Metal extraction technologies

Extraction, a unit operation, is a complex and rapidly developing subject area (1,2). The chemistry of extraction and extractants has been comprehensively described (3,4). The main advantage of solvent extraction as an industrial process Hes in its versatiHty because of the enormous potential choice of solvents and extractants. The industrial appHcation of solvent extraction, including equipment design and operation, is a subject in itself (5). The fundamentals and technology of metal extraction processes have been described (6,7), as has the role of solvent extraction in relation to the overall development and feasibiHty of processes (8). The control of extraction columns has also been discussed (9). 

In order to maintain a definite contact area, soHd supports for the solvent membrane can be introduced (85). Those typically consist of hydrophobic polymeric films having pore sizes between 0.02 and 1 p.m. Figure 9c illustrates a hoUow fiber membrane where the feed solution flows around the fiber, the solvent—extractant phase is supported on the fiber wall, and the strip solution flows within the fiber. Supported membranes can also be used in conventional extraction where the supported phase is continuously fed and removed. This technique is known as dispersion-free solvent extraction (86,87). The level of research interest in membrane extraction is reflected by the fact that the 1990 International Solvent Extraction Conference (20) featured over 50 papers on this area, mainly as appHed to metals extraction. Pilot-scale studies of treatment of metal waste streams by Hquid membrane extraction have been reported (88). The developments in membrane technology have been reviewed (89). Despite the research interest and potential, membranes have yet to be appHed at an industrial production scale (90). 

T0659 Resources Conservation Company, Basic Extractive Sludge Treatment (BEST) T0660 Retech, Inc., Plasma Arc Centrifugal Treatment (PACT) System T0667 RMT, Inc., Metal Treatment Technology (MTTTM)... 

TechXtract is an extraction technology that has been used to remove a variety of contaminants from the surfaces of concrete, steel, brick, and other materials. Target contaminant types include organics, heavy metals, radionuclides, and polychlorinated biphenyls (PCBs). The technology uses proprietary chemical formulations in successive steps to remove these contaminants. The process employs as many as 25 different components in 3 separate chemical formulations that are applied to the contaminated surface and then removed in a multi-step, multicycle sequence. TechXtract is commercially available and has been used at multiple sites. 

DeCaF treats soil, sludges, solids (e.g., slag), residues, and sediments contaminated with radioactive elements and other hazardous constituents. The technology has potential applications in the treatment of heavy metals. The technology can treat uranium-contaminated calcium fluoride matrices, rare-earth ore residues, and fluorspar contaminated with uranium. The technology can also extract more complex fluoride by-products. 

SOLFIX is an ex situ stabilization technology that treats heavy metals by reacting contaminated soils and sediments with cement, pozzolanic materials, and other additives to chemically immobilize contaminants into an insoluble form. SOLFIX can be used either as a stand-alone technology or it can be incorporated with Hydro-SEP (a sediment washing technology) and ORG-X (a solvent extraction technology) into a three-step remediation process termed integrated sediment decontamination system (ISDS). 

A typical sludge analysis is shown in Figure 2. The patented Rostoker, Inc. technology was evaluated with 12 experimental tests utilizing additives for deliberate metals extraction. A summation of the results is presented in Figures 3 and 4. Based on these results, the recovery system shown in Figure 5 is expected to be installed. 

Figure 4.4 Some fluoropolymer derived materials used in SCCO2 technologies (a) copolymer used as stabilizer in emulsion polymerizations of styrene (b) end functionalized polymer used in metal extraction studies (c) a ligand used for homogeneous catalysis in SCCO2.

Moore, J. N., and Luoma, S. N., 1990, Hazardous wastes from large-scale metal extraction a case study Environmental Science Technology, v. 24, p. 1279-1285. 

The oil shale in southwestern Montana occurs in structurally complex folded and faulted mountains. Mining and processing of large quantities of these shales would require difficult subsurface methods. Economical exploitation will depend upon the development of extraction technology that may require the recovery of the multiple resources of hydrocarbons, phosphorous, and the other metals. 

Applications technologies in metal ion, inorganic species, hydrocarbons separations, biochemical and biomedical applications, and fine particles preparation using ELM are reviewed. Commercial applications include the removal of zinc, phenol, and cyanide from wastewaters. Potential applications in wastewater treatment, biochemical processing, rare earth metal extraction, radioactive material removal, and nickel recovery are described. 

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