Bauxite leaching

Gallium Alkaline liquors from bauxite leaching (Bayer process) Extractants 8-hydroxyquinoline derivatives... 

Carbon Dioxide. As the debate of the effect of greenhouse gases rages on, the simple fact remains that carbon dioxide production is one of the known side reactions of most metal-production operations. Carbon is an effective metal reductant. Coke is used to produce pig iron from iron oxide ores and lead from sulfide ores in blast furnaces, carbon electrodes are used to produce aluminum from bauxite leaching products, and coal is used in the reduction of zinc oxide in retorting furnaces. All told, the resulting product of metal reduction is the oxidation of carbon to carbon dioxide. It is important to keep in mind that the production of carbon dioxide has been reduced dramatically since the start of the Industrial Revolution of the late nineteenth-century. This is best exemplified by the history of steel making in the world. 

In 1990, appioximately 66,000 metric tons of alumina trihydiate [12252-70-9] AI2O2 3H20, the most widely used flame retardant, was used to inhibit the flammabihty of plastics processed at low temperatures. Alumina trihydrate is manufactured from either bauxite ore or recovered aluminum by either the Bayer or sinter processes (25). In the Bayer process, the bauxite ore is digested in a caustic solution, then filtered to remove siUcate, titanate, and iron impurities. The alumina trihydrate is recovered from the filtered solution by precipitation. In the sinter process the aluminum is leached from the ore using a solution of soda and lime from which pure alumina trihydrate is recovered (see Aluminum compounds). 

Sodium aluminate [1302-42-7] is another source of soluble aluminum made by leaching bauxite with caustic soda. As with alum, the active species are really its hydrolysis products which depend on the chemistry of the system to which it is added. It tends to raise the pH. It is available both as a soHd and as a solution (see Aluminum compounds, aluminates). 

A commercial process which uses hydrothermal leaching on a large scale is the Bayer process for production of aluminum oxide (see Aluminum compounds). This process is used to extract and precipitate high grade alurninum hydroxide (gibbsite [14762-49-3]) from bauxite [1318-16-7] ore. The hydrothermal process step is the extraction step in which concentrated sodium hydroxide is used to form a soluble sodium aluminate complex ... 

A.lkaline Solutions. The most important example of alkaline leach is the digestion of hydrated alumina from bauxite by a sodium hydroxide solution at 160-170°C, ie, the Bayer process (see Aluminumand aluminum alloys). 

Aluminum. All primary aluminum as of 1995 is produced by molten salt electrolysis, which requires a feed of high purity alumina to the reduction cell. The Bayer process is a chemical purification of the bauxite ore by selective leaching of aluminum according to equation 35. Other oxide constituents of the ore, namely siUca, iron oxide, and titanium oxide remain in the residue, known as red mud. No solution purification is required and pure aluminum hydroxide is obtained by precipitation after reversing reaction 35 through a change in temperature or hydroxide concentration the precipitate is calcined to yield pure alumina. 

Potassium alum is manufactured by treating bauxite with sulfuric acid and then potassium sulfate. Alternatively, aluminum sulfate is reacted with potassium sulfate, or the mineral alum stone, alunite, can be calciaed and leached with sulfuric acid. Alunite is a basic potassium aluminum sulfate... 

Pedersen A process for extracting aluminum from bauxite, which also yields metallic iron. The ore is first smelted in an electric furnace with limestone, iron ore, and coke at 1,350 to 1,400°C to produce a calcium aluminate slag and metallic iron. Aluminium is leached from the slag by sodium carbonate solution, and alumina is then precipitated from the leachate by carbon dioxide. The process requires cheap electricity and a market for the iron. It was invented by H. Pedersen in 1924 and operated at Hoy anger, Norway, from 1928 until the mid-1960s. British Patent 232,930. 

Peniakoff A process for extracting aluminum from bauxite or other aluminous ores. The ore is roasted with coke and sodium sulfate in a rotary kiln at 1,200 to 1,400°C this converts the aluminum to sodium aluminate, which is leached out with dilute sodium hydroxide solution. The basic reactions are ... 

