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Keywords
USE
This keyword data block is used to specify which solution, surface assemblage, exchange assemblage, and pure-phase assemblage are to be used in the reaction calculation of a simulation. USE can also specify previously defined reaction parameters (REACTION keyword), reaction-temperature parameters (REACTION_TEMPERATURE keyword), and mixing parameters (MIX keyword) are to be used in the reaction calculation.
Example
Line 0a: USE equilibrium_phases none
Line 0b: USE exchange 2
Line 0c: USE gas_phase 3
Line 0d: USE mix 1
Line 0e: USE reaction 2
Line 0f: USE reaction_temperature 1
Line 0g: USE solution 1
Line 0h: USE surface 1
Explanation
Line 0: USE keyword, (number or none)
- USE is the keyword for the data block.
- keyword--one of eight keywords, equilibrium_phases, exchange, gas_phase, mix, reaction, reaction_temperature, solution, or surface.
- number--positive integer associated with previously defined composition or reaction parameters.
- none--the specified keyword will not be used in the reaction simulation.
Notes
Reactions are defined by allowing a solution or mixture of solutions to come to equilibrium with one or more of the following entities: an exchange assemblage, a surface assemblage, a pure-phase assemblage, or a gas phase. In addition, mixtures, irreversible reactions, and reaction temperatures can be specified for reaction calculations. Entities can be defined implicitly: a solution or mixture (SOLUTION or MIX keywords) must be defined within the simulation, then the first of each kind of entity defined in the simulation will be used in the reaction simulation. That is, the first solution (or mixture) will be brought together with the first of each of the following entities that is defined in the simulation: exchange assemblage (EXCHANGE), gas phase (GAS_PHASE), pure-phase assemblage (EQUILIBRIUM_PHASES), surface assemblage (SURFACE), reaction (REACTION), and reaction temperature (REACTION_TEMPERATURE); these entities will then be allowed to equilibrate. Alternatively, entities can be defined explicitly with the USE keyword. "USE keyword number" can be used to explicitly define an entity to be used in the reaction calculation. Any combination of the keyword keywords can be used to define a reaction. "USE keyword none" can be used to eliminate an entity that was implicitly defined to be in a reaction. For example, if only a solution and a surface are defined in a simulation and the surface is defined to be in equilibrium with the solution, then implicitly, an additional reaction calculation will be made to equilibrate the solution with the surface. Though not incorrect, the reaction calculation will produce the exact same compositions for the solution and surface. By including "USE surface none", the reaction calculation will be eliminated (see examples 8 and 9). The composition of the solution, exchange assemblage, surface assemblage, pure-phase assemblage, or gas phase can be saved after a set of reaction calculations with the SAVE keyword.
Example problems
The keyword USE is used in example problems 3, 6, 7, 8, and 9.
Related keywords
EQUILIBRIUM_PHASES, EXCHANGE, GAS_PHASE, MIX, REACTION, REACTION_TEMPERATURE, SAVE, SOLUTION, and SURFACE.
- Example
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- Explanation
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- Notes
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- Example problems
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- Related keywords
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User's Guide to PHREEQC - 07 MAY 96
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