Abstract: A method for reprocessing waste acid from methods for producing nitro-aromatics, in particular for producing dinitrotoluene (DNT) or trinitrotoluene (TNT), to recover concentrated and purified sulfuric acid and nitric acid, wherein in a first stage, the waste acid is separated in a stripping column countercurrently with water vapor from the bottom of the stripping column into at least one vapor phase, which contains nitric acid and possibly nitro-organics, and a pre-concentrated sulfuric acid, and the vapor phase and the pre-concentrated sulfuric acid are condensed and/or reprocessed in downstream method stages, wherein in the first stage of the method, in addition to the stripping, the nitric acid contained in the stripping vapor is concentrated in the presence of additional concentrated sulfuric acid so that nitric acid in a highly concentrated form suitable for feeding back into the nitration process is obtained directly in the first stage.

Abstract: A method for recovering diluted waste sulfuric acid by extractive rectification with concentrated sulfuric acid which is re-concentrated for reutilization. Waste sulfuric acid from the nitration process is fed into a first column, optionally together with another waste sulfuric acid in a DNT washing acid, and divided into an overhead product containing nitric acid and nitro-organic compounds and a prepurified sulfuric acid in the bottom product. The prepurified sulfuric acid withdrawn from the bottom of the first column is fed to the top of a second column, into the bottom zone of which another waste sulfuric acid is fed in the form of a diluted sulfuric acid recovered from the nitric acid concentration system so the prepurified sulfuric acid from the first column is further purified in the second column and is preconcentrated along with the diluted sulfuric acid recovered from the extractive rectification of nitric acid.