KCl', 1, units='mmol')
print('K mmol', round(solution.total('K'), 3), 'Cl mmol', round(solution.total('Cl'), 3))Removing components¶
remove removes a single component.
solution.remove('NaCl', 0.5)
print('Na mmol', round(solution.total('Na'), 3), 'Cl mmol', round(solution.total('Cl'), 3))Use remove_fraction to remove a fraction of an element.
sol = pp.add_solution_simple({'NaCl': 1})
sol.remove_fraction('Na', 0.5)
sol.remove_fraction('Cl', 0.5)
print('Na mmol', round(sol.total('Na'), 3), 'Cl mmol', round(sol.total('Cl'), 3))Changing several components at once¶
change does several additions and/or removals in a single REACTION step. The dictionary keys are formulas or elements; positive amounts are added, negative amounts are removed.
solution.change({'KCl': 1, 'NaCl': -0.5})
print('Na mmol', round(solution.total('Na'), 3))
print('K mmol', round(solution.total('K'), 3))
print('Cl mmol', round(solution.total('Cl'), 3))Temperature and pH¶
change_temperature sets the temperature. change_ph titrates with HCl or NaOH (or another acid or base you pass) until the target pH.
calcite = pp.add_solution({'Ca': 1, 'C': 2, 'pH': 8})
print('SI Calcite at 25 C', round(calcite.si('Calcite'), 2))
calcite.change_temperature(80)
print('SI Calcite at 80 C', round(calcite.si('Calcite'), 2))
calcite.change_ph(7)
print('pH', round(calcite.pH, 2))Mixing solutions¶
Scale and add solutions with * and +. copy() makes an independent duplicate. Mixing and copying each allocate a new number in the engine.
Mixing conserves total mass
a + b mixes the two full solutions. Two 1 kg (about 1 L) solutions become about 2 kg (about 2 L). It is not a 1:1 blend that is then made up to 1 L. Use fractions when you want a 1 kg mixture: a * 0.5 + b * 0.5.
a = pp.add_solution_simple({'NaCl': 1})
b = pp.add_solution_simple({'NaCl': 3})
half = a * 0.5 + b * 0.5
full = a + b
print('half Cl mmol', round(half.total('Cl'), 3), 'mass', round(half.mass, 3))
print('full Cl mmol', round(full.total('Cl'), 3), 'mass', round(full.mass, 3))
duplicate = full.copy()
print('copy SC', round(duplicate.sc, 1))Phase interactions¶
Solutions can be equilibrated with pure phases using saturate, desaturate, and equalize.
saturatedissolves a phase until a target saturation index if the solution is undersaturated.desaturateprecipitates (or degasses) until a target saturation index.equalizebrings one or more phases to their target SI in a single step.
mineral = pp.add_solution({'Ca': 1, 'C': 2, 'pH': 8})
print('SI Calcite', round(mineral.si('Calcite'), 2))
mineral.saturate('Calcite', to_si=0.5)
print('after saturate', round(mineral.si('Calcite'), 2))
mineral.desaturate('Calcite')
print('after desaturate', round(mineral.si('Calcite'), 2), 'Ca mmol', round(mineral.total('Ca'), 3))
mineral.equalize(['Calcite', 'CO2(g)'], [0, -3.5])
print('after equalize SI Calcite', round(mineral.si('Calcite'), 2), 'pH', round(mineral.pH, 2))To reuse a phase assemblage, create an EquilibriumPhase or Gas on the PhreeqPython instance and call interact. The Gases guide covers fixed-pressure and fixed-volume gas phases.
water = pp.add_solution({'pH': 7})
eq = pp.add_equilibrium_phase(['Calcite', 'CO2(g)'], [0, -1.5], [10, 10])
water.interact(eq)
print('pH', round(water.pH, 2), 'Ca mmol', round(water.total('Ca'), 3))
print('Calcite remaining', round(eq.components['Calcite'], 3))Forgetting solutions¶
PHREEQC keeps every numbered solution in the engine until you delete it. add_solution, copy(), and mixing each allocate a new number, so a long-running model (a loop that copies solutions, or a kinetic rate function that makes a temporary copy) can accumulate unused solutions and grow in memory.
Call forget() when you are done with a solution. That sends a PHREEQC DELETE for its number. Use get_solution_list() to see which numbers are still in the engine.
print('before', pp.get_solution_list())
duplicate.forget()
print('after', pp.get_solution_list())The Python object still exists, but the engine no longer has that number. Querying it afterwards is not meaningful (pH comes back as -999). Do not forget() a solution you still need.
See the API reference for Solution for every method, and the Examples for more examples of how to use PhreeqPython.