# PhreeqcUsers Discussion Forum

## Beginners => PHREEQC basics => Topic started by: PAILLEF on November 02, 2020, 03:37:20 PM

Title: Trace Saturation indice and pH vs NO3-
Post by: PAILLEF on November 02, 2020, 03:37:20 PM
Hi everyone,
This is my first question and i am a beginner with PHREEQC.
So my problem is :

I have 2 Solutions :
1. SiO2 + KOH
2. Mg(NO3)2 + HNO3
Then I mix them.
I would like to know how to trace the pH and the saturation indice of SiO2(am), Brucite, Talc in the MIX versus the amount of HNO3 I put in my solution 2.

Here is the begining of my code :

SOLUTION 2 Mg
temp      20
pH        7 charge
pe        4
redox     pe
units     mol/l
density   1
Mg        0.0625
N(5)      0.125
-water    1 # kg
SOLUTION 1 Si
temp      20
pH        7 charge
pe        4
redox     pe
units     mol/l
density   1
K         0.25
Si        0.125
-water    1 # kg

MIX 1
1    0.5
2    0.5
SAVE solution 3

Title: Re: Trace Saturation indice and pH vs NO3-
Post by: dlparkhurst on November 02, 2020, 04:15:21 PM
Seems like you are on the right track. Just a couple of things.

I would eliminate the reaction that forms N2(aq), otherwise, you may have a reaction that reduces NO3- to N2(aq). With the following added to your input file, NO3- should be conservative.

Code: [Select]
`SOLUTION_SPECIES2 NO3- + 12 H+ + 10 e- = N2 + 6 H2O #-log_k 207.08      -log_k      0 -delta_h -312.130 kcal -dw 1.96e-9 -Vm 7 # Pray et al., 1952, IEC 44. 1146END`
One way to add nitric acid is to use REACTION. If the acid is concentrated, the additional volume of solution is negligible, and you can simply add HNO3 in moles. You'll have to do a calculation to determine the number of moles of HNO3 in a volume of acid.

Code: [Select]
`REACTION 1HNO3 10.2 in 10`
Title: Re: Trace Saturation indice and pH vs NO3-
Post by: PAILLEF on November 02, 2020, 04:47:39 PM
Thanks it seems to work, but (there is always one) :
I don't know how to do for plotting only versus the amount of HNO3 added :
My code so far :

SELECTED_OUTPUT 1
-file                 Solution 3
-totals               N(5)
-saturation_indices   SiO2(am)  Brucite  Talc  pH_fix

USER_GRAPH 1
-axis_titles            "molalité N(5)" "Saturation index" "pH"
-chart_title            "pH"
-axis_scale x_axis      0.125 0.25 auto auto
-initial_solutions      true
-connect_simulations    true
-plot_concentration_vs  x
-start
20 graph_y SI("SiO2(am)")
30 GRAPH_X tot("N(5)")
40 GRAPH_SY -la("H+")
50 graph_y SI("Brucite")
60 graph_y SI("Talc")
-end
-active                 true