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This keyword data block is used to define the temperature and chemical composition of initial solutions. Speciation calculations are performed on each solution and the resulting speciated solutions may be used in subsequent reaction, transport, or inverse-modeling calculations. Facilities 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 0: SOLUTION [number] [description]
Line 1: temp value
- SOLUTION is the keyword for the data block.
- number--positive number to designate this solution. Default is 1. 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.
- description--optional character field that describes the solution.
Line 2: pH value [([charge] or [phase name] [saturation index])]
- temp--indicates temperature is entered on this line. Optionally, temperature, or -t[emperature].
- value--temperature in Celsius.
Line 3: pe value [([charge] or [phase name] [saturation index])]
- pH--indicates pH is entered on this line. Optionally, -ph.
- value--pH value, negative log of the activity of hydrogen ion.
- charge--indicates pH is to be adjusted to achieve charge balance. If charge is specified for pH, it may not be specified for any other element.
- phase name--pH will be adjusted to achieve specified saturation index with the specified phase.
- saturation index--pH will be adjusted to achieve this saturation index for the specified phase. Default 0.0.
- 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 physically possible to adjust the pH to achieve the specified saturation index.
Line 4: redox redox couple
- pe--indicates pe is entered on this line. Optionally, -pe.
- value--pe value, conventional negative log of the activity of the electron.
- charge--(not recommended) indicates pe is to be adjusted to achieve charge balance.
- phase name--pe will be adjusted to achieve specified saturation index with the specified phase.
- saturation index--pe will be adjusted to achieve this saturation index for the specified phase. Default 0.0.
- 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 physically impossible.
Line 5: units concentration units
- redox--indicates a redox couple is to be used to calculate the default pe. This pe will be used for all redox elements that need a pe to determine the distribution of the element among valence states. Optionally, -r[edox].
- redox couple--redox couple to use for pe calculations. A redox couple is specified by two valence states of an element separated by a "/". No spaces are allowed.
- 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 uses dissolved oxygen to calculate a default pe.
Line 6: density value
- units--indicates default concentration units will be entered on this line. Optionally, -u[nits].
- concentration units--default concentration units. Three groups of concentration units are allowed, concentration (1) per liter, (2) per kilogram solution, or (3) per kilogram water. 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 (kilogram water).
Line 7: element list, concentration, [units], ([as formula] or [gfw gfw]), [redox couple], ([charge] or [phase name] [saturation index])
- density--indicates density will be entered on this line. Optionally, dens, or -d[ensity].
- value--density of the solution, kg/L or g/cm3.
- The density is used only if the input concentration units are "per liter". Default 1.0.
- element list--an element name or a list of element valences separated by white space (see line 7d).
- concentration--concentration of element in solution or sum of concentrations of element valence states in solution.
- units--concentration unit for element (see line 7g). If units are not specified, the default units (units, line 5) are assumed.
- 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 Ca0.5(CO3)0.5; this is the default in 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 calculated 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 element or element valence states in element list. A redox couple is specified by two valence states of an element separated by a "/". No spaces are allowed. If the element list is a redox element or if more than one valence state is listed, 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. A redox couple is not needed for non-redox-active elements.
- 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.
- saturation index--the concentration of the element will be adjusted to achieve this saturation index for the given pure phase. Default 0.0.
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, be sure the correct gram equivalent weight is used to convert to equivalents (50.04), see as and gfw above.
After a reaction has been simulated, it is possible to save the resulting solution composition with the SAVE keyword. If the new composition is not saved, the solution composition will remain the same as it was before the reaction. After it has been defined or saved, the solution may be used in subsequent simulations through the USE keyword.
The keyword SOLUTION is used in all example problems, 1 through 12.
SOLUTION_MASTER_SPECIES, SOLUTION_SPECIES, SAVE solution, and USE solution.
- Example problems
- Related keywords
User's Guide to PHREEQC - 07 MAY 96
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