Dry Iron Ore Fluidization, Flowability, and Handling: Supporting Dry Processing of Iron Ores and Guiding Industrial Designing

Abstract

Renewed interest in dry processing has arisen due to challenges in water management. In dry iron ore beneficiation, flowability of bulk solids is a key concern, leading to issues like plugging and clogging in bins and chutes. Handling also faces challenges from environmental regulations, particularly regarding dust emissions. Enclosed conveyor technologies, such as air-assisted conveyors that use fluidization, offer effective solutions, though the maximum particle size that can be conveyed is a limitation that needs consideration. This paper examines how the size and chemical composition of bulk iron ore materials affect their handling behavior. By employing Geldart’s and Jenike’s methods, this document provides technical parameters and recommendations, which are lacking in the current literature, for the designing of dry processing plants. Findings indicate that ultrafines can have a flow function as low as 2.05, indicating cohesive behavior even when dried, while fluidization tests support these characteristics. In contrast, coarser fractions are easy for free-flowing materials. Samples with a top size of 0.5 mm fall between sand-like and spoutable groups in Geldart’s classification. Denser materials did not fluidize, while less dense ones did. Thus, air slides should avoid handling materials at this threshold and focus on finer materials. This paper offers guidance for designing dry processing plants to address handling bottlenecks.

1. Introduction

Crushing is the first stage of comminution, usually reducing rocks from around 1000 mm to a range between 4 and 19 mm [1,2,3]. Within the realm of iron ore mining and beneficiation of such coarse fractions, it is common to transport substantial quantities—often hundreds or even thousands of tons per hour—of natural or moistened bulk materials over distances ranging from a few meters to several kilometers. In this context, belt conveyors emerge as the predominant equipment adopted, given their adaptability in width and speed to accommodate a diverse range of applications [4,5], providing economic and reliable handling [6]. Moreover, belt conveyors are characterized by relatively low power consumption and quiet operation [7], being also capable of handling bulk materials that possess abrasive or corrosive properties.

Nevertheless, the decrease in the run-of-mine (ROM) grade is a continuous process arising from mining exploitation of iron deposits [6]. Thus, the operational continuity unavoidably undergoes the beneficiation of low-grade deposits, which requires fine comminution to separate the gangue and iron minerals. When it comes to low-grade itabirite ores, the so-called releasing size is as fine as 0.150 mm [8,9]. In such conditions, wet-way operations are primarily carried out to produce concentrates [10,11], and slurry pumping is the most frequently applied method to transport solids [12,13,14]. Meanwhile, deep concerns have been brought up as consequences of operational unresolved issues of water management [6,15,16], and players have faced a complex scenario. Large-scale wet-way operations require extensive amounts of water that can severely impact local supplies [17]. In addition, tailings are usually disposed and confined in large dams, and such structures present risks of rupture as evinced by historic records and underscored by recent events [18,19]. For such reasons, the interest in dry processing of iron ore has increased [15,16,17,18,19,20,21,22,23,24].

Important mining companies have guided investments and efforts on dry operations projects [25,26], but transitioning from consolidated conventional wet processing methods requires careful research to overcome the challenges posed by water-free processing [27]. The enhancement of iron ore dry beneficiation does not rely exclusively on concentration method development, but also on the selection of appropriate handling equipment and effective control of dust emissions, a relevant issue in mining [28,29,30,31,32,33,34]. These factors are vital to ensure safe and efficient operations to meet strict environmental and health standards, and prioritizing investments in mechanical equipment for transporting iron ore fines is essential to design and build cost-effective projects.

