D2EHPA

Nickel and Cobalt. Often present with copper in sulfuric acid leach Hquors are nickel [7440-02-0] and cobalt [7440-48-4]. Extraction using an organophosphoric acid such as D2EHPA at a moderate (3 to 4) pH can readily take out the nickel and cobalt together, leaving the copper in the aqueous phase, but the cobalt—nickel separation is more difficult (274). In the case of chloride leach Hquors, separation of cobalt from nickel is inherently simpler because cobalt, unlike nickel, has a strong tendency to form anionic chloro-complexes. Thus cobalt can be separated by amine extractants, provided the chloride content of the aqueous phase is carefully controUed. A successhil example of this approach is the Falcon-bridge process developed in Norway (274). 

Solvent Extraction. Liquid—hquid extractioa, well known ia the chemical iadustry, was first used ia extractive metallurgy for the processiag of uranium. When a dilute solution of uranium is contacted with an extractant such as di(2-ethylhexyl) phosphoric acid (D2EHPA) or R2HPO4, dissolved ia... 

PoUowing further development (38), a two-cycle process has been adopted by industry. In the first concentration cycle, the clarified feed acid containing 100—200 mg/L U Og [1334-59-8] is oxidized, for example, with hydrogen peroxide or sodium chlorate [7775-09-9] to ensure that uranium is in its 6+ valence state is not extracted. Uranium is extracted with a solvent composed of 0.5 Af D2EHPA and 0.125 Af TOPO dissolved in an aUphatic hydrocarbon diluent. 

Raffinate acid from the first cycle, containing approximately 7 to 14 g/L U Og is then reoxidized and re-extracted in the second, purification cycle using a solvent containing 0.3 Af D2EHPA and 0.075 AfTOPO. The loaded solvent is washed with iron-free acid to remove iron and then with water to remove extracted and entrained acid. The solvent is stripped with ammonium carbonate [506-87-6] to yield ammonium uranyl tricarbonate [18077-77-5] which is subsequendy calcined to U Og (yellow cake). The stripped solvent is regenerated with mineral acid before recycling (39). 

Beginning in approximately 1975, both IMG and Ereeport Minerals operated large uranium recovery plants in the United States using this technology. Several plants continue to mn but a number have been closed because of the depressed uranium prices that resulted when uranium from the former Soviet Union flooded Western markets. A relatively small plant is operated by Prayon in Belgium (40). TOPO is available from Cytec Industries Inc. as CYANEX 921 extractant. D2EHPA is available from Albright Wilson Ltd. and is also sold by Daihachi as DP-8R. 

It is interesting to note that some metal ions may exist in solution partly as cationic and partly as anionic species. The uranyl ion is a good example. From sulfate solution it is possible to extract species such as U02(S04)2 with amines. The uranyl cation, on the other hand, can be extracted with acidic extractants such as D2EHPA. 

The extractant is a commercial mixture of mono- and dioctyl phenyl phosphoric acid (OPPA). It is used in conjuction with tributyl phosphate (TBP). Stripping is by ammonium carbonate solution. The mixture shows synergism. Uranium is extracted in the tetravalent state. The process is much less expensive and possesses a higher extracting power than D2EHPA-TOPO combination. 

For divalent metals which readily form tetrahedral complexes and for trivalent metals which show a preference for octahedral donor sets, neutral D2EHPA complexes are formed with 4 1 and 6 1 ligand metal stoichiometries respectively,... 

The use of D2EHPA to purify and concentrate ZnS04 electrolytes from which the majority of the iron has been removed by precipitation has received much attention, forming the basis of the ZINCEX processes.165,190 These processes have been developed to treat a range of primary and... 

The use or safe disposal of the iron residues from zinc production (see Figure 7) presents a major technical problem.204 The use of chelating aminomethylene phosphonic acid extractants such as (28) and (29) to recover iron from these residues has been proposed.205 These give much higher FenI/Znn selectivity than D2EHPA but are more difficult to strip. A reductive-stripping process is proposed.187,205... 

D2EF1PA is thus a poor extractant for nickel as this shows a preference for a pseudo-octahedral structure in which two axial ligands are either fully protonated extractant molecules, fully protonated extractant dimers, or water molecules depending on extractant concentration, and four equatorial sites are occupied by deprotonated isolated D2EHPA molecules. 

Calculated R-P-R angles and dihedral angles between the RPR and OPO planes in D2EHPA,... 

Cheng, C. Y. Purification of synthetic laterite leach solution by solvent extraction using D2EHPA. Hydrometallurgy 2000, 56, 369-386. 

Sarangi, K. Reddy, B. R. Das, R. P. Extraction studies of cobalt (II) and nickel (II) from chloride solutions using Na-cyanex 272. Separation of Co(II)/Ni(II) by the sodium salts of D2EHPA, PC88A and Cyanex 272 and their mixtures. Hydrometallurgy 1999, 52, 253-265. 

L-Phenyl- alanine Di-2-ethylhexyl phosphoric acid (D2EHPA) H2SO4 Counter-trans-port of H+ ELM Concentration as cation [47]... 

Phenylalanine and Lysine D2EHPA KCl in receiving phase Counter-trans- BLM (RFP) port of K+ - Continuous extraction and concentration [96]... 

Di- and tripeptides D2EHPA HCl Counter-trans- ELM port of H - Concentration and permeation depends on hydrophobicity scale [97]... 

The use of organophosphorus acids, such as di(2-ethylhexyl)phosphoric acid (D2EHPA di(2-ethylhexyl) monohydrogen phosphate 2 R = C4H9CH(Et)CH2), is now well established in the recovery of base metals. This reagent has found commercial application in the separation of cobalt from nickel,67 68 the separation of zinc from impurities such as copper and cadmium,69 the recovery of uranium,68 beryllium70 and vanadium,71 and in separations involving yttrium and the rare-earth metals.72 73... 

The Nippon Mining Co. refinery in Japan, which had previously used D2EHPA to extract cobalt from solutions obtained in the leaching of a mixed cobalt—nickel sulfide in sulfuric acid, changed in 1978 to the new extractant 2-ethylhexyl 2-ethylhexylphosphonate enabling a much-improved selectivity for cobalt over nickel to be obtained.8990 The process is carried out in three counter-current stages with an organic solution of phosphonic acid that has been converted to the ammonium salt by contact with aqueous ammonia ... 

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