Column flotation of fine glass beads enhanced by their prior heteroaggregation with microbubbles

Abstract

The application of microbubbles as flotation carriers in fine minerals beneficiation processes can be a promising approach for solving challenges of fine particles flotation. This study explores the efficiency of column flotation of fine glass beads (ballotini). In test runs ballotini were first mixed with the air-in-water dispersion in CTAB (cetyltrimethylammonium bromide) solution, and then they were fed into a flotation column via a tubular flotation reactor. Independent of the total concentration of the collector in a flotation reactor and a column, the maximum increased recovery is achieved when a volume dosage of microbubbles per floated particles weight unit is 0.3 mL/g. The paper also offers the theoretical substantiation for this effect. The findings have shown that the average shear rate in a flotation reactor significantly influence the dependence of recovery on treatment time. It is suggested that the best performance can be achieved in flotation reactors, which generate shear rates in the range 300–500 s−1, and the treatment time amounts to 8–10 s. These conditions facilitate formation of hetero-aggregates comprising particles and microbubbles, and the size of the aggregates reaches several millimeters. In the test runs with the tubular flotation reactor of 6 mm in diameter at the shear rate of 500 s−1 and treatment time of 8 s, the recovery rate of ballotini increased from 63.2% to 77.6%. It was shown that the effectiveness of treating the mixture of particles and microbubbles in the flotation reactor significantly depends on the method of CTAB collector feed. The best results were achieved when the total amount of collector was fed into the flotation reactor with the microbubble dispersion in the concentrated solution of CTAB collector. In this case, the adsorption of CTAB cations on the microbubble surface caused the positive charging of the surface. As the surface of glass beads initially has a negative charge, the delivery of positively charged microbubbles into the feed creates favorable conditions for forming coarse hetero-aggregates due to Coulomb attraction of particles and microbubbles.