Improved flowability of iron ore using superabsorbent polymers

Journal Pre-proof Improved flowability of iron ore using superabsorbent polymers

N. Gurulaxmi Srikakulapu, Cheela Sai Srikar, Dilip Makhija, Narayan Sharma PII:

S0032-5910(20)30102-9

DOI:

https://doi.org/10.1016/j.powtec.2020.01.089

Reference:

PTEC 15158

To appear in:

Powder Technology

Received date:

26 July 2019

Revised date:

18 January 2020

Accepted date:

31 January 2020

Please cite this article as: N.G. Srikakulapu, C.S. Srikar, D. Makhija, et al., Improved flowability of iron ore using superabsorbent polymers, Powder Technology(2019), https://doi.org/10.1016/j.powtec.2020.01.089

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2019 Published by Elsevier.

Journal Pre-proof

Improved flowability of iron ore using superabsorbent polymers N Gurulaxmi Srikakulapu*, Cheela Sai Srikar, Dilip Makhija, Narayan Sharma R&D, Tata Steel Limited, India

ABSTRACT Numerous bulk solid processing plants have been experiencing flow problems during handling, storage and transportation. In the present work, the concept of using superabsorbent polymers (SAP) to improve the flow of bulk solids particularly iron ore was investigated.

oo

f

Physical properties, absorption properties and mechanical properties of different SAPs were determined. Flowability analysis was studied to understand the flow behaviors of iron ore at

pr

various moisture levels ranging from 4% to 12%. Flow function curves for 12% moisture iron ore showed the change of flow regime from cohesive to easy-flow in the presence of SAP.

e-

The dosage of 100g/ton and retention time of 30min were obtained and incorporated during plant trials. The iron ore processing plant has achieved an increase in production during trials

Pr

and 24% increase for long run of SAP during monsoon.

Jo u

rn

al

Keywords: Flowability, Cohesion, Super Absorbent Polymers (SAP), Moisture, Iron ore

* Corresponding author E-mail: [email protected], Tel +919204651669, Fax +91657 2345405.

1

Journal Pre-proof

1

Introduction

Numerous mineral processing industries particularly dry processing plants handle huge tons of bulk solids such as iron ore in process equipment, conveyors, storage and transportation. During monsoons, run-of-mine (ROM) ore get exposed to high levels of moisture flowing in bins, silos and chutes which are eventually plagued with flow problems [1]. The moisture in the ore fines induces cohesion due to growth of adhering layer around the particles that cause bridge or arch formation in the equipment [2,3]. The influence of moisture on flow properties of iron ores and iron ore granules in sintering was highlighted in the literature [4-6]. Nevertheless, these fines also exhibited a tendency to gain cohesive strength over time and

oo

f

upon stresses thereby consolidation occurs during processing [7]. Consequently, dry processing plants have been suffering from inconsistent and unpredictable flow that could

pr

lead to bridging, channelling and flooding and resulted in great disparity of flow. Each of these has negatively impacted production efficiency, operating hours, specification product

e-

quality due to segregation and cost. Besides, loading, unloading and transportation of these moist ores were quite challenging [8-10]. In literature, several research studies have cited

Pr

various flow properties (bulk density, tapped density, Hausner ratio, Carr index, packing coefficient, angle of repose, handleability index, flow function, internal friction, wall friction,

ores [11-22].

al

cohesiveness) and their different measurement methods to understand flow behaviours of

rn

Typically mechanical flow aids such as air blasting, aeration, vibration methods were

Jo u

employed to counter-act consolidation forces, generate forces to disperse loose agglomerates and break bridging that had taken place. However, these techniques should be used to resolve flow issues once they have occurred and ineffective when the strength of solids is greater than the force generated by these techniques. These techniques including thermal drying required large force fields or heat, or other energy sources to enhance the flow properties. Along with several constraints such as inaccessibility, physical damage, design change and deterioration or destruction of product, safety hazards also exist for the practical application of these techniques in the plant. Consequently, controlling the surface moisture was the trigger to improve the flowability of ore fines. Although low moisture levels can be attainable, these are limited to ≥10% by any centrifugal or mechanical means (press filters, dewatering screens) regardless of the pressure applied, and these levels increases as the proportion of fines in the feed increases [23]. This was the result of energy utilization in compression rather than destroying liquid bridges between the particles. Henceforth, the

2

Journal Pre-proof application of superabsorbent polymer (SAP) is considered to be more practical to destroy liquid bridges by absorbing surface moisture and enhance flow properties (Fig. 1) [24]. SAP’s are high molecular weight partially cross-linked hydrophilic network which imbibe several hundred times their own mass of water and expand in size, but still retain individual particle identity. Due to their excellent absorption and retention properties, SAP’s have pursued development into wide range applications such as biomedical, personal care, agricultural etc. These can be ionic or non-ionic and their superlative imbibing mechanisms physically entrap water via diffusion, capillary forces in their macro porous structure and hydration of functional groups. Due to ionization at surface cause mutual electrodynamic

oo

f

repulsion that increase osmotic pressure, allow more water to enter and inflate SAP’s (Fig. 2) [25]. Despite the presence of polar groups, the hydrophobic crosslinks between chains inhibit solubilisation of SAP thus governing the extent of swelling.

