Iron

Type
Element (Minerals/Ores of)

Mineral Classification
Oxide

Chemical Formula
Fe2O3, α-Fe2O3 (hematite), Fe2+Fe3+2O4 (magnetite)

Streak
red (hematite), black (magnetite)

Mohs Hardness
5.5–6.5

Crystal System
Trigonal (hematite), Isometric (magnetite)

Color
Metallic gray, dull to bright red (hematite), black, gray with brownish tint in reflected sun (magnetite).

Luster
Metallic

150TPH Iron Ore Processing Plant in Malaysia
150TPH Hematite Ore Crushing Plant in South Africa

The iron-rich ore that can be directly into the furnace in China only accounts for 2.6% of the total reserves. There are many types of lean iron ore, mainly magnetite, vanadium-titanium magnetite and hematite, as well as siderite, limonite, etc.
From the perspective of mineral processing technology, the iron ore is divided into:
magnetite ore, weak magnetic iron ore, mixed iron ore, multi-metal symbiotic composite iron ore, complex refractory iron ore, ultra-poor iron ore.

1 Preconcentration

Lean magnet ore preconcentration

In the 1980s, China developed the large particle size dry type magnetic machine suitable for pre-select ferromagnetic iron ore, which solved the technical problem of large particle size magnetite ore pre-concentration, including CTDG series permanent magnet dry magnetic separator and 1400*1600 dry magnetic separator.
For example, the BXSTEEL adopts CTDG1516 permanent magnet dry magnetic separators to process 350~0 mm ore, the processing capacity is 600~800t/h, the waste rock yield is 12.5%, the original ore grade is increased from 27.58% to 30.21%, and the total iron recovery rate is 95.84. %, the magnetic iron recovery rate of 99%.

2 Stage grinding and stage separation

According to the characteristics of raw ore, the use of stage grinding is an effective measure for energy saving in iron ore plants in China. The permanent magnet large-diameter magnetic separator can effectively separate 0-3mm coarse-grained iron ore with a trailing yield of 30-50% and a tailings grade of 8% or less.
Stage grinding, stage selection, coarse-fine separation, gravity-magnetic separation-reverse flotation process have been applied in China’s mixed iron ore dressing plant.

3 Fine screening and grinding process

Features
The fine sieving and re-grinding process is an effective method to improve the grade of iron concentrate. The fine mesh screen and return the coarse-grained high silicon content iron concentrate to re-grind, thus increase the grade of screened iron concentrate by 1%-1.5%.
The fine mesh can control the flotation particle size to improve the flotation effect.
Improve the grinding-classification efficiency to 50%-60%.

For example, the TISCO Iron, fine-grained embedded magnetite ore.
Three-stage crushing, stage grinding, single magnetic separation, fine screening and grinding process. Before the transformation, the concentrate grade was 60.5% and the SiO2 content was about 8%.

In order to further raise iron content and reduce silicon content, meet the requirements of high-quality iron raw materials. It adopts a fine screening and regrind process, and the final concentrate grade reaches over 69.5%.

Chinese iron process plant was adopted the fixed fine screen, nylon screen surface material. But the nylon screen surface has a low aperture ratio, low screening efficiency.
The Gongchangling iron ore uses electromagnetic vibration high-frequency vibrating mesh screen instead of nylon fine mesh. Compared with nylon fine mesh, the undersize yield is increased by 16%, the screening quality efficiency is increased by 35.96%, and the mass efficiency is improved by 40.17%. Not only reduces the circulation amount of re-grinding, but also creates conditions for the reverse flotation refining process, and improves the grinding efficiency of a ball mill.

4 Coarse-fine separation

The coarse fine separation process is a cost-effective technology used in mixed iron ore stage grinding and stage separation. The main equipment includes hydrocyclones, spiral chutes (coarse grains), weak magnetic separation-high gradient strong magnetic separation-reverse flotation (fine particles).

5 High gradient magnetic separation

The SLon series of vertical ring pulsating high gradient magnetic separators are developed for the selection of low-grade iron oxide ore, ilmenite, manganese ore and other weak magnetic ore.

6 Magnetic – reverse flotation separation

Magnetic separation is an effective means of pre-tailings discharge. Anion reverse flotation and cationic reverse flotation are effective methods to improve concentrate grade.
6.1 Magnetic separation – anion reverse flotation process
It includes “weak magnetic separation – anion reverse flotation process” and “weak magnetic separation – high gradient magnetic separation – anion reverse flotation process”. The former mainly selects magnetite ore, and the latter is mainly used for sorting hematite, mixed iron ore and weak magnetic ore.
6.2 Magnetic separation – cation reverse flotation process
The grade of iron concentrate increased from 65.55% to 38.89%, the silica content decreased from 8.31% to 3.90%, and the iron recovery rate was over 98.5%.

7 Magnetic – gravity separation

The magnetic induction strength of the ordinary cylindrical magnetic separator is generally 100-200 mT. By increasing the number of magnetic separations, the concentrate grade of the magnetite can be improved, but the magnetic mineral is repeatedly magnetized.
Studies have shown that for magnetite particles that have been dissociated from the monomer, a low magnetic induction of 13.9-86.5 mT can be selected. The magnetic gravity separation equipment developed by China can increase the concentrate grade by 2%-5% and the silica by 1.5%.
Commonly used equipment variable diameter magnetic condenser, magnetic separation column, magnetic field screening machine, etc.