A novel method for the recovery of 4,4′-dinitrostilbene-2,2′disulfonic acid from the wastewater obtained from 4,4′-diaminostilbene-2,2′-disulfonic acid production

HPLC and electrospray ionization tandem mass spectrometry were used to show that ∼30% of the DNS present in wastewater was reduced to 4-amino-4′-nitrostilbene-2,2′-disulfonic acid and 4,4′-diaminostilbene-2,2′-disulfonic acid during multiple-effect evaporation. A novel recovery method, which combines acidification and subsequent reduction, recovered of ∼90% of the DNS that is lost during evaporation and, thereby, increased the yield of 4,4′-diaminostilbene-2,2′-disulfonic acid by 5%. In addition, many of the organic compounds present in the wastewater were removed.