COLLOID-HYDRODYNAMIC REGULATIONS OF THE FLOTATION CHROM (IV) WITH VIOLATION

• Main Authors: V. V. Kostik, Vl. V. Kostik, A. N. Sofronkov, V. V. Menchuk
• Format: Article
• Language: English
• Published: Odessa I. I. Mechnikov National University 2018-11-01
• Series: Vìsnik Odesʹkogo Nacìonalʹnogo Unìversitetu: Hìmìâ
• Subjects: хром; флотація з носієм; дисперсна система; колоїдно-гідродинамічна взаємодія; кінетична теорія флотації
• Online Access: http://heraldchem.onu.edu.ua/article/view/147815

This paper presents theoretical and experimental studies of the regularities of colloid-hydrodynamic interactions of small particles and a collectively rising air bubble in a model and real system using finely dispersed paraffin as a carrier of BaCrO4 particles. Theoretical studies of the regularities of hydrodynamic interactions of a collectively popping bubble (with a radius of 295 μm) with small particles (with a radius of 3.2 to 12.8 μm) have been carried out. The values of dimensionless criteria were determined with the help of which the efficiency of collision of particles (taking into account their inertia) and the bubble of air rising in water in the transient hydrodynamic regime (Re = 57) was estimated. As a result of theoretical studies of the model of the flotation system, regularities of long-range and near-field hydrodynamic interaction of particles and a bubble are established, which show that the mechanism of such interactions depends on the radius of the particle and its density. It was found that particles with a small radius (from 3.2 μm) and a relatively high density (from 4.5 g/cm3) collide with the bubble surface (as a result of the predominance of inertial forces in the hydrodynamic interaction mechanism) above its equator. In this region, which is unfavorable for fixing particles on the bubble surface, relatively large particles whose density is smaller than the density of the medium also collide, and the radius exceeds 10.9 μm, which is due to the prevalence of viscous drag forces of the medium.It is shown that the extreme nature of the hydrodynamic interactions of particles with a bubble allows us to theoretically justify the optimum amount of carrier for the flotation of small particles. Thus, for example, calculations showed that for flotation of chromium (VI) using finely dispersed paraffin as a carrier, the optimal amount of paraffin corresponds to 7.2 g/g BaCrO4. The experimental values of the capture efficiency of particles by air bubbles, characterizing the joint effect of both hydrodynamic and inertial forces, as well as molecular, electrostatic and other interaction forces arising as a result of surface phenomena in similar colloidal systems are determined. At optimal paraffin consumption (6.3 g/g BaCrO4), the capture efficiency was 1.3×10-3, and the relative capture efficiency (calculated as the ratio of this value to the capture efficiency in the collision without taking into account the hydrodynamic interaction of the particle with the bubble) is 1.8×10-2. The obtained experimental values of capture efficiency agree with the data of the researchers who studied the flotation of small particles without the use of flotation reagents. It has been experimentally established that when about 4.0 g/g of BaCrO4 carrier is added to the system, then chromium(VI) is not flotated at all. A carrier that exceeds the optimum amount somewhat reduces the efficiency of chromium(VI) flotation. Theoretical and experimental data obtained in this paper are in good agreement.