PROCESS FOR EXPLOITING COAGULATION SLUDGES RESULTED AFTER TREATING SURFACE WATERS WITH ALUMINIUM SALTS

The invention relates to a process of exploiting coagulation sludges resulting from the treatment of surface waters with aluminium salts, as a source of reactive Al compounds for processes of sewage purification, namely for precipitating sulphate ions as ettringite. According to the invention, the process consists in gravitationally or gravitationally and mechanically concentrating the sludge, which is either further used to precipitate sulphate ions from sewage, which ions are contacted with concentrated sludge, while stirring, at a ratio of 0.21...0.50 kg Al for 1 kg of sulphate, as well as with Ca(OH), at pH=11.4...11.7, for 45...120 min, or an extract is obtained from the gravitationally concentrated sludge by contacting it with NaOH, at a dose of 2...3 kg NaOH for 1 kg Al, at a temperature of 23...55°C, for 15...60 min, followed by centrifugation, which is further used to precipitate the sulphate ions in the sewage, at a ratio of 0.19...0.25 kg Al for 1 kg SOand with Ca(OH)at a maximum dose of 2.5 kg for 1 kg of sulphate ions and a reaction time of 15...60 min.