pr

SAPs were applied in dewatering of coal, clays, activated sludge, metal plating sludge

e-

and achieved better results than centrifugal treatment [26]. The use of poly (N-isopropyl acrylamide) based SAP for coal slurry dewatering has reduced water content to 40% depend

Pr

on coal particle size [27, 28]. Based on polymer, dosage and polymer/coal contact time, the moisture of filer cake was reduced from 29% to ~12% [29]. Application of acrylamide-

al

acrylate copolymer based SAP for osmotic dewatering of fine brown coal has reduced moisture from 59% to 30% in a contact time of 4h [30, 31]. Similarly, SAP has reduced

rn

major amount of water during dewatering of fine coals [32, 33]. Further, modified SAPs with magnetic properties were developed to ease the dewatering of coal fines from 23.5% moisture

Jo u

to 10% moisture [34]. Moreover, SAP’s were also applied in rapid dewatering of bio-solids [35], densification of mature fine tailings [36-39], polymer-paste fills [40] and moisture absorption from natural gas, gasoline and kerosene [41]. Though these attempts confirmed potential application of SAP’s in dewatering, its practicality is still limited due to its dosage and regeneration issues [42]. Even SAP’s were found suitable in maritime transportation of mineral concentrates to prevent water migration and liquefaction that lead to subsequent capsize of cargoes [43]. SAP’s were also used to improve the handle ability of filter cake and fine clean coals [44]. Although, typically incorporated to improve process efficiency, SAP properties and its dosage could substantially influence the practical application [45]. These properties inherently depend on its composition, morphology, granulometry and process conditions. It is important to identify the lineaments required for any specific application to select the best suitable SAP (for e.g. SAP of high AUL is preferred for personal care application). Therefore, comprehensive understanding of SAP’s and their properties to design 3

Journal Pre-proof best suitable SAP for flowability and incorporating it at an optimal dosage in plant are crucial. The present study provides guidance on the selection and application of SAP’s (flow additives) for improving flowability of iron ore fines.

2

Materials and Methods

In the present work, bulk iron ore samples were collected from dry processing plant located in Northern India. A particle size distribution was determined for bulk ore using wet sieving method. The bulk iron ore sample was properly mixed and screened to minus 1mm particle size for testing. The screened iron ore sample was chemically analysed using inductively

oo

f

coupled plasma spectrometer. Mineralogical analysis of an iron ore was conducted using Xray diffraction method. Commercial Sodium Poly acrylate based SAP’s of 5.5-6.5 pH, max

2.1.1

SAP Characterization

e-

2.1

pr

moisture content of 6%, 0.53-0.73g/cc bulk density were used for flow properties study.

Physical Properties

Pr

Particle size distribution of SAPs was determined using dry sieving method. Morphological analyses of SAPs were conducted by a Scanning Electron Microscopy (SEM by JEOL Ltd).

al

These SAP samples were placed on electrical conductive platform using double-sided adhesive film and coated with a thin layer of gold in a vacuum chamber. Coated samples

rn

were analysed at an instrument accelerated voltage of 15kV and magnifications ranging from

Jo u

500x to 25000x. The flow properties such as Hausner ratio, Compressibility (Carr Index) were compared for these iron ore samples at different moistures. 2.1.2

Swelling Properties

Absorption capacities of SAPs were determined by gravimetric method. Approximately 0.2g of dry SAP was immersed in 200ml of distilled water and stirred with a magnetic stirrer for the intervals of 1, 2, 3, 5, 10, 30 and 60min. The swollen gel was subjected to filtration through a 100-mesh sieve and wiped rapidly before measuring the weight of the filtrate (sieve method). Water absorption capacity of SAP was determined (g of water per g of polymer) by the following equation [46]: ()

( )

( ) ( )

4

Journal Pre-proof Other media such as distilled water, tap water, plant process water was also used to understand the effect of water quality on the performance of SAP. 2.1.3

Mechanical Properties

Gel strength of SAP’s particles was determined using MCR P-PTD 200 rotational rheometer (Anton Paar GmbH, Austria) with air bearing system at 25o C. Approximately 100-150mg of SAP’s samples was incubated in 200ml of distilled water for 30min at room temperature to reach equilibrium swelling. Rheological behaviour was studied when SAP subjected to sinusoidal shear oscillation at a fixed deformation on the gel body located between the plates of parallel plate geometry (plate diameter of 25mm, gap height of 1mm). The applied strain

oo

f

or deformation was chosen to be in the linear viscoelastic (LVE) zone (i.e. G’ and G” independent of strain amplitude). Amplitude sweep was done from 0.01-100% strain at

pr

10rad/s frequency at 25o C to quantify the linear viscoelastic range of SAP. The oscillatory measurements were carried out in 0.1-10 rad/s angular frequency range at constant strain in

Flow Properties

Pr

2.2

e-

the LVE region.

