Seawater producing magnesium from

Synthetic magnesia is most often produced from seawater, known as seawater magnesia. Seawater contains approximately 1294 ppm Mg. Synthetic magnesia can also be produced from brine wells or lakes which have much higher concentrations of magnesium. Regardless of the source of magnesium, the sea or brine water is treated with hydrated lime, Ca(OH)2, that precipitates Mg(OH)2 ... 

Magnesium hydroxide is commonly produced from seawater, which is rich in Mg2+ ion. The average concentration of Mg2+ in seawater is about 1,300 mg/L. The first step of the process involves removal of interfering substances from seawater, the most notable being the water-soluble calcium bicarbonate. Bicarbonate removal is crucial, as it can form insoluble calcium carbonate, a side product that cannot be separated from magnesium hydroxide readily. Acidification of seawater converts bicarbonate into carbon dioxide, which is degassed by heating. Alternatively, seawater is treated with bme to convert calcium bicarbonate to carbonate ... 

Manufacture Magnesium is manufactured either electrolytically from magnesium chloride (from seawater or salt lakes and salt deposits) or by thermal reduction of ores, such as dolomite, with ferrosilicon. 40% of the magnesium producers in the Western world u.se electrolysis processes. 

Seawater magnesia produced by precipitation of magnesium hydroxide from seawater... 

Figure 5.5 Variation of crystallite size and surface area for magnesium oxide produced from seawater magnesium hydroxide.

Anhydrous magnesium chloride in the molten state has been produced extensively from MgO obtained either from calcined magnesium hydroxide from seawater or from calcined magnesite, as shown in reaction (14.7) ... 

Magnesia can be produced from seawater and magnesium-rich brines. About 60% of the U.S. production... 

The extraction of magnesium chloride from seawater is done first, using solar energy to vaporize a dynamic stream of preconcentrated seawater flowing along an inclined preferential salt separator (PSS). Magnesium chloride salts soluble in seawater will separate as the very end product. Distilled water will be produced as a by-product in this phase. It represents a typical feed of water for hydrogen production by electrolysis. 

Magnesium oxide is also produced from seawater and brines. About 1.28 g of magnesium ions is contained in 1 kg of seawater. A strong hydroxide is used to precipitate magnesium hydroxide from seawater, and the reaction for this precipitation is shown in Equation 12.4. 

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. 

Preparation and Manufacture. Magnesium chloride can be produced in large quantities from (/) camalhte or the end brines of the potash industry (see Potassium compounds) (2) magnesium hydroxide precipitated from seawater (7) by chlorination of magnesium oxide from various sources in the presence of carbon or carbonaceous materials and (4) as a by-product in the manufacture of titanium (see Titaniumand titanium alloys). 

In preparation of MgCl2 from seawater, magnesium hydroxide, Mg(OH)2, is first precipitated from seawater by the addition of dolime or lime. This is then treated with hydrochloric acid to produce a neutralized magnesium chloride solution. The solution obtained is evaporated and converted into soHd magnesium chloride hexahydrate (60,61). 

Metallic magnesium is produced by either chemical or electrolytic reduction of its compounds. In chemical reduction, first magnesium oxide is obtained from the decomposition of dolomite. Then ferrosilicon, an alloy of iron and silicon, is used to reduce the MgO at about 1200°C. At this temperature, the magnesium produced is immediately vaporized and carried away. The electrolytic method uses seawater as its principal raw material magnesium hydroxide is precipitated by adding slaked lime (Ca(OH)2, see Section 14.10), the precipitate is filtered off and treated with hydrochloric acid to produce magnesium chloride, and the dried molten salt is electrolyzed. 

All the magnesium produced in the world currently is derived from its minerals dolomite and carnallite, as well as from the underground brines and seawaters. In most processes, magnesium is recovered from its mineral or brine either as magnesium chloride or converted to the latter for electrolytic production. 

Magnesium oxide also is produced from sea water and subterranean brine. Magnesium ion is precipitated as hydroxide hy treating seawater with calcium or sodium hydroxide following a series of concentration steps (See magnesium). The hydroxide is then calcined to yield oxide. If hrine is the source, it is concentrated, purified and calcined ... 

In the process used by Norsk Hydro, magnesium hydroxide extracted from seawater with the aid of calcined dolomite is mixed with charcoal and magnesium chloride brine and is heated to 1000-1200°C in the presence of chlorine produced during subsequent electrolysis of magnesium chloride. The main reactions are [266]... 

Manufacture Magnesium is found in large quantities in nature. It is produced from different sources from the residual brines of the potash industry, (mainly as its hexahydrate), seawater, salt lakes, brines, magnesium carbonate (and hydrochloric acid) or magnesium oxide (and chlorine). 

As seawater contains about 1294 ppm Mg2+, 3785 L (1000 gal) of seawater would theoretically yield approximately 8 kg (18 lb) of MgO. If lime is used as the precipitating base, then the reaction would require approximately 1.4 kg of lime to produce 1.0 kg MgO. However, when dolime is used, approximately 1.2 kg is required to produce 1.0 kg of MgO. Since the concentration of magnesium ion in brine is generally much higher than that in seawater, it can be seen that a much lower volume of brine is required to produce an equivalent quantity of MgO from seawater. This implies that a plant utilizing brine should require smaller tank capacities. 

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