RECOVERY OF CLEAN COAL FINES THROUGH A COMBINATION OF GRAVITY CONCENTRATOR AND FLOTATION PROCESSES

Abstract

Flotation feed is a mixture of coarse and ultra-fine fractions. During conditioning of the flotation feed with collector and frother, the finer fraction consumes more reagents as compared to coarser particles. This is mainly due to more specific surface area of the ultra fine than the coarse fraction. This favors the adsorption of reagents toward ultra-finer fractions leads to less complete surface coverage of coarse particles and more entrainment of finer gangue particles. This results in the lower yield of coarse fractions from the flotation circuit and loss in selectivity. Hence, the major challenge is to improve the recovery of the coarser fraction and selectivity of ultra-fine fractions by improving flotation kinetics of all size fractions. This article deals with an approach to overcome the improper reagent adsorption by fine and coarse coal fractions in the flotation circuit through an innovative washing circuit containing gravity operation and flotation processes. Flotation performance between a new washing circuit having stub cyclone and flotation and normal single-stage reagent addition flotation process is compared in terms of selectivity, separation efficiency, rate constant, and size-wise recovery. The washing circuit having stub cyclone and flotation processes improves the fine clean coal yield by 10% and reduces the consumption of reagent compared to the normal single-stage reagent addition flotation process.

Keywords:

• fine coal
• flotation kinetics
• flotation reagents
• selectivity
• stub cyclone

ACKNOWLEDGEMENT

The authors thankful Mr. A. M. Mishra, Dr. D. Bhattacharjee, and Dr. Sanjay Chandra for their keen interest and guidance in carrying out this study. They would also like to thank Mr. M. V. S. Rao and his entire team of Geological Services and the members of West Bokaro Washery and S. C. Chowdhary, R&D, for their active involvement during laboratory studies.

Notes

∗Separation efficiency = Recovery of combustible–Recovery of ash.

^a = degree of freedom.

MS^b = mean sum of squares.

F^c ratio = MS/(MS of residual error)

F ^d _0.5  =  Hypothesis F statistics.

^e = Significant variables.

∗Separation efficiency = recovery of combustible – recovery of ash.