Powder Flow Tester (PFT) of Brookfield Engineering Laboratories, USA was used to study

al

the flow properties of iron ore at R&D Jamipol, Jamshedpur. This is based on Jenike’s principle and operated to drive a compression lid attached with vane vertically downward

rn

into a sample contained in an annular shear cell. The consolidating pressure in the shear cell causes the particles to move closer together, simulating what actually happens in the bins,

Jo u

hoppers etc. At each of increasing consolidating stresses, the annular shear cell is rotated through a relatively small angular displacement of 1 rev/h and 1mm/s of torsional and axial speed respectively. Samples were weighed, placed in the trough that is positioned on the shear cell and levelled using flat shaped blades. Powder Flow Pro software was used to analyse the data and obtain instantaneous flow function curves along with internal friction angle, compressibility curves (density). PFT was operated in a standard flow function mode with applied consolidation stress levels ranging from 0.2 to 4.8kPa. The test samples were prepared by screening bulk sample to less than 1mm particle size. This was undertaken, as it was considered that the fines dictate the flowability of the material and system should be designed to handle the fines. Initially, the effect of iron ore moisture ranging from 4% (dry) to 12% on its flowability was established in the absence of SAP. Later, the addition of different superabsorbent polymers (SAP’s) at various dosages to iron ore and its flow properties were analysed. During the lab tests, iron ore sample of 0.5kg was thoroughly 5

Journal Pre-proof mixed with SAP using spatula to prepare various relative weights of SAP’s to iron ore ranging from 0.01 to 0.06%. Each of these samples was allowed to set SAP to absorb moisture from the ore with a minimum time of 10min. During the process, a best suitable SAP at optimum dosage was selected for plant trials. 2.3

Plant Trials

Dry processing plant was designed for 1000tph at 30-35% fines in the ROM feed. Due to change in ore quality particularly fines content in ROM (increased to 60-80%) and a relative humidity or moisture level, plant was operated at low throughput (50% of designed tph).

f

Previously, plant has been using a flow additive such as ethoxylated sorbitan mono stearate

oo

(EOS) that lubricated interparticulate movement and disrupted cohesive bonds between particles. Despite this effort, plant throughput increased marginally up to 600tph. The

pr

problem of frequent jamming of equipment reduced the availability of the plant. Therefore, the use of SAP for improving flowability and throughput of iron ore fines was explored. In

e-

the initial phase, plant audit was performed to confirm the proper mixing points at transfer

Pr

chutes and maintain minimum retention time of 30 min. Dry SAP powder that stored in a hopper was continuous pneumatically conveyed to apron feeder of iron ore using venture eductor. SAP dosage was controlled through vibrofeeder speed regulator that fitted to the

3

rn

al

hopper discharge as shown in the Fig. 3.

Results and Discussion

Jo u

The iron ore sample comprises an assay of 63.5% Fe (T), 2.25% Al2 O3 and 2.8% SiO 2 . From the Fig. 4, the particle size distribution of iron ore showed 58% of fines (< 1mm) and 33% of ultra-fines (< 25 microns). Mineralogical analysis showed hematite, kaolinite and quartz as major mineral phases present in ore. Initially, Compressibility (Carr index) and Hausner ratios of screened iron ores at various moistures (relative friction between particles) are measured using the following equations and depicted in Table 1 [47]. An increase in the values of Hausner ratio and Compressibility with moisture depicts the increase in cohesiveness of the iron ore. These results has showed cohesive, very cohesive or very very cohesive flow character for iron ore with 8%, 10% and 12% moisture respectively. (

)

(

)

6

Journal Pre-proof

Where ρb and ρt are bulk density and tapped density of material. 3.1 3.1.1

SAP properties Structure Analysis

The surface morphologies of commercially available SAP particles are depicted in Fig. 5. It is observed that micrographs of SAP’s displayed different morphologies and particle size distributions. The particle shape and cracks (porosity) on the SAP surface affects the

oo

f

diffusion and water absorption properties. R1 has smooth non-crosslinked surface, globular shaped fine particles and high surface cracks that are uniformly interconnected forming a

pr

network with increased surface area. R2 has dense crosslinked surface, irregular shaped particles and moderate cracks on the surface. R3 has smooth surface with irregular shaped

e-

particles. Another morphological property i.e., particle size distribution also affects the water absorption properties of SAP used in flowability due to their high surface area. These

Pr

properties define the SAP retention time required for the plant application. Henceforth SAP is designed (R2 designed) by grinding R2 SAP particles in a ball mill to finer particle sizes to

al

improve their absorption properties. The fineness of SAP is observed in the following order

3.1.2

rn

of R2 (Designed) > R1 > R3 > R2 (Fig. 6). Absorption capacity

Jo u

The SAP particle of 1mm size will swell up to 2 to 4mm size after absorption in 30min of mixing time. Fig. 7 shows the absorption properties of these SAP’s in the presence of water. Absorption capacities of SAPs follow the rapid increasing trend before attaining constant at equilibrium. It was observed that absorption capacities are 310g/g, 237g/g, 214g/g, 258g/g for R1 , R2 Designed, R2 and R3 respectively. It was observed that the presence of cracks on surface has significant control on absorption capacities of SAP’s due to water diffusion in the cracks. Besides, it was indicated that absorption capacity of SAP can be enhanced (R2 designed) with fine particle size distribution of same SAP (R2 ). The minimum time required for attaining equilibrium for all SAP’s was about around 10-15min that defined the minimum retention time required for plant implementation. These results foresight the SAP’s behaviour in controlling flowability of iron ore fines at plant. The effect of quality of clear & process recycle water on absorption capacities of SAPs were also studied and observed not much change in absorption properties of SAP. 7

