DEHPA acid

Metal ions, amino acids Acidic, pH = 3 DEHPA Acidic, pH = 0 Complexes Counter transport of H+ [57]... 

The extractant is di(2-ethylhexyl) phosphoric acid (DEHPA) in conjuction with trioctyl phosphine oxide (TOPO). Stripping is by ammonium carbonate, and uranium precipitates as ammonium uranyl tricarbonate. The mixture shows a synergistic effect. The mixture is stable, and extracts uranium in hexavalent state. 

The development of more benign alternatives to cyanide for gold-leaching (see Section 9.17.3.1) such as thiourea, thiocyanate, or thiosulfate, which form stable complexes in water has prompted research to identify suitable solvent extractants from these media. Cyanex 301, 302, 272, Ionquest 801, LIX 26, MEHPA, DEHPA, Alamine 300 (Table 5) have been evaluated as extractants for gold or silver from acidic thiourea solutions.347 Whilst the efficacy of Cyanex 301 and 302 was unaffected by the presence of thiourea in the aqueous feed, the loading of the other extractants is severely depressed. Formation of solvated complexes of gold and of an inner-sphere complex of silver has been proposed.347... 

Available information on DEHPA indicates an effect of salt concentration similar to that shown for the carboxylic acids [17]. Figure 7.11 indicates a significant difference between sodium and ammonium salts and solutions containing sodium and ammonium hydroxides. Moreover, below about 5 wt% salt concentration, the solubility becomes uneconomic. However, all the data given in Fig. 7.11 are for alkaline systems. For acid systems... 

In the extraction and separation of zirconium from hafnium in a nitric acid system, using TBP, the system operates best if run at about 10% less than saturation [56]. As saturation of the solvent is approached, a zirconium compound precipitates in the presence of the solvent, causing cruds and emulsions. This problem is also encountered in rare earth circuits using DEHPA. 

Several different flow sheets have been developed around DEHPA, which, as discussed earlier, vary according to the precise composition of the feed material. A typical process using a nitric acid leach of a xenotime ore follows as an example. 

The leach liquor is first treated with a DEHPA solution to extract the heavy lanthanides, leaving the light elements in the raffinate. The loaded reagent is then stripped first with l.Smoldm nitric acid to remove the elements from neodymium to terbium, followed by 6moldm acid to separate yttrium and remaining heavy elements. Ytterbium and lutetium are only partially removed hence, a final strip with stronger acid, as mentioned earlier, or with 10% alkali is required before organic phase recycle. The main product from this flow sheet was yttrium, and the yttrium nitrate product was further extracted with a quaternary amine to produce a 99.999% product. 

The rate of extraction of the lanthanides by the 2-ethylhexyl ester of 2-ethylhexylphosphonic acid (e.g., PC88A, P507) is slower than for DEHPA but the higher distribution coefficients allow extraction from more dilute solutions. Also, as acidic stripping is easier than with DEHPA, the reagent has been used commercially to separate lutetium from terbium and ytterbium. 

For example, the extraction of nickel with di-(2-ethylhexyl)phosphoiic acid (DEHPA) at a pH below 3 is <10%. If the extraction of nickel is carried out between pH 3-4, the extraction of about 0.3gdm Ni will decrease the pH to below 3 and the mass transfer of nickel will stop. For copper, the extraction is performed between pH 2-3 and thus, an amount of 3 g dm Cu will decrease the pH from 3 to 2 and again extraction will stop. 

The extraction of vanadium is performed with a mixture of DEHPA and TBP in kerosene (Fig. 14.8). Half of the raffinate, with a somewhat increased acidity, is returned to leaching. The other half is further treated to... 

In this process [27], the metals are extracted successively by the same extractant, employing suitable pH values for each metal. The spent catalyst is first roasted in an air stream at 300°C to remove oil and sulfur deposited on the surface of the catalyst. Then the metals are dissolved in an ammonium carbonate leach liquor at 80°C. Finally, the three metals are isolated and purified from one another using solvent extraction with an alkylmono-thiophosphoric acid (MTPA) with a structure similar to DEHPA. The following flow sheet was suggested (Fig. 14.19) ... 

DCTA 1,2-diaminocyclohexane tetraacetic acid DBP dibutyl phosphoric acid DTP A diethylenetriamine pentaacetic acid DEHPA di-2-ethylhexyl phosphoric acid... 

Berthod et al. [325] employed countercurrent chromatography with diethyl-hexyl phosphoric acid (DEHPA) reverse micelles in heptane as a stationary phase to extract metaUic cations such as Fa +, Ce, Pr, and Nd + (lanthanide series). This technique was suggested for the application of ion filtering and concentration or for deionization of aqueous phases. Ashrafizadeh et al. [326] re-... 

Synergistic extraction, in the system DEHPA and TOPO, is quite interesting for its ability to extract uranium from high concentrations of phosphoric acid (38). This finds application in the recovery of uranium from dilute phosphoric acid medium in... 

Tachimori, S. 1979. Synergistic extraction of americium with MEHPA-DEHPA mixed solvent from nitric acid solution. J. Radioanal. Chem. 49(1) 31-35. 

Note TBP = tributyl phosphate DEHPA = diethylhexyl phosphoric acid STTA = monothio-thenolytrifluoroacetone DMABR = 5-(4-dimethylaminobenzylidene)-rhodanine TPTZ = 2,4,6-tri(2-pyridyl)-1,3,5-triazine LIX 63 = aliphatic a-hydroxyoxime LIX 65N = 2-hydroxy-5-nonylbenzophenoneoxime LIX 64N = a mixture of LIX 65N with approximately 1% (v/v) of LIX-63. 

In the mid-1960s liquid—liquid extraction processes were introduced and today all large-scale commercial production is done in this way. An aqueous solution of the Ln3+ ions is extracted in a continuous countercurrent process into a nonpolar organic liquid containing tri-n-butylphosphine oxide or bis(2-ethylhexyl)phosphinic acid (DEHPA). Typical separation factors for adjacent rare earths using DEHPA are 2.5 per extraction step so that under automatic multistep or countercurrent conditions purities of 99 to 99.9% are routinely achieved. 

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