Bremmell

Claridge

D.R. Nagaraj

Edwards

Eltham

Fitzpatrick

Hess

Hoatson

Lindström

M. Vasudevan

Maachar

P. Patra

P. Somasundaran

Pietrobon

Switzer

T. Bhambhani

Vasudevan

Patra, P.

Bhambhani, T.

Vasudevan, M.

Nagaraj, D. R.

Somasundaran, P.

University of Queensland eSpace

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Transport of fibrous gangue mineral networks to froth by bubbles in flotation
separation
P. Patra, T. Bhambhani, M. Vasudevan, D.R. Nagaraj, P. Somasundaran
PII: S0301-7516(11)00173-6
DOI: doi: 10.1016/j.minpro.2011.11.007
Reference: MINPRO 2377
To appear in: International Journal of Mineral Processing
Received date: 14 September 2011
Accepted date: 6 November 2011
Please cite this article as: Patra, P., Bhambhani, T., Vasudevan, M., Nagaraj, D.R.,
Somasundaran, P., Transport of fibrous gangue mineral networks to froth by bub-
bles in flotation separation, International Journal of Mineral Processing (2011), doi:
10.1016/j.minpro.2011.11.007
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Transport of fibrous gangue mineral networks to froth by bubbles in flotation separation 
P. Patra
a*
, T. Bhambhani
b
, M. Vasudevan 
b
,  D. R. Nagaraj
b
, P. Somasundaran
a
  
a 
Department of Earth and Environmental Engineering 
Columbia University, 
New York, USA 10091 
 
b 
Cytec Industries Inc 
Stamford Technology Center, 
1937 W Main St, Stamford, CT USA 06907 
 
 
 
Abstract 
Flotation beneficiation of ores containing fibrous minerals is highly problematic due to transport 
of such gangue minerals from pulp to the froth phase. Earlier studies have attributed such 
transport to the entrainment of fibrous minerals. In this work, this problem is investigated for the 
case of flotation of ultramafic Ni ore with fibrous serpentines (Mg silicates) interfering with their 
separation. Serpentines are proposed to form  large (~1-2 cm) networks in pulp and thus unlikely 
to be transported by entrainment. Various simulation based studies suggest that the networks are 
stable under the dynamic flotation conditions. Furthermore, the pores in the networks are 
relatively small (e.g. < 20 microns – SEM studies) for the bubbles (1-2 mm) to penetrate through 
the network of fibers in the pulp. This leads to the hypothesis that bubbles which cannot 
penetrate through the network accumulate below the network in the pulp with the buoyancy force 
of the bubbles thrusting the network to the froth phase. Model system studies were carried out 
with nylon fibers of size similar to that of serpentines. The phenomenon, of bubble-flux driven 
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transport of fibrous serpentines was clear from the model system studies, and is proposed to be 
the  key mechanism of  transport of fibrous serpentines to flotation concentrate.   
 
Key Words: Serpentines, fibrous, network, pore size, bubble flux 
 
 
 
 
 
 
 
 
*corresponding author:  
 
Partha Patra 
Earth & Environmental Engineering 
500 W. 120th Street 
918 SW Mudd, MC 4711 
New York, NY  10027 
Phone: (212) 854-2905 
Fax: (212) 854-7081 
E-mail: pp2295@columbia.edu 
Phone: +12128542926 
 
