Elsevier

Advanced Powder Technology

Volume 21, Issue 5, September 2010, Pages 573-577
Advanced Powder Technology

Original Research Paper
Dry dense medium separation of iron ore using a gas–solid fluidized bed

https://doi.org/10.1016/j.apt.2010.02.014Get rights and content

Abstract

The dry dense medium separation of iron ore based on floating and sinking of ore particles in a gas–solid fluidized bed was investigated using zircon sand as the fluidized medium. The float-sink of ore particles with mean size Dave = 23.6 mm was investigated as the fluidizing air velocity and the float-sink time were varied. It was found that gangue with density less than 2850 kg/m3 which float is able to be separated from valuable ore with density greater than 2850 km/m3 which sink. The set point (density where half the particles float and half the particles sink) decreases with increasing the air velocity, and that the float-sink separation is completed within 2 min. The influence of different sized ore particles in the float-sink experiments was also investigated. As a result, the iron ore with Dave  17.6 mm are successfully separated. As Dave decreases below 17.6 mm, the ore particles with density near the set point tend to scatter in the fluidized bed without floating or sinking, resulting in separation efficiency which decreases with decreasing Dave. This indicates that the size of the ore particles is one of the major factors to achieve high separation efficiency.

Introduction

Mineral processing [1] is used to improve the grade of run-of-mine ores to produce high purity mineral concentrates for use in metals production. Conventional processing techniques use large amounts of water to separate run-of-mine ore into waste gangue and valuable minerals. Separation of mineral particles based on their density alone can be achieved by float-sink separations in a dense fluid. The process known as dense medium separation uses a dense liquid which is typically a suspension of fine (50–100 μm) magnetite or ferrosilicon particles suspended in water. The magnetic properties of the fine particles allow them to be recovered and reused. Significant quantities of water are required when conventional wet dense medium separation is used. In many locations, such as Australia and Chile, the availability of water is scarce. Recent research has focused on the development of new mineral processing schemes to reduce the use of water in mineral processing. This is important especially in areas with drought due to global warming; hence, development of dry separations to replace the commonly used wet separations is in great demand.

It is well known that a gas–solid fluidized bed has liquid-like properties such as density and viscosity [2]. When an object is placed onto the top of the fluidized bed, the object floats or sinks in the fluidized bed. The float-sink is basically dependent on the density difference between the object and the fluidized bed. The apparent density of fluidized bed can be controlled by changing the air velocity for fluidization or the density of the solid particles. A wide range of apparent densities are possible by using a mixture of two types of particle with different densities for the fluidized medium [3]. The float-sink is also largely affected by the fluidizing intensity depending on the air velocity, bed height and size of fluidized medium [4], [5]. The gas–solid fluidized beds have been shown to be used as effective dry dense media for float-sink separations, initially applied to waste treatment [6], [7], [8], [9], [10], [11]. Continuous separators have been put to practical use for separation of waste plastics and waste nonferrous metals in Japan. Also, coal cleaning was demonstrated to be feasible using the fluidized bed separation [12], [13], [14], [15]. Silicastone and pyrophyllite which have only 200 kg/m3 density difference were successfully separated using the fluidized bed [16], [17].

Iron ore is an important raw material to make steel, which is powerfully supporting our sustainable life. Demand for iron ore will increase due to the growth of developing countries, in particular Asian countries. Typically, run-of-mine iron ore is crushed to be −100 mm for liberation of Fe-rich component such as hematite. The ore particles of +6  100 mm in size are treated by the wet dense medium separation [18], for which the density of the dense liquid is adjusted at 2750–3150 kg/m3. Although development of dry separations for iron ore is strongly needed, the dry dense medium separation has not been tested for iron ore. Therefore, in this study, the dry separation using the fluidized bed was applied to iron ore treatment for the first time. Iron ore used here consisted of gangue with density less than 2850 kg/m3 and valuable ore with density greater than 2850 km/m3. So we investigated the separation of the gangue and valuable ore. The effects of air velocity and float-sink time on the separation efficiency were studied using ore particles with mean size of 23.6 mm. We also focused on the effect of ore particle’s size on the separation efficiency; the size effect has not been investigated in detail so far. Here we used ore particles with mean size of 27.4 mm, 17.6 mm, 12.1 mm and 9.0 mm as well to study the size effect.

Section snippets

Experimental

Typical run-of mine iron ore from Australia was supplied by a mining company. The ore was screened into different size fractions of +6.3  10 mm, +10  15 mm, +15  20 mm, +20  25 mm, and +25  31.5 mm. Three hundred and nineteen ore particles in total were randomly selected from the different size fractions of the ore sample. Each ore particle was weighed in air and water to determine the density ρ and the equivalent volume diameter D. Fig. 1(a) and (b) shows distributions of ρ and D. The particles with

Results and discussion

The ore particles of Dave = 23.6 mm were used to investigate the effect of air velocity u0/umf on the float-sink at tf  s = 5 min. Fig. 2 shows xf  s as a function of ρ for each u0/umf. The xf  s for the low density ore particles is 1 and that for the large density ones is 0, indicating that the former particles float and the latter particles sink. The set point (density where half the particles float and half the particles sink, shown by grey area) decreases with increasing u0/umf due to the bed

Conclusion

In summary, iron ore was separated into gangue as floaters and valuable ore as sinkers in a dry dense medium of gas–solid fluidized bed using zircon sand as a fluidized medium. The set point decreases with increasing the air velocity. u0/umf = 1.2 is an optimum air velocity to separate gangue and valuable ore at a set point of 2850 kg/m3. The float-sink separation is completed within 2 min. The float-sink separation is significantly affected by the size of the ore particles. Ore particles with size

Acknowledgements

This study was supported by Industrial Technology Research Grant Program in 2008 from the New Energy and Industrial Technology Development Organization (NEDO) of Japan, the Core-to-Core Program promoted by Japan Society for the Promotion of Science. (Project No. 18004) and the Australian Research Council, AMIRA International, BHP/Billiton, Rio Tinto, Orica, Anglo Platinum, Xstrata, Freeport McMoran and AREVA NC through the Australian Minerals Science Research Institute (AMSRI) (LP0667828). We

References (19)

There are more references available in the full text version of this article.

Cited by (59)

View all citing articles on Scopus
View full text