Purification of Metals

Metals prepared by reduction usually need further treatment to remove impurities. The extent of purification depends on how the metal will be used. Three common purification procedures are distillation, electrolysis, and zone refining. 

Metals that have low boiling points, such as mercury, magnesium, and zinc, can be separated from other metals by fractional distillation. One well-known method of fractional distillation is the Mond process for the purification of nickel. Carbon monoxide gas is passed over the impure nickel metal at about 70°C to form the volatile tetracarbonylnickel (b.p. 43°C), a highly toxic substance, which is separated from the less volatile impurities by distillation  

Pure metallic nickel is recovered from Ni(C0)4 by heating the gas at 200°C  

The carbon monoxide that is released is recycled back into the process. 

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Pentanedione is widely used in extraction processes for the separation and purification of metals because of its abiUty to form covalent metal chelates. It is also used as an intermediate in the production of heterocycHc substances and dyes, as a fuel additive (324), and in metal plating and resin modification. 

Sepa.ra.tion of Plutonium. The principal problem in the purification of metallic plutonium is the separation of a small amount of plutonium (ca 200—900 ppm) from large amounts of uranium, which contain intensely radioactive fission products. The plutonium yield or recovery must be high and the plutonium relatively pure with respect to fission products and light elements, such as lithium, beryUium, or boron. The purity required depends on the intended use for the plutonium. The high yield requirement is imposed by the price or value of the metal and by industrial health considerations, which require extremely low effluent concentrations. 

Other industrial applications of electrolysis include extraction/purification of metals from ores, electroplating, and the manufacture of certain chemicals such as sodium hydroxide. In the latter, sodium chloride solution when electrolysed is converted to sodium hydroxide to produce chlorine at the anode and hydrogen at the cathode. Both of these gaseous by-products are collected for industrial use chlorine is used in the production of bleach and PVC hydrogen is used as a fuel, to saturate fats, and to make ammonia. 

The following pages will describe several examples of pyrochemical processing as applied to the recycle of plutonium, and will briefly review the fundamental chemistry of these processes. We shall review the conversion of plutonium oxide to plutonium metal by the direct oxide reduction process (DOR),the removal of americium from metallic plutonium by molten salt extraction (MSE), and the purification of metallic... 

The subject of the separation and purification of metals with the aid of chitosan has been reviewed by Inoue (1998) who collected data relevant to chitosans modified with chelating functional groups as well [111]. 

A CVD reaction can occur in one of two basic systems the closed reactor or the open reactor (also known as close or open tube). The closed-reactor system, also known as chemical transport, was the first typetobeusedforthe purification of metals. It is a hybrid process which combines vapor-phase transfer with solid-state diffusion. As the name implies, the chemicals are loaded in a container which is then tightly closed. A temperature differential is then applied which provides the driving force for the reaction. 

This is the Mond reaction, first developed by Ludwig Mond in 1890. It is still used forthe production and purification of metallic nickel. A similar reaction is used for the production of Fe(CO)5 but higher temperature is required. 

Metallurgy is the production and purification of metals from naturally occurring deposits called ores. It has an ancient histoiy and may represent the earliest useful application of chemistry. Metallurgical advances have had profound influences on the course of human civilization, so much so that historians speak of the Bronze Age (ca. 

Principally purification and characterization methods of monometallic nanoparticles are directly applied to those of bimetallic nanoparticles. Purification of metal nanoparticles dispersed in solution is not so easy. So, in classical colloid chemistry, contamination is carefully avoided. For example, people used pure water, distilled three times, and glass vessels, cleaned by steam, for preparation of colloidal dispersions. In addition, the reagents which could not byproduce contaminates were used for the preparation. Recently, however, various kinds of reagents were used for the reaction and protection. Thus, the special purification is often required especially when the nanoparticles are prepared by chemical methods. 

Conventional filtration cannot be applied to the separation in purification of metal nanoparticles. If the metal nanoparticles are protected by polymer, however, the membrane filter, which can cut off the pol5mer with certain molecular weight, can be used to separate the polymer protected metal nanoparticles. Free metal nanoparticles which are not protected by polymer can pass through the membrane. Ion filter like cellulose can be used to separate ionic species from the reaction mixtures. 

Purity is an indispensable requirement of any sensitizer in a dye-sensitized solar cell. While well worked out procedures exist for the efficient purification of metal complexes, we found that the isolation of the complexes at their isoelectric point, followed by column purification using Sephadex LH-20 gel, resulted in analytically pure samples. 

COORDINATION CHEMISTRY METHODS USED FOR PURIFICATION OF METAL ALKYL PRECURSORS ... 

