PROCESS FOR RECYCLING NITROGEN OXIDES FROM NITROSYL SULFURIC ACID TO PRODUCE CONCENTRATED OR HIGHLY CONCENTRATED NITRIC ACID AND SULFURIC ACID

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.