Enclosing devices are not usually required to convey iron ore particles. However, in dry operation conditions, environmental standards evolve and become increasingly rigorous; the issue of dust emissions gains prominence, particularly when handling fine bulk materials, such as pellet feed (fraction containing usually 95% passing 150 µm). Dust emissions may arise as a product of the movement of particles, particularly during transfers, combined with exogenous environmental factors [7,35], including wind intensity and frequency, and potential operational or maintenance inefficiencies. When addressing the handling and processing of completely dry iron ore, it is important to recognize that the associated conditions, criteria, and parameters undergo substantial changes that can adversely affect human health and safety and environmental integrity. Consequently, the use of open conveying equipment is typically deemed unsuitable. In situations where handling equipment is not enclosed, there is a necessity to contain the surrounding area. This requirement often calls for significant environmental sealing, which can dramatically elevate investment costs for short distances and render operations economically impractical for longer distances. To effectively navigate these challenges, four enclosed technologies have been identified as viable solutions for the handling of dry bulk materials on an industrial scale: pneumatic conveyors (PCs)—positive dense phase, drag chain conveyors (DCCs), screw conveyors (SCs), and air-assisted gravity conveyors, commonly referred to as air slides (ASs). Following consultations with respected manufacturers—including Aumund Group, Zeppelin, Vortex Global, Ibau Hamburg, Gambartotta Gschwendt, FLSmidth, and Dynamic Air—the key characteristics of each equipment type, along with their typical applications, are outlined in

Table 1. Enclosed conveyors of bulk materials for iron ore.

Features	PC	DCC	SC	AS
Distance covered 1	Max 200 m	Max 40 m–50 m	Max 12 m	Unlimited but requires verticalization
Tonnage 1	Low <50 t/h	Fair Max 650 t/h	Fairly low Max 250 t/h	Very high Max 4000 t/h
Power consumption 2	Very high 2 to 5 kWh/t	High 0.1 to 0.4 kWh/t	High 0.1 to 0.2 kWh/t	Very low 0.01 to 0.05 kWh/t
Investment expenditures 2	Very high	Very high	Very high	Low
Equipment weight 2	15 to 80 kg/m	800 to 2000 kg/m	40 to 200 kg/m	10 to 120 kg/m
Availability 1	Fairy high	Fairy high	Consistent high	Very high
Material temperature 1	Max 700 °C	Max 700 °C	Max 700 °C	Max 450 °C
Bulk material top size limit 1	500 mm	150 mm	400 mm	0.040 to 0.5 mm

¹ the higher, the better. ² the lower, the better.

.

As illustrated in Table 1, air slides present several notable advantages for the handling of iron ore, including high tonnage capacity, availability, low power consumption, reduced equipment weight, and lower investment costs. However, it is important to recognize that, despite their versatility, air slides necessitate the vertical alignment of facilities, as the movement of bulk materials is influenced by the combination of fluidization and gravitational forces. Typically, these conveyors are inclined at angles ranging from 2° to 14°, depending on the flowability and fluidization characteristics of the materials being transported. Furthermore, it is essential to acknowledge that the primary limitation of air slides pertains to the top size of the bulk materials that can be handled, which will be examined in greater detail within this paper.

Considering the advantages of air slides, this research aims to further explore the fluidization and flow properties of a selection of samples, which includes concentrates, tailings, and ultrafines typically present in iron ore beneficiation. Additionally, this study seeks to characterize dry iron ore in accordance with the theories of Geldart and Jenike to identify material limitations. The findings from this investigation will provide valuable insights for the future design of bins, hoppers, and air slide systems in the context of dry iron ore processing projects.

Bulk Materials Handling and Iron Ore Processing

The management of bulk materials represents a sophisticated and critical area of expertise, essential for enhancing operational productivity. A comprehensive understanding of the physical and chemical properties of bulk materials—such as particle size distribution (PSD), density, cohesiveness, and compressibility—is paramount to effectively assessing their conveying behavior. The precise design of material handling systems, including bins, hoppers, conveyors, and chutes, is contingent upon evaluating the interactions between solids, surface contact materials, geometries, and various operational conditions, including throughput, storage duration, application of pressure, and temperature [36,37].

While the importance of meticulous handling practices is well acknowledged, it is not uncommon to observe a lack of diligence in iron ore projects. Standardized solutions may be implemented, or existing conditions replicated without careful consideration of variations in bulk material properties (such as size and moisture content) or changes in operational circumstances. Such oversights can lead to unfavorable phenomena, including plugging, “rat holes,” bridging, and sticking, which may cause interruptions in operations, loss of material, and inaccuracies in processing. These inaccuracies can result in erroneous dosing of reagents or additives, as well as safety incidents involving equipment and personnel, such as landslides.

