Patent ID: 6416723
Filing Date: 2002-07-09
Classification: C01C,C01F,C01G,C01P,C04B

Abstract:
A process for the production of gypsum and an iron oxide pigment from the waste acid accumulating during the production of titanium dioxide by the sulfate process comprisinga) partially neutralizing in a first stage the waste acid with a calcium compound to precipitate gypsum and obtain a remaining solution, b) subsequently further neutralizing the remaining solution in a second stage to precipitate a deposit containing Ti, Al, Cr, V and optionally Fe(III), c) separating the deposit to obtain a solution containing iron sulfate, d) in a third stage adding ammonia and an oxidizing agent to the solution containing iron sulfate thereby forming an iron oxide pigment and a solution containing (NH4)2SO4 and separating the iron oxide pigment and e) liberating ammonia by adding CAO and/or CA(OH)2 to the solution containing (NH4)2SO4 that is obtained after separation of the iron oxide pigment.