Processes > Mixing

Gypsum precipitation inhibition

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Markk31:
Hi all

I started to use PHREEQC a couple of months ago.
I'm trying to simulate an incompatible mixture of two brines ( seawater and reservoir formation water)

I used the simple script below to reach the amount of gypsum precipitated at ambient temperature.

SOLUTION 1    #formation water
temp     22
pH       6
units    ppm
Na       74051.65
Ca       19680
Mg       2916
Cl       157520.42
-water   0.05

SOLUTION 2    #Sea water
temp     22
pH       6
units    ppm
Na       18328.3
Ca       650
Mg       2210
S(6)     4290
Cl       32695
-water   0.05
END

USER_PRINT
10 gyp_mol = EQUI("Gypsum")
20 gyp_mg_1000cc = (gyp_mol * GFW("CaSO4:2H2O") * 1000 / SOLN_VOL)
30 anh_mol = EQUI("Anhydrite")
40 anh_mg_1000cc = (anh_mol * GFW("CaSO4") * 1000 / SOLN_VOL)
50 PRINT "Gypsum scale, mg/1000cc:    ", STR_F$(gyp_mg_1000cc, 10, 1)
60 PRINT "Anhydrite scale, mg/1000cc: ", STR_F$(anh_mg_1000cc, 10, 1)

#########################################################
EQUILIBRIUM_PHASES 1
Gypsum   0 0
Anhydrite 0 0

MIX 1
1 0.5   #FRACTION 0.5 OF Formation water
2 0.5   #FRACTION 0.5 OF Sea water
END


The next step of my project is to apply scale inhibitors, such as HEDP, PBTC, EDTA, PPCA, and etc to see the effect of scale inhibition mechanism in the presence of scale inhibitors.

My question is that is this possible using PHREEQC? and which dataset is better for this brine mixture?
If anyone can help with this, that would be a great help.
thank you in advance.

dlparkhurst:
For high ionic strength, pitzer.dat database would be best, but the set of elements considered is limited, and it would be difficult to consider the inhibitors.

The database minteq.v4.dat has some data for EDTA. Not sure if you will be able to find data for the other inhibitors.

This calculation assumes that complexing of Ca by EDTA is the reason for inhibition. (I guess it is possible that the mechanism could be inhibiting nucleation of a solid, which is not considered.)


--- Code: ---SOLUTION 1    #formation water
temp     22
pH       6
units    ppm
Na       74051.65
Ca       19680
Mg       2916
Cl       157520.42
-water   0.05

SOLUTION 2    #Sea water
temp     22
pH       6
units    ppm
Na       18328.3
Ca       650
Mg       2210
S(6)     4290
Cl       32695
-water   0.05
END

USER_GRAPH 1
    -headings               moles Gypsum Anhydrite
    -axis_titles            "Na4EDTA added, moles" "Scale, mg/L" ""
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 gyp_mol = EQUI("Gypsum")
20 gyp_mg_1000cc = (gyp_mol * GFW("CaSO4:2H2O") * 1000 / SOLN_VOL)
30 anh_mol = EQUI("Anhydrite")
40 anh_mg_1000cc = (anh_mol * GFW("CaSO4") * 1000 / SOLN_VOL)
50 GRAPH_X RXN
60 GRAPH_Y gyp_mg_1000cc
70 GRAPH_Y anh_mg_1000cc
  -end
    -active                 true
EQUILIBRIUM_PHASES 1
    Gypsum   0 0
    Anhydrite 0 0
MIX 1
    1 0.5   #FRACTION 0.5 OF Formation water
    2 0.5   #FRACTION 0.5 OF Sea water
REACTION 1
    Na4Edta    1
    0.02 moles in 10 steps
END

--- End code ---

Markk31:
Well, thank you for the help.

You're right. Other inhibitors perform via crystal distortion or nucleation inhibition mechanisms.

But I have to add the inhibitors that I mentioned to check the inhibition efficiency even if only one mechanism can be checked.

Do you have any suggestions for me? or any dataset? or any way to add inhibitors to datasets?

dlparkhurst:
Other inhibitors could be added provided you can find equilibrium constants. You need equilibrium constants not only for Ca+2, but for other competing cations as well. As an example You can look how "Edta" and its complexes are defined in minteq.v4.dat (SOLUTION_MASTER_SPECIES and SOLUTION_SPECIES).

You'll have to get into the literature. A scholar google search with "HEDP cation complexes equilibrium constants" gave at least one possibility.

Sinaatalebi:
Dear dlparkhurst

I have the same problem. However, I could not find any data regarding the inhibitors' equilibrium constants.
Would you please help me with this?
There are lots of antiscalants, such as AA-AMPS / HPAA / ATMP / PAA / HEDP / PBTC / PAPEMP / DTPMPA / PESA / PASP ...

Appreciate your time and consideration

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