Bayer process liquors

M.E. Afonso de Magalhaes and M. Tubino, Recovering Gallium from Residual Bayer Process Liquor, JOM 43, 37-39, June (1991). 

Xiao, J.B. Identification of organic adds and quantification of dicarboxyUc adds in Bayer process liquors by GC MS. Chromatographia 2007, 65 (3/4), 185 190. 

Some of the earliest flocculants were based on starch which did find a particular use in the separation of Bayer Process liquors [6], but have since been largely replaced by synthetic flocculants. 

Recovery from Bayer Liquor. The significant amount of primary gallium is recovered from the alumina industry. The main source is the sodium aluminate Hquor from Bayer-process plants that produce large quantities of alumina. Several methods have been developed to recover gallium from Bayer Hquor. 

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

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. 

Fine particulate aluminum hydroxide is obtained either by introducing special seeding processes into the Bayer process or by precipitation processes precipitation from cooled and strongly diluted aluminate liquors. 

The Bayer Process produces a highly alkaline spent liquor which when treated with gaseous CO2 precipitates dawsonite, NaAlC03(0H)2 which can be recovered as a useful by-product or recycled into the Bayer Process. Na and Al MAS NMR, CP and DOR have been used to provide detailed structural information on dawsonite and on the X-ray amorphous phase which occurs as an intermediate in its thermal decomposition to NaA102 (Bastow et al. 1995). The Na and Al NMR spectra of dawsonite from Bayer liquor revealed the presence of the minor impurity phases NaHC03 and Al(OH)3 which were too amorphous to be detected by X-ray powder diffraction. The NMR spectra of dawsonite heated at 350°C for 16 h suggested the amorphous intermediate material contains a mixture of disordered phases related to NaHC03, NaAlOa and an amorphous alumina (Bastow et al. 1995). 

The most common technique used to prepare the /i-type (i.e., or / ") alumina is to mechanically blend the component oxides or precursor compounds in powder form prior to a calcination or prereaction step at temperatures between 1000 and 1260°CT Commercially available aluminum oxide powders (0.3-0.5 pm average crystallite size) in the alpha (corundum) polymorph are typically usedT They are derived from three common sources decomposition of gibbsite [Al(OH)3], which is precipitated from soda liquors in the Bayer process preparation and decomposition of alum salts and preparation from aluminum chloride precursors NaaCOs is usually the source of Na20. Sources of Li20 have included Li2C03, LiNOs, and Li2C204- MgO is usually added as the commercially available oxide. 

In the aluminium industry the most widely used method for the extraction of alumina (AI2O3) from bauxite is the Bayer process, in which aluminium and silica are leached from bauxite under pressure with hot caustic soda. The residue is red mud , a silt-like mixture of iron oxides, titanium dioxide, silica, caustic and many impurities. Roughly one ton of insoluble residue of red mud is produced for each ton of alumina. The liquors, following appropriate treatment to recover alumina, are recycled. In view of its high solubility in nature, it seems that most of the uranium must also be leached and possibly build up in the leach liquors. Small mills are now recovering this Uranium, but analyses of red muds show uranium contents that vary from 12 to 40ppm uranium, which suggest that it is not all leached. 

This represents a specialty filler which contributes to paper brightness, ink receptivity and acts as a flame retardant. The effect on flame retardancy can be explained by the 35% of bound water based on material weight. The bound water is released at temperatures above 150 °C. The raw material source for the production of aluminum trihydrate (ATH) is bauxite. Bauxite is a blend of AI2O3, Fc203, Si02, H2O, Ti02 and other minerals. To produce ATH it is necessary to stabilize the alumina content and to separate out the other minerals. This is done by the so-called Bayer process. After final filtration, the clear liquor of sodium aluminate is seeded with specially prepared fine crystals of ATH. This seeding causes the sodium aluminate to decompose to ATH or Al(OH)3 which forms a precipitate. 

The Bayer process was invented in 1887 by Karl Bayer. Bayer discovered in 1887 that the aluminum hydroxide that precipitated from alkaline solution is crystalline and can be easily filtered and washed. By dissolving aluminum from bauxite, the rest can be separated from the liquor as solids. The aluminum hydroxide is then dried and calcined to give alumina. These inventions sealed the fate of aluminum, and by 1890 the cost of aluminum had tumbled about 80%. The process is still in use today all over the world. 

Also, supernatant solution in the Bayer liquor still contains an appreciable amount of soluble aluminum salt that needs to be removed by electrolysis prior to gallium recovery. This may be done either by treating the solution with lime to precipitate out calcium aluminate or by neutralizing the solution with carbon dioxide to precipitate alumina hydrate (Hudson, L.K. 1965. J. Metals, 17, pp. 948-51). Removal of most aluminum by these processes enhances the concentration of gallium in the solution to a level of approximately 0.1% whereupon the solution may be electrolyzed using an anode, cathode, and cell made of stainless steel. 

Liquid—Liquid Extraction. Among the various extractants available for the recovery of metals from aqueous streams, only 8-hydroxyquinoline derivatives are effective for the recovery of gallium from Bayer liquor. A process has been developed and patented (7—12). Production began in 1980 in Salindres, France, followed in 1989 in Pinjarra, western Australia. 

Ion-Exchange Resins. Some attempts have been carried out to recover gallium by ion exchange (qv). Only the commercially available amidoxime resin has proved to be effective for the recovery of gallium from Bayer liquor. The process has been developed and patented (13) and is reported to be under operation in Japan. 

Once mycelia have been separated via continuous filtration from exhausted production media, citric acid may be recovered by using three different methods, such as direct crystallization upon concentration of the filtered liquor, precipitation as calcium citrate tetrahydrate, or liquid extraction. Since molasses are extremely rich in impurities, direct crystallization cannot be applied unless very refined raw materials, such as sucrose syrups or crystals, are used. The precipitation process (that is based on subsequent addition of sulfuric acid and lime to clarified fermentation broths) is used by the great majority of world citric acid manufacturers, including Archer Daniels Midland Co. (ADM) in the United States. Liquid extraction with mixtures of trilaurylamine, n-octanol, and Cio or Cn isoparaffin was used by Pfizer Inc. in Europe and Bayer Co. (formerly Haarmann Reimer Co., subsidiary of Miles) in the Dayton (OH, USA) and Eikhart (IN, USA) plants only (Moresi and Parente, 1999), even if such plants might have been shut down in 1998. 

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