Effect of primary flocculant type on a two-step flocculation process on iron ore fine tailings under alkaline environment.

Graphical abstract Highlights • With anionic or nononic polymer as primary flocculant, two-step flocculation was used for iron fine tailings treatment. • Better flocculation effect was achieved with the single nononic flocculant, but a higher water recovery rate was obtained with anionic primary flocculant. • Broken flocs produced by anionic flocculant had larger strength factors and a more significant reversibility with the appropriate amount of the cationic flocculant and they also achieved a higher total water recovery rate. • Flocs size distributions were measured and strength factor and recovery factor were calculated for mechanism study. • The flocculation mechanism involves polymer bridging and charge neutralisation. Abstract Dewatering of fine tailings is one of the major challenges faced by the mining and mineral processing industries worldwide. In order to facilitate the separation of released water and solid sediments, different kinds of polymeric flocculants and their combinations have been widely used. A two-step flocculation experiment using two separate primary flocculants in alkaline environment was carried out in this study. The underflow concentration of the two-step flocculation process was higher than that of any single flocculant. Compared to the widely-used flocculation process with a single polymer flocculant, this two-step process could not only significantly improve the total water recovery rate of the slurry, it could also produce a full re-growth of flocs. The first part of the study compared the effects of adding 2 different flocculants to the slurry under alkaline conditions: a non-ionic flocculant, and an anionic flocculant. Compared to the anionic flocculant, the addition of the non-ionic flocculant resulted in a more compact structure and a higher strength by bridging. Conversely, after shear disruption and the addition of the cationic flocculant to the slurry, the re-aggregating broken flocs produced by the anionic flocculant in the first step resulted in a higher reversibility, the formation of a closer and more complex floc structure, and consequently a higher total water recovery rate. This was achieved by drastically re-aggregating broken flocs through the addition of a cationic flocculant that neutralized the charge of the slurry, which in turn is an indication of significant reversibility of the floc break-up process. The dosage of the secondary flocculant had an optimal value to achieve the maximum total water recovery rate. If the dosage exceeded the optimal value, the interaction between the flocculant molecules adsorbed on the same floc occured, which hindered the re-aggregation of flocs and even reduced the secondary water recovery of the slurry. [ABSTRACT FROM AUTHOR]