When it comes to handling, major efforts are taken to evaluate natural moistened or wet bulk materials. Investigations using the Jenike method of iron ore and raw materials for ironmaking are equally reported, but always dealing with materials exhibiting relevant moisture contents targeting the better comprehension and evaluation of their cohesiveness [38,39,40,41].

Nonetheless, the handling of dry iron remains largely uncharted territory due to its relative novelty. Insufficient information is reported in the literature [42,43,44,45,46], which is primarily centered on supporting equipment selection and design. Bulk materials are mentioned as general examples, usually categorized in classes, and a detailed characterization focusing on iron ore raw material and outputs (tailings and concentrates) with very distinct characteristics is still missing.

The newness of iron ore dry beneficiation requires further research on material flowability and handling, including different classes of iron ore, such as coarse and fine high-grade, run-of-mine, concentrates, tailings, and ultrafines, which are inherently produced in processing routes. Findings from Geldart’s and Jenike’s theories and their cross checking represent a powerful tool to support these assessments.

2. Materials and Methods

2.1. Jenike’s Flowability Determination

100 tons of crushed ROM, with a P80 of 35 mm, were collected from an industrial itabirite beneficiation plant in Minas Gerais, located in the southwest of Brazil, and transported by trucks to a 6 t/h dry processing pilot plant. The iron ore was dried to residual moisture levels (<0.2% w.b.) in a rapid dryer, air classified in cyclones, and concentrated by 150 mm rare earth type N-52 1.2 T high-intensity permanent magnet separators according to previous dry processing proposed [47]. The 100 kg samples, identified as S.1 to S.10, were collected from feed tailing, and concentrate streams exhibiting distinct particle size distributions (PSDs) and chemical compositions.

The characterization included physical characteristics and chemical composition. After homogenizing and quartering samples in a rotary divisor, particle size distributions were determined through wet sieving for openings ranging from 2400 to 45 μm. The fraction passing through the bottom sieve was then dried in a stove for 24 h at 105 ± 5 °C and analyzed by a LALLS (low angle laser light scattering) Malvern^® Mastersizer 2000 (Malvern Panalytical, Worcestershire, UK). Thirty grams of each sample were pulverized, and cast chips were submitted to X-ray fluorescence analysis to determine chemical composition. Loss on ignition (LOI) was measured by gravimetry before and after increasing temperature from ambient up to 1000 °C in muffle under ambient/oxidizing atmosphere.

The flow function and the wall yield locus were determined with the aid of different weights on a standard 3.75 in shear cell. Repose and drawdown angles were determined through the formation of a pile over plates with ultra-high molecular weight polyethylene (UHMW) coating, followed by its separation. Hopper angles were then estimated, according to Jenike and Johanson’s method [48,49,50] for conical and pyramidal geometries, for the wall surface tested UHMW-PE in this case to assure mass flow through a 0.5 m exit.

Tests to determine angles required for non-conveying flat chutes were conducted. The procedure consisted of cleaning a 12 mm layer after 0.2 to 8 kPa impact pressures that reduced speed to zero on a UHMW-PE liner plate.

Loose and tapped density were conducted through filling and weighing a 4.5 L mold. Loose density was measured after pouring the material through a sieve and gently falling into the mold. Tapped density was measured by consolidating the material after tapping (or gently filling/letting it fall from approximately 12 mm) repeatedly until no more consolidation was observed.

This group of tests was conducted at Jenike & Johanson’s facilities in Vinhedo, Sao Paulo, Brazil.

2.2. Geldart’s Fluidization Properties

Fluidization tests were conducted based on ASTM D7743:12 [51] at 25 °C. All samples exhibited residual moisture content, i.e., 0.1 to 0.2% w.b. A 150 mm diameter × 120 mm height cylindrical apparatus (Figure 1) was used to feed the solids where a bed of particles was confined.

