Divided Flocculant addition:way to minimize Flocculant Addition

The present paper reports the flocculation behaviour of iron ore slimes from a typical mine of Bihar (India) when synthesized graft copolymer of starch and polyacrylamide and poly acrylamide based commercial flocculant (magnafloc 1011) are added in stages vis-a-vis one time addition. The studies on settling and filtration following flocculation were carried out with the objective to minimize the flocculant dose. The ploymer requirements for the settling and filtration have been observed to be different. The settling rate with graft co-polymer is higher than that with magnafloc 1011 at lower flocculant dose. In case of filtration, the performance of graft copolymer is marginally inferior to that of magnafloc 1011. The settling rate improves considerably at lower flocc- ulant dose (10 ppm, solid / solid basis), specially when the same amount is added in two stages; whereas in case of filtration, the effect of divided flocculant addition is more pronounced when 20 ppm (s/s) is added in two stages (rather than at 10 ppm). This effect is also more pronounced at lower pulp density compared to higher one. The effect of divided flocculant addition in relation to minimising the flocculant dose has been explained by the fact that greter compactness of the flocs is achieved which results in improvement of flocculation efficiency and has been schematically shown in the present paper