Journal Pre-proof 3.1.3

Gel Strength

In practical application, SAP’s should have sufficient physical integrity (non-sticky, high elasticity) to resist the stresses generated during handling and transportation. Mechanical or gel strength of SAPs are represented through G’, storage modulus measures reversible elastic storable deformation energy (gel nature) and G”, loss modulus measures irreversible energy dissipated during flow [48]. The frequency dependency of storage and loss modulus for different SAPs is depicted in Fig. 8. According to this figure, G’ > G” that indicates high gel nature of SAP, and its plateau length and magnitude defines deformability of SAP and gel strength respectively. The gel strength of these SAPs are in the order of R2 (Designed) > R2 >

oo

f

R3 > R1 . Though R1 has showed high absorption properties, gel strength is low due to lack of surface crosslinking. R2 (Designed) has moderate absorption properties and good gel strength with stiffer particles due to surface crosslinking. Detailed analysis of gel strength, yield stress

pr

and yield strain are represented in the Table 2. From the Fig. 9, constant G’ was observed

e-

against the frequency. At low frequency, G’ and G” are tending to converge slowly. The crossover of G’ and G” may happen at a high frequency that indicate the good physical

Pr

integrity of SAP particles to prevent the bleeding of water from the swelling matrix. The absorbed liquid is not released easily or quickly as it is immobilized by sequestration rather

al

than being retained in polymer structure. Though it is limited to equilibrium point, the

3.2

Flowability Analysis

rn

quantity of absorbed water during flowability is much lesser than the equilibrium point.

Jo u

Most recognized flow indicator is the yield locus that represents shear stress (τ) viewed as a function of the consolidation stress (σ), defined in a simplest form of Mohr-Coulomb failure criteria (Flow Function, eq1) at any given pre-shear condition [49]. (

)

Where, φ is the angle of internal friction and intercepts C is cohesion. Mohr circles and yield loci of bulk solids give major consolidation stress (σ1 ) and the corresponding unconfined yield strength (σc) at all consolidation end points (σE). 3.2.1

Effect of Moisture

Fig. 10 indicates the instantaneous flow function curves for iron ore at different moistures ranging from 4% (dry) to 12% without SAP. These flow behaviours were explained by Jenike’s

classification

of

flowability

using

instantaneous

flow

function

(FF)

values

(reciprocal of flow function slope (σ1 /σc)). Table 3 shows the flow properties of iron ore at 8

Journal Pre-proof different moisture levels. Table 4 shows the flow behaviours of iron ore samples that followed free flow for 4% moisture, easy flow for 8% moisture, and cohesive flow behaviour for 10%-12% moisture. The presence of moisture generate capillary forces due to capillary pressure of liquid bridges in the contact zone of particle and thereby increase the unconfined yield strength of the ore. The maximum unconfined yield strength can be attained depends on ore and its minerology, particle size distribution and other parameters. It was also noted that greatest difference in flow behaviour appeared to occur at the low consolidating pressures. This has been analogous to the situation where the fill level of ore in the bin or hopper has reduced significantly. Results showed moisture as a significant parameter that most likely to

oo

f

affect flowability of iron ore. The range of 10% to 12% moisture in iron ore is critical for easy flowing of iron ore during production at plant. Effective internal friction angle (δ) measures the resistance of the solids to flow in a steady state condition. Fig. 11 shows the

pr

effect of iron ore moisture on effective internal friction angle with respect to major

e-

consolidation stress. This effective internal friction angle is high at lower major consolidation stresses for iron ore samples and represents the relative contribution of adhesive forces to Effective internal friction angle increases with increase in the moisture

Pr

frictional forces [50].

3.2.2

Effect of SAP

al

to represent the increase in cohesiveness of the iron ore.

rn

The addition of different SAP’s to improve flow characteristics of iron ore was studied. In the view of optimization of dosage, interactions of SAP with ore and its role in enhancing flow

Jo u

behaviour is to be explored. Therefore flow properties such as cohesive strength, effective internal friction angle, FF values were measured to understand how easily an ore particle moves against other particle in the presence of 12% moisture using SAP. Though cohesive strength of iron ore at 12% moisture is about 1.074kPa under high major consolidation stress, it is decreased to 0.5-0.7kPa at same moisture by using 200ppm SAP (Fig. 12). Due to their superlative moisture absorption and disrupting the cohesive bonds between the particles, SAP showed excellent ability to control flow of the ore. The effective internal friction angle was decreased in the presence of SAP in a range of 40o -42o . Fig. 13 shows the flow function curves of iron ore at 12% moisture using various SAPs of 200ppm with retention time of 10min. Further flowability improvement is experienced with increase in the retention time. Though R1 has better absorption properties, its mechanical strength is much lesser than other SAP’s. SAP gel strength is an important property that defines the water retention required to hold absorbed water for longer travel distances and stresses. Based on moderate absorption 9

Journal Pre-proof properties, good gel strength and finer particle size distribution, R2 (Designed) was selected for iron ore flowability enhancement. Besides, R2 Designed was high available at low cost and used at a dosage of 100ppm (for 50% of fines) with retention time of 30min for plant trials.

