 So, after learning the complexation of actinides with inorganic as well as organic livings, we see their separation chemistry and this has application in the nuclear fuel cycle. Now, the separation of actinides in the nuclear industry mostly based on precipitation solvent extraction and ion exchange and this precipitation was used in the monotone project where the plutonium separation was done by the Bismuth phosphate process and there is a schematic of this Bismuth phosphate precipitation process is shown in the right side. You see that mixture of plutonium 4 plus, EO2 2 plus and the trivalent actinides, trivalent lanthanides and the net 3 nil plus pi and this fission products, they are mixture to which this Bismuth nitrate is added along with H3 PO4. You get the precipitation of Bismuth phosphate, the solution goes and all other ions actually they are coming in a solution while this plutonium 4 plus is precipitated. This precipitate can be filtered and then re-dissolved to get a clear solution of plutonium 6 and then this can be again re-precipitated that is how this Bismuth phosphate precipitate of plutonium 4 is done and plutonium 6 goes into the solution. Subsequently, the solvent extraction processes become more popular in the nuclear industry for both the front as well as the back end of the nuclear fuel cycle and in this case what one needs is a extractant which is responsible for forming a complex with the actinide ion and then which is subsequently partitioned into a diluent. So, now this is the organic phase which contains the diluent, the extractant and the metal extractant complex whereas, the aqueous phase which contains metal ions and other impregnable elements. Now, in case of solute extraction I have shown a schematic where actually the mixture of two ions marked with the orange and the red color they are initially in the aqueous phase and you mix the two phases and then you allow to settle you find that the red pieces they go to the organic phase while the orange pieces they remain in the aqueous phases. So, that is how this suppression is done in case of the solvent extraction. So, they follow the non-distribution law where we have this distribution ratio which is defined as the concentration of the metal ion in the organic phase and the concentration of the metal ion in the aqueous phase. The metal ion in the aqueous phase remains in the variety of species including the free metal ion and the complex metal ions with the medium of the aqueous phase that is in case of the nitric acid medium you have the nitrate complexes of the metal ion. On the other hand the organic phase contains the extractable complex species in the single species or some cases if you have a mixture of extractive species then you know the mix. The extraction of the metal ion depends on the ligand concentration, metal ion concentration, aqueous phase acidity and other condition like the dilute composition also. Now, for the metal ion extraction the requirement is that we need to neutralize the metal ion charge because the charged metal species is not partisan into the organic phase and it is mostly present in the aqueous phase because of the hydration sphere of this metal ions particularly for the actinide ions very strong hydration spheres. So, they can never go into the organic phase as such it is a non-polar organic medium and therefore they call extractant is required to form a complex and also you need a complex thing anion also. So, like if you have a neutral extractant then you need a complex thing anion like nitrate ion which makes the extracted species charge neutralize and because of the extractant the species become hydrophobic and it gets partisan into the organic phase. So, there are different types of extraction mechanism that is the solvation, the ion pair, the ion exchange and finally the chelation. The extractants can also be classified as neutral acidic will as basic extractant. The basic extractants are the amines like triaphylamine or trilorelamine I have mentioned here for the ion pair extraction the neutral extractants can be TPP, tithal ether or triaphyl for spin oxide. So, in those cases you need necessarily a counter anion that is the nitrate ion which can form charge neutralized complex along with these neutral donor ligands that is how the extraction is done. In case of ether you need to do the extraction into the organic phase by something called salting out you have to add large consumption of salts so that it partisans favorably into the organic phase. We also have these acidic extractants some of them are like thenoid trifluoracetone or STTA, dibenzoyl methane or DBM. So, they are actually acidic extractants and they are existing in the in all form and that is how they give away one proton and then form charge neutralized complex with that. Similar also is a case for this diethyl ethyl ethyl phosphoric acid or TEPA. This also can form charge neutralized complex with the actinide ion that is does not need a counter anion with a DEPA. In most of the cases there are of course cases where you need counter anions with DEPA as well. Now, this aliquot 336 this is actually a liquid anion exchanger in this case the extraction is taking place by ion exchange that is the chloride part of this extractant is exchanged with anionic complex. Now, coming to this extractant properties most of these extractants should be insoluble in water and freely soluble in the organic solver. So, this is the prime requirement otherwise the complex will be present in the aqueous medium and not partisan into the organic. There are of course some extractants which have reasonably good solubility in the aqueous medium as well like the crown ethyl or esthyl acetone which have good aqueous solubility and in those cases the partisan is there to the aqueous phase also to some extent but major amount of the complex is partisan into the organic phase that is how the