Abstract: A process for recovery of reusable chromic acid from waste chromic acid solution containing impurities, which process comprises a first step in which the solution containing chromic acid is introduced into the cathode compartment in an electro-dialysis process and free chromic acid or chromate ions in the above solution are transferred to the anode compartment, a second step in which H.sub.2 SO.sub.4 is added in at least equivalent amounts to the heavy metallic ion contained in the outlet solution, in which chromic acid ion concentration is reduced, in order to convert chemical species of the contained metallic ion and increase the H.sup.+ ion concentration and then chromate ions in the resultant solution are extracted into an organic phase with contact of an organic solvent (A), and a third step in which residual amounts of chromic acid ion remaining in the aqueous raffinate from the second step are extracted into an organic phase with contact of an organic solvent (B).

Abstract: This invention relates to a process for recovery of waste H.sub.2 SO.sub.4 and HCl which are used for pickling metallic materials and articles and contain a large quantities of Fe ions. Furthermore, it offers a process for the recovery of H.sub.2 SO.sub.4 and HCl from waste H.sub.2 SO.sub.4 which contains large amounts of Fe ions after removal of Ti ions by a hydrolysis process in the production of TiO.sub.2 and also for the recovery of high-purity electrolytic iron or iron hydroxide.

Abstract: Production of titanium dioxide which is characterized by recovery of reusable H.sub.2 SO.sub.4, highly pure Fe oxide and hydroxide and fractional recovery of Mn, V and Cr, etc., from FeSO.sub.4. nH.sub.2 O and waste acid of 20 - 40% H.sub.2 SO.sub.4 containing abundant heavy metallic ions, which are by-produced in the production of TiO.sub.2 by dissolution of Ti raw materials such as ilmenite, steel production slag, such as electric furnace slag, convertor slag with H.sub.2 SO.sub.4.