In a process for workup of mixed acid and wastewater from the nitration of aromatics in which the nitric acid present is converted by reaction with an aromatic under adiabatic conditions, a. at least one waste stream component selected from waste acid (mixed acid) generated in the nitration, acidic washing water from the workup of crude nitroaromatics and dilute nitric acid generated in an off-gas treatment in the course of the nitration is provided, b. the at least one waste stream component is mixed with re-concentrated sulfuric acid, c. an aromatic is added to the mixture in stoichiometric excess based on the nitric acid, d. the obtained reaction mixture is reacted in an adiabatically operated reactor, e. the obtained organic phase is separated from the sulfuric-acid-containing phase in a separator, f. the sulfuric-acid-containing phase is concentrated under vacuum and g. at least one substream of the re-concentrated sulfuric acid from step g) is employed in step b).

In a process for workup of mixed acid and wastewater from the nitration of aromatics in which the nitric acid present is converted by reaction with an aromatic under adiabatic conditions, a. at least one waste stream component selected from waste acid (mixed acid) generated in the nitration, acidic washing water from the workup of crude nitroaromatics and dilute nitric acid generated in an off-gas treatment in the course of the nitration is provided, b. the at least one waste stream component is mixed with re-concentrated sulfuric acid, c. an aromatic is added to the mixture in stoichiometric excess based on the nitric acid, d. the obtained reaction mixture is reacted in an adiabatically operated reactor, e. the obtained organic phase is separated from the sulfuric-acid-containing phase in a separator, f. the sulfuric-acid-containing phase is concentrated under vacuum and g. at least one substream of the re-concentrated sulfuric acid from step g) is employed in step b).

A process for recycling of a mixed acid containing nitrosyl sulfuric acid and sulfuric acid to obtain nitric acid and sulfuric acid, the process including adding (i) a dilute nitric acid to (ii) the mixed acid comprising nitrosyl sulfuric acid and sulfuric acid to effect the decomposition of the nitrosyl sulfuric acid and to obtain (iii) a liquid phase and (iv) a gaseous phase, adding steam to the liquid phase to separate (v) a purified sulfuric acid, and evaporate (vi) a mixture of concentrated nitric acid and nitrogen oxides, cooling the gas phase and the mixture of nitric acid and nitrogen oxides in order to separately obtain (vii) a purified nitric acid condensate and (viii) nitrogen oxides, absorbing nitrogen oxides (viii) in water to obtain dilute nitric acid (ix), and optionally, introducing at least part of the obtained dilute nitric acid (ix) into the process.