Regeneration of dye-saturated quaternized cellulose by bisulfite-mediated borohydride reduction of dye azo groups: An improved process for decolorization of textile wastewaters
Cellulosics modified to contain quaternary ammonium groups have a strong affinity for anionic dyes. Therefore, ion exchangers based on quaternized cellulose or lignocellulose can be used to remove textile dyes from wastewater. However, restoration of exchanger binding capacity is poor using conventional, low-cost regenerants. Experiments were conducted with two monoazo dyes, Orange II (Acid Orange 7) and Remazol Red F3B (Reactive Red 180), to determine whether reductive cleavage of dye azo bonds improves exchanger regenerability. Treatment with the redox couple KBH4/NaHSO3 fully restored the binding capacity of Orange II-saturated quaternized cellulose. KBH4/NaHSO3 treatment of quaternized cellulose saturated with Remazol Red F3B (hydrolyzed, unreactive form) restored 74% of the exchanger binding capacity, which increased to 95% with a subsequent wash with NaOH or NaClO4. High-performance liquid chromatography was used to confirm that KBH4/NaHSO3 reductively cleaved dye azo bonds. Bisulfite was found to f...