Process for purifying wastewater by separating sulphate ion as ettringite with aluminium hydroxylated products recovered from water

The invention relates to a process for purifying usual acidic wastewater such as pit water and industrial wastewater. The process, as claimed by the invention, consists in the recovery of aluminium from wastewater, in one step of semi­-selective precipitation, at a pH of 4.5...5.5, as amorphous hydroxylated
products, mostly Al(OH)3, reacting in the reaction of ettringite formation, and the utilization of the products obtained thereby for precipitating sulphate ions as ettringite, either only after some intermediary treatment steps which allow the concentration of sulphate ions in the water to be reduced by precipitation as CaSO4
x2H2O up to 1 450...1 750 mg/l, or directly in the ettringite precipitation reaction stage for purifying wastewater polluted with sulphate ions.