Re: PHREEQC

["David L Parkhurst" <dlpark@xxxxxxxx>]

> I'm new to PHREEQC (usually use Geochemist's Workbench but our PC has
died)

Slumming a bit, I see.

> I am trying to produce pH and species concentration data (to eventually
construct a speciation diagram) for Cu++ in pure water and Cu++ in 0.1 M
NaNO3.  I require both calculations to be performed with the suppression of
CuO (s)  and Cu(OH)2 (s) and then would like to repeat the calculations
with
the suppression of just CuO (s) (so letting Cu(OH)2 (s) precipitate).

> I have amended the llnl database to include the following aqueous species

Cu+2 + H2O = CuOH+ + H+
    log_k    -8.2
Cu+2 + 2 H2O = Cu(OH)2 + 2 H+
    log_k     -17.5
2Cu+2 + 2 H2O = Cu2(OH)2+2 + 2 H+
    log_k    -10.59
Cu+2 + 3 H2O = Cu(OH)3- + 3 H+
    log_k    -27.8
Cu+2 + 4 H2O = Cu(OH)4-2 + 4 H+
    log_k    -39.6

You can add these to the input file without changing the database file. The
new definitions will supercede the definition of CuOH+ in llnl.dat and add
the species Cu(OH)2, Cu(OH)3, and Cu(OH)4. However, llnl.dat also has a
CuO2-2 species which will not be removed unless you modify the data base.

> and solids

Cu(OH)2(s)
        Cu(OH)2 + 2H+ = Cu+2 + 2H2O
        log_k = 9.12

> and i have removed Cu+ (and all references to it).

Probably not necessary for the problems you are doing, but it is reasonable
if you want to remove any possibility of reduction to Cu+.

> I have successfully produced two speciation output files in pure water
(see
attached) - at pH 6 and 8 - to illustrate the increasing extent of
Cu(OH)2(s) precipitation with pH (seen as a change in the SI for Cu(OH)2
(s))....do i now assume that the Cu++ deficit (ie: the difference between
the total Cu++ in the system and the total Cu++ aqueous species as listed
in
the output file) is the mol/L of precipitate?

There is a section of the output file that is headed "Phase assemblage",
which gives the mole transfer of each mineral. In this block, positive
Delta indicates the amount of the mineral has increased (precipitated).
Units are actually moles and generally there will be approximate 1 kg of
water.

> So in summary!  Could you help me produce

> a) speciation of Cu++ in pure water; CuO(s) and Cu(OH)2(s) suppressed
> b) speciation of Cu++ in 0.1 M NaNO3; CuO(s) and Cu(OH)2(s) suppressed
> c) speciation of Cu++ in pure water; CuO(s) suppressed - so eventual
speciation diagram actually showing the fraction of Cu(OH)2(s) present with
pH
> d) speciation of Cu++ in 0.1 M NaNO3; CuO(s) suppressed - so eventual
speciation diagram actually showing the fraction of Cu(OH)2(s) present with
pH

I admit that GWB is probably better for phase diagram kinds of
calculations. PHREEQC requires that you explicitly add acid or base to
attain a given pH. The following uses the technique shown in example 8 in
the manual to fix the pH at different values. The fraction of the total
copper is written in a data block headed by "User Print".

David



SOLUTION_SPECIES
Cu+2 + H2O = CuOH+ + H+
    log_k    -8.2
Cu+2 + 2 H2O = Cu(OH)2 + 2 H+
    log_k     -17.5
2Cu+2 + 2 H2O = Cu2(OH)2+2 + 2 H+
    log_k    -10.59
Cu+2 + 3 H2O = Cu(OH)3- + 3 H+
    log_k    -27.8
Cu+2 + 4 H2O = Cu(OH)4-2 + 4 H+
    log_k    -39.6
PHASES
Cu(OH)2(s)
        Cu(OH)2 + 2H+ = Cu+2 + 2H2O
        log_k = 9.12
Fix_pH
      H+ = H+
      log_k 0
SOLUTION 1 A: Speciation in pure water
# Note that the pH is fixed at 7.0
# and that the solution is not charge balanced
      pH    7
      units mmol/kgw
      Cu(2) 1
END
SOLUTION 2 B: Speciation in NaNO3 solution
      pH    7
      units mmol/kgw
      Cu(2) 1
      Na    100
      N(5)  100
END
#  C: pH dependence
USER_PRINT
10 tot_cu = TOT("Cu") + EQUI("Cu(OH)2(s)")
20 PRINT "Dissolved Cu:            ", TOT("Cu"), "Fraction of total: ",
TOT("Cu")/tot_cu
30 PRINT "Precipitated Cu(OH)2(s): ", EQUI("Cu(OH)2(s)"),"Fraction of
total: ", EQUI("Cu(OH)2(s)")/tot_cu
USE solution 1
EQUILIBRIUM_PHASES 1
      Cu(OH)2(s)  0     0
      Fix_pH      -6    HNO3
END
USE solution 1
EQUILIBRIUM_PHASES 1
      Cu(OH)2(s)  0     0
      Fix_pH      -7    NaOH
END
USE solution 1
EQUILIBRIUM_PHASES 1
      Cu(OH)2(s)  0     0
      Fix_pH      -8    NaOH
END
USE solution 1
EQUILIBRIUM_PHASES 1
      Cu(OH)2(s)  0     0
      Fix_pH      -9    NaOH
END




David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled