Execution+of+PHREEQC+Calculations

Back to Main The median composition of the Askola groundwater is given in table 1:

Table 1. Median composition of the Askola ground water (GTK 2008)
 * || mg/L ||
 * HCO 3 - || 128 ||
 * SIO 2 || 11.7 ||
 * Na + || 34.05 ||
 * K + || 2.36 ||
 * Ca 2+ || 14.05 ||
 * Mg 2+ || 6.33 ||
 * Sr 2+ || 0.13 ||
 * B 3+ || 0.05 ||
 * SO 4 2- || 17.85 ||
 * Cl - || 25.6 ||
 * F - || 0.38 ||
 * Br - || 0.02 ||
 * I - || 0.02 ||

The pH of the water is 7.7, temperature 10 centigrade and the uranium concentration 340 μg/l. In oxic conditions the Eh of the water is 500 mV and the density of water 1.0 kg/l.

math Eh=\frac{2.303 RT}{F}pe math

where R is the gas constant, T temperature and F the Faraday constant R = 8.3145 J K -1 mol -1 F = 96485.3 C/mol

Modify the given .phrg input file (below) based on data given above and do the following exercises using PHREEQC:

1. Calculate the prevailing uranium species at pH range 2-12 using llnl.dat database. Create a "selected output" file with most relevant prevailing uranium species. Open your .txt file with excel or another relevant program and produce a figure of uranium species as a function of pH. What uranium species are most prevailing in oxic conditions? Save your output file as a text file for the next exercise.

2. Open your output file, and from ”Saturation indices” block look at the SI-values. Write in your input file a command line for the SI values of the most relevant solid uranium phases and produce a figure representing the SI values as a function of pH.

3. If we assume that a uranium-bearing groundwater attains equilibrium with a strongly reducing mineral, such as FeS, how will pH, pe, uranium species and SI values of solid uranium phases change?

Input file for modification based on given data:

SOLUTION 1 Speciation exercise #use llnl-database -temp -pH -pe -units
 * 1) write the correct values, calculate pe based on Eh:


 * 1) write the water composition here:

SAVE SOLUTION 1 END USE SOLUTION 1
 * 1) SELECTED_OUTPUT
 * 2) -RESET false
 * 3) -file #here the name of the file
 * -PH
 * 1) -TOTALS #here the oxidation states of uranium
 * 2) -molalities #here the species of interest
 * 3) -SATURATION_INDICES #here satiration indices

PHASES Fix_H+ H+ = H+ log_k 0.0

USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -2.0 HCl 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -3 HCl 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -4 HCl 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -5 HCl 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -6 HCl 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -7 HCl 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -8 NaOH 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -9 NaOH 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -10 NaOH 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -11 NaOH 10.0 END USE solution 1 EQUILIBRIUM_PHASES 1 Fix_H+ -12 NaOH 10.0 END