extraction is achieved. And this extractant should form a reversible complex with the metal ion so that you can strip it out at a later stage so that you first have the extraction of the metal ion and then you can strip it into the aqueous phase in a subsequent step so that the overall process is complete. Then this kinetics of this extraction should be faster when the if it is slow complexation kinetics with this extractant then it will take a unusually large time for this extraction to be complete it is not practically viable to use such extractants for application purpose. Now, these extractants should have good stability now when I talk about the stability generally it should have the hydraulic stability that is it should be in the acid medium the acid hydrolysis of these extractants should not be taking place. And in case of actinides because most of the actinides are radioactive so the extractants would also have radius instability and finally the extractant properties would be no cost and easy availability that is how the process cost can be reduced. Now, along with the extractant as I mentioned we also needed diluents so the diluents should have these following properties like it should be non-polar it should have no aqueous solubility it should be having easy phase separation ability and the diluents also should have no viscous if there are some of the diluents they are highly viscous like the room temperature ionic liquids that is why it is a not proposed for the separation in a large scale because in that case the time required for separation will be much much larger. Some of the extractants like Aliquon 336 this is very viscous so it needs to be diluted properly with a suitable diluents so that the extraction can be done in a favorable candidate so that separation can be done in an acceptable time limit. I give some example here the actinide extraction by salvation now the salvation mostly is by tbp there are also other examples of this uranium extraction by diethylene picture methyl isoblutrile ketone or hexone and butyx so these are some of the extractants which have been used in the middle of this last century where this uranium extraction studies were carried out in different laboratories and this is the extraction equilibrium what I have shown here is for the tbp where uranil ion that is uo22 plus is present in the active phase it can form a complex with two nitrates to neutralize its charge that is uo2 plus two nitrate becomes uo2 nitrate twice but as such these species cannot get partitioned into the organic phase that is why you need two tbp also in the organic phase which is coming to the aqua phase so in such case what happens the tbp is partitioned into the aqua phase forms a complex with the uo2 2 plus 2 nitrate this species and finally get this complex species which is uo2 NO3 twice to tbp which is stable in the organic phase. The schematic has been shown here in the aqua phase medium we have this hydrated uranil ion which is forming a complex with the nitrate ion to give this type of species at 3 to 4 molar nitric acid and the tbp which is there in the organic phase it can get partitioned slightly to the aqua phase and incidentally tbp has a reasonably good aqua solubility and then this tbp present in the aqua phase can form a complex with the uranil nitrate 2 H2O species this 2 H2O is replaced by the tbp and then you have this species which is present in the organic phase. Now this is example of this phosphate complexation I was talking this tbp is a organic phosphate then there are other phosphates also like other phosphates means which are having phosphoryl groups like in case of phosphate, phosphonate, phosphinate as well as phosphinoxide and these are shown in this figure where we are comparing the extraction of uranil ion from different aqua's conditions. Now you see here that the phosphate that is the tbp is giving the lowest distribution ratio values that is in all cases you find that the extraction of tbp is lower than the other extractants but nevertheless depending on the concentration the tbp extraction can be made high but all these cases the concentrations are much lower the anionic complexing ion here in this case it is either sulphate or chloride or nitrate. Sulphate data is not given in the figure for simplicity but we are also spreading this extraction strategy at a much much lower than the centre sub nitrate that is 0.1 molar nitrate that is why this extraction of uranium is very very low with nitrate and tbp. But if you have a phosphonate that is this ligand dhsp or dihexyl xyl phosphonate in this case you have this extraction of uranium significantly higher than that of tbp and you get the condition where you have the tbp extraction of uranium and around 0.01 it has increased to little less than that of 1. Now same also you get for the phosphonates so these phosphonates they also form stronger complexes so this bdhp in this case the extraction of uranium becomes significantly larger than that of the phosphonate dhsp and you get more than 10 as the distribution ratio of uranium under the condition where the extraction of uranium was around 0.01 with tbp so for phosphonate you have higher extraction and if you go to phosphine oxide that is trioptile phosphine oxide then you get the distribution ratio of uranium around 1000 or maybe little more than that of 1000 so this suggests that it depends on the basicity of these extractants and trioptile phosphine oxide is a strong base and it forms a stronger complex that is how the uranium extraction is much higher with topop. Also I have shown here a comparison of actinide extraction by tbp so this trivalent actinides extraction I have shown in the right side for plutonium III from HCl medium and that of americium III from the nitric acid medium in the left side figure and you can see that in the hydrochloric acid medium the extraction of trivalent actinide is