| abstract |
Process for the production of gypsum and also of an iron-oxide pigment from the waste acid that accumulates in the course of the production of titanium dioxide in accordance with the sulfate process, characterized in that in a first stage a partial neutralization of the waste acid is effected with a calcium compound subject to precipitation and optionally direct separation of gypsum, subsequently the remaining solution is neutralized further in a second stage subject to precipitation of a deposit containing Ti, Al, Cr, V and optionally Fe(III) and from the solution containing iron sulfate that is obtained after separation of the solids an iron-oxide pigment is produced in a third stage by addition of alkaline compounds and also of an oxidizing agent. |