Magnetite and Dolomite Processing Line For Sale in Uited States
There are ten magnesium compound producers in the United States. Each of the facilities obtains its raw source material from either magnetite, lake brines, well brines, or seawater. In addition, there are three facilities that produce magnesium metal. Magnesia, the primary magnesium compound, is produced at three facilities. Exhibits 1 through 3 present the na mes and locations of f acilities involved in the prod uction of magnesium , magnesium meta l, and magnesia from br ines, re spect ively.
Magnetite and dolomite, which have a theoretical magnesium content of 47.6% and 22%, respectively, comprise the largest mineral sources of magnesium and magnesium compounds. Other sources of magnesium and its compounds include seawater, brines, and bitterns.
Magnesium and its alloys are used in th e manufactu re of structural com ponents for automob iles, trucks, aircraft, computers, and power tools. Because of its light weight and ease of machinability, magnesium is used by the iron and steel industry for external hot-metal desulfurization and in the production of nodular iron. Producers of several nonferrous meta ls often use magne sium as a reduc ing agent. Magne sium anodes are used for cathodic protection of underground p ipe and water tanks. Small quantities of m agnesium are u sed as a catalyst in the synthesis of organic compounds, as p hotoengraving plates, a nd in alloys (other than alu minum). Caustic m agnesia can b e used as a ce ment if combined with magnesium chloride.
Refractory magn esia represen ts the largest use of ma gnesium in compou nds. It is used principa lly for linings in furnaces and auxiliary equipment used to produce iron and steel. Caustic-calcined magnesia (partially calcined magnesite) is used in the agricultural, chemical, construction, and manufacturing industries.
The most commonly used source for magnesia is magnesium carbonate, with the largest source being magnesiarich brines and seawater. Magnesite is one of the minerals directly and widely exploited for its magnesia content. When pure, it contains 47.8% magnesia and 52.2% carbon dioxide. Sintered magnesia is used for refractory manufacturing while lighter fired caustic magnesia is used in fluxes, fillers, insulation, cements, decolorants, fertilizers, chemicals, in the treatment of waste water including p H control, and in the removal of sulfur com pounds from gas e xhaust stacks. In addition to naturally occurring magnesia, refractory grade magnesia can also be produced synthetically. This involves the calcination of either magnesium hydroxide or magnesium chloride.
Electrolytic Production
Hydrous Magnesium Chloride Feed. The Dow Chemical Company is the only magnesium producer using hydrous magnesium chloride as feed for the electrolytic cells. A f low sheet of the Dow process is presen ted in Exhibit 4. In this process, magne sium is precipitated from seawater as magnesium h ydroxide by addition of lime or c austic in large agitated flocculators. The magnesium hydroxide is then settled in Dorr thickeners. The overflow enters the plant wastewater system where it is neutralized and returned to the ocean. The thickened underflow is pumped to rotary filters where it is dewatered, washed, and reslurried with wash water from the magnesium chloride purification step. It is then pumped to the neutralizers where it is treated with hydrochloric acid and enough sulfuric acid to precipitate excess calcium as ca lcium sulfate. The brine is filtered to remove calcium sulfate a nd other solids such a s clays and silica and is further purified to reduce sulfate and boron and f orwarded to the d ryer. The purified brine is dried by direc t contact with combustion gases in a fluid-bed dryer to produ ce granules of ma gnesium chloride. T he granules are stored in large tanks from which they are fed to the electrolytic cells. The cells are fed semicontinuously and produce both magnesium and chlorine. The dilu te, wet chlorine gas is dr awn into refrac tory regenerative furn aces and con verted to HCl whic h is recycled to neutra lize magnesium h ydroxide. The ma gnesium collects in com partments in the fr ont of the cell from which it is periodically pum ped into a compute r-controlled crucible car operating at grou nd level. The cru cible is conveyed to the castin g house where it is em ptied into a holding furn ace or into alloying pots from wh ich the metal is pumped into molds on continuous mold conveyors.
Surface Brine Fe ed. A second process for magnesium production, shown in Exhibit 5, utilizes surface brine from the Great Salt Lake as feed to a series of solar evaporation ponds. This brine is further concentrated and treated with CaCl2. Solids such as calcium sulfate and potassium and sodium chlorides are removed in a thickener. Further concentration provides feed for the spray dryer whose waste gases provide heat for the concentration process. The spray dryers convert the brine into a dry MgCl2 powder containing about 4% magnesia, 4% water, and other salts which comprise the cell bath. The dryers are heated with exhaust gases from gas-fired turbines that generated some of the power used to operate the cells. The spray-dried MgCl2 powder is melted in large reactors an d further purifie d with chlorine and other reactants to remove magnesium oxide, water, bromine, residual sulfate, and heavy metals. The molten MgCl2 is then fed to the elec trolytic cells. Only a part of the ch lorine produced is required for chlor ination, leaving up to 1kg/kg magnesium produced available for sale as byproduct chlorine.
Underground Brine Feed. A third process for magnesium rec overy uses undergrou nd brines as its sourc e of raw material. Brine is pumped from below the ground into a large system of plastic-lined solar evaporation ponds, where the magnesium chloride concentration is increased to 25% which reduces the solubility of sodium chloride to 1%. The brine is then moved by pipeline to the plant where it is further concentrated, purified, and spray dried. The spray-dried feed is further purified by chlorination. The magnesium chloride is electrolyzed in diaphragmless cells and the molten magnesium is removed by vacuum ladle. It is then transported to a refining furnace where it is cast into ingots. The chlorine is collected, cleaned, and liquefied.6 Exhibit 5 presents a flow diagram of the process for recovering magnesium from underground brines and surface brines.