There are many methods for preparing aluminum hydroxide, such as Bayer process, alkali lime sintering method, ammonium bicarbonate method and so on. In fact, the reaction of alumina is a good preparation method, and the specific reaction process is as follows:
Because alumina is an amphoteric oxide that is difficult to dissolve in water, aluminum hydroxide is an amphoteric hydroxide that is difficult to dissolve in water. They all dissolve in strong acid and strong alkali, but do not dissolve in ammonia water (weak base) and do not dissolve in carbonic acid (weak acid). So we can make the following methods:
1, the alumina solution is dissolved in sulfuric acid, and then the excess ammonia is added into the aluminum sulfate solution, that is, the precipitation of aluminum hydroxide, filtration, washing and drying can be obtained.
Al2O3+3H2SO4=Al2 (SO4) 3+3H2O
Al2 (SO4) 3+6NH3.H2O=2Al (OH) 3 +3 (NH4) 2SO4
2, dissolve alumina in sodium hydroxide to get sodium aluminate solution, and then into sodium aluminate solution into excess carbon dioxide, that is, alumina, precipitation, filtration, washing and drying can be obtained.
It is important to note that the purpose of adding excess ammonia and carbon dioxide is to ensure that alumina can be completely converted into aluminum hydroxide to get a more pure product.