FIELD OF THE INVENTION

This invention relates to a novel method for production of iron ore concentrates suitable for iron and steel making processes from iron ore deposits. Consequently this invention further relates to removal of the gangue minerals present in the ore bodies. These are achieved by using hindered settling classification techniques followed by magnetic separator on the basis of their physical properties.

BACKGROUND OF THE INVENTION

Commonly run of mine (ROM) iron ore minerals are not directly used in iron and steel making processes. Till the recent past the high quality iron ore deposits are abundant all over the world. However, exponential increase in demand for steel all over the world is rapidly depleting above kind of high grade iron ore deposits. Hence, in search of alternative source of iron ores, the steel industries are forced to use the low grade ores, mine tailings (slimes) and other deposits with high iron content as the source of raw materials. But these types of ore deposits demand new methods of beneficiation techniques which can generate the suitable quality of iron ore concentrates for iron and steel making processes because of higher concentration of gangue minerals than that in high quality iron ores. The most common methods so far used in iron ore industry for treating these ores are crushing and sizing followed by gravity concentration (Jigs, Tables, etc) and magnetic separations. But these methods are not suitable for all types of ores and report appreciable loss of iron value in the tailings (lower recovery). Also the flow sheeLs are complex with series of unit operations which also makes it less attractive to economics. Since concentration of gangue is high in low grade deposits some times this creates complex textural relationship with iron ore minerals due to complicated geological conditions to form the ore bodies. Post formation processes such as weathering of such deposits some times results in formation of coatings made up of oxyhydroxyde minerals around iron ore minerals. These coatings are difficult to remove by conventional beneficiation techniques including magnetic operations. Therefore a novel method is developed to beneficiate variety of iron ore deposits, products various stages of mines and beneficiation plant and other deposits containing sizable iron content.

OBJECTS OF THE INVENTION

An object of this present invention to propose a novel method for production of iron ore concentrates by selectively reducing the gangue minerals;

Another object of this invention is to propose a suitable beneficiation process for treating various types of iron ore deposit, slimes, tailings and other deposits containing high iron values;

Further object of this invention is to propose the techniques of hindered settling classification on the basis of physical properties of iron ore minerals and gangue minerals;

Still further object of this invention is to propose hindered settling classification for oxidized ore.

BRIEF DESCRIPTION OF THE PRESENT INVENTION:

According to this invention there is provided a method for production of iron ore concentrate comprising the steps of: crushing low grade ore, slimes and other deposits to produce iron ore particle of the size less than 1.5 mm; Subjecting the said particles to the step of selective separation to isolate iron ore mineral from gangue minerals; and

Obtaining enriched ore with high iron content from (60% to 67%) using low intensity magnetic separator (LIMS) and high intensity magnetic separator (HIMS).

BRIEF DESCRIPTIN OF THE ACCOMPANYING DRAWING:

The invention is explained in greater details with the accompanying drawing:

Figure 1 : shows the textural relationship between iron ore minerals and gangue minerals.

Figure 2: shows the proposed flow sheet for iron ore which is used for the development of present invention.

Figure 3: shows particle size distribution of underflow fraction and overflow fraction of the hinder settling classifier.

DETAILED DESCRIPTION OF THE INVENTION

In iron ore deposits hematite, magnetite and goethite are principle iron bearing minerals. Based on the concentration of these minerals deposits are commonly classified into two types such as hematite and magnetite. Common gangue minerals are silicates and carbonates. Textural relationships between of these gangue minerals and ore minerals are dictated by geological conditions during the formation of the deposits and subsequent hydrothermal alterations and weathering. Therefore it is vital to understand the detailed textural relationships and their effect on liberation analysis of these ore bodies. For this invention state of the art equipments were used to carryout detailed textural and liberation analysis. Also it is identify the type of gangue minerals (quartz, alumino silicates, calcite, dolomite, oxyhydroxy minerals) and their physical properties. This data was used to select the comminution (crushing and grinding) parameters and subsequent unit operation. Iron ore minerals are commonly heavier than gangue minerals and also their crushing properties are different compared to associated gangue minerals due to difference in hardness and cleavage. Therefore, in comminution the gangue minerals reduce to finer size whereas most of iron ore minerals form coarse size.

