Alum Recovery from Water Treatment Sludges

Abstract

The potential for reclamation of aluminium sludge as liguidalum was investigated. Batch extraction with sulphuric acid, sodium hydroxide and limeindicated that liquid alum production was feasible. Sulphuric acid was used to depress the pH of the sludge to 3 and recover about 80 per cent of alum in the sludge. At this pH level the metal impurities and the organic content of the recovered alum was at a minimum value. The build up of these impurities during recycling the alum canbe controlled by means of a continious blowdawn. Sodium hydroxide extraction was optimized at pH range of 11,3 to 11,9. Eventhough, good recovery rate was obtained at this pH level the impurities are very significant. Partial recycling of alum by using lime is useful in pH adjustment during the water treatment process. The result of this investigation has practical value for further design study of the recovery process. /Kir09