The test started through the gas, in this case air, flow through a porous media pad at the bottom of the device. The air flow was controlled by a valve and monitored by a rotameter flow measurer. The pressure drop was measured with the aid of two pressure transmitters positioned at the bottom and 150 mm above. The bed’s expansion was continuously verified by the scale along the chamber device. The fluidization was gradually increased until the material was highly fluidized, and the air flow was gradually returned to zero. The pressure gradient reached its maximum and then slightly reduced to a given plateau, remaining constant even when air velocity was increased. A de-aeration test was carried out in the same device by the continuous registering of pressure drop after full fluidization and airflow cut. De-aeration time is considered as the time spent by the bed to release the air between particles corresponding to the pressure drop of 95% of the initial fully fluidized value.

Fluidization tests were conducted at TUNRA facilities in Newcastle, Australia.

3. Results

3.1. Chemical Composition

Chemical composition results are summarized in

Table 2. Identification and chemical composition of samples.

ID	Description	Fe	SiO2	P	Al2O3	Mn	TiO2	CaO	MgO	LOI
S.1	Ground ROM −2.000 mm	49.38	27.28	0.057	0.69	0.014	0.066	0.020	0.048	1.08
S.2	Ground ROM −1.000 mm	47.50	31.06	0.051	0.65	0.013	0.068	0.010	0.051	0.95
S.3	Ground ROM −0.500 mm	42.49	38.70	0.037	0.58	0.010	0.061	0.010	0.024	0.72
S.4	Ground ROM −0.150 mm	40.13	41.79	0.032	0.57	0.010	0.054	0.010	0.014	0.67
S.5	Ground ROM deslimed −0.150 + 0.010 mm	45.79	33.05	0.049	0.59	0.013	0.062	0.015	0.035	0.94
S.6	Ultrafines −0.025 mm	51.07	17.17	0.085	5.99	0.125	0.260	0.021	0.149	3.10
S.7	Pellet feed concentrate −0.150 + 0.015 mm	67.73	1.82	0.010	0.18	0.080	0.038	0.095	0.167	0.36
S.8	Pellet tailings −0.150 + 0.010 mm	36.51	46.99	0.016	0.74	0.016	0.120	0.011	0.052	0.56
S.9	Coarse concentrate −0.500 + 0.150 mm	65.60	5.64	0.022	0.46	0.013	0.041	0.010	0.085	0.43
S.10	Coarse tailings −0.500 + 0.150 mm	39.12	38.11	0.043	1.02	0.029	0.091	0.010	0.041	4.38

and aligned to sample identification. As can be seen, pellet feed (S.7) and coarse concentrate (S.9) exhibit the highest iron ore content, evincing the performance of the dry magnetic concentration. Pellet feed is richer due to finer particle size distribution and higher liberation. Conversely, pellet and coarse tailings, S.8 and S.10, respectively, unite gangue minerals, which are weakly affected by the magnetic field. As a result, such tailings report the lowest iron ore contents, the highest amounts of SiO₂ (main constituent in quartz), Al₂O₃, relevant contaminants in clay minerals, and LOI. Chemical composition determination is primary performed since iron phases and gangue minerals have very distinct specific densities, which have important influence on fluidization response [52,53,54,55,56,57,58,59,60]. It is also important to note that clay minerals exhibiting higher Al₂O₃ and LOI tend to concentrate in ultrafine fractions, S.6, and non-magnetic tailings, S.8 and S.10. These phases may contribute to increasing solid cohesiveness due to their affinity to water keeping higher residual moisture.

3.2. Particle Size Distributions

Figure 2 illustrates the particle size distribution (PSD) for samples submitted to the investigation of flowability. S.1 to S.4 are samples of ground ROM with distinct top size to evaluate the response in fluidization tests. Ultrafines, S.6, are the finest sample and particles are predominantly smaller than 10 µm with a top size close to 25 µm. Deslimed ground ROM (S.5), pellet feed (S.7), and pellet tailings (S.8) exhibit P95 around 150 µm, which is a standard market specification for commercial pellet feed to the iron-making industry. Coarse concentrate and tailings, S.9 and S.10, exhibit a PSD similar to fine commercial sinter feed, ranging from 150 µm to 0.500 mm. Particles size also strongly influences the fluidization behavior (bed expansion, minimum fluidization velocity, de-aeration rate) and supports their categorization [52,54,56].

