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Waxy Layer Formation after Multiple Extractions (7 replies)
I am not an organic chemist or expert in solvent extraction hydromet but usually if you are getting wax type materials it usually means you have esters forming from acidic acid groups (phosphoric acid groups in your case i take it).
If it’s not separating from organic- water phase properly in addition to the densities, polarities may be something that is changing in the organic phase when the acidic groups are undergoing esterification.
I would do a quick solids ICP OES analysis on the wax as it may likely have some of the metals you are trying to extract in addition to simple IR or solid state nmr on wax to check for composition. Likely the wax substance you can dissolve in a non polar liquid.
I have seen waxy organic in Zn SX Circuit. I collected this and add acid solution and mixed. Waxy organic was converted to organic phase.
If all fails aqua-regia or HF does the trick to dissolve most solids 🙂
I think that you passed the LOC (limiting organic concentration). From my point of view it's not a "classical" third phase (organic phase split into two phases: a diluent rich phase and anextractant rich phase) but a precipitation of a complex. I have already observed it before with DEHPA and lanthanides.To avoid these phenomena, you need to increase the phase modifier content of your solvent or minimize the organic concentration of your cations.If you want to identify the cation in the complexes, you can use an acidic aqueous phase used for your stripping and analyze by ICP the aqueous phase.
May I know your operational condition such as the concentrations of ions, the composition of acid, the volume percentage of used D2EHPA and the O: A ratio?
The waxy layer you said is not the common third phase, the definition of third phase is introduced.
Did you know the composition of waxy layer, what's this?
Of course, you can solve it with adding acid in it.
However, I think you should consider whether it' true that no impurity in the aqueous phase.Both of us know the impurity is the main cause of third phase and emulsion.Besides, you said this phenomenon occurred after 4th and 5th contact. The contact you said is organic phase mixed with aqueous phase and then phases separation, is that process?If it's, after 4-5 times extraction, did the organic phase degenerate? Maybe you should also consider your O: A ratio or you need to increase the phase modifier content and take others into consideration.
With respect to my previous tests, if you had more ion concentrations than that of concentration corresponding to D2EHPA capacity, the D2EHPA structure would start to decompose like a waxy layer you mentioned. In literature belonging to SX, you can't see the term waxy. It is not a scientific word. Also, in order to understand the reasons, it is important to the operational condition of the system.
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I am working with a DEHPA/Isodecanol/Kerosene system and I contact the organic phase multiple times with fresh aqueous solution. To build up the concentration of the element I am interested in. However, at the same time ferric is extracted as well as Mn, Al and Cr. After the 4th or 5th contact I start seeing the formation of a "waxy" in the organic phase and the phase separation becomes slower. If I centrifuge the organic phase I obtain 3 things entrapped aqueous solution, the "original" liquid organic phase and this wax like layer. The density of this is apparently lower than water since it forms in the middle while centrifuging. Is there a name for this phenomenon? Does it have to do with an "overloading" of the extractant phase causing some kind of "polymerization". Ideally some pointers to literature discussing this would be welcome or the correct name of this behavior. From my understanding it would not be third phase formation as this would be considered to be liquid still, right? It would be great, if someone can give me some pointers. Also there are no solids present in the aqueous phase.