Acidic aqueous strips

Kawasaki et /. (1996) have used a supported membrane catalyst for extraction of erythromycin from its dilute, slightly alkaline aqueous solutions. 1-Decanol was used as an intermediate fluid membrane phase and a buffered acidic aqueous solution was used to strip the organic membrane. 

Analytical techniques such as adsorptive stripping voltammetry rely on complex formation to improve detection limits of metals such as V(IV) and V(V) [51]. An example is in the use of cupferron and KBr03 as additives to acidic aqueous solutions, which result in the adsorption of the V(V)-cupferron complex to the electrode surface that catalyzes the reduction of the Br03 ion in solution. This technique has good selectivity over Cu, Pb, Cd, Fe, and Ti, but the response is dependent on pH. 

The quaternary R4-alkyl-substituted ammonium chlorides are commercially available, and can be stripped with a surplus of chloride, hydroxide, etc. thus, the solute is regenerated in the re-extraction or stripping step. The quaternary compound has the advantage of being able to be used in alkaline media compared to the frequently used ternary amines. Primary, secondary (both are water-soluble, less used) and tertiary amines are only stable in acidic aqueous media, as hydroxide destroys the ammonium complex ... 

Figure 12. DAm vs. aqueous strip acidity for 30 vol % DBBP-70 vol % lsopar H at 21°C, organic. aqueous = 1 1...

Danesi et al. studied the kinetics of transport of Am(lll) from aqueous nitrate solutions to formic acid aqueous solutions using an SLM, which consisted of a solution of a new (carbamoylmethyl)phosphine oxide in diethylbenzene (DEB) [110]. In an attempt to treat simulated low-level radioactive wastewater, Teramoto et al. [Ill] have used an SLM containing CMPO for the uphill transport of Ce(III) from aqueous solution containing a mixmre of nitric acid and sodium nitrate. The simulated waste contained Ce(III), Fe(III), Cr(III), and Ca(II), while the strip solution contained water or sodium citrate solution. Though TBP has been used along with CMPO and w-dodecane as the carrier solution, it also facilitates the transport of HNO3 to the strip side. The acid transport was significantly decreased when CMPO alone in 2-nitrophenyl octyl ether was used as the carrier solution. 

Figure 5 shows a comparison of U(IV) concentration profiles realized experimentally for the mixer settler and the pulsed column. The U(IV) profile in the columns shows an inventory of about a tenfold stoichiometric excess for the aqueous phase, relative to the Pu profile to be expected from LWR fuel. The U(IV) production rate in the column can easily be increased to an extent higher than the feed rates of externally produced U(IV) normally required in the conventional reduction column. Therefore one can at least expect equally good results for the U/Pu separation with the electro-reduction column as with the normal procedures. This is also confirmed by experiments in the USA which resulted in the installation of an electro-reduction column in the AGNS Plant at Barnwell. In these experiments even with high acid concentrations (2 M HNO in the aqueous strip, BXS) high plutonium decontamination factors have been achieved (17). 

The aqueous strip solution will form directly the feed solution of the Am, Cm/RE countercurrent separation step, to be performed according to the operating conditions of the TALSPEAK process (15). The presence of a complexing agent like DTPA will prevent the extraction of Am and Cm whereas the RE will be more easily extracted by di(2-ethylhexyl)phosphoric acid (HDEHP) in n-dodecane (pH = 3). 

The hot run was made with the feed solution obtained by dissolving highly irradiated Pu-Al alloy in HNO3 with mercuric ion catalyst. Uranium was added to the solution to produce a typical Purex feed. Uranium and most of the plutonium were recovered by the normal Purex process. The aqueous waste containing Am, Cm, Cf, fission products, Al, and Hg was evaporated and acid was stripped to produce the feed (Table 2). The results are as expected from the laboratory tests excellent recovery of Pu, Am, and Cm but low decontamination factors (DF). 

Neptunium and plutonium are partitioned by reducing Pu(IV) or Pu(VI) to inextractable Pu(III) neptunium is simultaneously reduced to Np(IV). Neptunium is kept in the organic phase by adjusting the acid in the aqueous strip solution (1BX) and the organic-to-aqueous flow ratio to maintain the extraction factor of neptunium greater than one. 

Plutonium purification proceeds by reducing the aqueous phase pH that oxidizes the plutonium to Pu" +, which then extracts into the TBP phase. Impurities stay in the aqueous phase. The TBP phase strip-ping/extraction cycle is repeated to complete the plutonium purification. The uranium is purified using the same TBP/nitric acid extraction/stripping cycle. Careful control of the each element s oxidation state in the extraction cascade produces the plant-scale separations of uranium from plutonium of 10 . Fission product decontamination factor was 10. The plutonium and uranium recovery is about 99.9% with 95% of the nitric acid values and 99.7 /o of the organic solvent recycled. ... 

This ionic liquid, having A AiAi-trimethylglycine as cation and being practically the oxidized form of choline, is able to dissolve large amounts of metal oxides. This metal solubilizing power is selective, making possible separation of metals. Moreover, the metals can be stripped from the ionic liquid by treatment with an acidic aqueous solution. Protonated betaine bis(trifluoromethylsulfonyl)imide can be switched from a hydrophobic IL to a hydrophilic one by temperature or pH control. At high temperature, or under basic condition (pH > 8), this IL and water form a sole phase whereas... 

The acidity of the aqueous strip solution is a very strong variable whose value should be carefully selected in order to effect a compromise among the iron removal, the zinc concentration in the iron product, the stoichiometry of the process, the process rate and the iron-zinc separation index. As demonstrated, it is possible to separate iron from zinc sulfate electrolyte and recover a concentrated, potentially usable form of iron. It is interesting to contemplate the use of galvanic stripping for the removal of other less concentrated impurities or valuable by-products from zinc processing solutions or from other hydrometallurgical streams, eith in conjunction with iron removal or separately. 

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