4

Plant trials and Implementation

Based on the inherent properties, cost and ability to improve iron ore flowability, R2 (Designed) was selected for plant trials. During the trial period, plant throughput data and the corresponding SAP dosage was collected. From the Fig. 14, it is clear that TPH per shift of

oo

f

production has increased to >700 tph. Low TPH points were due to other issues such as unavailability of ROM ore, mechanical maintenance etc. encountered during the plant trials.

pr

On an average of 40% increase in production rate (TPH) was found at iron ore dry processing plant. During the trials, the consumption of the SAP was slightly higher than the 100ppm,

e-

later further optimized and decreased to < 100ppm. From the Fig. 15, it is indicated that an average of 5500TPH of iron ore production was increased. Therefore the production of iron

Pr

ore at dry processing plants was observed to be increased using SAP. After the trials, plant has implemented SAP as flow additive to improve flowability of iron ore. Fig. 16 showed

al

that 24% increase in production of iron ore at dry processing plant during monsoon season (June to Sep). Henceforth, it was proved the application of SAP for enhancing flowability of

rn

iron ore and its production at dry processing plant. Furthermore, SAP simultaneously

Jo u

implemented at dry solids handling (logistics). It has showed substantial effect on response to consolidation, compressibility etc., that benefitted during rail transportation and unloading.

5

Conclusions

Iron ore fines of -1mm size were used to study their flow characteristics at 8 to 12% moisture levels. Compressibility, Hausner ratio, effective angle of internal friction and cohesion properties was quantified for iron ore at each moisture level. The applicability of superabsorbent polymers for iron ore flowability enhancement was investigated. Physical, absorption and mechanical properties of various SAP’s were assessed and selected best suitable SAP for flowability application. The key parameter for the selection of suitable SAP for flowability was identified as particle size. Moderate absorption, good gel strength and finer particle size distribution of SAP was required for flowability application. Flow function curves of 12% moisture iron ore demonstrated the change of flow regime from cohesive to 10

Journal Pre-proof easy-flow in the presence of SAP. SAP dosage of 100g/ton of ore (50% of fines in ROM) with maximum retention time of 30min was identified for plant trials. Pneumatic mixing of SAP with iron ore and its dosage optimization (75-150g/ton of ore) depending on ore feed moisture was implemented at dry processing plant. The results showed 40% increase in production during trials and 24% increase in long run implementation of SAP during monsoon. However, it is important that proper mixing of SAP with iron ore could affect the performance of SAP used for flowability application. Also, SAP dosage depends on the mineral chemistry, granulometry and their surface morphology. Henceforth, flowability

6

oo

f

studies of mineral are essential to optimize SAP dosage prior to the implementation.

Acknowledgments

pr

Authors are gratefully acknowledging Jamipol Management team especially Mr Naresh Rao for providing facilities to conduct flow property tests. Support provided by dry processing

e-

plant professionals to execute trials and implement at their production sites is also duly

References

al

[1] J. Plinke, J. D. Prigge, K. C. Williams, Development of new analysis methods for the

294, pp.252-258.

rn

characterization and classification of wet sticky ores, Powder Technology (2016),

[2] M. E. Plinke, D. Leitch and F. Loffler, Cohesion in granular materials, Bulk Solids

Jo u

7

Pr

acknowledged.

Handling (1994), 14, pp.101-106. [3] N. Mitarai and F. Nori, Wet granular materials, Advances in Physics (2006), 55, pp.145.

[4] W. Chen, A. Roberts, K. Williams, J. Miller and J. Plinke, On uniaxial compression and Jenike direct shear testings of cohesive iron ore materials, Powder technology (2017), 312, pp. 184-193. [5] M. Zhou, H. Zhou, T. Honeyands, D. P. O’dea, B. G. Ellis, P. Ma and Y. Li, Evaluation of compression strength and shear strength of the adhering layer of granules in iron ore sintering, Powder Technology (2018), 338, pp.599-607. [6] C. Li, R. Moreno-Atanasio, D. O’dea and T. Honeyands, Experimental study on the physical properties of iron ore granules made from Australian iron ores, ISIJ International (2019), 59(2), pp.253-262. 11

Journal Pre-proof [7] A. W. Roberts and O. J. Scott, Bulk materials handling in the mining industry, http://www.maden.org.tr/resimler/ekler/5a0f1963430da06_ek.pdf ,1993. [8] G. O’Brien, J. Graham, S. Gnanananthan, D. Nemeth, M. O’Brien, B. Firth and P. Girgenti, Improving the unloading of Queensland coal from rail wagons, Proceedings of IX Australian Coal Preparation Conference (January 2002), Rockhampton, Australia. [9] W. Chen, A. Roberts, A. Katterfeld and C. Wheeler, Modelling the stability of iron ore bulk cargoes during marine transport, Powder Technology (2018), 326, pp.255264.

f

R. F. Ferreira, T. M. Pereira and R. M. F. Lima, A model for estimating the

oo

[10]

PFD80 transportable moisture limit of iron ore fines, Powder Technology (2019), 345, pp.329-337.

