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Halite/Gypsum Precipitation
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Topic: Halite/Gypsum Precipitation (Read 2407 times)
sttr6
Contributor
Posts: 1
Halite/Gypsum Precipitation
«
on:
September 25, 2015, 02:16:10 PM »
Hi
I have 2 questions:
1) I want to calculate the amount of halite precipitation in a certain period of time from a solution. I tried to use "rates" block but I don't know which equations should I use and the right coding. I tried to use Calcite example in the user guide but I got confused. I appreciate if anyone can help me.
2) I used Equilibrium Phases to calculate the amount of precipitation of Gypsum. Ca in the solution is 0.003 mole but phreeqc calculated d_gypsum=10.01 mole. How is that possible ?
Thanks
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dlparkhurst
Top Contributor
Posts: 3710
Re: Halite/Gypsum Precipitation
«
Reply #1 on:
September 25, 2015, 04:27:39 PM »
Here is an example of kinetic dissolution of halite using a common rate equation. However, the rate of dissolution (rate constant k) was arbitrarily adjusted to reach equilibrium within 1 day. The rate is not consistent with any experimental data.
As for the d_gypsum, I cannot say. Perhaps you had 10 moles of anhydrite that converted to gypsum? I don't know. Perhaps example 2 in the manual would be helpful.
SOLUTION
END
RATES
Halite
10 k = 20/86400 # 1 per day
20 rate = k * (1 - SR("Halite"))
30 moles = rate * TIME
40 SAVE moles
END
USER_GRAPH 1
-headings Days SI(Halite) TOT(Na)
-axis_titles "Days" "SI(Halite)" "Moles dissolved"
-initial_solutions false
-connect_simulations true
-plot_concentration_vs x
-start
10 GRAPH_X TOTAL_TIME/86400
20 GRAPH_Y SI("Halite")
30 GRAPH_SY TOT("Na")
-end
-active true
USE solution 1
KINETICS
Halite
-m 10
-steps 86400 in 10 steps
END
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Kinetics and rate controlling factors
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Halite/Gypsum Precipitation