Loaded organic phase

The purified acid is recovered from the loaded organic stream by contacting with water in another countercurrent extraction step. In place of water, an aqueous alkafl can be used to recover a purified phosphate salt solution. A small portion of the purified acid is typically used in a backwashing operation to contact the loaded organic phase and to improve the purity of the extract phase prior to recovery of the purified acid. Depending on the miscibility of the solvent with the acid, the purified acid and the raffinate may be stripped of residual solvent which is recycled to the extraction loop. The purified acid can be treated for removal of residual organic impurities, stripped of fluoride to low (10 ppm) levels, and concentrated to the desired P2 s Many variations of this basic scheme have been developed to improve the extraction of phosphate and rejection of impurities to the raffinate stream, and numerous patents have been granted on solvent extraction processes. 

The loaded organic phase is stripped of beryUium using an aqueous ammonium carbonate [506-87-6] solution, apparently as a highly soluble ammonium beryUium carbonate [65997-36-6] complex, (NH 4Be(C02)3. AU of the iron [7439-89-6] contained in the leach solution is coextracted with the beryUium. Heating the strip solution to about 70°C separates the iron and a smaU amount of coextracted aluminum as hydroxide or basic carbonate... 

Scrubbing the loaded organic phase with water or ammonia removes HC1, transferring the copper to the pH-swing extractant, e.g., as in,... 

Although silver is not treated by solvent extraction in any of the flow sheets, silver is recovered from aqueous solution in several other situations. For these processes, Cytec developed reagents with donor sulfur atoms to extract this soft element. For example, tri-isobutylphosphine sulfide (CYANEX 47IX) extracts silver from chloride, nitrate, or sulfate media selectively from copper, lead, and zinc [32]. The silver is recovered from the loaded organic phase by stripping with sodium thiosulfate, and the metal recovered by cementation or electrolysis. Silver can also be extracted from chloride solution by a dithiophosphinic acid (CYANEX 301) [33]. 

Few details have been revealed concerning the commercial extraction of beryllium by organophosphorus acids. However, alternative processes involve the stripping of the loaded organic phase... 

In the Dapex process, uranium is usually stripped from the loaded organic phase with a solution of sodium carbonate, which converts the extractant to the sodium salt form, while retaining uranium in solution as sodium uranyl tricarbonate ... 

Both process alternatives use a second cycle of extraction of U022+ by 0.3 M D2EHPA plus 0.075 M TOPO in kerosene. Uranium is stripped from the loaded organic phase with a solution of ammonium carbonate (2 to 3 M), which converts the D2EHPA to the ammonium salt form... 

Organophosphorus acid extractants have also been used commercially to recover thorium from barren solutions obtained from uranium ion-exchange plants. For instance, Rio Tinto Dow Ltd of Canada installed a plant at Elliot Lake in 1959 to extract thorium(IV) from solutions containing only 0.15 g of thorium per litre.137 The loaded organic phase is stripped with 5 M sulfuric acid, from which the product subsequently crystallizes as an acid thorium(IV) sulfate. 

It can be seen from Figure 11 that, by the appropriate choice of the equilibrium concentration of chloride ion in the aqueous phase, separations between certain pairs of metals can be made, for example between copper(II) and manganese(II) at a chloride concentration of 3.0 M, and between cobalt(II) and nickel(II) at a chloride concentration of 6 to 8 M. Furthermore, the metals can be stripped from the loaded organic phase by being contacted with an appropriate volume of water so that the equilibrium concentration of chloride ion in the strip liquor lies on the lower portion of the extraction curve, where substantial aquation of the extracted chlorometallate occurs... 

Uranium can be stripped from the loaded organic phase with a variety of reagents, such as concentrated solutions of sodium chloride, ammonium sulfate, sodium carbonate or ammoniacal ammonium sulfate (equations 54-57). 

Vanadium is recovered from the loaded organic phase by stripping with an ammoniacal solution of ammonium sulfate, which results in the precipitation of the sparingly soluble ammonium metavanadate ... 

The loaded organic phase, containing 20—40 g of tungsten per litre, is washed with water to remove entrained sodium ions, and stripped with aqueous ammonia ... 

