Functions Module¶

pyEQL functions that take Solution objects as inputs or return Solution objects.

copyright:: 2013-2023 by Ryan S. Kingsbury
license:: LGPL, see LICENSE for more details.

pyEQL.functions.autogenerate(solution='')[source]¶

This method provides a quick way to create Solution objects representing commonly-encountered solutions, such as seawater, rainwater, and wastewater.

Parameters:: solution (str) – String representing the desired solution Valid entries are ‘seawater’, ‘rainwater’, ‘wastewater’,and ‘urine’
Returns:: A pyEQL Solution object.
Return type:: Solution

Notes

The following sections explain the different solution options:

‘’ - empty solution, equivalent to pyEQL.Solution()
‘rainwater’ - pure water in equilibrium with atmospheric CO2 at pH 6
‘seawater’ or ‘SW’- Standard Seawater. See Table 4 of the Reference for Composition [1]_
‘wastewater’ or ‘WW’ - medium strength domestic wastewater. See Table 3-18 of [2]_
‘urine’ - typical human urine. See Table 3-15 of [2]_
‘normal saline’ or ‘NS’ - normal saline solution used in medicine [3]_
‘Ringers lacatate’ or ‘RL’ - Ringer’s lactate solution used in medicine [4]_

References:¶

[1]
Millero, Frank J. “The composition of Standard Seawater and the definition of the Reference-Composition Salinity Scale.” Deep-sea Research. Part I 55(1), 2008, 50-72.

[2]
Metcalf & Eddy, Inc. et al. Wastewater Engineering: Treatment and Resource Recovery, 5th Ed. McGraw-Hill, 2013.

[3]
https://en.wikipedia.org/wiki/Saline_(medicine)

[4]
https://en.wikipedia.org/wiki/Ringer%27s_lactate_solution

pyEQL.functions.donnan_eql(solution, fixed_charge)[source]¶

Return a solution object in equilibrium with fixed_charge.

Parameters:

solution (Solution object) – The external solution to be brought into equilibrium with the fixed charges
fixed_charge (str quantity) – String representing the concentration of fixed charges, including sign. May be specified in mol/L or mol/kg units. e.g. ‘1 mol/kg’

Returns:

A solution that has established Donnan equilibrium with the external (input) Solution

Return type:

Solution

Notes

The general equation representing the equilibrium between an external electrolyte solution and an ion-exchange medium containing fixed charges is

\[\frac{a_{-}}{\bar a_{-}}^{\frac{1}{z_{-}} \frac{\bar a_{+}}{a_{+}}^{\frac{1}{z_{+}} = exp(\frac{\Delta \pi \bar V}{{RT z_{+} \nu_{+}}})\]

Where subscripts \(+\) and \(-\) indicate the cation and anion, respectively, the overbar indicates the membrane phase, \(a\) represents activity, \(z\) represents charge, \(\nu\) represents the stoichiometric coefficient, \(V\) represents the partial molar volume of the salt, and \(\Delta \pi\) is the difference in osmotic pressure between the membrane and the solution phase.

In addition, electroneutrality must prevail within the membrane phase:

\[\bar C_{+} z_{+} + \bar X + \bar C_{-} z_{-} = 0\]

Where \(C\) represents concentration and \(X\) is the fixed charge concentration in the membrane or ion exchange phase.

This function solves these two equations simultaneously to arrive at the concentrations of the cation and anion in the membrane phase. It returns a solution equal to the input solution except that the concentrations of the predominant cation and anion have been adjusted according to this equilibrium.

NOTE that this treatment is only capable of equilibrating a single salt. This salt is identified by the get_salt() method.

References

Strathmann, Heiner, ed. Membrane Science and Technology vol. 9, 2004. Chapter 2, p. 51.: http://dx.doi.org/10.1016/S0927-5193(04)80033-0

Functions Module¶

References:¶

See Also:¶