Mi,,crds Engineering, Vol. 9,No. 4,pp.465-468,1996 Copyright 0 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved
P11:S0892-6875(96)00031-3
CARRYING
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TECHNICAL NOTE CAPACITY IN J?LOTATION COLUMNS S.R.S.
SASTRI
Regional Research Laboratory, Bhubaneswar 75 1013, India (Received 22 June 1995; accepted 17 November 1995)
ABSTRACT
i’Ie equation proposed by Espinosa-Gomez et.al. for the carrying capacity in flotation columns is revised to give better fit to the data. Flotation columns are found to be normally operated around 60% of their maximum carrying capacities. Keywords
Froth flotation; column flotation; particle size
INTRODUCTION
The rate of concentrate removal in terms of mass of solids overflowing per unit time per unit column cross sectional area is generally referred to as the carrying capacity of the column. This is related to the maximum achievable coverage of air bubbles by particles and gives an upper limit to the capacity of flotation columns. The capacity of a flotation column is limited by the amount of bubble surface available to carry the particles into the froth launder, since the specific surface area, defined as the ratio of froth surface to the volume of pulp held is about one order of magnitude less in flotation columns compared with conventional cells.
ESTIMATION
OF CARRYING
CAPACITY
Under normal column operating conditions, the quantity of solids carried over into the froth through entrainment is low due to the effect of wash water, and can be neglected [1,2]. Further, the size of particles is also small compared to the size of the bubbles, except in cases such as coal flotation. Under these conditions it can be shown that [3-51 C = K D, p St,
(1)
where C is carrying capacity, K is an empirical factor which accounts for the particle packing on the bubble surface D, is a characteristic diameter of the particle in the froth, St, is the superficial bubble surface area rate (surface area of bubbles passing through the column per unit time per unit cross sectional area) and p is the density of the particles in the froth.
465
Technical Note
466
According to this equation, the carrying capacity for a given product can be increased by increasing the superficial bubble surface area rate, which in turn can be increased by increasing aeration rate or by reducing the bubble size. It has been shown [6,7] that a maximum gas rate exists, beyond which the carrying capacity reduces due to resultant changes in the mode of operation of the column [7]. It was also concluded, that in the normal range of operation, air rate and column diameter have only a marginal effect on carrying capacity [8-lo]. Based on the data from laboratory test work and some commercial plants, the maximum carrying capacity was related [9] to the particle size and density of solids in the froth according to the equation C,
= 0.068 d, p
(2)
where C, is the maximum
carrying
capacity,
g min-1cm-2,
d, is the 80% passing size of solids in froth products, and p is the density of the particles Equation 1 was found obvious from the data logic for selecting the constant and revising C,
microns
in the froth, g cme3.
to give too high values for maximum carrying capacity [ 111. The reason for this is in Table 1, which are the same as those used by Espinosa-Gomez et.al.. [9,12]. The highest value of 0.068 as the constant in Equation 1 is not known. By using a smaller Equation 1 to read as
= 0.049 d, p
(3)
the data in Table 1 can be represented TABLE
more accurately.
1 Experimental
RESULTS
data on carrying
capacity
AND DISCUSSION
Figure 1 compares the maximum carrying capacities estimated from Equation 3 with the experimental data in Table 1. It can be seen that the revised correlation represents the experimental data with a maximum deviation of +25 % while the original correlation always predicts values greater than the experimental ones.
Technical Note
c,expt.,
g
467
n-m”cm+
Fig. 1 Comparison of experimental and estimated maximum carrying capacities in flotation columns 0 Equation 3; ??Equation 2 Since Equation 3 is based on the maximum achievable operating capacities, the normal operating capacities of flotation columns are expected to be generally well below the values predicted by this equation. The data available from some pilot and industrial columns of Cominco [ 13,141 indicate that the operating capacities are around 60% of the maximum values indicated by Equation 3. Table 2 gives a comparison of the operating data with those estimated on this basis. It can be seen that the agreement is good. TABLE 2 Comparison of actual and estimated operating of some pilot and industrial flotation columns
Detail
Sullivan zinc
Column dia. m
capacities
Capacity, g min-1cm-2 Actual
Estimated
Reference
0.28 2.4
5.3 6.9
5.5 5.5
13
cont.
Polaris lead cont.
