Process Description
The manufacturing of alums entails just one step additional to the aluminium sulphate process. Practically all alums and aluminium sulphates are now made-from bauxite by reaction with sulphuric acid. The bauxite ore is crushed to a fine powder until 80% passes through 200-mesh; next it is conveyed to storage bins. The reactants are thoroughly mixed and heated with the aid of agitators and live steam in lead lined steel tanks. These reactors are operated in series. In the last reactor, barium sulphide is added in the form of black ash to reduce ferric sulphate to the ferrous and to precipitate the iron. The mixture from the reactors is sent through a series of thickeners. The residue is washed to remove the alum from the residue. The clarified aluminum solution is concentrated in an open, steam coiled heated evaporator from 35o to 59o or 62 oBe. The concentrated liquor is poured into flat pans, where it is cooled and completely solidified. The solid cake is broken and ground to size for dispatch in bags.