3.3. Flow Function and Material Flowability According to Jenike’s Method

The flow function summary is presented in

Table 3. Flow function and Mohr semi-circle data for flowability determination.

Sample	W (kN)	σ1 (kPa)	FC (kPa)	FF	Yield Locus (°)	Eff. Angle (°)
S.1	0.015	5.44	1.10	4.95	39	44
	0.103	31.90	6.10	5.23	35	40
	0.221	62.86	10.80	5.82	35	40
S.5	0.015	5.30	0.30	17.67	40	41
	0.074	23.30	1.40	16.64	37	39
	0.152	46.10	2.50	18.44	37	39
S.6	0.015	6.04	3.60	1.68	32	51
	0.064	17.00	8.16	2.08	27	42
	0.132	36.60	15.40	2.38	31	44
S.7	0.015	5.78	0.40	14.45	38	39
	0.113	37.60	3.20	11.75	36	38
	0.221	62.43	4.85	12.87	35	37
S.8	0.005	2.50	0.20	12.50	34	36
	0.074	24.40	1.60	15.25	37	38
	0.142	47.40	3.20	14.81	35	36
S.9	0.010	4.20	0.64	6.56	34	36
	0.054	17.50	1.30	13.46	37	38
	0.103	38.10	2.70	14.11	35	36
S.10	0.005	2.60	0.66	3.94	37	43
	0.103	37.70	3.80	9.92	39	41
	0.201	65.91	5.58	11.81	37	39

W = working cell normal load; σ₁ = maximum consolidation stress; F_C = unconfined yield strength; FF = flow function; Samples S.2, S.3, and S.4 were not tested in a shear cell test.

. With the exception of S.6, categorized as cohesive, all materials were classified as easy (S.1) or free-flowing materials (all other samples). The results are in accordance with the theory where the finest particles, usually smaller than 20 µm, despite their low moisture content, exhibit cohesive behavior due to interparticle electrostatic forces.

The effective angle of ultrafines, S.6, is higher than the ones measured for the other samples, indicating that this material is more susceptible to arching and rat holing if stored in bins or hoppers, especially if discharged in a funnel-flow pattern. In this case, the design of hoppers and bins will require angles more inclined to horizontal to assure a mass flow regime. The results of repose and drawdown angles are also in line with the flowability. Ultrafines presented a sharp angle, reaffirming the cohesive behavior of their particles (Figure 3).

Loose and tapped density measurements confirmed the insights from previous results. According to the Hausner ratio [55], only the ultrafine fraction presented values corresponding to cohesive materials (HR > 1.4), indicating that this material should be classified in group C. Other materials exhibited lower Hausner ratio values (

Table 4. Loose and tapped density and Hausner ratio summary at residual moisture content, i.e., less than 0.2% w.b.

Sample ID	Loose Density (kg/m3)	Tapped Density (kg/m3)	HR
S.1	2189	2703	1.23
S.5	1632	1963	1.20
S.6	920	1524	1.66
S.7	2514	2883	1.15
S.8	1521	1902	1.25
S.9	2408	2654	1.10
S.10	2254	2536	1.13

), i.e., they are covered by groups A, B, or D materials, in accordance with Ref. findings [52,53].

The results of tests to investigate material flowability in hoppers and chutes are listed in

Table 5. Mass flow angles for hoppers and chute (angles related to horizontal) at residual moisture content, i.e., less than 0.2% w.b.

Sample ID	Conical Hopper—Exit 0.5 m (°)	Pyramidal Hopper—Exit 0.5 m (°)	Chutes (°)
S.1	73	61	29
S.5	75	65	34
S.6	80	69	44 * (86)
S.7	73	61	30
S.8	73	62	25
S.9	78	66	32
S.10	72	61	26

* Test performed with mild steel A36 ¼′.

, showing that S.6 required more inclined walls as compared to other samples.

