Resourceful Utilization of Dye Intermediate Mother Liquor from Sulfonation Processes by Low-Temperature Crystallization

Four dye intermediate mother liquors from sulfonation processes were treated by low-temperature crystallization, and the influences of temperature, pH and the kind of alkali were investigated. The results showed that the removal of chemical oxygen demands (COD) of simulated wastewater increased with decreasing temperature. Adjusting pH of simulated 2-naphthalene-6,8-disulfonic acid dipotassium salt (G salt )wastewater by adding KOH improved the performance of treatment, while the effect of treatment for simulated 2-naphthalenesulfonic acid sodium salt(β salt) wastewater decreased with increasing pH under acidic condition. The real G salt mother liquor was frozen for 12 h at -12 ℃, and reached the removal of COD of 55% with the main production of 2-naphthol-3,6-disulfonic acid disodium salt (R salt). Then the pH of G salt filtering medium was adjusted to 7.0, and frozen 12 h at -16 ℃, the removal of COD increased to 62% while the main component of crystal production was G salt. The removal of COD of β salt mother liquor reached 78.8%, and β salt was partly recovered.The recovery of organic components in G salt and β salt mother liquors by low-temperature crystallization was feasible.