Hydrofluoric acid metal extraction from

Columbium (also known as niobium) and tantalum metals are produced from purified salts, which are prepared from ore concentrates and slags resulting from foreign tin production. The concentrates and slags are leached with hydrofluoric acid to dissolve the metal salts. Solvent extraction or ion exchange is used to purify the columbium and tantalum. The salts of these metals are then reduced by means of one of several techniques, including aluminothermic reduction, sodium reduction, carbon reduction, and electrolysis.19-21 Owing to the reactivity of these metals, special techniques are used to purify and work the metal produced. 

While the liquid-liquid extraction of inorganic elements as coordination complexes with thiocyanate ions can be traced back to Skey (1867), the extraction from hydrochloric acid into ether of iron(III) (J. W. Rothe, 1892) or gallium (E. H. Swift, 1924) depends on the formation of solvated acido complexes derived from HMC14 extractions of metal complexes from nitric, thio-cyanic, hydrofluoric, hydrochloric and hydrobromic acids were studied exhaustively by Bock and his collaborators (1942—1956).6... 

As might be expected from the quite different types of complexes formed by metals with F-, extractions from hydrofluoric acid (despite the experimental difficulties and hazards) can lead to useful separations within a quite different set of metals as indicated in Figure 8. 

The problem of the speciation of metals in sediments continues to attract attention, both from the point of measurement techniques and from the point of bioavailabihty and, consequently, effects such as toxicity. Some workers prefer to measure total metals after full digestion of sediments with hydrofluoric acid, others favor sequential extractions [84]. The concentrations of heavy metals in coastal sediments are remarkably similar world-wide [85] Cu30pg/g, Ni 30 )ig/g, Pb 40 )ig/g, Zn 120 pg/g, Ag 1 pg/g, Cd 1 pg/g, Hg 0.5 pg/g dry sediment containing at least 20% of silt and clay, respectively. High levels are about... 

The column medium is a polystyrene-divinylbenzene polymer with octylphenyl-N,N-diisobutyl carbamo-ylphosphine oxide extractant adsorbed on the hydrophobic polymer matrix. The carbamoylphosphine oxide functional group is an avid chelator for actinides in 0.16 M or higher concentration nitric acid, whereas alkali and alkaline earth metals are poorly bound. Lanthanides are only retained on the column at much higher nitric acid concentrations (>6 M). Therefore, even these are eliminated from the final matrix under the rinse conditions employed. A very hard base anion ligand is necessary to compete effectively with the carbamoylphosphine oxide ligands and elute actinides, including uranium, in a small volume. In Protocol 1, the fluoride ion from dilute hydrofluoric acid (HF) was chosen for this purpose. 

Fluid handling systems and ultra-purity water (UPW) systems are flushed with UPW, acids, or bases to extract ions and remove the loose particles from surfaces. Diluted hydrofluoric acid is effective in leaching out metals from fluoroplastics. Ultra pure water removes anions and particles. It is not unusual to flush a system with several hundred liters of water. 

Metal extraction results of PTFE and a special grade of PFA are shown in Table 15.12. Extractions were carried out in a 2% by weight nitric acid solution in water for 2 days at 20°C and measured by ICP-MS. The data in Table 15.6 indicate that hydrofluoric acid is more potent than nitric acid. Higher metal con-eentrations are expected if the type of acid is switched from nitric to hydrofluoric or to a higher concentration, longer duration, and increased temperature of extraetion. 

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