The summary of results for fluidization and de-aeration tests is presented in

Table 6. Absolute density and parameters read in fluidized condition: minimum fluidization velocity plateau, time to air releasing through bed voidage, i.e., de-aeration rate, and initial and final bed heights. Bulk solids at residual moisture contents, i.e., less than 0.2% w.b.

Sample ID	Absolute Density (kg/m3)	Min. Fluid. Velocity (mm/s)	De-Aeration Rate (s/m)	Fluidized Bulk Density (kg/m3)	Initial/Fluidized/Final Bed Height (mm)
S.1	4151	-	-	-	-
S.2	4055	-	-	-	-
S.3	3821	75	111	1145	204/370/228
S.4	3755	45	142	1179	221/350/230
S.5	3984	145	113	1099	212/390/218
S.6	4326	120	203	631	206/295/208
S.7	5205	20	174	1219	206/308/197
S.8	3633	55	146	1115	209/360/217
S.9	5006	-	-	-	-
S.10	3725	100	151	1318	214/340/221

. The results are correlated to the content of iron in the samples. Three samples—S.1 and S.2, the coarsest ones, and S.8, the coarse concentrate—did not reach a steady state when submitted to air percolation (Figure 4a). All other sample responses exhibited a pressure gradient plateau as superficial velocity increased (Figure 4b). Samples that reached fluidized state conditions were submitted to de-aeration tests to evaluate the capacity of air retention after the air flow supply was cut off.

Figure 5 illustrates the results for samples S.5 and S.6 by recording the decay of pressure gradient until 95% of the initial fluidized bed condition.

4. Discussion

Based on Jenike’s method and the results, all materials are classified as free- or easy-flowing according to their flow functions obtained from tests, with the exception of the S.6 sample, ultrafines. The results of drawdown and repose angles are the highest for S.6 and confirm the findings from Mohr semi-circles as stated by Refs. [48,49]. If compared to the Mills classification [45], ultrafines would be classified as easy-/free-flowing. However, complementary tests for chutes and hoppers revealed the presence of cohesive interparticle forces. The results indicated more inclined angles for ultrafines as compared to the other samples. With the aim to assure the mass flow regime, conical and pyramidal hoppers must be inclined to horizontal 80° and 69°, respectively, which is very steep, making the design of these bins especially challenging. In such cases, fluidization at the bottom, vibrating mechanisms, “Chinese hats”, or pulsating air may be evaluated to assist powder flow and avoid building verticalization. The inclination required in chutes also showed that ultrafines may accumulate if the stream velocity is not reduced to zero after impact. The results indicated at least 44° from horizontal to ensure ultrafines will be able to slide by gravity after an impact that reduced stream velocity to zero. Other materials indicated that angles ranging from 25° to 34° to horizontal would be sufficient. Such findings confirm the low flow function value for ultrafines obtained from Jenike’s shear cells test for confined and unconfined states and Geldart’s theoretical diagram categorization of cohesive bulk material, even in the absence of moisture.

For the other samples, the Mills classification is slightly pessimistic when used to predict solid flowability. Most cases classified as easy-flowing by Ref. [45] presented free-flowing functions according to Jenike’s categorization (

Table 7. Comparison between Mills’s indicative procedure and Jenike’s classification based on flow function.

Sample ID	Flow Function (Jenike’s Method)	Mills Classification
S.1	Easy-flowing	Easy-flowing
S.5	Free-flowing	Free-/Easy-flowing
S.6	Cohesive	Easy-flowing
S.7	Free-flowing	Easy-flowing
S.8	Free-flowing	Easy-flowing
S.9	Free-flowing	Free-/Easy-flowing
S.10	Easy-flowing	Free-flowing

).

Based on the PSD results (Figure 2) and specific density analyses (Table 6), samples may be plotted on Geldart’s schematic theoretic diagram to predict the fluidization behavior of powders (Figure 6). As verified, S.6 is also listed as a cohesive material (Group C) and, although its d95 is close to an empiric boundary between groups A and C, the S.6 Hausner ratio was 1.66, emphasizing its allocation to group C, confirming the Ref. [55] and Ref. [61] findings. Due to its high surface area, a de-aeration rate of S.6 was the highest one (Table 6), i.e., even with the air flow supply suspended, this powder’s ability to retain air is high, allowing its conveyance in air slides for some time. The fluidization of group C powders is not trivial due to interface interaction among the high surface particles. Nevertheless, the presence of nanoparticles may increase gas hold-up and minimum fluidization velocity [58,59] as observed in sample S.6.

