PURIFYING EFFLUENT AND OBTAINING CALCIUM SULPHATE THEREFROM

摘要

A process for the treatment of aqueous sulphuric acid solutions containing dissolved ferrous sulphate comprising forming such a solution containing from 140 to 220 grams/liter free sulphuric acid in a first zone; adjusting the pH value of the solution in this zone to one in the range 3 to 4 by the addition of finely-divided calcium carbonate thereby precipitating calcium sulphate; passing the slurry thus produced to a second zone; adding to the second zone an aqueous solution of sulphuric acid containing from 3 to 80 grams/liter of free sulphuric acid; adjusting the pH value of the mixture in the second zone to one in the range 3.5 to 6 by the addition of finely-divided calcium carbonate thereby precipitating calcium sulphate and thereafter recovering from the second zone calcium sulphate suitable for use in the manufacture of plasterboard.