Aluminum hydroxide is a hermaphroditic hydroxide, which can react with acid and can react with strong alkali. Therefore, there are many kinds of preparation methods, such as laboratory method, industrial production method and so on, and the reaction of raw materials and different substances can be made.
1, ammonium bicarbonate method
Ammonium bicarbonate method is used to add alkali solution in the aluminum sulfate solution and agitated. The precipitates are washed, filtered, and dried at low temperature. The dried paste can also be used as a product directly. In the process of preparation, the concentration of solution, temperature, control of reaction temperature and drying temperature affect the quality of products. Ammonium bicarbonate is used to produce aluminum sulfate by sulfuric acid and aluminum or aluminum ash. Then, aluminum hydroxide is prepared by metathesis reaction with ammonium bicarbonate.
Its 2Al (OH) 3+3H2SO4, A12 (SO4) 3+6H2O+A12 (SO4) 3+6NH4HCO3, 2AI (OH) 3+3 (NH4), sodium aluminate and aluminum ash are reacted above 100 degrees centigrade to prepare sodium aluminate solution. Sulfuric acid and aluminum ash react with 1.25:1 at 110 C to produce aluminum sulfate solution. Then the sodium aluminate solution and the aluminum sulfate solution are neutralized to pH6.5, and the aluminum hydroxide is precipitated. After washing and pressing, it is dried for 12h at 70~80 C and then crushed to get the finished product of aluminum hydroxide.
Its A12O3+2NaOH, 2NaAlO2+H2O+Al2O3+3H2SO4, A12 (SO4) 3+3H2O+6NaAIO2+A12 (SO4) 3+3H2O+6NaAIO2+A12 (SO4) 3+12H2O - 8Al (OH) 3 +3Na2SO4 recovery method reacts the recycled aluminum trichloride through water, decolorizing activated carbon and filtering impurities, and reacts with sodium carbonate to produce aluminum hydroxide. Then the aluminum hydroxide is obtained by filtration, washing and drying.
Reaction of 2, four sodium hydroxy aluminate with excess carbon dioxide
Na[Al (OH) 4]+CO2 (over) =NaHCO3+Al (OH) 3
3, the reaction of soluble aluminum salt and ammonia water to prepare Al (OH) 3
AlCl3+3NH3. H2O=Al (OH) 3 +3NH4Cl
Al2 (SO4) 3+6NH3. H2O=2 Al (OH) 3 +3 +3 (NH4) 2SO4 (Al3++3NH3. H2O=Al (H2O=Al) 3 x)
Because strong base (such as NaOH) is easy to react with Al (OH) 3, so the laboratory does not use strong alkali to prepare Al (OH) 3, but uses ammonia water.
Excess carbon dioxide does not react with aluminum hydroxide to ensure that [Al (OH) 4]- all forms aluminum hydroxide.
The above three methods are commonly used. In addition, aluminum hydroxide can be prepared by Bayer process, alkali lime sintering method and Bayer sintering method. However, in the process of preparation, these methods are simple and complex.