Acidification of the leach liquor with sulfuric acid produces solutions containing Mog0264-, which is extracted into a solution of tertiary amine hydrogen sulfate as described previously. Loaded organic phases are stripped with aqueous ammonia to give solutions from which ammonium paramolybdate can subsequently be crystallized ... 

The back-extraction (stripping) of palladium is achieved in the hydroxyoxime process by contacting the loaded organic phase with a concentrated solution of hydrochloric acid (about 6 M), thus causing the reversal of reaction (76). Palladium can be recovered from the strip liquor by the addition of ammonia, and the precipitated Pd(NH3)2Cl2 can be calcined to yield pure palladium metal. In the dialkyl sulfide process, however, the extraction reaction (75) is independent of acidity, and is therefore reversed by the use of aqueous ammonia, which forms a stable cationic complex with palladium(II) ... 

The extraction of gold from PGM solutions by dibutyl carbitol is used by Inco,226 whereas extraction by methyl isobutyl ketone is used by Matthey Rustenburg Refiners.224 In both instances, the extraction of the gold immediately precedes the respective extraction steps for palladium described previously. Base-metal anions, such as FeCl4 , which are extracted at high concentrations of aqueous chloride, can be removed by contacting the loaded organic phase with water or dilute hydrochloric acid. Under these conditions, the base-metal chloro anions are converted to the aquated cations, e.g. 

The solvent extraction of rare-earth nitrates into solutions of TBP has been used commercially for the production of high-purity oxides of yttrium, lanthanum, praseodymium and neodymium from various mineral concentrates,39 as well as for the recovery of mixed rare-earth oxides as a byproduct in the manufacture of phosphoric acid from apatite ores.272 273 In both instances, extraction is carried out from concentrated nitrate solutions, and the loaded organic phases are stripped with water. The rare-earth metals are precipitated from the strip liquors in the form of hydroxides or oxalates, both of which can be calcined to the oxides. Since the distribution coefficients (D) for adjacent rare earths are closely similar, mixer—settler assemblies with 50 or more stages operated under conditions of total reflux are necessary to yield products of adequate purity.39... 

In the TBP process, which was developed in the USA283 and in England,286 zirconium(IV) hydroxide (produced, for example, by the hydrolysis of the material obtained from the caustic fusion of zircon sand) is dissolved in nitric acid to give a solution containing 30-100 g of zirconium (plus hafnium) per litre and 5-8 M free nitric acid. The zirconium is extracted into a 50-60% solution of TBP in a suitable hydrocarbon diluent, the loaded organic phase is washed in 5 M nitric... 

At the Falconbridge Nikkelverk in Norway, iron(III) is extracted from a solution of 4.5 M hydrochloric acid containing nickel (120 g 1 1) and iron, copper and cobalt (2 g 1 1 each). The organic phase consists of a 4% solution of TBP in an aromatic solvent, and two stages of extraction suffice to reduce the iron content of the aqueous phase to 0.005 g l-1. The loaded organic phase... 

After the U/Pu partition stage the uranium loaded organic phase may be back extracted with water or dilute nitric acid to give an aqueous uranium stream which passes to further purification... 

Kolarik Z, Grimm R. Acidic organophosphorous extractants XXIV the polymerization behavior of Cu(II) Cd(II), Zn(II) and Co(II) complexes of D2EHPA in fully loaded organic phases. J Inorg Nucl Chem 1976 38 1721-1727. 

Nickel and cobalt often occur with copper, and must be separated in pure form from hydrometallurgical leach liquors. Organic acid extractants can quite readily separate copper from cobalt and nickel, but the separation of cobalt from nickel is rather difficult. In one Ni/Co separation process, di-2-ethyl hexyl phosphoric acid (D2EHPA) is used as extractant, with strict control of the pH of the aqueous phase to take full advantage of the slightly different equilibrium constants for the Co and Ni reactions. Pulsed column contactors are used rather than mixer-settlers, and nickel impurity is removed from the loaded organic phase by scrubbing it with a cobalt-rich phase. 

---