Flocculation of fine hematite and quartz suspensions with anionic cellulose nanofibers

•We produced dicarboxylic acid and sulfonic acid cellulose nanofibers.•Anionic nanofibers were tested in flocculation of hematite and quartz suspensions.•Anionic nanofibers did not flocculate quartz but flocculated hematite.•Flocculation efficiency was affected by suspension pH and type of anionic nanofiber.•Kinetics of flocculation and floc strength dependent on the type of nanofiber.

Research was undertaken to investigate the efficiency of anionic dicarboxylic acid (DCC) and sulfonated (ADAC) cellulose nanofibers in flocculating fine hematite and quartz particles. Flocculation was studied at pH levels varying from 5 to 10 and chemical dosages of 0–2000 ppm, with turbidity measurements after sedimentation and with analytical centrifugation after a short intense mixing stage. Results showed that DCC and ADAC cellulose nanofibers did not flocculate quartz within pH range 5–10 but were able to flocculate hematite. DCC's ability to flocculate hematite and the ability of formed flocs to withstand the shear forces of subsequent intense stirring depended markedly on the pH of the suspension. The most effective performance was obtained at a pH of 8–9, and a DCC dosage of 200–500 ppm was enough to flocculate hematite efficiently. In addition, unlike ADAC nanofibers, DCC nanofibers were able to flocculate hematite under short vigorous stirring. ADAC nanofibers proved to be as efficient a hematite flocculant as DCC nanofibers at a dosage of 500 ppm after longer conditioning time and less vigorous stirring. Furthermore, the operational pH region was wider for ADAC nanofibers, and the hematite flocs did not show any pH-dependent breakage.