Purifying metals

The purification of the galHum salt solutions is carried out by solvent extraction and/or by ion exchange. The most effective extractants are dialkyl-phosphates in sulfate medium and ethers, ketones (qv), alcohols, and trialkyl-phosphates in chloride medium. Electrorefining, ie, anodic dissolution and simultaneous cathodic deposition, is also used to purify metallic galHum. 

The process objectives defined earlier must relate to the process routes. A process route essentially consists of several sequential steps with the ultimate aim of achieving the process objective. There are one or more of basic objectives, namely, separation, production of a compound intermediate, metal reduction, and metal refining. With a given starting source material the four basic objectives can be pursued singly or in combination to arrive at the ultimate aim. For example, if the ultimate aim is to prepare a concentrate for the market then it is only the separation that is required for reaching to the product. If, on the other hand, purified metal production is the ultimate aim then possibly all the four objectives have to be fulfilled. 

An advantage of the adduct purification method is that it combines chemical purification (forming an adduct) with physical purification when the purified metal alkyl is obtained by distillation, e.g., through a fractionating column. 

Carbon is an excellent reducing agent because it readily combines with oxygen to form CO and COj. Thus, in the form of coke in blast furnaces, it purifies metals by removing the oxides and other impurities from iron. 

Lanthanum in purified metallic state may be obtained from its purified oxide or other salts. One such process involves heating the oxide with ammonium chloride or ammonium fluoride and hydrofluoric acid at 300° to 400° C in a tantalum or tungsten crucible. This is followed by reduction with alkali or alkaline earth metals at 1,000°C under argon or in vacuum. 

Plutonium is recovered from uranium and fission products by solvent extraction, precipitation, and other chemical methods. In most chemical processes, plutonium first is converted to one of its salts, usually plutonium fluoride, before it is recovered in purified metallic form. The fluoride is reduced with calcium metal to yield plutonium. Electrorefining may produce material of higher purity. 

If the actinide metal is available in sufficient quantity to form a rod or an electrode, very efficient methods become applicable eiectrorefining, zone melting, solid state electrotransport. Thorium, uranium and plutonium have been refined by electrolysis in molten salts An electrode of impure metal is dissolved anodically in a molten salt bath, e.g. in LiCl-KCl eutectic the purified metal is deposited on the cathode as a solid or a liquid. 

Charles Wood, a metallurgist and assayer, found in Jamaica some platinum from Cartagena [Colombia], and in 1741 took some of it to his relative, Dr. Brownrigg, After preparing a thorough and accurate description of the metal and its properties, Dr. Brownrigg in 1750 presented these specimens to the Royal Society of London. The exhibit included the ore as found in Nature, the purified metal, the fused metal, and a sword with a pummel made partly of platinum (2). 

A third method Is to hoat tho metal for several hours. to 130°, with a small quantity of commercial nitric acid diluted with twice its volume of pure water. The foreign metals being more easily oxidised than the mercury, are dissolved, and this operation having been repeated as often as required, the purified metal is then washed and dried. "... 

Electrolysis is used to purify metals from metal ores. An example is aluminum, the third most abundant element in Earths crust. Aluminum occurs naturally bonded to oxygen in an ore called bauxite. Aluminum metal wasn t known until about 1827, when it was prepared by reacting bauxite with hydrochloric acid. This reaction gave the aluminum ion, Al3 ", which was reduced to aluminum metal with sodium metal acting as the reducing agent ... 

Most phosphorus and sulfur impurities are removed in a basic oxygen furnace, but the purified metal still contains about 3 percent carbon. For the production of iron, this carbon is desirable. Iron atoms are relatively large, and when they pack together, small voids are created between atoms, as shown in... 

The preparations reported here are all on a 0.5 molar scale and the yields given are typical, within a few percent, of what might be expected by an experienced worker. The preparations can be scaled up or down, but on a small scale the overall yield of a purified metal alkyl is likely to fall significantly from the figure given in the text. 

Metallurgy, the science of extracting and purifying metals from their ores, makes use of numerous redox processes. We ll see in Section 21.2, for example, that metallic zinc is prepared by reduction of ZnO with coke, a form of carbon ... 

