Aluminum hydroxide is a widely used flame retardant filler, which has three functions :filling, flame retardant and smoke elimination.Today we will take a cursory look at the industrial production of aluminum hydroxide.

More than 90% of the industrial production is Bayer method production, Bayer method is generally for the relatively high alumina-silica ratio bauxite.The Baeyer process was invented by Austrian engineer Karl Joseph Bayer, whose main principle was to dissolve the alumina in bauxite at high temperatures into caustic soda (a solution of sodium hydroxide), resulting in a solution of sodium aluminate.After the solution is separated from the residue (red mud), aluminum hydroxide crystal seed is added after cooling. After a long time of stirring, aluminum hydroxide is precipitated out of the solution.The same sodium hydroxide solution can be used in the next round of production.

The sintering method is generally to add alkali powder and limestone to  low alumina-silica ratio bauxite, and get sodium aluminate solid by sintering at high temperature, in which iron oxide forms sodium ferrite which is easy to hydrolyze, and silica and calcium oxide form insoluble calcium orthosilicate.Sodium aluminate from the clinker was dissolved with dilute alkali solution and the obtained sodium aluminate solution was separated from red mud.The solution containing part of silicon dioxide was removed to get sodium aluminate refining solution, and then carbon dioxide gas was added to get aluminum hydroxide and mother liquor.The sintering process is aimed at low grade bauxite and consumes only cheap sodium carbonate.Compared with Bayer process, the total recovery of alumina is higher and alkali consumption is lower under the same condition.But the process is complicated, the investment is large, the product alumina quality is poorer, the cost is higher.

In order to make full use of mineral resources, the advantages of the two methods are integrated to improve the alumina recovery rate and reduce the production cost. The two methods are used together, so the combined method is produced.The combined method is divided into series, parallel and mixed method. The parallel method uses the Bayer method to treat higher grade ore and the sintering method to treat lower grade ore.The series method only deals with the red mud produced by the Bayer process by sintering.Adding low grade ore to Bayer red mud can improve production operations. This combination of series and parallel methods is called mixed method.