Flocculation behavior of a new recyclable flocculant based on pH responsive tertiary amine starch ether

We designed a new tertiary amine starch ether (2,4-bis(dimethylamino)-[1,3,5]-triazine-6-yl)-starch (BDATS) via etherification of starch with 2,4-bis(dimethylamino)-6-chloro-[1,3,5]-triazine (BDAT), which demonstrated a reversible pH response in aqueous solution. BDATS could be utilized as an effective flocculant because of its favorable interaction with anionic dyes. The flocculation was solution pH dependent and that color removal as high as 97% was possible at pH 2. BDATS shows high flocculation capacity, with the maximum flocculation capacity (DS = 0.63) at 1158 mg g−1 for C.I. Reactive Red 141, 873 mg g−1 for C.I. Acid Red 1 and 2296 mg g−1 for C.I. Acid Blue 324, respectively. The theoretical flocculation capacity was calculated, and the results showed that the experimental flocculation capacity was near to the theoretical one. At pH 8, the dye-loaded flocculant could be regenerated and the recovery ratio of the flocculant was 80%. After five cycles of flocculation/regeneration, color removal ratio was still above 94%. BDATS made it a good candidate for an effective re-cycled flocculant for the treatment of colored effluents.

► A novel cationic starch ether was synthesized via an etherification reaction.
► BDATS showed a reversible pH response in aqueous solution.
► BDATS showed high flocculation capacity for anionic dye.
► The exhausted BDATS could be regenerated and reused over five cycles.