Another of the new techniques for extractive preconcentration, separation, and/or purification of metal chelates, biomaterials, and organic compounds is based on the use of surfactant micellar systems. 

Electrolytic purification of metals is considered at length in Chapter 17. In essence, metals can be deposited in high purity from solution on a cathodic surface, by careful control of the voltage and other parameters. The anode can be a billet of the impure metal, and the impurities will either stay in solution or form an insoluble anode slime here, both dissolution and reprecipitation of the desired metal are accomplished in a single electrolytic step. Alternatively, a crude solution of the metal ion might be prepared by some other means, and the pure metal deposited on a cathode with an anode of some inert material the product of electrolysis at the anode will normally be oxygen gas. 

F or some time the United States Department of the Interior has been carrying out a program aimed toward the selection of an economical method of obtaining potable water from sea water. One method investigated at the Battelle Memorial Institute (1) is an adaptation of the zone-purification process which had previously been used satisfactorily in the purification of metals (5). In the process, as applied to purification of sea water, a narrow zone of water is frozen in a tube containing sea water. As this zone is made to traverse the length of the tube, the formation of ice crystals tends to concentrate the salt in the solution ahead of the crystals. This results in the concentration of the salt at one end of the tube and the depletion of salt at the other end. 

Application of metal alkoxides in preparation of oxide materials assumes their high purity, which satisfies the requirements formodem electronic materials. Nevertheless, there are only few works that consider the question of purification of metal alkoxides and that give the characteristics of their purity [522]. Future studies of the syntheses of metal alkoxides should pay special attention to the problems of their purification. 

Simple fractional distillation processes for purification of metalorganics can be employed to remove some of these impurities, but this is a very inefficient approach. A dramatic improvement in the yield of many high-purity metal alkyl compounds resulted from the development of the adduct-purification scheme for the purification of metal alkyls, which was commercially developed by A. C. Jones and coworkers. This process uses the strong tendency of many metal alkyls to form stable adduct compounds with other reactants, thus making a difficult problem that is encountered in the epitaxial growth arena into an useful advantage in the synthetic arena. Actual synthetic and purification routes employed in the manufacture of metal alkyls are proprietary. It is a challenge to develop an optimized synthetic process that has the required purity, efficiency, volume, reproducibility, and yield. 

Electroraffination — (see also electrorefining) Purification of metals by means of dissolution and subsequent electrodeposition. Common method in - electrometallurgy for the removal of impurities from raw metals. Upon anodic dissolution the metallic constituents of the anode are dissolved as cations, oxyanions, or complex ions. All impurities - whether metallic or not - are also dissolved or will fall to the bottom of the cell. At the cathode set to a suitable potential (in most cases only fractions of one volt are needed) the desired metal is deposited. Less noble metals stay in solution, they can be recovered by processing the electrode solution. Metals more noble than the metal under consideration are in most cases not dissolved anodically, instead they settle in the solid deposit at the cell bottom. From this residue they can be recovered. 

The preparation and purification of metal halides for hlgh-temperature spectroscopy present certain difficulties which vary for the different salts. All chemicals used In the present work were "anhydrous salts purchased from Cerac/Pure Inc. AICI3,... 

Purification of metals is another important application of electrolysis. For example, impure copper from the chemical reduction of copper ore is cast into large slabs that serve as the anodes for electrolytic cells. Aqueous copper sulfate... 

The methods of preparation and purification of metal derivatives of 1,3-diketones have been described in a previous volume. Because of the interest in the structure " and reactions of metal derivatives of /3-keto imines, RC0CH2C(=NR )R", it is desirable to consider the methods of preparation of these compounds. Inasmuch as /3-keto imines are closely related to 1,3-diketones and to salicylaldimines, o-HOC6H4CH==NR, the methods of preparation show similarities. Although this review is concerned principally with /3-keto imines, some comparisons with 1,3-diketones and salicylaldimines are made. 

Discuss the importance of electrolysis in the smelting and purification of metals. 

Purification of ores Another application of electrolysis is in the purification of metals such as copper. Most copper is mined in the form of the ores chalcopyrite (CuFeS2), chalcocite (CU2S), and malachite (Cu2C03(0H)2). The sulfides are most abundant and yield copper metal when heated strongly in the presence of oxygen. 

In Section 17.6 we discussed applications of electrolysis in the extraction and purification of metals from their ore sources. Here we examine the electrolysis of water and aqueous solutions. Consider first the electrolysis of water between inert electrodes such as platinum, for which the half-cell reactions are... 

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