R. O. Grey and J. K. Beddow, On the hausner ratio and its relationship to

pr

[11]

[12]

e-

some properties of metal powders, Powder Technology (1969), 2(6), pp.323-326. E. C. Abdullah and D. Geldart, The use of bulk density measurements as

[13]

Pr

flowability indicators, Powder Technology (1999), 102, pp.151-165. D. Geldart, E. C. Abdullah, A. Hassanpour, L. C. Nwoke and I. Wouters,

al

Characterization of powder flowability using measurement of angle of repose, China Particuology (2006), 4(3-4), pp.104-107. M. Viana, C. M. D. Gabaude-Renou, C. Pontier and D. Chulia, The packing

rn

[14]

Jo u

coefficient: a suitable parameter to assess the flow properties of powders, KONA (2001), 19, pp.85-93. [15]

W. Wang, J. Zhang, S. Yang, H. Zhang, H. Yang and G. Yue, Experimental

study on angle of repose of pulverized coal, Particuology (2010), 8(5), pp.482-485. [16]

A. Santomaso, P. Lazzaro and P. Canu, Powder flowability and density ratios:

the impact of granules packing, Chemical Engineering Science (2003), 58, pp.28572874. [17]

D. W. Brown and N. J. Miles, Assessment of coal handleability, Coal

Preparation (2004), 24, pp.99-122. [18]

R. A. Mikka and J. B. Smitham, Coal handleability assessment, Coal

Preapartion (1993), 12, pp.187-201. [19]

K. Terashita, K. Miyanami, T. Konishi and K. Furubayashi, Flowability

assessment of fine coals based on dynamic properties, KONA (1986), 4, pp.35-45.

12

Journal Pre-proof [20]

H. Tsunakawa, D. Kunii, F. Takagi, M. Sugita, T. Tamura and H. Haze,

Comparing the flow properties of bulk solids by tri-axial shear, unconfined yield and direct shear tests, KONA (1988), 6, pp.15-22. [21]

P. A. Kulkarni, R. J. Berry and M. S. A. Bradley, Review of the flowability

measuring

techniques

for

powder

Institution of Mechanical Engineers,

metallurgical industry,

Proceedings

of the

Part E: Journal of Process Mechanical

Engineering, 224, pp.159-168. [22]

A. P. Grima, B. P. Mills and P. W. Wypych, Investigation of measuring wall

friction on a large scale wall friction tester and the Jenike direct shear tester.

oo

f

Proceedings of 3rd International Conference Exhibition BulkSolids Europe (2010), Wuerzburg, Germany, pp.1-14. [23]

F. Peer, and T. Venter, Dewatering of coal fines using a superabsorbent

pr

polymer, The Journal of The South African Institute of Mining and Metallurgy

[24]

e-

(2003), July/August, pp.403-410.

G. P. T. Dzinomwa, C. J. Wood, and D. J. T. Hill, Fine coal dewatering using

Pr

pH- and temperature-sensitive superabsorbent polymers, Polymers for Advanced Technologies (1997), 8, pp. 767-772.

P. Brown, Superabsorbent principles & properties, VISION Consumer

al

[25]

Products Conference (January 23-26, 2012), New Orleans, Louisiana. K. Masuda and H. Iwata, Dewatering of particulate materials utilizing highly

rn

[26]

[27]

Jo u

water-absorptive polymer, Powder Technology (1990), 63, pp.113-119. S. H. Gehrke, Synthesis, equilibrium swelling, kinetics, permeability and

applications of environmentally responsive gels, Advances in Polymer Science (1993), 110, pp.81-114. [28]

S. H. Gehrke, L. Lii-Hurng, and B. Kristopher, Dewatering fine coal slurries

by gel extraction, Separation Science and Technology(1998), 33(10), pp. 1467-1485. [29]

G. P. T. Dzinomwa, C. J. Wood and R. Rong, Dewatering of fine coal using

superabsorbent polymers, PhD Thesis (1996), University of Queensland. [30] Brown

S. Devasahayam, M. A. Ameen, T. V. Verheyen, and S. Bandyopadhyay, coal

dewatering

using

superabsorbent polymers. Minerals [31]

poly(acrylamide-co-potassium

acrylic)

based

(2015), 5, pp.623-636.

S. Devasahayam, S. Bandyopadhyay and D. J. T. Hill, Study on Victorian

brown coal dewatering by super absorbent polymers using attenuated total reflection

13

Journal Pre-proof fourier

transform

infrared

spectroscopy,

Mineral

Processing

and

Extractive

Metallurgy Review (2016), 37(4), pp.220-226. [32]

D. Osborne, Super polymers In: The coal handbook – Towards cleaner

production (2013),

Volume 1:Coal Production, Woodhead Publishing Limited,

Cambridge, UK. [33]

P. E Hand, Super absorbent polymers, Dewatering and drying of fine coal to a

saleable

product,

Coaltech

2020

report,

http://www.wrc.org.za/wp-

content/uploads/mdocs/, 2000 [34]

S. Zhang, H. Chen, S. Liu and J. Guo, Superabsorbent polymer with high

oo

f

swelling ratio, and temperature-sensitive and magnetic properties employed as an efficient dewatering medium of fine coal, Energy Fuels (2017), 31, pp. 1825-1831. H. Xia., A. Takashi, U. Hajime and H. Okihiko, Dewatering of biological

slurry

by

using

water-absorbent

[36]

gel,

Biotechnology

and

e-

Bioengineering(1989), 34, pp. 102-109.

polymer

pr

[35]

A. Roshani, M. Fall, and K. Kennedy, Drying behaviour of mature fine

Pr

tailings pre-dewatered with super-absorbent polymer (SAP): Column experiments, Geotechnical Testing Journal (2017), 40 (2), pp.210-220. A. Roshani, Drying behaviour of oil sand mature fine tailings pre-dewatered

al

[37]

with superabsorbent polymer, Ph.D. Thesis (2017), University of Ottawa. A. Roshani, M. Fall, and K. Kennedy, Impact of drying on geo-environmental

rn

[38]

