Separation and Concentration Processes

The leaching process produces a solution rich in the primary metal value or values but with an appreciable amount of undesirable impurities. 

There are many methods of separating and concentrating the elements in a given solution as exemplified by the techniques used in analytical chemistry. Oxidation, hydrolysis, and precipitation are among the techniques used in large-scale operation. 

The mass transfer in solvent extraction takes place when a water immiscible organic phase is intimately mixed with an aqueous phase fron which one or more constitutents are transferred to the organic phase Stripping of the loaded organic phase with an aqueous solution concentrate the desired components, while at the same time regenerating the organii solvent for recycle. 

The general characteristics of ion-exchange resin have been presente by Preuss and Kunin (P12) with special emphasis on those used fo uranium recovery. In the selection of ion-exchange resins for use in an  

The resin beads used in most columnar operations range in size from 0.3 to 0.9 mm in diameter, which is a compromise based on the effect of ion-exchange rates, capacities, and hydraulic characteristics. The especially made resins used in resin-in-pulp operations range in size from 0.8 to 1.6 mm in diameter. The apparent density of a resin is defined as that weight of backwashed and settled wet resin per cubic foot, which for resins used in the uranium industry is about 38-45 Ib/ft . In column operations, the attrition losses due to swelling and contraction of resin, abrasion of resin-resin surfaces, and abrasion of resin-equipment surfaces are negligible. In resin-in-pulp operations, an appreciable amount of attrition loss is encountered. 

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That benzene hexachloride isomer mixture is then the raw material for lindane production. The production of lindane per se is not a chemical synthesis operation but a physical separation process. It is possible to influence the gamma isomer content of benzene hexachloride to an extent during the synthesis process. Basically, however, one is faced with the problem of separating a 99%-plus purity gamma isomer from a crude product containing perhaps 12 to 15% of the gamma isomer. The separation and concentration process is done by a carefully controlled solvent extraction and crystallization process. One such process is described by R.D. Donaldson et al. Another description of hexachlorocyclohexane isomer separation is given by R.H. Kimball. 

This book covers several of the emerging areas of separations in biotechnology and is not intended to be a comprehensive handbook. It includes recent advances and latest developments in techniques and operations used for bioproduct recovery in biotechnology and applied to fermentation systems as well as mathematical analysis and modeling of such operations. The topics have been arranged in three sections beginning with product release from the cell and recovery from the bioreactor. This section is followed by one on broader separation and concentration processes, and the final section is on purification operations. The operations covered in these last two sections can be used at a number of different stages in the downstream process. 

The adsorption at the water-air interface is used in separation and concentration processes (foam separation and flotation extraction) [87]. To remove the traces of metals that are present in the anionic form, the method of foam fractionation is used. (The foam is formed during air bubbhng through the water solution of hexade-cyltrimethylammonium bromide) [88]. In this process the selectivity coefficients are determined by the anion hydration energies. 

A similar process has been devised by the U.S. Bureau of Mines (8) for extraction of nickel and cobalt from United States laterites. The reduction temperature is lowered to 525°C and the hoi ding time for the reaction is 15 minutes. An ammoniacal leach is also employed, but oxidation is controlled, resulting in high extraction of nickel and cobalt into solution. Mixers and settlers are added to separate and concentrate the metals in solution. Organic strippers are used to selectively remove the metals from the solution. The metals are then removed from the strippers. In the case of cobalt, spent cobalt electrolyte is used to separate the metal-containing solution and the stripper. MetaUic cobalt is then recovered by electrolysis from the solution. Using this method, 92.7 wt % nickel and 91.4 wt % cobalt have been economically extracted from domestic laterites containing 0.73 wt % nickel and 0.2 wt % cobalt (8). 

During geological time, a number of separating and sorting processes—melting, crystallization, solution, precipitation—have concentrated various elements in local deposits. In these, the elements tend to be grouped together in rather stable compounds. These are called minerals. Many of the minerals have compositions similar... 

Cooperative effects are of considerable interest for high capacity chromatography of BAS, since for practical purposes high-selectivity bonding is possible only in cooperative processes. This is very important for carrying out the sorption, separation and concentration of BAS. 

Ultrafiltration (UF) is used for the separation and concentration of macromolecules and colloidal particles. Ultrafiltration membranes usually have larger pore sizes than RO membranes, typically 1 to 100 nanometer (nm). Operating pressures are generally low (30-100 psig). Applications include electropaints, gray water, emulsions, oily wastes, and milk, cheese, and protein processing. 

Some of the types of equilibria involved in the unit operations separation and concentration are listed in the introduction, Section 9.17.1. Those which depend most on coordination chemistry, and for which details of metal complex formation are best understood, are associated with hydrometallurgy. Once the metal values have been transferred to an aqueous solution, the separation from other metals and concentration can be achieved by one of the following processes.3... 

The Met-Tech separation process is a liquid ion exchange process for the ex situ recovery, separation, and concentration of a wide range of heavy metals. The technology is commercially available and, according to the vendor, has been tested at the pilot scale. According to the vendor, future applications will be in soil remediation, acid mine drainage, and the recycling of spent nuclear waste. 

Long-lived radionuclides occur at extremely low concentrations, especially in environmental samples, therefore several authors have proposed matrix separation and enrichment of the analytes before analysis.21,24,26,3 39 Radiochemical methods often require very careful and time consuming separation and enrichment processes and measurement procedures of a-, (3- and -emitting radioactive species at the trace and ultratrace level using conventional radioanalytical techniques 40-43 Trace/matrix separation, which is performed offline or online in order to avoid possible isobaric interferences, matrix effects and to reduce the detection limits for the determination of long-lived radionuclides, is also advantageous before ICP-MS measurements as the most widely applied mass spectrometric technique. 

For this paper, process modification for the purpose of source reduction in a plating operation will be defined as changes in equipment which lead to reduced generation of wastes. Purposely excluded are separation and concentration technologies covered elsewhere in this conference. The intent of this section is to list options, in rough order of simplicity of implementation, and provide information about each... 

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