Patent ID: 6861041

Claim:
A process for the treatment of effluents containing at least one metallic sulphate, the process comprising the steps of: 1.) adding a solution of ammonia NH 3 to the effluent to obtain ammonium sulphate (NH 4 ) 2 SO 4 in solution and a precipitation of iron oxy-hydroxides Fe(OH) x wherein x=2 and/or 3; the addition of ammonia enables basification of the effluent to give pH values between 7 and 9.5; 2.) separating the metallic phase Fe(OH) x wherein x=2 and/or 3 precipitated during the previous step from the rest of the effluent; 3.) after separating Fe(OH) x wherein x=2 and/or 3, adding calcium hydroxide Ca(OH) 2 to the effluent to make the sulphate in solution precipitate in the form of hydrated calcium sulphate CaSO 4 ; the added quantity of Ca(OH) 2 satisfying the stoichiometric reaction for the formation of calcium sulphate; 4.) separating the hydrated calcium sulphate CaSO 4 precipitated during the previous step from the rest of the effluent; the residue may be washed and upgraded.