Jo u

properties of mature fine tailings pre-dewatered with super absorbent polymer, International Journal of Environmental Science and Technology (2016), 14 (3), pp. 453-462. [39]

A. Farkish and M. Fall, Rapid dewatering of oil and sand mature fine tailings

using super absorbent polymer (SAP), Minerals Engineering (2013), 50-51, pp.38-47. [40]

M. Fall, J. Celestin, and H. F. Sen, Potential use of densified polymer-pastefill

mixture as waste containment barrier materials, Waste Management (2010), 30, pp. 2570-2578. [41]

A. Javad, H. B Saeid and R. Zahra, Application of hydrogels in drying

operation, Petroleum and Coal (2005), 47(3), pp.32-37. [42]

J. S. Laskowski, Superabsorbents, in: Coal flotation and fine coal utilization,

Developments in Mineral Processing (14), Elsevier, Netherlands, 2001, pp. 314-316. [43]

Rene Pich, Pascal Boehm and Gilles Zakosek, Method for loading loose iron

ore partially treated by means of superabsorbents, US Patent 2016/0101949 A1. 14

Journal Pre-proof [44]

G. Moody., The use of polyacrylamides in mineral processing, Minerals

Engineering (1992), 5(3-5), pp.479-492. [45]

H. Baloch, M. Usman, S. A. Rizwan and A. Hanif, Properties enhancement of

super absorbent polymer (SAP) incorporated self-compacting cement pastes modified by nano silica (NS) addition, Construction and Building Materials (2019), 203, pp.1826. [46]

M. J. Zohuriaan-Mehr and K. Kabiri, Superabsorbent polymer materials: A

review, Iranian Polymer Journal (2008), 17(6), pp.451-477. [47]

R. L. Carr, Evaluating flow properties of solids, Chemical Engineering (1965),

oo

[48]

f

72, pp.163-168.

M. J. Ramazani-Harandi, M. J. Zohuriaan-Mehr, A. A. Yousefi, A. Ershad-

Langroudi and K. Kabiri, Effects of structural variables on AUL and rheological

pr

behaviour of SAP gels, Journal of Applied Polymer Science (2009), 113, pp.3676-

[49]

J. Schwedes, Review on testers for measuring flow properties of bulk solids,

Pr

Granular Matter (2003), 5, pp. 1-43. [50]

e-

3686.

G. Vivek, S. S. Mallick, P. Garcia-Trinanes and J. B. Robert, An investigation

al

into the flowability of fine powders used in pharmaceutical industries, Powder

Jo u

rn

Technology (2018), 336, pp.375-382.

15

Journal Pre-proof Table 1 Flowability characteristics of moist iron ores based on Hausner Ratio and Carr index. ρb (kg/m3 )

ρt (kg/m3 )

Compressibility

Hausner Ratio

Flow Character

Dry iron ore

1901

2318

17.99

1.22

Fair

6% iron ore

1497

2099

28.68

1.40

Poor

8% iron ore

1380

2056

32.88

1.49

Very cohesive

10% iron ore

1411

2199

35.83

1.56

Very cohesive

12% iron ore

1622

2840

42.86

1.75

Very very poor

Sample

f

Table 2 Mechanical properties of swollen SAP Gel Strength (Pa)

Yield Stress (Pa)

Yield Strain (%)

R1

647

4.3

0.9

R3

872

5.6

1.3

R2

1044

9.5

1.4

R2 (Designed)

1390

12.7

1.4

Pr

e-

pr

oo

Sample

Table 3 Test data for flow property testing for iron ore samples

0.350

IO(8% Moist)

IO(10% Moist)

Cohesion(kPa)

Effective

internal

friction angle (o )

0.642

0.098

35.8

0.025

39.5

1.222

0.128

35.5

0.033

38.1

Jo u

0.646

al

IO(Dry)

σE(kPa) σ1 (kPa) σc(kPa) Angle(o )

rn

Sample

1.245

2.370

0.177

35.9

0.045

37.7

2.451

4.655

0.387

35.4

0.100

37.4

4.888

9.054

0.636

35.6

0.163

37.3

0.337

0.630

0.168

35.6

0.043

42.5

0.633

1.202

0.387

32.6

0.106

41.4

1.234

2.374

0.633

32.8

0.173

40.0

2.438

4.752

1.099

33.1

0.298

39.2

4.877

9.184

1.89

33.7

0.506

39.0

0.331

0.595

0.304

29.8

0.088

45.9

0.63

1.192

0.409

31.4

0.115

41.1

1.227

2.332

0.771

30.6

0.220

40.0

2.435

4.624

1.319

31.6

0.369

39.4 16

Journal Pre-proof

IO(12% Moist)

