Base metal recovery solvent extraction

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

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. 

Another important technology for the concentration and winning of minerals and metals is solvent extraction. Up to the time of writing there is only one area where RR-based chemicals are used commercially. Tertiary amines (- fatty amines) with short- to medium-length alkyl chains and their - quatenary derivatives form ion pair complexes with certain metals that are dissolved in an aqueous medium. These reagents are widely used for the recovery of uranium, vanadium, nickel and, to a lesser extent, molybdenum. 

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. 

Spent domestic batteries cause environmental repercussions for a number of reasons the presence of soluble heavy metals the increase in their use the short life cycle, and the low efficiency of their recovery and recycling procedures. To improve the situation, a solvent extraction process plant has been built and operated in Spain [15]. It is based on the modified Zincex process (MZP) and has a capacity of processing 2800t/year of batteries in a continuous operation. 

Various processes separate rare earths from other metal salts. These processes also separate rare earths into specific subgroups. The methods are based on fractional precipitation, selective extraction by nonaqueous solvents, or selective ion exchange. Separation of individual rare earths is the most important step in recovery. Separation may be achieved by ion exchange and solvent extraction techniques. Also, ytterbium may be separated from a mixture of heavy rare earths by reduction with sodium amalgam. In this method, a buffered acidic solution of trivalent heavy rare earths is treated with molten sodium mercury alloy. Ybs+ is reduced and dissolved in the molten alloy. The alloy is treated with hydrochloric acid, after which ytterbium is extracted into the solution. The metal is precipitated as oxalate from solution. 

It is apparent from the foregoing discussion that both ILs and supercritical carbon dioxide do indeed offer promise as alternative solvents in the reprocessing of spent nuclear fuel and the treatment of nuclear wastes. It is equally apparent, however, that considerable additional work lies ahead before this promise can be fully realized. Of particular importance in this context is the need for an improved understanding of the fundamental aspects of metal ion transfer into ILs, for a thorough evaluation of the desirability of extractant functionalization of ILs, and for the development of new methods for both the recovery of extracted ions (e.g., uranium) and the recycling of extractants in supercritical C02-based systems. Only after such issues have been addressed might these unique solvents reasonably be expected to provide the basis of improved approaches to An or FP separations. 

Kim, B.M. (1984) Membrane-based solvent extraction for selective removal and recovery of metals. Journal of Membrane Science, 21, 5. 

Reverse osmosis also serves some of the waste management and resource recovery needs in the metals and metal finishing industry. Effluent streams from mining and plating operations containing heavy metals, acids, and other chemicals can be treated with reverse osmosis to recover both the metal as its salt, and purified water for reuse. For metal ion recovery from dilute solutions, however, reverse osmosis faces competition from conventional solvent extraction, membrane-based solvent extraction, and its variant, coupled transport (see Section V.F.3). 

Off-line dicarbamate solvent extraction and ICP-MS analysis [317] provided part-per-trillion detection limits Cd (0.2 ppt), Co (0.3 ppt), Cu (3 ppt), Fe (21 ppt), Ni (2 ppt), Pb (0.5 ppt), and Zn (2 ppt). Off-line matrix removal and preconcentration using cellulose-immobilized ethylenediaminetetraacetic acid (EDTA) have also been reported [318]. Transition metals and rare earth elements were preconcentrated and separated from the matrix using on-line ion chromatography with a NTA chelating resin [319]. Isotope-dilution-based concentration measurement has also been used after matrix separation with a Chelex ion-exchange resin [320]. The pH, flow rate, resin volume, elution volume, and time required for isotope equilibration were optimized. A controlled-pore glass immobilized iminodiacetate based automated on-line matrix separation system has also been described [321]. Recoveries for most metals were between 62% and 113%. 

The solvent extraction process is based on the treatment of the acid leach with an extractant in an organic solvent. The desired metal is then released back into an aqueous phase with strong acid and the final recovery conducted by electrolysis. 

It is used in the mining industry to recover metals such as copper and nickel. Parasite plants, based on solvent extraction, are used in the phosphate industry to recover by-product uranium from crude phosphoric acid. The uranium concentration in phosphoric acid is very low but, because of the high volume of phosphoric acid that is produced to meet agricultural needs, considerable uranium can be recovered using solvent extraction. In the nuclear industry [5], solvent extraction is used to purify uranium and plutonium [using the plutonium and uranium recovery by extraction (PUREX) process], zirconium from hafnium, and for many other applications. It is also used in environmental applications to clean soil, say, to remove polychlorinated biphenyls (PCBs), dioxins, pesticides, and other hazardous pollutants. 

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