Kinetics and Equilibrium > Equilibrium

Precipitation at equilibrium

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hmal:
Hi all,

Could David or anyone please let me know how PHREEQC calculate the amounts (moles) of minerals that precipitate at equilibrium (under the EQUILIBRIUM block)?

Is it mole = IAP - logK?

Many thanks,
Hmal

hmal:
Hi David, could you please help me with the answers for my previous post on amounts of minerals precipitate at equilibrium. I understand that the minerals will precipitate so that their SI (higher than reach target SI, for example 0.0) will decrease to target SI, but cannot fig out how PHREEQC calculates the amounts/moles.

dlparkhurst:
I thought I answered this, but I'll try again.

The equation for equilibrium is K = IAP

PHREEQC also has mole balance equations for each element. So the mineral is added or removed, which affects the number of moles of the constituent elements. Which in turn affects the activities of the aqueous species. So, moles of mineral are added until the activities of the aqueous species produce IAP = K.

Look in the manual for PHREEQC version 2 for a complete list of equations and some of the numerical method for solving them.

hmal:
Thank you so much, David!

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