BASIC within PHREEQC

The BASIC code can be used within the keyword RATES, but also for USER GRAPH, USER PRINT and USER-PUNCH and always occurs between the commands 

IF (expr) THEN statement ELSE state ment [f, then, else statement (on one line a V may be used to concatenate lines) 

MID (string, n) Extract characters from position n to end of string. 

REM At beginning of line, line is a remark with no effect on the calculations 

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To be able writing own kinetics programs it is necessary to get familiarized with the programming language BASIC and particularly with the special BASIC-codes within PHREEQC. 

Table 26 presents a list of the standard commands within the BASIC interpreter of PHREEQC, Table 27 the special codes in BASIC of PHREEQC. 

As reaction rates can be fitted mathematically in very different manners, there is an option (and need) in PHREEQC to declare any mathematical term in the form of a little BASIC program within the keyword RATES as will be shown in the following example of a time-dependent calcite dissolution ... 

Model the dissolution of quartz and K-feldspar (adularia) over time. Are the parameters temperature and C02 partial pressure of any importance Within the key word RATES use the BASIC program from the data set PHREEQC.dat. The calculation is done with distilled water (pH = 7, pE = 12) as a batch reaction over a time span of 10 years in 100 time steps at a temperatures of 5 °C and of 25 °C and at C02 partial pressures of 0.035 Vol% (atmosphere) and of 0.7 Vol% (soil). Calculate also the kinetics of the dissolution with 0.035 Vol% C02 and 25 °C for a period of 10 minutes. 

Model the carbonate precipitation in this carbonate channel by means of a Id transport with 40 cells of 10 m length each. Dispersivity is assumed with lm. Use the key words KINETICS and RATES and the BASIC program for calcite from the data set PHREEQC.dat describing the kinetics for both the calcite dissolution and the calcite precipitation. How much calcite precipitates each year within the channel s first 400 meter after the discharge How much C02 degasses at the same time ... 

The acid mine water is defined as SOLUTION 0 and the water in the carbonate channel as SOLUTION 1. Within the key word KINETICS 1-10 the calculation tolerance as well as the initial and the total mole mass of calcite can be defined. Obligatory are only the parameter 50 and 0.6. These are needed by the BASIC program, which must be implemented within the key word RATES. Here, we use the BASIC program listed at the end of the database PHREEQC.dat. If the database PHREEQC.dat is used (which is not free of troubles, since there are, e g., no data for uranium) or if the paragraph is copied into another database, it is not necessary to define a RATES block in the input file. PHREEQC uses automatically the RATES block from the database. Yet, if any other kinetic rates are to be used, the BASIC program must be copied into the input file under RATES. In any case, the KINETICS block is required. 

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