significantly larger compared to that with the nitric acid medium. Now I have discussed earlier also in one of the previous lectures that is americium III extraction with tbp from nitric acid medium is very insignificant and if it is possible it is only possible by salting it out in the absence of nitric acid so that is by taking large concentration of sodium nitrate you can carry out the extraction of americium III using tbp. Now in european also is extracted poorly but higher than that of americium III so you get slightly higher extraction of the european compared to americium maybe around one order of magnitude higher but then at higher concentration of nitric acid maybe around five to six molar you can have a good separation of americium from european. Thorium extraction because it's a tetravalent ion extraction with nitric acid is very good and plutonium extraction plutonium IV plus is even more than that of thorium because of the ionic potential. Uranium VI extraction is much larger than that of plutonium IV in view of the fact that plutonium IV can form stronger complex but uranium extraction is much higher than that of plutonium most part of this figure I have shown that is because uranium VI has two nitrates and plutonium IV has four nitrates and that is how under tbp present in these two species that is uranium VI extraction species and plutonium IV extraction species have two tbp in this case so the hydrophobic part is same but the hydrophilic part is much higher for plutonium IV that is the nitrate ion that is how the extraction of plutonium is lower than that of plutonium VI plutonium IV extraction is lower than that of plutonium VI and same also for nectronium VI that it is more than that of plutonium IV up to maybe around two to three molar nitric acid however beyond that nectronium VI extraction is lower than that of plutonium IV but nectronium VI extraction is lower than that of uranium VI that is because of the less strong complex formation of nectronium VI as compared to uranium VI. Now in case of the chloride medium as you see in the right side of the figure plutonium IV extraction is lower plutonium VI extraction is higher similar to what we have seen in case of nitrate medium for uranium VI and plutonium IV but the distribution ratio values indicate that this plutonium extraction is relatively larger than that of what we see in the nitric acid medium. Now coming to the ion pair extraction I give some example where this alumine 336 the commercial extractant it is tricapryl amine it extracts the uranium which has application in the front end of the nuclear fuel cycle and as I have mentioned the sulfate complexation the anionic sulfate complexes are formed and which is extracted by the sulfate form of this amine which is protonated so you have R3NH plus twice and SO4 2 minus this type of species is there and this here uranil sulfate also forms an ion pair and the sulfate from the amine part is going to the aqueous phase and this is soluble in the organic phase. Now increasing the alumine 336 concentration increases the uranium extraction, increasing the sulfuric acid concentration decreases the uranium extraction as shown in this figure. Here the solvent used is 5 percent alumine in 2 percent isodecannol 93 percent paraffin and the sulfate concentration increase suggests lower extraction that is because of competition between sulfate as well as the anionic uranil sulfate species indicated here. In this extraction method isodecannol is used as a phase modifier that is used to prevent the third phase production. We also have this ion pair extraction of actinides I have made a comparison of this extraction of uranium 6, neptanium 6 and plutonium 6 from nitric acid medium using 10 percent trioptylamine in xylene, trioptylamine again is a tertiary amine and this data is presented in the right side figure. You can see here that this neptanium extraction is highest at a lower acid concentration that is less than 6 molar nitric acid concentration. This neptanium 6 is extracted to a larger extent compared to that of plutonium extraction. Plutonium extraction is larger compared to that of the uranium extraction and you get this type of curves are formed here. That means at higher concentration of nitric acid there is a competition between the nitrate ion and that of the anionic complexes formed. So, that is how this ion pair extraction of the actinides are taking place from the nitric acid medium with xylene. For neptanium and plutonium the XRL and state they are forming anionic complexes to a significantly higher extent as compared to that of uranium and that is the reason of this extraction. Now, another application of this ion pair extraction of actinides is the depression of trivalent actinides and lanthanides as shown in the left side figure. 0.6 molar alumine 336 which is a tri caprilamine that is a tertiary amine. Alumin 336 is used in xylene and you see the excess medium is 11 molar lithium chloride containing 0.2 molar HCl. HCl is added to prevent the hydrolysis of the metal ions. And the extraction of actinides is significantly larger compared to that of the lanthanides and that is how this trivalent actinides can be separated from the trivalent lanthanides which have relatively lower distribution ratio values and this is used initially for the separation of trivalent actinides and lanthanides. Now, metal ion extraction by ionic zinc here I have given an example of extraction of uranium ion by aliquar 336 from hydrochloric acid medium 7 to 8 molar uranium ion forms species like this EO2Cl4 2- and this anionic species gets exchanged with aliquar 336 chloride ion that is what is shown here this aliquar 336 is a tri capril methyl chloride and this actually for simplicity purpose we have shown here only three octile groups here but it can be anywhere between hexile to octile in our commercially available region. Now, the chloride of the