FIELD OF THE INVENTION
The present invention relates to a process to recover ferrochrome particles from
granulated slag of ferrochrome furnace slag.
BACKGROUND OF THE INVENTION
Ferrochromium is an alloy which contains or consists of 25 to 70% chromium,
0.02 to 10% carbon, and the rest iron and other impurities. According to known
process, ferrochrome is produced in the submerged electric arc furnace and
metal losses occur during slag metal separation. The metal content in the slag
vary between 3-10% and size distribution of slag also vary between 0-40mm.
Processing of large amount of slag of wide size distribution in conventional
gravity separation methods is difficult. Ferrochromium is formed through a
melting reduction of iron-containing chromium ores, especially chromium iron
ore, with reductant according to the equation FeCr2O4+4C=Fe+2Cr+4CO. The
melting-reduction is conducted with a lumpy ore, pellet, briquettes-coke mixture
or with pre-reduced ore-fine coke-pellets and coke, particularly in a submerged
arc furnace. Tapping of the material from the furnace takes place intermittently.
When enough smelted ferrochrome has accumulated in the hearth of the
furnace, the tap hole is opened and slag rushes down a trough into a chill or
ladle. The ferrochrome solidifies in large castings, which is crushed for sale or
further processed. In the tapping process small amount of ferrochrome metal
also wash away with the slag. Ferrochrome is costly material and recovery of the
small losses of ferrochrome (30-100 kg/ton of slag) also needs to be minimized.

Prior art magnetic separation of ferrochrome slag entail the following
disadvantages:
1. Most of the existing techniques are designed to recover the Chrome oxide
from the ferrochrome slag, which is inefficient to recover the mettalics.
2. Low metal content in the slag (3-10% of total Slag) cause unnecessary
processing of huge amount of the slag, which results in poor efficiency of
gravity separation processes.
3. Communition of metallics is difficult to prepare feed for efficient gravity
separation process.
4. Wide size distribution (0-40mm) of the slag makes the manual sorting
inefficient.
Improper slag metal separation according to prior art causes losses of metals in
the slag. The metal content in the ferrochrome furnace slag vary between 3-10%
and size distribution of slag also varies between 0-40mm. The density of
mettalics varies between 5000 and 6500 kg/M3, whereas density of slag particle
vary between 2700 to 3300 kg/M3. Metallic particles are ferromagnetic whereas
slag particles are nonmagnetic or feebly magnetic in nature. Chemical
composition also showed variation in Cr, C, Fe, Si and AI content.
OBJECT OF THE INVENTION
It is therefore, an object of the invention to propose a magnetic separation
process to recover metallics from ferrochrome furnace slag.

SUMMARY OF THE INVENTION
According to the invention, a magnetic separation process has been developed to
recover the metallics present in the slag. An optimized magnetic separation
process can recover~87% of the metallic from the slag with more than 90%
purity.
According to the invention, representative samples of granulated slag samples
are collected from ferrochrome plant. Chemical and physical chartaerstics of the
slag and metal particles has been studied and a process flow sheet is developed
to separate the metallics from the nonmetallic. The recovered product can be
sold as product according to size and chemical composition.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows a process flow-sheet for magnetic separation of ferrochrome
furnace slag.
DETAILED DESCRIPTION OF THE INVENTION
The process developed according to the invention for recovery of mettalics from
ferrochrome furnace slag reduces substantial cost. The impact of the inventive
process is highly important as it produces a remunerative product which is
marketable in batches including batches as per its chemical composition and size
distribution. The developed process provides the methodology to recover
mettalics from ferrochrome slag.

The first stage of the process is to crush the oversize fines (>25mm) into
<25mm size. Further fine grinding will cause unnecessary energy consumption
as well as reduce the size of ferrochrome particles which reduces its market
prices. Size distribution and chemical analysis of samples are given in table 1 &
2.

It is necessary to have detailed information of the liberation and association
characteristics of minerals before selected the process parameters so to achieve
desire quality product. Characterization studies were carried out using optical
microscopy and sink float test. It was found that metallic content in the slag vary
between 3 to 10% and it is ferrochrome metal with variation in chemical
composition. The sample provided contains~7% metallic and metallic particles are
present in the all sizes ranges but 75% metallic are in 3-25 mm size fractions. Slag
is partly crystalline solid with three different phases, which are amorphous glass

phase, crystalline and zonal Fe-Mg-Cr-AI-spinels and metal drops. Presence of
metal phases controls the magnetic properties of the slag. Slag-metal attachment
is not significant in coarser sizes (>lmm) and metal particles can be recovered by
gravity as well as magnetic separation processes. Slag metal association is more
dominating in fines sizes which require grinding to liberate the valuables.
Particle size distribution is broad (0-25mm) and in this case heavy media
separation using liquid of >3.3gm/cc density can give the best results (Metal
recovery>90%) but it will be an complex and costly process. Hence, magnetic
separation process is explored. Magnetic susceptibility of these particles varies
between 500gauss to 7000 gauss and pure metallic can be recovered at 500-
2000gauss using magnetic pulley or low intensity magnetic separator. Response of
magnetic separation process for different size materials is given in table-3.
Table-3: Separation response of slag for various sizes @ 1000 gauss intensity)

An optimized magnetic separation process at 1000gauss magnetic intensity can
recover -87% of the metallic from the slag with more than 90% metal purity.

Wide size range of slag affects the efficiency of magnetic separation process. So,
screening at 0-1, 1-3, 3-6, 6-10 and +10mm sizes will be required to optimize the
magnetic separation process. Magnetic separation in 25mm into <25mm size
particles;
- screening the ground slag into 0-1, 1-3, 3-6, 6-10, and 10-25 mm size
particles;
- separating the ground and screened particulars in a magnetic separation
process under optimized process conditions; wherein
- the recovered metallics contain a product of Cr:48-60%, C:3-8%, Si:4-9%
and Fe:26-31% with metal recovery rate >87%.
2. The method as claimed in claim 1, wherein chemical composition of the
ferrochrome furnace slag and metals consists of 0.25: 7.14: 4.72: 0.45:
59.74: 27:01 respectively of Mg, C, Si, Al, Cr, and Fe, and wherein by weight
percent the size analysis of the slag is 10.89, 36.33, 18.78, 17.22, 16.78 for
particle size of 0-1, 3-6, 6-10,10-25 mm respectively.

ABSTRACT
The invention relates to a method to recover metallics from the
ferrochrome furnace slag, comprising the steps of : grinding the
ferrochrome furnace slag of>25mm into <25mm size particles; screening
the ground slag into 0-1, 1-3, 3-6, 6-10, and 10-25 mm size particles;
separating the ground and screened particulars in a magnetic separation
process under optimized process conditions; wherein the recovered
metallics contain a product of Cr:48-60%, C:3-8%, Si:4-9% and Fe:26-
31% with metal recovery rate >87%.