Dear Mona

Just add calcite as an equilibrium phases with initial amount 0 an target SI 0.

Regards

is that possible if I am trying to add new phase such as struvite?

I have huge difficulty operating ..I added the equation to the phases on the database but it doesn't show in the species ... I don't know what should be done

In order to add a phase to your calculation you don't necessarily need to manipulate your database , however you have to get the equilibrium constant K for your equation. Maybe you find some data in the other databases ... 

I still can't see it

I tried for Hydroxyapatite

and all it gave me was the below massage

Reading input data for simulation 4.

------------------------------------

EQUILIBRIUM_PHASES 1

Hydroxyapatite 0 0 precipitate_only

END

Is that mean that 0 moles precipitated ? or what ? and I marked Phase only as true!

I use Visual MINTEQ (also freeware), which I find more user-friendly than PHREEQC. You may consider it, if its limitations are acceptable for your work.

If you could post a full input for your simulation and what your intention is we could surely help you out with the interpretation.

Regards

What is the database you use ? Have you tried others ? (like Thermoddem, wich is free to dl)

Here is my input. Maybe it could help you to find the solubility limits of your minerals and the amount of precipitate (mineral in excess). Good luck for your work !

Thank Anne-Laure for your contribution. Your entry seems correct. But the concern of Mona was to find out the amount of hydroxyapatite that precipitate and not just the saturation index. For this aim, she needs to add an equilibrum phase. Here is the added entry

Find amount of hydroxyapatite dissolved to reach hydroxyapatite saturation

USE solution 1

EQUILIBRIUM_PHASES 1

Hydroxyapatite 0.0 Ca5(PO4)3(OH) 10e-6 #0.0 saturation index of hydroxyapatite at equilibrum

END

Attached is the overall entry review

Hay Guys

Thanks for all the willing to help

I tried using Visual MINTEQ but due to the fact that I need to mix two solutions I couldn't use it as the only option I found was titration

I am Actually facing trouble due to that mixture thing as one of the two solutions is supposed to be tested under various pH values( 7, 7.5, 8, 8.5, 9)

I couldn't do it through solution_spread then mix with another solution. I am using phreeqc interactive 3.1

The only thing I could do is to make many simulations! I am actually looking for struvite and hydroxyapatite values.

I have been advised also to do electron balance for the solutions which I am still trying to figure out.

Also my input file (but please note that 1- First Solution is wastewater, second is seawater and for both I am not sure what PE should be! Also solution one is supposed to have range of pH while solution 2 is constant!)

Thanks a Lot guys

Mona

Dear Gilles Valdez

I tried what you wrote me

it gives

Reaction 1.

5.000e-07 moles of the following reaction have been added:

Relative

Reactant moles

Hydroxyapatite 1.00000

Relative

Element moles

Ca 5.00000

H 1.00000

O 13.00000

P 3.00000

-------------------------------Phase assemblage--------------------------------

Moles in assemblage

Phase SI log IAP log K(T, P) Initial       Final            Delta

Hydroxyapatite                      0.00       -57.50          -57.50

Ca5(PO4)3(OH) is reactant 1.000e-05  5.813e-02 5.812e-02

The final in all the steps in the same (5.813* 10^ -2   - 1*10^-5 ) moles/L ...right? that's what it shows (Final - initial )? so If I put the initial moles zero ...it will give me the final

But what is the use of the reaction step? why not only (EQUILIBRIUM_PHASES)?

The steps all gave same final Moles...and if I simulate with EQUILIBRIUM_PHASES only it gave result a bit different 5.868 *10^-2 Moles

Sorry for asking a lot

Thanks

Mona

Hi Mona, I think you are right,

There is no need to run the reaction step. Just use the equilibrum phases

TITLE Solubility of Hydroxyapatite.

SOLUTION 1 Pure water

pH 7.0

temp 25.0

PHASES

Hydroxyapatite

Ca5(PO4)3(OH) + 7H+ = 5Ca++ + 3H2PO4- + 1H2O

log_k 14.35

EQUILIBRIUM_PHASES 1

Hydroxyapatite 0.0 Ca5(PO4)3(OH) 10e-6 #0.0 saturation index of hydroxyapatite at equilibrum

END

SELECTED_OUTPUT

-file try_hydroxyap # file name

-reset false

-saturation_indices Hydroxyapatite #follows the SI evolution, find the concentration for SI=0

SAVE solution 1

Here are the results

-------------------------------Phase assemblage--------------------------------

Moles in assemblage

Phase SI log IAP log KT Initial Final Delta

Hydroxyapatite 0.00 14.35 14.35

Ca5(PO4)3(OH) is reactant 1.000e-05 8.663e-06 -1.337e-06

This means that the amount of hydroxyapatite which dissolved to reach hydroxyapatite saturation is 1.337e-06 if we consider initial moles of 1.000e-05

Mona,  Did you figure it out yet and do you still need to (given the term is over)?  

If you still need to make this work, then am I understanding correctly - you need to mix a wastewater and seawater together and determine how much struvite and hydroxyapatite will precipitate?   If yes, this can be done in PHREEQC.  The SOLUTION_SPREAD approach is probably not the best way to go.  BTW - this is a non-trivial problem to set up.

Easiest if you send me your solution compositions, mixing ratios and minerals you want to track and I can send you back an input file and you can examine what I did.

Dear Geoffrey

thanks a lot for your willing to help. I already managed with that! Thank you again.

I recommend Geoffrey's answer

Best Regards