 
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1. Introduction 
Economic beneficiation of the Ni ores containing large amounts of serpentines (Mg silicates) has 
been a longstanding challenging problem in the mineral industry (Claridge and Tenbergen, 1975; 
Edwards et. al., 1980; Eltham, J. A. and Tilyard, 1973). Typically, large amounts of serpentines 
are transported to the froth phase resulting in Ni grade dilution, affecting the smelter efficiency 
and lifetime. Serpentine minerals are alteration products of parent silicates, such as peridotite and 
pyroxene (Hess, 1933; Hoatson et. al., 2006). The alteration products have varying 
physicochemical properties which impact the separation of the value minerals from their ores in 
froth flotation in various ways. For example, talc is naturally hydrophobic and floats readily, 
competing with the value minerals in the froth phase and resulting in lower concentrate grades. 
Serpentines, on the other hand, are  hydrophilic (Bremmel, 2005), so they do not report to the 
concentrate via true flotation. Various mechanisms for serpentine transport to the froth phase 
have been suggested such as: a) entrainment (Pietrobon, 1997), b) heterocoagulation (attachment 
of Mg silicates to Ni sulfides) (Edwards et. al., 1980) and c) transport of Mg silicates via 
composite particles having hydrophobic sites (Bremmell, 2005).  
In this investigation, the transport behavior of serpentines, especially ultramafic ores containing 
fibrous minerals is examined. The transport rates of serpentines showed a linear trend 
irrespective of the reagent and condition schemes used in flotation tests. To understand such  
trends, the physicochemical aspects of the serpentines in the pulp and froth phase were studied 
using optical microscopy, SEM and EDX techniques. Model system studies were carried out 
with nylon fibers in a micro-flotation cell to phenomenologically simulate the trend observed in 
transport of serpentines to the froth phase.  
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2. Material and Methods 
2.1 Materials 
Ultramafic Ni ore samples were supplied by Vale Technical Services in Mississauga, Canada. 
Based on MLA (Mineral Liberation analysis) and XRD, the ore samples contained 
approximately 1% (by weight) pentlandite and 60% serpentine. Nylon fibers with dimension of 
1cm long and approximately 15 micron in diameter were obtained from Nyconn Industries.  The 
fibers were also subjected to size reduction to about 700 µ using a locally available fiber cutter. 
After size reduction of the nylon fibers the aspect ratios (d/l) of the fibers were estimated to be 
around 50 (based on average length and thickness observed under SEM) .  
2.2 Flotation tests 
Ore ground at 50% solids used for flotation tests. Flotation tests were carried out with ultramafic 
Ni ores at 25% solids in a Denver cell using  a dithiophosphate-based collector (40 g/t) and 
MIBC (20 g/t)  frother for 12 minutes. Flotation tests were adjusted to pH levels ranging from 4-
5. Flotation tests were carried out at an impeller speed 1000 rpm and aeration rate of 3L/min. 
Concentrates were collected at 0.5, 1.5, 2, 3, and 5 mins. 
2.3 Optical microscopy and the SEM of pulp phase and froth samples 
Pulp phase samples were collected before and after the flotation test using a plastic dropper. 
Samples were also collected from the top half of the froth phase at regular intervals during the 
flotation test. Samples were immediately transferred to be observed under the optical microscope 
(Olympus BH-2). The samples viewed were as collected and also after 5 times dilution. For SEM 
studies the samples were collected in 10 ml glass vials and gently tumbled before placing a drop 
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of the froth/pulp sample on a SEM stub. A technique known as acetone-replacement drying 
(Fitzpatrick, 1980) was used instead of conventional drying to maintain the structural integrity of 
the sample. After drying and carbon coating the SEM/EDX of the samples were obtained using 
the Zeiss DSH 982 Gemini SEM and the Princeton Gamma Tech EDX system using low 
electron beam voltage (3KeV) to obtain high resolution images.  
2.4 Micro-flotation tests 
Micro-flotation tests were carried out in 100 ml glass cells with a porous frit. Nylon fibers of 
aspect ratio 50 were used in these experiments. Nylon fibers micro-flotation tests were carried 
out at 3-5 % (w/w) solids and for less than 5 minutes. Air flow rate was maintained at 100 
ml/min. 
3. Results and Discussions 
3.1 Flotation results 
According to Figure 1 Ni recovery showed a parabolic trend which is typical for minerals 
reporting to the concentrate by true flotation. In contrast, the trend for serpentine recovery (as 
determined by MgO assay) is linear irrespective of the reagents and conditions used in flotation. 
Such a linear trend is uncharacteristic of true flotation. As serpentines are typically not 
hydrophobic, it is reasonable to consider that the serpentines transport to the froth phase is not 
