Synthesis, characterization and evaluation of amphoteric chitosan-based grafting flocculants for removing contaminants with opposite surface charges from oilfield wastewater

BACKGROUND Contaminants with either negative or positive surface charges in wastewater generated from oilfields are normally very difficult to remove by traditional flocculants owing to their strong pH-dependence and high health risks. Natural polymer flocculants, especially chitosan-based flocculants, have attracted much interest for their environmental friendliness, excellent flocculation efficiencies and cost-effectiveness. RESULTS A series of amphoteric chitosan-based grafting flocculants (CM-chi)- g -PDMDAAC (denoted as C g PD) were successfully synthesized by grafting diallyl dimethyl ammonium chloride (DMDAAC) onto carboxymethyl chitosan (CM-chi) with different grafting ratios. By carboxymethyl and grafting modification, dramatically increased water solubility of chitosan was obtained. The physicochemical structure of C g PD products was characterized by 1 H NMR and elemental analysis proving that DMDAACC was grafted onto CM-chi appropriately. Flocculation effects of C g PD were studied in kaolin and hematite suspensions having opposite surface charges. These C g PD flocculants demonstrated an excellent performance in respect of flocculation window, optimal dosage and pH sensitivity. In addition, C g PD was proven to be applicable as a flocculant in water treatment of oilfield sites. CONCLUSION The biodegradability flocculants, C g PD, can effectively remove contaminants with opposite surface charges from oilfield wastewater with low optimal dosage, wide flocculation window, low pH sensitivity and less environmental impacts than traditional flocculants. © 2017 Society of Chemical Industry