Gibbsite solubility curve

[woodS]

I am trying to reproduce gibbsite solubility curve on PHREEQC. I have attached my excel work. Here is the code. Any suggestion is appreciated.

Code: [Select]


SOLUTION 1
    temp      25
    pH        7 charge
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    Al     0.2
    -water    1 # kg

PHASES
Fix_H+
H+ = H+
log_k 0
END

#SOLUTION_MASTER_SPECIES
    XI            XI               0     XI              0.0
#SOLUTION_SPECIES
XI- = XI-
    log_k     0
END

USER_GRAPH 1
    -headings               pH Al3+ Al(OH)+2 Al(OH)2+ Al(OH)3 Al(OH)4-, Al total
    -axis_titles            "pH" "pC" ""
    -chart_title            "Gibbsite solubility curve"
    -axis_scale x_axis      0 14 auto auto
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X -LA("H+")
20 GRAPH_Y LOG10(TOT"Al+3"),LOG(TOT"AlOH+2"), LOG10(TOT"Al(OH)2+"), LOG10(TOT"Al(OH)3"), LOG10(TOT"Al(OH)4-"), LOG10((TOT"Al+3") +(TOT"AlOH+2") + (TOT"Al(OH)2") + (TOT"Al(OH)3") + (TOT "Al(OH)4-"))
  -end
    -active                 true
END

Use solution 1
EQUILIBRIUM_PHASES 1
    Fix_H+    -14 NaOH 10
END

USE solution 1
EQUILIBRIUM_PHASES 1
    Fix_H+    -13 NaOH 10
END
...
...

USE solution 1
EQUILIBRIUM_PHASES 1
    Fix_H+    -1 HXI 10
END



[dlparkhurst]

This file performs your calculation between pH 14 and 4. Below pH 3.5, the solubility of gibbsite is several molal, and the numerical method of PHREEQC fails.

The input file uses SELECTED_OUTPUT and USER_PUNCH to write the repetitive input for each pH, and then INCLUDE$ to run the file that was created.

The input file also uses the trick in the footnote of example 8 to add acid or base as necessary.

Code: [Select]

SOLUTION_MASTER_SPECIES
    Xl            Xl-               0     Xl              1.0
SOLUTION_SPECIES
Xl- = Xl-
    log_k     0
PHASES
Fix_H+
    H+ = H+
    log_k     0
NaXl
    NaXl = Na+ + Xl-
    log_k     -20
END
SOLUTION 1
    temp      25
    pH        7 charge
SELECTED_OUTPUT 2
-file input_file.pqi
USER_PUNCH 2
10 FOR i = 14 to 4 STEP -0.25
20   PUNCH "USE solution 1", EOL$
30   PUNCH "EQUILIBRIUM_PHASES 1", EOL$
40   PUNCH "  Fix_H+ ",-i," HXl 20",EOL$
50   PUNCH "  NaXl   0 20", EOL$
60   PUNCH "  Gibbsite 0 5", EOL$
70   PUNCH "END",EOL$
80 NEXT i
END
SELECTED_OUTPUT 2
-active false
END
USER_GRAPH 1
    -headings               pH Al3+ Al(OH)+2 Al(OH)2+ Al(OH)3 Al(OH)4-, Al total
    -axis_titles            "pH" "pC" ""
    -chart_title            "Gibbsite solubility curve"
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X -LA("H+")
20 GRAPH_Y LM("Al+3"),LM("AlOH+2"), LM("Al(OH)2+"), LM("Al(OH)3"), LM("Al(OH)4-"), LOG10(TOT("Al"))
  -end
END

INCLUDE$ input_file.pqi
END


[woodS]

Thank you very much!!!