Metal recovery techniques

Electrolytic recovery (ER) is the oldest metal recovery technique. Metal ions are plated-out of solution electrochemically by reduction at the cathode.34 There are essentially two types of cathodes used for this purpose a conventional metal cathode and a high surface area cathode (HSAC). Both cathodes can effectively plate-out metals, such as gold, zinc, cadmium, copper, and nickel.22... 

In the past, electrochemical metal recovery techniques have been limited by low efficiencies in recovering low concentrations of metal ions from a process effluent. Recent advances in cell design, coupled with the availability of new cathode materials, now make it possible to achieve higher current efficiencies. 

The NaCl-KCl eutectic is used when the pregnant extraction salt is to be processed by aqueous recovery (this is the salt currently used at Rocky Flats because calcium follows americium in the present aqueous recovery process). The NaCl-CaCl system is used when the salt is processed by pyrochemical means to recover the americium and residual plutonium. When the pyrochemical recovery technique is used, the NaCl-CaCl2-MgCl2 salt is contacted with liquid calcium metal at approximately 850°C in a batch extractor. The calcium reduces A111CI3,... 

A widely used metal salt recovery technique is evaporation. With evaporation, plating chemicals are concentrated by evaporating water from the solution. Evaporators may use heat or natural evaporation to remove water.22 28 Additionally, evaporators may operate at atmospheric pressure or under vacuum. 

Precious metal wastes can be treated using the same treatment alternatives as those described for treatment of common metal wastes. However, due to the intrinsic value of precious metals, every effort should be made to recover them. The treatment alternatives recommended for precious metal wastes are the recovery techniques—evaporation, ion exchange, and electrolytic recovery. 

Although the problem of disposal of large amounts of metal waste is faced by most industrialized countries, relatively few centrally located operations for waste recovery have, to date, been started. Sweden still deposits its dewatered metal waste in a simple landfill, although Swedish industry has been in the forefront of developing both hydrometallurgical and pyrometallurgical recovery techniques. The same applies to most European countries however, interest in environmentally safe recovery has increased in recent years and recovery plants are now being considered. 

Inorganic cations, although probably isolated by ion exchange, should not be soluble in the dichloromethane extract of the aqueous eluents and should probably remain therein. The experiment with lead(II) nitrate, which yielded <0.2 of the spiked Pb ion, supported this expectation. Therefore, heavy metal toxicity to bioassay systems should not be a problem for testing organic residues. Conversely, when inclusion of inorganics in a test residue is desirable, other recovery techniques should be considered. 

Onsite extraction Chemical mobilization Chelators or surfactants used to mobilize metals, needs associated recovery technique... 

This technique is referred to by a variety of terms, depending on the application immersion deposition, galvanic deposition (galvanic corrosion), conversion, cementation (in the metal recovery industry), and so on. 

Figure 2. Schematic of the cross section through a number stamped into metal. Removal of metal down to level (a) results in incomplete obliteration although the number may no longer be readily visible because metal has been smeared into the groove forming the number recovery is easiest in this case. Removal of metal to level (b) leaves behind plastically deformed material this is the situation for which recovery techniques, e.g., etching, can bring out the obliterated numbers. Removal of metal down to level (c) removes all metal plastically deformed during the stamping of the number in this case, recovery is impossible.

In substitution reactions, solutions of a salt and an acid with the same anion are fed through alternate compartments of an array of cation-exchange membranes. The dissociated metal ions from the salt are removed and replaced by protons to generate the free acid. For example, amino acids are produced from their sodium salts in this way. Compared with conventional neutralization and recovery techniques, the membrane-mediated process is considerably simpler and gives a higher yield of the purified product. 

The next sections describe three reactor studies with emphasis on the lithium-structure compatibility. HYLIFE is a liquid metal wall (LMW) ICF reactor considered here for electricity production. It has also been adapted to fissile fuel production ( 5). The Tandem Mirror Reactor (TMR) Cauldron Blanket Module is an MCF concept designed to produce hydrogen. The TMR Heat Pipe Blanket Module is designed to produce either hydrogen or electricity. All three studies emphasize materials compatibility with lithium. Tritium recovery techniques and two aspects of lead-lithium liquids are also discussed. 

Size exclusion chromatography (SEC, also known as gel permeation chromatography) is a method of separating compounds of different molecular masses and sizes. Because steric interactions between analytes and the stationary phase are relatively weak, unstable forms of metals can be separated from more stable complexes and from adducts stabilized by ionic interactions. Unfortunately, the process of sorption and ionic interactions between the investigated substances and the stationary phase can decrease metal recovery by as much as 50 % these interactions are also responsible for the instability of retention times [146]. The separation can be performed both in the aqueous environment and in the presence of organic solvents. Because the technique is not selective, it is utilized primarily as the first stage of multidimensional chromatography [147]. 

In addition, a few crystalline phases, such as ice III, IV and VII, are not accessible through the recovery technique and measurements have to be made at the necessary pressures. So far only ice III (having an almost identical structure as ice IX) and VII has been measured under direct pressure [52]. Although this requires the presence of bulky metal pressure cells in the neutron beam, a correct choice of elements (e.g. A1 and a special ZrTi alloy) with high quality background measurements would minimise the problems associated with data reduction processes. 

In view of the unsatisfactory position of nonferrous metals in India, research is proposed on development of roasting techniques, treatment of residues for increased metal recovery, utilization of waste for conservation of metals, imported substitutes, treatment of lower-grade ores to supplement the indigenous supply, and preventing surface tarnishing of metal products. 

Although the overall processes have evolved for specific metals, and leachants, there are principally only two leaching techniques that provide the pregnant leach solution for metal recovery percolation leaching and agitated tank leaching. 

In all Ni-Zn batteries, various techniques aiming at the reduction of the inactive Ni content (e.g., 60% in sintered electrodes) have been proposed. The limited reserves of the metal and the sensitivity of the battery s initial cost to nickel price would require an extremely efficient (—85%) metal recovery program. 

Quantitative measurements were performed by data accumulation at a recycle time greater than 5Tj of the resonance of interest. The spin lattice relaxation times, Tj, of hydrogen on the metal were determined by the inversion recovery technique [3]. Absolute intensities were obtained by referring to a water sample. The reference sample was sealed in a capillary tube of the length of the catalyst samples to account for field inhomogeneities in the NMR coil [2]. 

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. 

NDSX techniques have been deployed in separation science applications such as metal recovery from leach solutions, recovery of precious and strategic metals, and treatment of large volumes of effluents including toxic and hazardous waste generated by chemical industries [33-36]. Recovery of Sb, Cu, and Zn from industrial waste has been reported using NDSX method [37,38]. 

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