This keyword data block is used to define the temperature and chemical composition of initial solutions. All input concentrations are converted internally to units of molality or, equivalently, moles of elements and element valence states and mass of water. Speciation calculations are performed on each solution and each solution is then available for subsequent batch-reaction, transport, or inverse-modeling calculations. Capabilities exist to adjust individual element concentrations to achieve charge balance or equilibrium with a pure phase.
Line 0: SOLUTION 25 Test solution number 25 Line 1: temp 25.0 Line 2: pH 7.0 charge Line 3: pe 4.5 Line 4: redox O(-2)/O(0) Line 5: units ppm Line 6: density 1.02 Line 7a: Ca 80. Line 7b: S(6) 96. as SO4 Line 7c: S(-2) 1. as S Line 7d: N(5) N(3) 14. as N Line 7e: O(0) 8.0 Line 7f: C 61.0 as HCO3 CO2(g) -3.5 Line 7g: Fe 55. ug/kgs as Fe S(6)/S(-2) Pyrite Line 8a: -isotope 13C -12. 1. # permil PDB Line 8b: -isotope 34S 15. 1.5 # permil CDT Line 9: -water 0.5 # kg
number --Positive number to designate the following solution composition. A range of numbers may also be given in the form m-n , where m and n are positive integers, m is less than n , and the two numbers are separated by a hyphen without intervening spaces. Default is 1.
If line 2 is not entered, the default pH is 7.0. Specifying both charge and a phase name is not allowed. Be sure that specifying a phase is reasonable; it may not be possible to adjust the pH to achieve the specified saturation index.
If line 3 is not entered, the default pe is 4.0. Specifying both charge and a phase name is not allowed. Adjusting pe for charge balance is not recommended. Care should also be used in adjusting pe to a fixed saturation index for a phase because frequently this is not possible.
redox--Indicates the definition of a redox couple that is used to calculate pe. This pe will be used for any redox element for which a pe is needed to determine the distribution of the element among its valence states. Optionally, -r[ edox].
If line 4 is not entered, the input pe value will be the default. The use of -redox does not change the input pe. The example data block uses the dissolved oxygen concentration [defined by O(0) in line 7e] and the redox half-reaction for formation of O 2(aq) from water (defined in the SOLUTION_SPECIES data block of the default databases) to calculate a default pe.
concentration units --Default concentration units. Three groups of concentration units are allowed, concentration (1) per liter ("/L"), (2) per kilogram solution ("/kgs"), or (3) per kilogram water ("/kgw"). All concentration units for a solution must be within the same group. Within a group, either grams or moles may be used, and prefixes milli (m) and micro (u) are acceptable. Parts per thousand, "ppt"; parts per million, "ppm"; and parts per billion, "ppb", are acceptable in the "per kilogram solution" group. Default is mmol/kgw (millimoles per kilogram water).
element list --An element name or a list of element valence states separated by white space (see line 7d). The element names and valence states must correspond to the items in the first column in SOLUTION_MASTER_SPECIES.
as formula --Indicates a chemical formula, formula , will be given from which a gram formula weight will be calculated. A gram formula weight is needed only when the input concentration is in mass units. The calculated gram formula weight is used to convert mass units into mole units for this element and this solution; it is not stored for further use. If a gram formula weight is not specified, the default is the gram formula weight defined in SOLUTION_MASTER_SPECIES. For alkalinity, the formula should give the gram equivalent weight. For alkalinity reported as calcium carbonate, the formula for the gram equivalent weight is Ca 0.5 (CO3) 0.5 ; this is the default in the phreeqc.dat and wateq4f.dat database files distributed with this program.
gfw gfw --Indicates a gram formula weight, gfw , will be entered. A gram formula weight is needed only when the input concentration is in mass units. The specified gram formula weight is used to convert mass units into mole units only for this element and this solution; it is not stored for further use. If a gram formula weight is not specified, the default is the gram formula weight defined in SOLUTION_MASTER_SPECIES. For alkalinity, the gram equivalent weight should be entered. For alkalinity reported as calcium carbonate, the gram equivalent weight is approximately 50.04 g/eq.