S.3, S.4, S.5, S.7, and S.8 should be categorized as group B and group A, sand-like and aeratable materials, respectively. All of them were well fluidized (Table 6), confirming the diagram prediction [52,53]. It should also be noted that S.4 and S.8, pellet feed ROM and pellet tailings, which are the finer and less dense phases, required lower minimum superficial velocity, confirming that materials closer to or in group A need less air than those in group B.

S.1 is into the group D region of spoutable materials. Due to its coarse PSD and high specific density, it is not likely to be fluidized. Results in Table 6 and Figure 4 confirmed the assumptions.

S.2, S.9, and S.10 are materials positioned close to the group B and D boundary. Deeper investigation is recommended to classify them, since this division of groups is not very accurate but rather a preliminary categorization [52]. S.2, ground ROM −1 mm powder, did not fluidize. This material is coarser than S.9 and S.10, and the air flow rate and pressure gradient were not able to keep particles in stable, continuous suspension. Although finer than S2, S.9 and S.10, coarse concentrate and coarse tailings, exhibited different results. S.9 did not reach steady-state fluidization, while S.10 did. Such a difference is due to the distinct specific density. The S.9 concentrate particles, with 65.60% Fe, are heavier than S.10 tailings, with 39.12% Fe, and therefore S.9 is a group D material whereas S.10 is part of group B. For such a narrow difference, it is recommended to avoid fluidization conveyance for iron ores with coarser liberation. For fine liberation ores, some margin to the group D boundary must be considered to avoid operational issues likely to occur in the upstream comminution stages, such as the presence of harder rocks or lack of process control, which may make fluidization inappropriate for handling the material. Therefore, it is a high-risk procedure to design comminution or handling at the edge of technologies. Further investigation on the pilot-scale testing of air slides is equally valuable for high-accuracy design.

For all materials in groups A, B, and C, the optimal recommend fluidization velocity range is listed in

Table 8. Optimal recommend fluidization velocity range.

Sample ID	Optimal Fluidization Velocity Range (mm/s)
S.3	113 to 150
S.4	68 to 90
S.5	218 to 280
S.6	180 to 240
S.7	225 to 300
S.8	83 to 110
S.9	* not reached steady-state fluidization (group D)
S.10	150 to 200

* S.1 and S.2 not tested since they are very coarse (group D materials).

, according to Singh et al. apud Ref. [43] and Woodcock et al. apud Ref. [43].

5. Conclusions

Geldart’s and Jenike’s methods were used to investigate dry iron ore ROM, concentrates, and tailing flowability and fluidization processes aiming to support the future design of industrial beneficiation plants.

Based on the results, the following statements can be made:

• Bulk materials with pellet feed fraction (S.4, S.5, S.7, and S.8) are free-flowing, exhibiting a steady-state fluidization condition and good air retention to air-assisted conveying.
• Coarse iron ore fractions (S.1, S.2, S.3, S.9, and S.10) are easy-flowing bulk material. However, most of them are not likely to be handled through air slides due to low air retention.
• Ultrafines, even though dried, are cohesive and may require air-assisting to aid the discharge from a bin. They are frictional and require steep walls on hopper and chute structures and may be conveyed on air slides.
• Air-assisted conveyors are highly recommended to handle fine liberated iron ore, a latent reality for low-grade deposits. However, some margin to the group D boundary must be considered to avoid designing at the edge of the technology, which may cause operational issues.

This paper fulfills the needs to support technical effective handling of fine iron ore in future dry processing plants and is not limited to the investigated itabirite samples. Bins, chutes, hoppers, and conveyances on air slides were addressed, and operational issues are unlikely to occur and savings in investments can be captured if recommendations based on the results are adopted.