0.76 x 0.76#
14
16.8
14
Sullivan dezincer
0.28
3 5.3
3.6 5.1
Pine Point zinc cont.
0.38
15 19 14
16 14 14
* Estimated from C = 0.03 d,p # Square cross section
468
Technical Note
CONCLUSIONS
The model proposed by Espinosa-Gomez etal.. for the carrying capacities in flotation columns was found to be satisfactory not only for predicting the maximum carrying capacity but also the operating capacities of these columns. However, the constant proposed was found to give too high values for the maximum carrying capacities. The use of 0.049 and 0.03 as the constants for calculating the maximum and operating capacities respectively according to the model was found to represent the experimental data for these with a maximum deviation of + 25 % .
ACKNOWLEDGEMENT-
The author wishes to acknowledge Prof. H.S. Ray, Director, Regional Research Laboratory, Bhubaneswar for permission to publish this paper.
REFERENCES
1. 2. 3. 4. 5. 6.
7.
8. 9. 10.
11. 12.
13.
14.
Yianatos, J.B., Finch, J.A. and Laplante, A.R., Cleaning action in column flotation froths, Trans. Instn. Min. Metall. (Sect. C, Mineral Process. Ext. Metall.), C96, Cl99 (1987). Falutsu, M. & Dobby, G. S., Froth performance in commercial sized flotation columns, Minerals Engg., S(lO-12) 1207, (1992). Flyer, S.A. & Woodburn, E.T., Development of a froth model for fine particle beneficiation by flotation, Trans. Znstn. Min. Metall. (Sect. C, Mineral Process. Ext. Metall.), C96, Cl91 (1987). Yoon, R.H., Mankosa, M.J. & Luttrell, G.H., Design and scale up criteria for column flotation, XVIII, International Mineral Processing Congress, Aus. IMM Sydney, Australia, 785 (1993). Davis, V.L.Jr., Stanley, F.L., Bethel, P.J., Luttrell, G.H. & Mankosa, M.J., Column flotation at the Middle Fork preparation facility, Coal Preparution, 14, 133 (1994). Xu, M., Uribe-Salas, A., Finch J.A. & Gomez, C.O., Gas rate limitation in flotation column, in Dobby , G.S. and Rao, S.R., (ed) Processing of Complex Ores, Proceedings of 28th Annual Conference of Metallurgists of CZM, Pergamon Press, New York, 397 (1989). de1 Villar, R., Gomez, C.O., Finch J.A. & Espinosa-Gomez, R., Flotation column amenability and scale up parameter estimation tests, in Dobby, G.S. and Rao, S.R., (ed) Processing of complex ores, Proceedings of 28th Annual Conference of Metallurgists of CZM, Pergamon Press, New York, 349 (1989). Finch J.A. & Dobby. G.S., Column Flotation, Pergamon Press, New York, (1990). Espinosa-Gomez, R., Finch J.A., Yianatos, J.B. & Dobby. G.S., Flotation column carrying capacity : particle size and density effects, Minerals Engg., l,(l), 77 (1988). Espinosa-Gomez, R., Yianatos, J.B. & Finch J.A., Carrying capacity limitations in flotation columns, in Sastry , K.V.S., (Ed), Column Flotation-88, Proceedings of the International Symposium on Column Flotation, Sot. of Mining Engineers, Littleton, 143 (1988). Finch J.A., Personal communication, (1990). Espinosa-Gomez, R., Johnson, N.W., Pease, J.D. & Munro, P.D., The commissioning of the first flotation columns at Mount Isa Mines ltd., in Dobby, G.S. and Rao, S.R., (ed) Processing of complex ores, Proceedings of 28th Annual Conference of Metallurgists of CZM, Pergamon Press, New York, 293 (1989). Redfearn, M.A. & Egan, J.R., Large diameter column optimisation and scale up. in Dobby, G.S. and Rao, S.R., (ed) Processing of complex ores, Proceedings of 28th Annual Conference of Metallurgists of CZM, Pergamon Press, New York, 303 (1989). Fairweather, M.J., Process mineralogy of column flotation. in Dobby, G.S. and Rao, S.R., (ed) Processing of complex ores, Proceedings of 28th Annual Conference of Metallurgists of CZM,
Pergamon Press, New York, 369 (1989).