via true flotation. The linear trend is typical of mechanisms such as entrainment (Pietrobon, 
1997). If serpentines transport is via entrainment mechanism the a correlation between particle 
size of serpentines and their degree of entrainment (Maachar and Dobby, 1992) should exist. In 
order to determine the particle size of the serpentines, the sample in the pulp and froth phase was 
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characterized using optical microscopy, SEM/EDX. Screens and automated particle size 
analyzers were found to be ineffective for fibrous mineral particles. 
3.2 Particle size analysis of pulp and froth phase samples 
It can be seen from the optical microscopic images (Figure 2 a-b) of pulp and froth phase that 
macro-networks as large as 1-2 cm were observed. SEM of the networks carefully separated is 
shown in Figure 2c. It can be observed from SEM images that the networks are comprised  of 
fibrous as well as  fine particles. EDX spectra of this network structure showed Fe, Mg, Si and O 
peaks which are typical of serpentines. The XRD of these samples also indicated that they are 
Lizardite and Chrysotile type of serpentines.  
It is clear from the optical and SEM images that the serpentines do not exist as individual 
particles in the suspension but rather exhibit a macro-network like structure and their transport 
by entrainment is an unlikely mechanism. In fact  it seems that it is indeed the network of 
serpentines that is transported  through the suspension-bubble three phase system  to the froth 
phase. To develop an understanding of the mechanism of transport of such a macro-network our 
approach was to study the impact of the pore size of the network and the effect of bubble 
buoyancy using systems comprising of either chrysotile fibers or nylon fibers. Results with nylon 
fibers are reported here. 
3.3 Network pore sizes 
SEM micrographs (Figure 2c), suggest that the pore sizes for the serpentine network were as 
small as 20 microns. Based on various simulation based studies reported in literature, the 
apparent pore sizes across the network bed is expected to be even smaller, as the macro-network 
is typically in the form of layers (Switzer, 2004) of many small networks. Based on rheological 
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studies, the network is stable under high shear conditions typical of that observed in flotation 
cells (Vasudevan, 2010). It is also known from other simulation based studies (Lindström and 
Uesaka, 2008) that a network similar to that in this investigation can be quite sturdy and resistant 
to shear. 
3.4 Bubble-network interaction 
Typical bubble size in flotation is 1-2 mm and this is larger than the pore size of the network. It 
is thus unlikely that the bubbles will penetrate through the network. This suggests  that bubbles 
will accumulate at the network-water interface, and it is likely that large accumulation of bubbles 
will provide enough buoyancy force to thrust the network upward through the pulp phase and 
final reaching the froth phase. We have developed a phenomenological model to test this 
concept. 
3.5 Model system studies using nylon fibers:  
The transport of nylon fibers was studied in a micro-flotation. It was observed that layers of 
nylon fibers reported to the froth phase (Figure 3). A schematic of the whole transport process as 
observed is illustrated in Figure 3.  Figure 3a shows network of nylon fibers under turbulent 
conditions of the flotation cell. Figure 3b shows a schematic accumulation of air bubbles at the 
layers of network of nylon fibers. We observed that for the first 5 seconds there was neither 
transport of fibers nor formation a froth (Figure 3b) phase indicating the need for accumulation 
of bubbles at the nylon network-water interface developing a thrust due to the bubble-flux at the 
interface. Development of froth phase was observed after 5 seconds. Figure 3c shows that the 
entire network is transported to the froth phase. 
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Even though bubble entrapment in the fibrous network phenomenon has been widely studied, 
bubble flux driving a network from pulp to froth phase is largely unknown. Based on the above,  
the predominant mechanism in transport of the serpentines is proposed  to be  the bubble-flux-
driven upward flow of the network of serpentines.  
4. Conclusions 
Bubble-flux driven lift of the fibrous serpentine network contributes significantly to the transport 
of serpentines to the froth phase. The fibers entangle and form a network with an effective pore 
size much smaller than the bubble size which restricts percolation of the bubbles through the 
network. Thus, a swarm of bubbles is proposed to build up at the base of the network in the pulp, 
resulting in enough buoyancy thrust to enable the network to be transported from the pulp to the 
froth phase.   It is also important to note that other non-fibrous minerals can be  expected to be 
trapped in the network and  transported to the froth phase.  
 
