Hello!
Can you, please, help me to find an equation for calculating theoretical steps for separating two components by liquid extraction (not graphically)
I`ve performed extraction for two individual components and got data: distribution and separation coefficients for individual substances, phase volumes, concentrations of individual substances in both phases.
I found several variants of equations for calculating the number of steps for individual components, but still can`t find an equation for mixture.
Thank you!
Hi,
The extraction behaviour of a metal in a single metal solution is indeed vary to that when the metal is in a multi metal solution. There is currently no known equation to predict the extraction behaviour of individual metals in a mixture from their behaviours in single metal solutions as the shifts in the behaviour differ for different extraction system. Often in dilute solutions, however, the shift in the extraction behaviour is not significant when the other operating parameters are kept constant.
Regards,
Zela
Zela Tanlega Ichlas
Thanks for your answer!
Then is it right that if I have a distribution coefficient of 8 for one metal, 2 for another (in the same system, all parameters are the same) and if I combine them, then I will first extract the one whose distribution coefficient is higher? Or in conditions of competing extraction they`ll behave unpredictably?
I just can’t understand, it looks like I can’t theoretically evaluate the possibility of separation of two metals??
Hi Arina,
If you mean by the condition of competing extraction is the condition where the concentration of extractant ([HA]) is not significantly higher than those of the metals ([M]), I'd say a notable change in the extraction behaviour of the two metals will occur but not unpredictably as the metal with higher distribution coefficient (M1) is usually favoured over the one with smaller coefficient (M2). You may observe that M2 is not extracted at all under a condition where extraction of M2 usually occurs when M1 presents. The actual degree of this so-called crowding effect needs to be determined empirically (cannot be predicted from single metal solutions).
If [HA] >> [M], the two metals will be extracted together (one with D ~ 8 and the other with D ~ 2).
If the goal is to theoretically evaluate the possibility of separation, you can compare the separation factor for the two metals (DM1/DM2) under varying operating conditions, e.g. pH. Still, the actual degree of separation needs to be determined empirically, and the McCabe-Thiele method is the most common means to predict the composition of the aqueous phase after a certain number of extraction step.
Please go through my power point presentations on my site and see whether your question was answered.
Suggested reference: D.A. Ellis, "Prediction of multistage solvent extraction operation from limited data", Industrial and Engineering Chemistry, 52(3) March 1960, 251-252.
On application of McCabe-Thiele (graphical) method to extraction mass-transfer problems at liquid-liquid extraction: https://www.researchgate.net/post/How_to_construct_McCabe_Thiele_diagram_for_LLE_and_is_there_any_software_for_LLE_simulation
The paper called 'static simulation program of copper solvent extraction configurations using excel solver' on my researchgate profil gives you equilibrium correlations between concentrations of copper in organic and aqueous. You can try to do that for your case.
You can use Kremser’s equations to calculate the number of stages in counter current SX process. You can refer to my publication in Hydrometallurgy journal.
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