Seawater magnesium metal, extraction

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. 

Dow seawater A process for extracting magnesium from seawater. Calcined dolomite (CaO-MgO, dololime), or calcined oyster shell, is added to seawater, precipitating magnesium hydroxide. This is flocculated, sedimented, and filtered off. For use as a refractory it is calcined for the manufacture of magnesium chloride for the manufacture of magnesium metal, it is dissolved in hydrochloric acid. Developed by the Dow Chemical Company and later operated by the Steetly Company in West Hartlepool, UK, and Sardinia. 

The proposed process offers a scheme that provides three products as compared to one product only by the Solvay process. Magnesium chloride is an important product for the manufacture of magnesium metal. As a matter of fact, one can claim that the proposed process could compete with the well-known Dow process for the extraction of magnesium chloride from seawater. 

Table 1 gives the average metal content of the earth s cmst, ore deposits, and concentrates. With the exceptions of the recovery of magnesium from seawater and alkaU metals from brines, and the solution mining and dump or heap leaching of some copper, gold, and uranium (see Uranium and uranium compounds), most ores are processed through mills. Concentrates are the raw materials for the extraction of primary metals. 

Ke and Regier [71] have described a direct potentiometric determination of fluoride in seawater after extraction with 8-hydroxyquinoline. This procedure was applied to samples of seawater, fluoridated tap-water, well-water, and effluent from a phosphate reduction plant. Interfering metals, e.g., calcium, magnesium, iron, and aluminium were removed by extraction into a solution of 8-hydroxyquinoline in 2-butoxyethanol-chloroform after addition of glycine-sodium hydroxide buffer solution (pH 10.5 to 10.8). A buffer solution (sodium nitrate-l,2-diamino-cyclohexane-N,N,N. AT-tetra-acetic acid-acetic acid pH 5.5) was then added to adjust the total ionic strength and the fluoride ions were determined by means of a solid membrane fluoride-selective electrode (Orion, model 94-09). Results were in close agreement with and more reproducible than those obtained after distillation [72]. Omission of the extraction led to lower results. Four determinations can be made in one hour. 

Magnesium (Mg) is a valuable metal used in alloys, in batteries, and in the manufacture of chemicals. It is obtained mostly from seawater, which contains about 1.3 g of Mg for every kilogram of seawater. Referring to Problem 1.69, calculate the volume of seawater (in liters) needed to extract 8.0 X 10 tons of Mg, which is roughly the annual production in the United States. 

A series of commercial styrene-divinylbenzene copolymers called Amberlite XAD (Rohm and Haas Co., Philadelphia) has been used as a base to immobilize a variety of complexing agents (269). On XAD-2, tri-/i-octylamine (270), several ferroin-type chromogens (277), and phenylarsonic acid (272) have been used to concentrate and separate several trace species from seawater and fresh water. An EDTA ligand (273) and phenylarsonic acid on XAD-4 can also extract trace metals such as Cr(III), Pb(II), Hg(II), U(VI), Zr(IV), and Zn(II) at the sub-parts-per-billion levels, even in the presence of excess calcium and magnesium if the pH is less than 3.0. 

One advantage of chitosan in chelating transition and post-transition metals is the low activity shown for magnesium and other alkaline earths, which makes it very useful for the analysis of seawater copper and zinc have been preconcentrated from 10 liters of seawater into 5 ml prior to analysis (344). Another report indicates a more efficient extraction from pH 3-5 ammonium-sulfate solutions of Cr(III), Fe(III), Ni(II), Cu(II), Zn(II), and Hg(II) (350). Although a chitosan membrane has a lower capacity than the powdered material. 

Barraclough, K.C., Steelmaking Before Bessemer, Vol. 2, Crucible Steel, The Metals Society, London, U.K., 1984,87,299. Chesney A process for extracting magnesium from seawater. Developed by British Periclase in 1937. 

Some metal salts, such as NaCl, are quite soluble in water, while others, such as AgCl, are not very soluble at all. In fact, so little AgCl dissolves in water that this compound is generally considered to be insoluble. Precipitation reactions occur when certain cations and anions combine to produce an insoluble ionic solid called a precipitate. One laboratory use of precipitation reactions is in identifying the ions present in a solution, as shown in Figure 5-7. In industry, precipitation reactions are used to manufacture numerous chemicals. In the extraction of magnesium mefal from seawater, for instance, the first step is to precipitate Mg " " as Mg(OH)2(s). In this section, the objective is to represent precipitation reactions by chemical equations and to apply some simple rules for predicting precipitation reactions. 

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