The purified metal is hard but malleable and ductile. Its silvery white appearance can be polished to a lustrous finish, and provides about l/4th of the American 5-cent piece. Its corrosion resistance makes it good for coinage. The ancient Chinese produced an alloy called Paktong by smelting ores containing copper, nickel, and zinc thatis now known as nickel silver and is the base for high-grade silver-plated ware. 

Electro preparation 10 Preparation of highly purified metals and methods for electroplating... 

In this cool procedure, you can learn how to make highly purified metals, and the foundations of electroplating. 

Method 2 Preparation of highly purified metal crystals of iron, zinc, nickel, gold, chromium, silver, cadmium, titanium, cobalt, or zirconium using an open cell, and dilute hydrochloric... 

This Regulus is then amalgamated with purified metallic mercury, washed and then distilled. The amalgamation and distillation is repeated seven to ten times and is referred to as letting the eagles fly. The Regulus of antimony will not amalgamate very easily with mercury... 

Electrolysis is used in a wide variety of ways. Three examples follow (1) Electrolysis cells are used to produce very active elements in their elemental form. The aluminum industry is based on the electrolytic reduction of aluminum oxide, for example. (2) Electrolysis may be used to electroplate objects. A thin layer of metal, such as silver, can be deposited on other metals, such as steel, by electrodeposition (Eig. 14-2). (3) Electrolysis is also used to purify metals, such as copper. Copper is thus made suitable to conduct electricity. The anode is made out of the impure material the cathode is made from a thin piece of pure copper. Under carefully controlled conditions, copper goes into solution at the anode, but less active metals, notably silver and gold, fall to the bottom of the container. The copper ion deposits on the cathode, but more active metals stay in solution. Thus very pure copper is produced. The pure copper turns out to be less expensive than the impure copper, which is not too surprising when you think about it. (Which would you expect to be more expensive, pure copper or a copper-silver-gold mixture )... 

Zone refining a method of purifying metals. An ingot of metal passes through an induction heater, and in this way impurities are accumulated in the melted portion of the ingot... 

Most metals are obtained through physical and chemical modiflcation of ores that contain a sufficiently high concentration of the desired metal. Table 3.1 lists some metals, regions of their primary occurrence, and some applications for the metallic materials. Quite often, the processing steps used to isolate and purify metals from ores have a significant impact on the overall microstructure, which will affect the physical properties of the materials fabricated from them. 

Figure 3.1. Schematic of electrometallurgical processes used to purify metals. Shown is the (a) Downs cell used to purify sodium metal and (b) Hall cell used to purify aluminum metal. Reproduced with permission from Chemistry The Central Science, 8th ed., Brown, LeMay, Bursten. Copyright 2002 Prentice-Hall.

In Boerhaave s view alchemy is a respectable part of chemistry, concerned with metals. From the early days of his chemical career Boerhaave was concerned with alchemical experiments aimed at purifying metals. His high admiration for the old alchemists is clear in Boerhaave s correspondence with Cromwell Mortimer, secretary of the Royal Society. The existing correspondence consists of eight letters, six in the hand of Boerhaave and two written by Mortimer. They were written between July 1733 and September 1738, the last letter being written by Boerhaave two weeks before his death. The main topics of the letters are Boerhaave s experiments with mercury, which I shall discuss at a later stage, and the related issue of the trustworthiness of alchemical writings. 

Boerhaave s first experiment on 27 October 1693 is the production of a tincture through mixing and digesting sulphur and oil, soon followed in 1694 by similar experiments involving sal ammoniac, antimony and mercury. On the third of December 1695 Boerhaave wrote the first entry in which he describes how he tried to create gold out of purified mercury and sulphur. In the years between 1693 and 1718 Boerhaave must have changed his mind about the possibility of transmutation as the experiments in the second notebook mainly describe the process of purifying metals, mercury in particular. The results of Boerhaave s mercury experiments have been published in the Philosophical Transactions. Moreover, Boerhaave wrote about them to his friends Bassand and Mortimer, who was also secretary of the Royal Society. 

The methods that have been used to purify metal derivatives of jS-keto imines are surprisingly limited. Generally, recrystallization has been used, with acetone, ethanol, and benzene as common solvents. Very few quantitative solubility data are available. However, the solubilities of 4,4 -(ethylenedinitrilo)di-2-pentanonatocopper(II) and its 1-hydrate in water and in 12% ethanol have been determined at several temperatures. ... 

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