5. Acknowledgements 
The authors would like to express their thanks to Zongfu Dai, Manqiu Xu, Andrew Lee and Ken 
Scholey at Vale Technical Services for their support of the collaborative program between 
Columbia University and Cytec Industries and for their input. We  also acknowledge the 
Industry/University Co-operative Research Center (IUCRC) at Columbia University for their 
support of the program.  
 
 
 
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6. References 
Bremmell, K., Fornasiero, D., Ralston, J., 2005. Pentlandite-Lizardite interactions and 
implications for their separation by flotation, Colloids and Surfaces A: Physicochemical and 
Engineering Aspects, Vol. 252, 207-212. 
Claridge, P. G., Tenbergen, P. A., 1975. Pipe ore processing developments in the Thompson 
Mill, Canadian Mining Journal, Vol. 96, No.6,  29-31. 
Edwards, C. R., Kipkie W. B., Agar, G. E., 1980. The effect of slime coatings of the serpentine 
minerals, chrysotile and lizardite, on pentlandite flotation, International Jounal of Mineral 
Processing, Vol. 7,  33-42. 
Eltham, J. A., Tilyard, P. A., 1973. An approach to the flotation of Western Australian Ni ores. 
Proceedings, Australasian Institute of Minerals and Metallurgy Annual Conference, Western 
Australia,  417-429. 
Fitzpatrick, E. A., Soil Microscopy and micromorphology, John Wiley and Sons, New York, 
NY, USA, 1993. 
Hess, H. H., 1933. The problem of serpentinization and the origin of certain chrysotile asbestos, 
talc, and soapstone deposits, Economic Geology, Vol. 28, No. 7, 634-657. 
Hoatson, D. M., Jaireth, S., Jaques, A. L., 2006. Nickel sulfide deposits in Australia: 
Characteristics, resources, and potential, Ore Geology Reviews, Vol. 29, 177-241. 
Lindström, S. B., Uesaka, T., 2008. Particle-level simulation of forming of the fiber network in 
papermaking, International Journal of Engineering Science, Vol. 46, 858–876. 
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Maachar, A., Dobby, G. S., 1992. Measurement of feed water recovery and entrainment solids 
recovery in flotation columns. Canadian Metallurgy. Quarterly, 31(3):, 167-172. 
Pietrobon, M. C., Grano, S. R., Sobieraj, S., Ralston, J., 1997. Recovery mechanisms for 
pentlandite and MgO bearing gangue minerals in Nickel ores from Western Australia, Minerals 
Engineering, Vol. 10, No. 8, 775-786. 
Switzer, L. H., Klingenberg, D. J., Scott, C. T., 2004. Handsheet formation and mechanical 
testing via fiber-level simulations. Nordic Pulp and Paper Research Journal. Vol. 19(4), 434-439. 
Vasudevan, M., Nagaraj, D. R., Patra, P., and Somasundaran, P. Effect of Altered Silicates on   
Metallurgical Performance - Part 1: Studies on the role of pulp rheology. Conference of 
Metallurgists, Vancouver, Canada, Oct 2010. 
 
 
 
 
 
 
 
 
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List of Figures 
Figure 1. Cumulative Ni/MgO recovery at various stages of flotation 
Figure 2. Optical images of samples taken from (a) pulp and (b) froth phase. Figure 2 c is the 
SEM image of the network carefully separated from the froth phase sample ( Sampling 
procedure detailed in experimental section). Note: The lines drawn in Figure a and b are the 
network observed under the optical microscope. 
Figure 3. Schematic of various steps in transport of fibrous network from flotation pulp to froth 
phase. The white colored material in the micro-flotation cells are nylon fibers. The fibers are 
represented as irregular lines in the schematic of micro-flotation cells. Gray colored circles are 
represented as air bubbles.  
 
 
  
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Figure 1. Cumulative Ni/MgO recovery at various stages of flotation 
 
 
 
 
 
 
 
 
 
 
MgO recovery 
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Figure 2. Optical images of samples taken from (a) pulp and (b) froth phase. Figure 2 c is 
the SEM image of the network carefully separated from the froth phase sample ( Sampling 
procedure detailed in experimental section). Note: The lines drawn in figure a and b are the 
network observed under the optical microscope 
 
 
 
 
 
 
 
 
 
 
 
 
a b 
c 100 µm c 
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Figure 3. Schematic of various steps in transport of fibrous network from flotation pulp to 
froth phase. The white colored material in the micro-flotation cells are nylon fibers. The 
fibers are represented as irregular lines in the schematic of micro-flotation cells. Gray 
colored circles are represented as air bubbles.  
  
Step (a) – 0 secs 
Nylon fibers suspended 
in pulp and without air 
bubbles 
Step (b) – at 5 secs 
Nylon fibers in pulp and 
after air bubbles were 
introduced 
Step (c) –  5 secs 
onwards 
Nylon fibers collected 
by bubble flux at the 
froth phase 
a b c 
Impeller 
Micro-
flotation cell 
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Graphical abstract 
 
 
 
 
 
 
 
 
 
 
 
 
 
Schematic of various steps in transport of fibrous mineral network from flotation pulp to 
froth phase. The white colored material in the micro-flotation cells are nylon fibers. The 
fibers are represented as irregular lines in the schematic of micro-flotation cells. Gray 
colored circles are represented as air bubbles.  
 
  
Step (a) – 0 secs 
Nylon fibers suspended 
in pulp and without air 
bubbles 
Step (b) – at 5 secs 
Nylon fibers in pulp and 
after air bubbles were 
introduced 
Step (c) –  5 secs 
onwards 
Nylon fibers collected 
by bubble flux at the 
froth phase 
a b c 
Impeller 
Micro-
flotation cell 
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Highlights: 
 Transport of gangue to flotation froth is problematic with fibrous ores  
 Entrainment/true flotation are proposed mechanisms by earlier researchers 
  Fibers entangle and form network in pulp with pore sizes less than bubbles 
 Bubbles percolation is restricted and thus accumulates at the network  
 Bubbles accumulation results  enough buoyancy thrust for network transport  


Transport of fibrous gangue mineral networks to froth by bubbles in flotation separation

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Transport of fibrous gangue mineral networks to froth by bubbles in flotation separation

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