4.873

9.293

2.451

32.2

0.676

39.3

0.327

0.791

0.721

27.4

0.219

69.5

0.625

1.457

1.031

30.3

0.295

55.5

1.223

2.728

1.472

31.0

0.416

48.0

2.439

5.473

2.510

31.5

0.702

45.2

4.885

11.441

3.945

32.8

1.074

42.4

Table 4 Jenike’s Flow Function (FF) and their Flow Regimes of moist iron ores

FF

Standard

Flow Regime

Dry

14.28

10 < FF

Free-flowing

8% Moisture

4.76

4 < FF <10

Easy-flowing

10% Moisture

3.85

2 < FF < 4

Cohesive

12% Moisture

3.0

2 < FF < 4

Cohesive

Jo u

rn

al

Pr

e-

pr

oo

f

Iron Ore Sample

17

Journal Pre-proof

Proper mixing

Wet Iron ore particles

Dry Iron ore particles

Swollen wet SAP

f

Dry SAP

pr

oo

Fig. 1. Absorption of iron ore moisture by SAP particles

al

Pr

e-

Hydrophobic crosslinks

rn

Figure 2: Mechanism of water absorption in SAP

Jo u

Fig. 2. Schematic representation of SAP swelling and its mechanism (Courtesy of BASF) Nozzle SAP Hooper

Apron Feeder/Transfer

Vibrofeeder (control the flowrates)

chute of conveyor

Chute

Air Compressor

Φ 1”

Isolating

Φ 0.5”

Φ 1.5” Venturi Eductor, nozzle ϕ 0.25”

Fig. 3. Schematic diagram of pneumatic dosing of SAP in plant trials 18

Journal Pre-proof 100

Cum. Passing, Wt%

90 80

70 60 50 40

30 20 10 100

1000 Particle Size, microns

oo

10

f

0

10000

Jo u

rn

al

Pr

e-

pr

Fig. 4. Particle size distribution of bulk iron ore from dry processing plant

19

Journal Pre-proof

a)

a)

a)

Pr

e-

pr

oo

f

a)

b)

Jo u

rn

al

b)

b)

b)

20

Journal Pre-proof c)

c)

c)

Pr

e-

pr

oo

f

c)

al

Fig. 5. SEM Micrographs of SAP’s (a) R1 (non-crosslinked surface) (b) R2 (dense crosslinked

rn

surface by 80%) (c) R3 (smooth crosslinked surface) 100.00

Cum. Wt% Retained

80.00 70.00 60.00

R2(Designed) R1 R3 R2

Jo u

90.00

50.00 40.00 30.00

20.00 10.00 0.00 0

0.2

0.4

0.6 Size,mm

0.8

1

1.2

Fig. 6. Particle size distribution of various SAP particles

21

Journal Pre-proof

250

200 R1

150

R3 R2

100

f

R2(Designed)

oo

50

0

300

pr

0 600

900

1200

1500

1800

e-

Time, s

R2

G’ R1

rn

al

Pr

Fig. 7. Absorption capacities of SAP’s in the presence of water

Jo u

Absorbed water (g of water/g of SAP)

300

G”

R3

R2 Designed

Fig. 8. Storage and Loss modulus of swollen SAP at amplitude sweep

22

Journal Pre-proof

R3

R1

R2

oo

f

R2 Designed

Jo u

rn

al

Pr

e-

pr

Fig. 9. Storage and Loss modulus of swollen SAP at frequency sweep

Fig. 10. Instantaneous flow function curve for moist iron ores without SAP

23

Journal Pre-proof

Effective angle of Internal Friction (o )

60 Dry 8% Moisture 10% Moisture 12% Moisture

55

50 45 40

35 30 25

20 1

2

3

4

5

6

7

8

9

10

11

12

f

0

oo

Major Principal Consolidation Stress, kPa

e-

pr

Fig. 11. Effect of iron ore moisture on effective internal friction angle

1.2

Pr

12% MOI IO 12%MOI & R1 12%MOI & R2 12%MOI & R2 Designed 12%MOI & R3 12%MOI & EOS

al

0.8

rn

0.6 0.4 0.2

Jo u

Cohesive Strength, kPa

1

0

0

2

4

6

8

10

12

14

Major Principal Consolidation Stress, kPa

Fig. 12. Cohesive strength of 12% moisture iron ore with SAPs

24

al

Pr

e-

pr

oo

f

Journal Pre-proof

Jo u

rn

Fig. 13. Flow Function curves of 12% moisture iron ore with SAP (200ppm)

Fig. 14. TPH data per shift during SAP plant trials

25

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

Fig. 15. Tonnage per day data during SAP trials

Fig. 16. Dry plant production using SAP during monsoon (June to Sep)

26

Journal Pre-proof Declaration of interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Jo u

rn

al

Pr

e-

pr

oo

f

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

27

Journal Pre-proof

Improved flowability of iron ore using superabsorbent polymers N Gurulaxmi Srikakulapu*, Dilip Makhija, Cheela Sai Srikar, Narayan Sharma R&D, Tata Steel Limited, India

Jo u

rn

al

Pr

e-

pr

oo

f

Graphical Abstract

28

Journal Pre-proof

Improved flowability of iron ore using superabsorbent polymers N Gurulaxmi Srikakulapu*, Dilip Makhija, Cheela Sai Srikar, Narayan Sharma R&D, Tata Steel Limited, India

Research Highlights

Flowability tests of iron ore using superabsorbent polymers were carried out in Powder Flow Tester. Superabsorbent polymers were selected based on physical, absorption and mechanical property studies. Effect of moisture and SAP dosage on improvement of flowability of iron ore was studied. SAP application increased production of iron ore at dry processing plant during monsoon. 24% of increase in iron ore production was achieved at production sites.

pr

e-

Pr



al



rn



Jo u



oo

f



29