Phosphoric acid metal extraction

Crude phosphoric acid is often black and contains dissolved metals and fluorine, and dissolved and colloidal organic compounds. Suspended solid impurities are usually removed by settling and solvent extraction (using a partially miscible solvent, such as n-butanol, /.so-butanol, or n-heptanol), or solvent precipitation is used to remove the dissolved impurities. The phosphoric acid is extracted, and the impurities are left behind. Back-extraction with water recovers the purified phosphoric acid. Solvent precipitation uses a completely miscible solvent plus alkalis or ammonia to precipitate the impurities as phosphate salts. After filtration, the solvent is separated by distillation and recycled. 

Uses Extractant for recovery of cadmium from phosphoric acid selective extractant for separation of cobalt from manganese, and for impurity cations such as calcium and magnesium complexing agent for extraction of transition metals... 

Alkyl esters of phosphoric acid and phosphine oxides will extract metals and mineral acids by direct solvation. Tri-//-butyl phosphate (TBP) and tri- -octyl phosphine oxide (TOPO)... 

Alternative strategies have also been proposed, in which the metal components are removed from the wood prior to incineration. These include extraction using phosphoric acid (Kazi and Cooper, 2002), ethylenediaminetetracetic acid (Nami Kartal, 2003) or oxalic acid combined with bacterial culture (Clausen, 2004a,b), and electrodialysis (Mateus etal., 2002). 

Di-(2-ethylhexyl)phosphoric acid ( diisooctyl phosphate) [272I5-I0-7] [298-07-7] M 322.4. Contaminants of commercial samples include the monoester, polyphosphates, pyrophosphate, 2-ethylhexanol and metal impurities. Dissolved in n-hexane to give an 0.8M soln. Washed with an equal volume of M HNO3, then with saturated (NH4)2CO3 soln, with 3M HNO3, and twice with water [Petrow and Allen AC 33 1303 1961], Similarly, the impure sodium salt, after scrubbing with pet ether, has been acidified with HCl and the free organic acid has been extracted into pet ether and purified as above. For purification via the copper salt see McDowell et al. [JINC 38 2127 1976]. 

Extractive distillation processes are still widely used for nitric acid concentration. Because the operational and maintenance problems associated with sulfuric acid concentration plants are considerable, and their capital cost substantial, attention has been directed periodically to the use of extractive agents other than sulfuric acid. Phosphoric acid (I) acts like sulfuric acid but poses similar problems of reconcentration. Solutions of certain metallic salts, in particular metallic nitrates, permit similar enhancement of relative volatility and are readily reconcentrated in straightforward evaporation equipment, offering the possibility of a compact integrated concentration process. 

The extraction of some metal ions by di(2-ethylhexyl)phosphoric acid is shown in Figure 9.7 The order of extraction of the divalent metals of the first transition series, viz. Zn > Cr > M > Cu > Fe > Co > Ni > V, shows important differences from that observed with carboxyli acid extractants, particularly with respect to the relative positions of zinc and copper and of coba... 

Organophosphorus acid extractants have found considerable use in recent years for the recovery of uranium as a byproduct in the manufacture of wet-process phosphoric acid. This acid is obtained by the digestion of phosphate rock with sulfuric acid, and typically contains 0.1 to 0.2 g of uranium per litre.120 It has been estimated that, in 1976, the wet-process acid produced in the USA alone contained some 2500t of dissolved uranium 121 this therefore represents a valuable potential source of this strategic metal. 

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... 

Di(2-ethylhexyl) phosphoric acid, used in the TALSPEAK process, which extracts trivalent metallic cations at low acidity by proton exchange. 

As a consequence, the selectivity of extraction of first transition series dications does not follow the Irving Williams order when these reagents are used in base metal recovery. The bis(2-ethylhexyl)ester of phosphoric acid (D2EHPA) shows [1] a preference Zn2+ > Cr21 > Mn2+ > Fe2+ > Co2+ > Ni2+ V2+ which is exploited in the recovery of zinc from primary sources. [69] M2+ ions which form tetrahedral complexes and M3+ ions which show a preference for octahedral donor sets give neutral complexes with 4 1 and 6 1 D2EHPA metal stoichiometries respectively,... 

D. H. Liem On the Solvent Extraction of Metal Ions by Dialkyl Phosphoric Acid and Some Non-Acidic Complexing Agents, Stockholm 1971... 

As well as the broad category of metal extraction processes, there are several inorganic processes involving the extraction of acids. Phosphoric acid has some solubility in organic solvents such as higher alcohols, ethers, and alkyl phosphates, and this can be utilized in several ways. 

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