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Cleaning of Dulmial-Punjab Coal by Froth Flotation.

In recent years, froth flotation has been investigated extensively with major focus on studying the effects of various operation and design parameters on product yield and recovery (Cheng et al., 2016; Liao et al., 2016; Patil et al., 2010; Mondal and Mohanty, 2009; Jena et al., 2008; Dell, 1964). Various parameters such as solid percentage, impeller speed, air flow rate, particle size, collector type and dosage, frother type and dosage, pH of coal slurry and conditioning time affect the flotation process (Xia et al., 2016; Oney et al., 2015; Chaudhuri et al., 2014; Gui et al., 2013; Cheng et al., 2013; Jena et al., 2008; Dey and Bhattacharya, 2007; Jia et al., 2002).

In this study, the floatability of Dulmial-Punjab coal was assessed by Dell release analysis and the effects of various flotation parameters such as coal particle size, impeller speed, collector and frother dosage, and conditioning time were investigated. The gross sample was crushed and divided into four quarters by coning and quartering. One quarter was further crushed and divided into two parts. One part was prepared according to ASTM standards (ASTM, 2004) to perform proximate analysis and the results are tabulated in Table 1.

The other part was ground to -0.50 mm and sieve analysis was performed on it. The distribution of ash in various size fractions along with their weight percentages are given in Table 2. The lowest fractions with smallest particle size (-0.074+0.044 and -0.044 mm) and the coarsest fraction (-0.500+0.250 mm) contained the highest amount of ash. The remaining intermediate fractions contained relatively lower amounts of ash.

Release analysis was performed on -0.250 mm sample in Denver flotation cell. Kerosene oil was used as collector and methyl iso-butyl carbinol (MIBC) was used as frother. The release curve of Dulmial coal is shown in Fig. 1. It is clear from the curve that the coal has poor floatability. Theoretically 60% coal can be floated with clean coal ash of approximately 36%.

The batch flotation tests were conducted in Denver flotation cell. A 10% feed slurry was used and mixed for 5 min before addition of collector. Kerosene oil and methyl iso-butyl carbinol (MIBC) were used as collector and frother, respectively.

The effect of particle size on clean coal yield and ash was investigated by performing flotation tests on the following size fractions; -0.250+0.177, -0.177+0.105, -0.105+0.074, -0.074+0.044 and -0.044 mm. The results of these tests are shown in Fig. 2. Both clean coal yield and clean coal ash showed a decreasing trend with increasing particle size. The maximum yield of 72.61% was obtained at the smallest particle size e.g. -0.044 mm. Minimum clean coal ash of 26.9% was obtained for particle size range of -0.250+0.177 mm with yield of 41.40%.

The impeller speed was varied from 1000 to 1600 rpm. The effect of impeller speed on clean coal yield and ash is given in Fig. 3. High agitation rate increased the yield. The clean coal ash was increased first and then decreased. Maximum yield of 48.6% was achieved at 1600 rpm. The clean coal ash was minimum at this rpm which was 40.3%. This optimum rpm was set for next sets of flotation tests.

The collector dosage was varied from 400 to 1600 g/t. The effect of collector dosage on the concentrate yield and ash is shown in Fig. 4. The concentrate yield was increased initially and then decreased. The ash contents were decreased by increasing the collector dosage and then slightly increased by further increase in collector quantity. The optimum collector dosage was 1200 g/t at which the clean coal yield and ash were 50.63% and 39.4%, respectively.

The results of tests performed with variation in frother dosage are shown in Fig. 5. The frother dosage was varied from 200 to 800 g/t. Both clean coal yield and ash contents were increased initially and reached maximum at frother dosage of 600 g/t resulting in 52.08% clean coal yield with 42.2% ash. After this point, a decrease in trend was observed. The effect of frother dosage was more pronounced on ash contents than clean coal yield. The optimum frother dosage was 200 g/t at which the ash contents were found minimum e.g. 40.3% with a concentrate yield of 50.42%.

The effect of conditioning time on clean coal yield and ash are depicted in Fig. 6. The clean coal yield was increased by increasing conditioning period. Maximum yield of 51.25% was achieved with 10 min conditioning. It was found that conditioning time did not impart a substantial effect on clean coal ash. Only slight variation was observed in clean coal ash with minimum of 39.5% at 10 min conditioning time.