In this inventive process, the iron ore minerals and gangue minerals are separated by using difference in their physical properties, size and density. When the solids particles are dropped in the fluid medium they settle according to the different in size, shape and density (buoyancy force). In the hinder settling classification, the separation of these settling solid particles in fluid medium is controlled by adjusting a flow and density of fluid medium (pseudo liquid formed by solid suspended in the medium). In this process, the heavier and coarser particles settles down below fluidized zone and termed as an underflow fraction which is collected from the bottom of the classifier. On the other hand, the lighter and finer particles flows along with the fluid medium from the side of the classifier and this fraction is called overflow fraction.

In this invention, the size distribution of feed particles was controlled in the range of 0 - 1 mm size and velocity of fluid medium (teeter water) was adjusted in innovative way to separate heavy and large iron ore minerals from lighter and fine gangue minerals. The teeter water flow rate depends on the design parameters of the unit

(hinder settling classification). In present invention, the iron ore minerals with > 75 microns size and 4 - 5.5 gm/cc density were collected as a underflow fraction and in overflow fraction the gangue minerals with 75 - 200 microns size and 2 - 4 gm/cc density were reported.

An exemplary embodiment of the present invention provides a novel method for simultaneously desliming the ore minerals with beneficiation. In view of the association of gangue minerals and their fine size range (generated during the comminution), the de-sliming operation is generally carried out after size reduction to remove the slimes, the separation of which is difficult in subsequent beneficiation unit operations. The flow of fluid medium and attritioning effect caused by particle movement was used in innovative way to remove the coatings on the ore minerals and also to de-slime. Hence, the hindered settling classifier is best option as compared to the conventional de-sliming operations like cyclones because also acts as concentrating unit operation by separating gangue phases on the basis of particle size and density difference.

One of the major advantages of this innovative process is simultaneously concentrating magnetite and hematite ore minerals. When ore body contains magnetite and hematite minerals, in conventional beneficiation process (after de- sliming), first magnetite is separated from the feed using low intensity magnetic separator (LIMS) and then the non-magnetic fraction of this process is further treated in high intensity magnetic separator (HIMS) to recover the hematite ore minerals. This two step process is required as magnetite is ferromagnetic and hematite is paramagnetic minerals. In both magnetic separation techniques, more than two cycles (steps) are essential to achieve the desired quality of concentrates. Hence, in conventional process the loss of Fe values (Fe recovery) is much higher due to three stages of operations namely de-slime, LIMS and HIMS. On the other hand, the innovative process can simultaneously perfumes de-sliming and recovery of both hematite and magnetite in one step, and thereby generate a desired quality concentrates with higher Fe recovery values.

In the present invention, for achieve further improvement in Fe values (grade of the concentrate) the additional beneficiation of underflow of hinder settling classifier is carried out by using conventional techniques. The magnetic and gravity separation techniques were used in present invention to recover Fe values from overflow fraction of hinder settling classifier. EXAMPLE:

Weathered Magnetite ore (Fe distribution -50% Magentite, 30% hematite and 20% goethite)

The experiments were carried out using this novel process and using magnetite ore containing 55% to 65% of iron. In one trial, 1 tonne of ROM was crushed and ground to less than 1 mm size and then was treated in hinder settling classifier. The experimental conditions were like feed pulp density 20 - 30% wt, feed rate 0.1 - 0.5 t/hr, teeter bed pressure 0.04 - 0.09 bar, and teeter water flow rate 3 -12 LPM. The concentrate with 64 - 67.5% Fe was achieved by this process. The results of experiments (hindered settling classifier) are depicted in Figure 3. The overflow fraction was treated in LIMS and/or HIMS and about 60% of ore minerals were separated as a magnetic fraction. The underflow concentrate of ranging from 64% to 66% Fe was also treated in LIMS and/or HIMS to generate concentrate of +67% Fe grade.