Extraction base metal recovery

The Design of Solvent Extractants for Base Metal Recovery... 

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,... 

Applications and process techniques for impregnated resins in base metal recovery on an industrial scale come either directly or after a solvent extraction unit, for (1) refining concentrated metal salt solutions (e.g., by adsorbing interfering heavy metal traces from nonferrous metal electrolytes and (2) extracting special metals from acid to neutral solutions in which the metal ions to be adsorbed are present in low concentration. 

Due to their relevance in solvent extraction and metal recovery, the facilitated transfer of transition metal ions has been investigated by the type of electrochemical methodology described above. This electrochemical approach has in fact proven to be a valuable tool for the study of the mechanism of solvent extraction processes. Wendt et al studied the transfer of Fe, Ni, and Zn assisted by bidentate nitrogen bases, such as phenanthroline and bipyridine. Similar studies were carried out by Wang et al and by Doe and Freiser, who also studied the transfer of cadmium assisted by diphenylthiocarbazone, a weak monobasic acid. Solomon et studied terpyridine as an extractant for transition metals. An interesting result from this type of work is... 

If a neutral chelate formed from a ligand such as acetylacetone is sufficiently soluble in water not to precipitate, it may stiH be extracted into an immiscible solvent and thus separated from the other constituents of the water phase. Metal recovery processes (see Mineral recovery and processing), such as from dilute leach dump Hquors, and analytical procedures are based on this phase-transfer process, as with precipitation. Solvent extraction theory and many separation systems have been reviewed (42). 

The application of these methods is described in some detail for recovery of base metals and platinum group metals in Sections 9.17.5-9.17.6 focusing mainly on solution-based hydrometal-lurgical operations, largely those involving solvent extraction, because the nature of the metal complexes formed is usually best understood in such systems. NB. Extraction of lanthanides and actinides is not included as this subject is treated separately in Chapters 3.2 and 3.3. 

Sulfate process streams are commonly used in metal recovery because they are readily derived by leaching with sulfuric acid or by oxidation of sulfidic ores. Metal recovery from such streams rarely involves the formation of metal sulfate complexes because the sulfate ion is a weak ligand for base metal cations and consequently acidic ion exchange extractants are commonly employed (see Section 9.17.5), which generate sulfuric acid which can be returned to the leaching stage,... 

Whilst carboxylic acids are readily available and inexpensive, they are relatively weak extractants and have not found much use in the recovery of base metals until recently when Versatic 10 has been piloted for the separation of Ni from Mn and Mg (Section 9.17.5.4). As with the phosphorus(V) acid extractants, the propensity for association leads to substantial levels of solvation of caboxylato... 

The use of solvating extractants in the recovery of gold and platinum-group metals (PGM) was described in the previous section. These extractants have also found some specialized applications in the extractive metallurgy of base metals. For example, they have been used in the recovery of uranium, the separation of zirconium and hafnium, the separation of niobium and tantalum, the removal of iron from solutions of cobalt and nickel chlorides, and in the separation of the rare-earth metals from one another. 

The sulfide minerals are at present the major source of the base metals. Associated with most of the sulfide ores are the minerals pyrite and pyrrhotite. If the hydrometallurgical processing of ores becomes the predominant method of metal extraction, the recovery of elemental sulfur as a by-product is a very promising possibility. The formation of elemental sulfur has been observed by many investigators as a reaction product of sulfide minerals under certain experimental conditions. 

Today, hydrometaUurgy is well established as the principal method for extraction of many important industrml metals. Hydrometallurgy for the direct treatment of base metal sulfide concentrates, as a widely used technology, must yet prove itself. The roast-leach electrowinning of zinc is a noteworthy exception and is evolving as standard practice hi the zinc industiy worldwide. Relatively recent developments by way of jarosite and iron oxide hydrolysis and precipitation processes have improved recovery and helped secure zinc hydromemllurgy as standard in the industiy.w... 

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