redox couple --Redox couple to use for the element or element valence states in element list. Definition of a redox couple is appropriate only when the element being defined is redox active and either (1) the total amount of the element is specified (no parentheses in the element name) or (2) two or more valence-states are specified (a valence state is defined in parentheses following element name); definition of a redox couple is not needed for non-redox-active elements or for individual valence states of an element. Initial solution calculations do not require redox equilibrium among all redox couples of all redox elements. Specifying a redox couple will force selective redox equilibrium; the redox element being defined will be in equilibrium with the specified redox couple . A redox couple is specified by two valence states of an element separated by a "/". No spaces are allowed. The specified redox couple overrides the default pe or default redox couple and is used to calculate a pe by which the element is distributed among valence states. If no redox couple is entered, the default redox couple defined by line 4 will be used, or the pe if line 4 is not entered.
charge--Indicates the concentration of this element will be adjusted to achieve charge balance. The element must have ionic species. If charge is specified for one element, it may not be specified for pH or any other element. (Note that it is possible to have a greater charge imbalance than can be adjusted by removing all of the specified element, in which case the problem is unsolvable.)
phase name --The concentration of the element will be adjusted to achieve a specified saturation index for the given pure phase. Be sure that specifying equilibrium with the phase is reasonable; the element should be a constituent in the phase. Phase name may not be used if charge has been specified for this element.
name --Name of the isotope. The name must begin with mass number followed by an element or element-valence-state name that is defined through SOLUTION_MASTER_SPECIES.
uncertainty limit --The uncertainty limit to be used in inverse modeling. This value is optional in the SOLUTION data block and alternatively a default uncertainty limit may be used (see INVERSE_MODELING) or an uncertainty limit may be defined with the -isotopes identifier of the INVERSE_MODELING data block.
-water--Indicates mass of water is entered on this line. Molalities of solutes are calculated from input concentrations and the moles of solutes are determined by the mass of water in solution. Optionally, water, or -w[ ater].
The order in which the lines of SOLUTION input are entered is not important. Specifying both " as" and " gfw" within a single line is not allowed. Specifying both " charge" and a phase name within a single line is not allowed. Specifying the concentration of a valence state or an element concentration twice is not allowed. For example, specifying concentrations for both total Fe and Fe(+2) is not allowed, because ferrous iron is implicitly defined twice.
Alkalinity or total carbon or both may be specified in solution input. If both alkalinity and total carbon are specified, the pH is adjusted to attain the specified alkalinity. If the units of alkalinity are reported as calcium carbonate, the correct formula to use is " as Ca0.5(CO3)0.5", because the gram equivalent weight is 50.04, which corresponds to one half the formula CaCO 3 . However, to avoid frequent errors, if " as CaCO3" is entered, the value of 50.04 will still be used as the equivalent weight.
All concentrations defined in the SOLUTION data block are converted into molality. The absolute number of moles is usually numerically equal to the molality because a kilogram of solvent water is assumed. It is possible to define a solution with a different mass of water by using the -water identifier. In that case, the moles of solutes are scaled to produce the molality as converted from the input data. A 1-mol/kgw solution of NaCl with " -water 0.5" has 0.5 moles of Na and Cl and 0.5 kilograms of water. Batch-reaction calculations may also cause the mass of water in a solution to deviate from 1 kilogram.
Isotope values are used only in conjunction with the INVERSE_MODELING data block. Uncertainty limits for isotopes in mole-balance modeling may be defined in three ways: default uncertainty limits may be used, uncertainty limits may be defined in the SOLUTION data block, or uncertainty limits may be defined in the INVERSE_MODELING data block. Uncertainty limits defined in the INVERSE_MODELING data block take precedence over the SOLUTION data block, which in turn take precedence over the defaults given in table 5.
After a batch reaction has been simulated, it is possible to save the resulting solution composition with the SAVE keyword. If the new batch-reaction composition is not saved, the solution composition will remain the same as it was before the batch reaction. After it has been defined or saved, a solution may be used in subsequent simulations through the USE keyword. Solution compositions for a cell are automatically saved after each shift in transport calculations.
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