Patermarakis, G. Paspaliaris,Y. (1989) The leaching of iron oxides in boehmite-bauxite by hydrochloric acid. Hydrometallurgy 23 77-90... 

In the Bayer process, the bauxite is leached with hot sodium hydroxide, thus forming a solution of sodium aluminate. After purification this solution is seeded with crystals of gibbsite and cooled. The process steps are summarised in Eqs. (1) and (2) ... 

Alkali leach methods axe exemplified by the Bayer process for the preparation of pure a-A C for electrolysis (Section 17.5) from the mineral bauxite. Bauxite consists mainly of a-AlO(OH) (diaspore) and/or 7-A10(0H) (boehmite), the difference between these being essentially that the oxygen atoms form hep and ccp arrays, respectively. The chief contaminants are silica, some clay minerals, and iron(III) oxides/hydroxides, which impart a red-brown color to the mineral. Aluminum (III) is much more soluble than iron(III) or aluminosilicates in alkali, so that it can be leached out with aqueous NaOH (initially 10-15 mol L 1) at 165 °C under approximately 0.6 MPa pressure, leaving a red mud of iron (and other transition metal) oxides/hydroxides and aluminosilicates ... 

Leaching of ores Cryo processing 100-300 aluminium (from bauxite) technical gases (N2, 02, H2, He. ..) gas liquefaction... 

Versatic acid has been used in Japan to recover indium and gallium from solutions obtained from the leaching of bauxites, zinc minerals, coal ash and flue dusts.40 41-63 Extraction is carried out at a pH value of 2.5 to 4.0 some coextraction of tin(II), iron(III) and aluminum(III) occurs if these metals are present. In the extraction of indium(III) by n-hexanoic acid,64 the predominant species in the organic phase was found to be InA3(HA)3 whereas in the extraction by n-decanoic acid65 the existence of trimeric (InA3-HA)3 and hexameric [InA2(OH)]g species was also postulated. 

Aluminum oxide is produced during the recovery of bauxite, which is crushed, ground, and kiln dried, followed by leaching with sodium hydroxide, forming sodium aluminate, from which alumina trihydrate is precipitated and calcined (Bayer process) (HSDB 1995). 

Bauxite consists of a group of closely related oxides and hydrated oxides, and it is a secondary mineral that results when silica is leached from minerals such as kaolin, Al2Si205(0H)4. The conditions for this type of leaching are favorable in the tropical areas in which bauxite is frequently found. 

In an attempt to upgrade the siliceous bauxites and other aluminous materials, such as clay where the alumina usually is in the form of complex silicates, Skow and Conley (Si 9) considered the removal of the silica by caustic digestion. Prior to leaching, the aluminuous materials were calcined at 970°C, resulting in an optimal removal of silica with little loss in alumina content in the subsequent leaching step. The desilication step is necessary prior to using the raw materials as feed to the standard Bayer process (E3). The pilot plant operation to extract alumina from an anorthosite ore has been reported by St. Clair et al. (S24). 

One of the most important developments in the field of hydrometallurgy has been the application of elevated pressures and temperatures to complex sulfide and oxide ores (B21, F8, G8, M5, M6). The pressure-leaching of bauxite ores by the Bayer process (E3) is probably the first successful commercial application of this technique. The bauxite ore is leached with sodium hydroxide solution with a specific gravity of 1.36-1.4 at 160-170°C for 1 2 hr under a working pressure of 100 psig. The alumina is produced by calcining the aluminum hydrate precipitated from the leach liquor. 

Aluminum, the third most abundant element in the Earth s crust, is mined as bauxite, a mixure of gibbsite, boehmite, and diaspore. These ores occur dominantly in Cenozoic deposits formed by lateritic weathering of aluminous parent rock, which has broken down to leave a high proportion of aluminum-bearing minerals. These deposits are residual in nature, with the balance of the rock constituents removed by selective leaching. These deposits form most commonly in tropical and subtropical areas. 

As an example of the action of water, we can explain the formation of bauxite (hydrated AI2O3) deposits by the leaching away of the more soluble salts from aluminosilicate deposits. The silicate portion is soluble enough in water that it can be leached away, leaving a higher concentration of aluminum. This is shown in the reaction... 

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