FREMGANGSMAADE TIL OPLUKNING AF LERJORD

1388976 Aluminium sulphate; purifying water HOECHST AG 11 June 1973 [16 June 1972] 27683/73 Headings C1A and C1C Crude Al 2 (SO 4 ) 3 is produced by adding a suspension of uncalcined clay in H 2 SO 4 to an agitated bed of pre-formed Al 2 (SO 4 ) 3 , produced by reacting clay with H 2 SO 4 , of particle size up to 10 mm. maintained at 300-600‹ C., to give a granular product. The H 2 SO 4 has a concentration of 20-90% by wt. and the H 2 SO 4 /clay wt. ratio if from 0À4 to 1À2 and the H 2 SO 4 : Al 2 O 3 ratio is substantially stoichiometric for Al 2 (SO 4 ) 3 formation. The rate of addition is such that the product has the same particle size as the initial Al 2 (SO 4 ) 3 , preferably 0À1-10 mm. The process may be operated continuously, volatilized H 2 SO 4 being recycled. The reaction time is at least 15 minutes, preferably 30 minutes. The composition, in wt. per cent, of the clay used may be Al 2 O 3 15-40, SiO 2 40-70, Fe 2 O 3 1-10, H 2 O 5-20, and of the product, Al 2 (SO 4 ) 3 40-90, SiO 2 5-40, Fe 2 (SO 4 ) 3 0-10. The crude products which consist of 40 to 90% of Al 2 (SO 4 ) 3 , 5 to 40% of SiO 2 and 0 to 10% of Fe 2 (SO 4 ) 3 may be used as a precipitating agent in effluent water. Alternatively, it may be dissolved and the Al 2 (SO 4 ) 3 solution filtered from the residue.