It was concluded that maximum clean coal yield of 51.25% with ash content of 39.4% was found at 1600 rpm, 1200 g/t collector dosage, 200 g/t frother dosage with 10 min conditioning for particles less than 0.250 mm.


ASTM, 2004. Annual Book of ASTM Standards, vol. 05.06, ASTM, D-2013; ASTM, D-3173; ASTM, D-3174; ASTM,D-3175. American Society for Testing and Materials, West Conshohocken, PA, USA.

Chaudhuri, S., Kalyani, V.K., Charan, T.G., Kumari, S., Sinha, A. 2014. Improved collector for beneficiation of low-volatile medium ash clean coal fines by froth flotation. International journal of Coal Preparation and Utilization, 34: 321-331.

Cheng, G., Shia, C.L., Liuc, J.T., Yand, X.K. 2016. Bubble-distribution measurement in a flotation column. International journal of Coal Preparation and Utilization, 36: 241-250.

Cheng, G., Gui, X.H., Liu, J.T., Xu, H.X., Wang, Y.T., Zhang, Q.D., Song, C.A. 2013. Study on size and density distribution in fine coal flotation. International Journal of Coal Preparation and Utilization, 33: 99-116.

Dell, C.C. 1964. An improved release analysis procedure for determining coal washability. Journal of Institute of Fuel, 37: 149-150.

Dey, S., Bhattacharya, S. 2007. Effect of frother type in collectorless flotation of two high-rank coking coals of Gondwana origin. Coal Preparation, 27: 4-27.

Gui, X., Cheng, G., Liu, J., Cao, Y., Li, S., He, Q. 2013. Effects of energy consumption on the separation performance of fine coal flotation. Fuel Processing Technology, 115: 192-200.

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Jia, R., Harris, G.H., Fuerstenau, D.W. 2002. Chemical reagents for enhanced coal flotation. Coal Preparation, 22: 123-149.

Liaoa, Y., Caoa, Y., Liub, C., Zhub, G. 2016. A study of kinetics on oily-bubble flotation for a low-rank coal. International Journal of Coal Preparation and Utilization, 36: 151-162.

Mondal, K., Mohanty, M.K. 2009. A theoretical approach to coal flotation washability correlation. International Journal of Coal Preparation and Utilization, 29: 140-151.

Oney, O., Samanli, S., Celik, H., Tayyar, N. 2015. Optimization of operating parameters for flotation of fine coal using a box-behnken design. International Journal of Coal Preparation and Utilization, 35: 233-246.

Patil, D.P., Parekh, B.K., Klunder, E.B. 2010. A novel approach for improving column flotation of fine and coarse coal. International Journal of Coal Preparation and Utilization, 30: 173-188.

Xia, W., Ni, C., Xie, G. 2016. Effective flotation of lignite using a mixture of dodecane and 4-dodecyl-phenol (ddp) as a collector. International Journal of Coal Preparation and Utilization, 36: 262-271.

Muhammad Shahzad (*), Zulfiqar Ali and Asim Siddique

Mining Engineering Department, University of Engineering & Technology, Lahore, Pakistan

(*) Author for correspondence; E-mail:

(received July 22, 2016; revised August 25, 2017; accepted September 11, 2017)
Table 1. Proximate analysis of coal

Characteristic        Value

Moisture content (%)   2.6
Ash content (%)       47.6
Volatile matter (%)   22.4
Fixed carbon (%)      27.4

Table 2. Sieve analysis and ash tests results on each size fraction

Size fraction (mm)  Weight (%)  Ash content (%)

-0.500+0.250        30.70       48.1
-0.250+0.177        10.57       43.5
-0.177+0.105        11.31       45.3
-0.105+0.074        11.65       44.7
-0.074+0.044        27.63       49.5
-0.044               8.14       52.1
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Title Annotation:Short Communication
Author:Shahzad, Muhammad; Ali, Zulfiqar; Siddique, Asim
Publication:Pakistan Journal of Scientific and Industrial Research Series A: Physical Sciences
Date:Sep 1, 2017
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