Abstract: A method for manufacturing titanium oxide, comprising bringing a sulfuric acid solution containing predominantly titanium ion together with one or more kinds of metal ions into contact with an organic solvent containing one or more species selected from the group of oxygen-containing organic solvents, alkyl amines, and alkyl aryl amines to extract the titanium ions in a form of a sulfuric acid complex from the sulfuric acid solution, and bringing the organic solvent containing the extracted titanium into contact with water or an aqueous dilute sulfuric acid solution to inversely extract the titanium from the organic solvent to the water or the dilute sulfuric acid solution and to regenerate the organic solvent.

Abstract: A method for neutralizing a sulfuric acid solution containing predominantly Zn ion, comprising adding, to the sulfuric acid solution, at least one compound selected from the group of chlorine-containing compounds of Na ion, K ion, Mg ion, Ca ion, and NH.sub.4 ion in an amount at least chemically equivalent to SO.sub.4 ion contained; and then bringing the sulfuric acid solution into contact with an organic solvent composed of one or more species selected from the group of oxygen-containing organic solvents and alkylamine organic solvents to extract Zn ion from the sulfuric acid solution as a chloride complex to the organic solvent. The sulfuric acid solution after extraction of Zn ion is further treated by addition of an oxidizing agent or by an electrochemical means to convert Fe.sup.2+ into to Fe.sup.

Abstract: A method for neutralization of sulfuric acid containing Fe ions, comprising adding ions selected from the group consisting of Na ions, K ions, Mg ions, Ca ions and NH.sub.4 ions in the form of a compound containing chlorine to a sulfuric acid solution to be treated in an amount corresponding at least to the chemical equivalent to SO.sub.4.sup.2-, and bringing the resultant solution into contact with an organic solvent containing oxygen or comprising alkylamine for extracting Fe ions from said aqueous solution into the organic phase as chloride complex. Iron chloride can be recovered from the organic phase by distilling or evaporating the organic solvent or by extracting back it into water.