aliquar 336 is exchanged with the EO2Cl4 2- species present in the aqueous phase and that is how uranium is extracted using aliquar 336. Another class of this extractant is this beta diketones which are again acetic extractant and they form actually chelate complexes where this beta diketones like enol trifluoracetium or HDTA simply TTA which is written here and they form generally present in the ketro form and they are in equilibrium with the enol form and at a given condition the aqueous phase containing the metal ion for example, let us take the plutonium ions then this enol form of TTA forms a complex with the plutonium ions and that is how the plutonium ions can be extracted into the TTA medium. So, by adjusting the conditions of the aqueous phase this plutonium extraction can be achieved. If you are having plutonium in the plus 4 oxidation state and your aqueous phase is 1 molar nitric acid then only plutonium 4 will be extracted. So, that is how the plutonium 6 and plutonium 3 species can be left behind in the aqueous phase. Now subsequently if you want to extract the plutonium 6 from the aqueous phase leaving behind the plutonium 3 then you adjust the pH of the aqueous phase to 2 that is how my TTA extraction plutonium 6 can be separated from the aqueous phase and finally whatever you are having in the aqueous phase is a plutonium 3 or you can simply extract the plutonium 3 into the TTA phase by pH value around 4 to 5. So, if you go to beyond pH 6.2 then it will have hydrolysis of TTA as well and that will create problem for the metallone extraction. Now finally, we come to the reprocessing of this fan fuel which is the application of the TPP extraction and I have discussed for uranium and also for plutonium. So, this process is called the purex process or plutonium uranium redox extraction process. Now where actually this TPP the structure which is given here it forms a complex with plutonium 4 and also uranium 6 that is the uranium ion and both these metal ions are extracted into the TPP phase which is taken in end ore taken and the major advantage of this purex process is that the organic solvent containing the TPP it extracts only uranium 6 ion as well as plutonium 4 plus ion and then these are extracted leaving behind the fissile products like Cgm plus, Tonsium 2 plus and also the trans plutonium elements like americium 3 plus, cerium 3 plus etc. And fissile products they contain most of the ryanic elements also that is how this trivalent actinides and lanthanides are addicted to the radioactive waste stream and the separation scheme is actually the co-extraction of plutonium 4 and uranium 6 by the TPP and in a subsequent state this plutonium and uranium partisthenin is done by reducing plutonium to the plutonium 3 oxidation state. So, now the steps are we will be discussing in a next slide, but here one thing I would like to mention that only 30 percent TPP is used because if you use higher concentration of TPP then there are problems like there will be viscosity of this medium increased and also the metal and loading can be significantly higher and that will create problem in the operations in the plants. So, the major problem in case of this that TPP underpulls radiolytic as well as hydrolytic degradation and continuous use in the plant and the degradation products of TPP are the monobutyl phosphoric acid or the di-butyl phosphoric acid they form strong complexes with plutonium and that is how it is not possible to recover plutonium from the extracted space. So, because of that this degradation products that is the MVP and DPP they can be separated from the TPP phase by giving a alkali was the sodium carbonate was that is how this is removed and this TPP can be reset and subsequently at a long time operating used this TPP which is a spent solvent we can call this is again given for the cementation in the waste management. So, that is how this TPP is finally separated from this plant and also this kinetics of this fraction of uranium and plutonium is relatively fast TPP is non-toxic and it has a very low cost view of this several good physical properties this TPP is used in the after reprocessing plant worldwide last several decades and also one of the major advantage of the TPP is that this decontamination factors from fission products are very high. Now, the schematic of the purex process is given here that you have the spent fuel and which is dissolved and the freed adjustment is done to 3 molar nitric acid and finally the plutonium valency adjustment is a must. So, plutonium as you know it exists in different oxidation states like plus 3 plus 4 plus 5 and plus 6 but plus 5 the ability is much less because of the disproportionation that is how this plutonium 3 and plutonium 6 they are actually adjusted to plutonium 4 plus oxidation state by the nitrite ion as shown here you get this nitrite ion by dissolving this NO2 as shown here in the first equilibrium and in the second one the plutonium 3 plus is converted to plutonium 4 plus and the third equilibrium shown here with plutonium and that is PUO22 plus is converted to PU4 plus up there. So, nitrite ion is actually in the dual role that is this oxidizing plutonium 3 plus and also reducing plutonium in the plus 3 plus. By using 30 percent TPP the organic phase is having both uranium and plutonium as the extracted species that I have already discussed before. Now, subsequently the aqueous phase which is coming out of these extractions cycle this will have all the fission products and also the trans plutonium elements like americium curium etc. Then this organic phase containing the uranium and plutonium extract in TPP this is actually given a partisan state where uranium 4 plus is passed and then plutonium 4 plus is reduced to plutonium 3 plus. So, it goes to the aqueous phase and the uranium which is there in the organic phase is subsequently recovered and then used for the subsequently.