Metal extraction processes

The process of extraction requires first smelting (to obtain the crude metal) and then refining. In smelting, iron ore (usually an oxide) is mixed with coke and limestone and heated, and hot air (often enriched with oxygen) is blown in from beneath (in a blast furnace). At the lower, hotter part of the furnace, carbon monoxide is produced and this is the essential reducing agent. The reduction reactions occurring may be represented for simplicity as ... 

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). 

Other Metals. Because of the large number of chemical extractants available, virtually any metal can be extracted from its aqueous solution. In many cases extraction has been developed to form part of a viable process (275). A review of more recent developments in metal extraction including those for precious metals and rare earths is also available (262). In China a complex extraction process employing a cascade of 600 mixer—settlers has been developed to treat leach Hquor containing a mixture of rare earths (131). 

The depressed prices of most metals in world markets in the 1980s and early 1990s have slowed the development of new metal extraction processes, although the search for improved extractants continues. There is a growing interest in the use of extraction for recovery of metals from effluent streams, for example the wastes from pickling plants and electroplating (qv) plants (276). Recovery of metals from Hquid effluent has been reviewed (277), and an AM-MAR concept for metal waste recovery has recentiy been reported (278). Possible appHcations exist in this area for Hquid membrane extraction (88) as weU as conventional extraction. Other schemes proposed for effluent treatment are a wetted fiber extraction process (279) and the use of two-phase aqueous extraction (280). 

A. P. Lama2e and D. Charquet, in K. C. Liddell and co-workers, eds.. Refractory Metals Extraction, Processing and Applications, The Minerals, Metals Materials Society, Warrendale, Pa., 1990, pp. 231—253. 

AH metals come originally from natural deposits present in the earth s cmst. These ore deposits result from a geological concentration process, and consist mainly of metallic oxides and sulfides from which metals can be extracted. Seawater and brines are another natural source of metals, eg, magnesium (see Chemicals frombrine Magnesium and magnesium alloys Ocean raw materials). Metal extracted from a natural source is called primary metal. 

The principle of solvent extraction in refining is as follows when a dilute aqueous metal solution is contacted with a suitable extractant, often an amine or oxime, dissolved in a water-immiscible organic solvent, the metal ion is complexed by the extractant and becomes preferentially soluble in the organic phase. The organic and aqueous phases are then separated. By adding another aqueous component, the metal ions can be stripped back into the aqueous phase and hence recovered. Upon the identification of suitable extractants, and using a multistage process, solvent extraction can be used to extract individual metals from a mixture. 

Soil Leaching. Soil leaching or acid extraction uses acid to solubilize metals for removal from soils, a technique akin to that ia the mining industry. After extraction with an acid such as hydrochloric, sulfuric, or nitric, the soil is separated from the acid, rinsed with water to remove excess acid and metals, dewatered, and neutralized. The acid is regenerated and recycled back to the process. The extracted metals can be precipitated and recovered. 

Bubble formation during metal extraction processes... 

Chlorine and chlorides G SPA Chlorinated hydrocarbons Chloralkali Paper and pulp processing Petrochemicals Metal extraction and refining... 

Kinetic observations for decomposition of some representative transition metal sulphides are summarized in Table 13. Several instances of an advancing interface [contracting volume, eqn. (7), n = 3] rate process have been identified and the rate may be diminished by the presence of sulphur. Diffusion control is, however, believed to be important in the reactions of two lower sulphides (Ni0.9sS. [687] and Cu1-8S [688]). These solids have attracted particular interest since both are commercially valuable ores and pyrolysis constitutes one possible initial step in metal extraction. 

Processes for extracting metals from their ores are generally classified as pyrometallurgical, when high temperatures are used (Fig. 16.12), or hydrometal-lurgical, when aqueous solutions are used. Copper is extracted by both methods. In pyrometallurgical extraction, the enriched ore is roasted ... 

Nathaniel Arbiter and Kenneth N. Han, eds., Gold- Advances in Precious Metals Recovery, Mineral Processing and Extractive Metallurgy Review, vol. 6,1990. 

Water is present in the materials of interest as free water or water of crystallization, or as combined water. The process of dehydration refers to the removal of the water of crystallization, while the removal of combined water is called dehydroxylation because hydroxyl groups in the material are broken down to form water vapor. The dehydroxylation process is very often alternately described as calcination. The drying process used in the present text pertains to both dehydration and dehydroxylation. In the processing of ores for metal extraction, drying essentially implies the removal by evaporation of water which a material holds in it in various forms. 

Chlorination and fluorination, as processes of metal extraction, are important not only because they are effective in liberating metal values from refractory ores but also because the chlorides and the fluorides are excellent interprocess intermediates for metal reduction. The chlorides have the additional advantage of being compounds which may be made very pure by certain additional processes. 

J. C. Sehra and A. K. Suri, Refractory and Reactive Metal Extraction by Fused Salt Electrolysis, High Temperature Materials and Processes, Vol. 11, Nos. 1-4, p. 255,1993. 

Electrorefining Process for Vanadium Metal Extraction, Trans. Indian Inst Metals, Vol. 26, No. 6, p. 24, Dec. 1973. 

When nonrenewable mineral resources are processed for metal extraction and the metals extracted are utilized in various ways and in diverse forms, they become potentially available for reclamation and recycling. Recycled metals produced by the extraction and refining of metallic wastes are known as secondary metals, whereas metals produced from primary ores are termed primary metals. A classification of recyclable metalliferous resources such... 

Secondary metals production may refer to secondary metal extraction or to secondary alloy production. Secondary metal extraction normally extracts one metal from the waste and sells any valuable by-products to other metal extractors or chemical processors. In secondary alloy production, the scrap is blended and refined so as to yield an alloy of the desired chemistry. In both cases it is necessary to deal with various sizes, shapes, and compositions of waste materials and the processing route adopted moreover, the plant where the process is implemented should have sufficient flexibility to handle such widely varying input material. 

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