TREATMENT OF WASTE ACID

PURPOSE: To efficiently form sulfur oxide to recover the same, in a method mixing and reacting iron oxide with waste acid in the case of the treatment of waste acid containing org. matter and a sulfate group to obtain a solid product and heating the solid product to form sulfur oxide and heating the residue to higher temp., by specifying heating temps. in respective processes. CONSTITUTION: When waste acid containing org. matter and a sulfate group and/or a bisulfate group is treated, at first, iron oxide is mixed with the waste acid containing the org. matter and the sulfate group and/or the bisulfate group to be reacted therewith in a process (i). The solid product obtained in the process (i) is heated to 550-750 deg.C in a process (ii) to form sulfur oxide. The residue in the process (ii) is heated to 800 deg.C) in a process (iii). At this time, iron oxide regenerated in the process (iii) is circulated to the process (i) to be used and the content of sulfur trioxide in sulfur oxide formed in the process (ii) is set to 70% or more.