Determination of precipitation amount

[sadegh66]

Hi all
I want remove sulphate, carbonate and calcium ions with CaCl2, HCl and H2SO4 in a solution containing Ca2+, Mg2+, Na+, K+, CO3 2-, SO4 2- and Cl- ions, respectively. How I can find out required amounts of this salt and acids as well as amount of forming compounds with PHREEQC, finally?

[dlparkhurst]

Here is a simplified example. Given a Na2SO4 solution, let's say you want to precipitate gypsum by adding CaCl2.

SOLUTION 1
      pH 7 charge
   Na 20
   S(6) 10
END
REACTION 1
      CaCl2
   4 mol in 100 steps
END
EQUILIBRIUM_PHASES 1
   Gypsum 0 0
END
USE solution 1
USE reaction 1
USE equilibrium_phases 1
USER_GRAPH 1
    -headings               Reaction SO4 Gypsum
    -axis_titles            "CaCl2 added, moles" "SO4, mol/kgw" "Gypsum, mol/kgw"
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 graph_x RXN
20 graph_y TOT("S(6)")
30 graph_sy EQUI("Gypsum")
  -end
    -active                 true
END

[sadegh66]

Hi,
Its very good. Is this method suitable for remove of salts mixture that is dissolved in water?
I want remove all of this ions.
How calculate amount of mole Precipitator needed?
Thank you

[dlparkhurst]

It sounds like you want to evaporate to dryness and see the salts that are formed?

First, you will attain very high ionic strengths, and the aqueous model may not be accruate.

If this is what you have in mind, use the pitzer.dat database. Remove water incrementally and look at the minerals that have positive values for saturation indices and include them in the EQUILIBRIUM_PHASES definition. At some point, I think the calculations will fail because PHREEQC will fail at very small amounts of water.

There is an example in the manual of evaporation of Black Sea water.

[sadegh66]

My goal is magnesium recovery from bittern sample. I want use from Mg(OH)2 precipitation method. But my sample has many impurity. So, I should remove them. Now, I want use this program to forecast deletation of sulphates, cabonates and Ca ions. I do not know how simulate their deletation simultaneously!!!

[dlparkhurst]

You can include multiple minerals in the EQUILIBRIUM_PHASES. You can add multiple reactants with REACTION, or you can sequentially react with REACTION, SAVE the solution, and add another REACTION.

I think you should use the script I gave you, read the manual, and try some simulations.

[sadegh66]

Thank you

[sadegh66]

Hi, My dear friend
How realize required amount of additives for remove impurities, accurately(required CaCl2 for deleting sulphate ion, for example).
Thank you

[dlparkhurst]

The graph in the example shows the amount of sulfate left in solution as a function of CaCl2 added. It seems to me that is what you wanted to know.

[sadegh66]

Yes, It is true completely.