At a Ferroalloy Plant producing High Carbon Ferro Chrome, the slag co-produced is granulated. The separation between slag and metal is not perfect and the granulated slag contains ~1% to 3% of entrapped ferrochrome. Apart from being a loss of valuable Ferro Chrome, local miscreants climb the unstable slag heaps to manually recover and steal the carry over Ferro Chrome granules, which is both a security and safety risk. We have successfully implemented a magnetic separation method for the recovery of metallics from the slag.

1. 1Slide
Project Title : Separation of Ferro Chrome fines from mixed
slag by High Intensity Magnetic Separation
Date: 13-Mar-2020

2. 2Slide
A. Trigger
• Ferro alloy plant produces 50,000 MT/year of high carbon ferro chrome
• Separation of slag and metal not perfect
• Slag contains (1% - 3%) entrapped metal (ferrochrome).
• Waste of valuable Ferro Chrome
• Local miscreants climb on unstable slag heap to steal metal
• Safety Risk and Security Risk  main trigger for innovation
Local Miscreants Climb
on top of slag dump
Cr Ore Pellets, Coke,
Fluxes
Power
Liquid FeCr &
Slag tapped
Slag Granulation
FeCr Casting &
Sizing
Slag Sent to
Slag Dump
Slag
skimmed
Liq FeCr
Some metal is carried over with slag
Submerged Arc Furnace
Gas flared out

3. 3Slide
Separation Methods : analysis of slag & metal
Technical Analysis :
1. Metal content in the ferrochrome furnace slag : between 1% to 3%
2. Size distribution of slag varies : 0 mm - 40mm.
3. Density of metallics : 5,000 and 6,500 kg/m3
4. Density of slag particle : 2,700 to 3,300 kg/m3
5. Available Methods :
a) Gravity Separation Methods: require narrow size range
crushing slag difficult
capex intensive – metallics only ~3% max
well established
b) Magnetic Separation : untried commercially for such applications
wide magnetic susceptibility range of metallics
wide size range : will it work for entire size range?

4. 4Slide
Results of Microscopic Analyses
FeCr Metal Within Slag : slag is porous and
binding with metal is not very strong
Stereo microscopic image at higher
magnification shows metal phases in mostly
liberated state
Elemental Mapping of FeCr Slag using EPMA shows FeCr
particle in a Mg-Si matrix in a liberated state

5. 5Slide
Study Results : Particle Size v/s Magnetic Susceptibility
• Wide size distribution (0mm - 40mm) of the slag makes process inefficient
→ reduce size to 0 mm to 25 mm → screening
• Characterization studies carried out using optical microscopy and sink float test
• Slag - partly crystalline with three different phases : amorphous glass, crystalline and zonal Fe-Mg-
Cr-Al spinels
• Slag-metal attachment not significant →
metal particles can be recovered by gravity / magnetic separation
• Heavy media separation using liquid of >3.3gm/cc density
→ give the best results but costly
• Magnetic susceptibility of FeCr varies between
500 gauss(strongly magnetic) to 2500 gauss(weakly magnetic)

6. 6Slide
Particle Size
Nonmagnetic
(%)
Magnetic
(%)
Metallic in
Magnetic (%)
Meta Recovery (%)
-25,+10mm 90 10 92 96
-10,+6mm 86.5 13.5 84 83
-6,+3mm 89 11 85 88
-3,+1mm 96 4 80 85
-1mm 93.5 6.5 68 83
0-10mm 80 20 83 87
Separation response of slag for various sizes (@ 1000gauss intensity)
Findings :
• Wide size range of slag affects the efficiency of magnetic separation process.
• Screening at 0-1, 1-3, 3-6, 6-10 and +10mm sizes required to optimize magnetic separation
• Magnetic separation in <1mm difficult : this fraction can be separated by jigging (gravity separation
process already in use for removal of slag particles from fine FeCr)
Study Results : Particle Size v/s Magnetic Susceptibility

7. 7Slide
B. Technical Challenges
Technical Challenges for Magnetic Separation were :
1. Magnetic separation of Ferro Chrome not tried ever before.
2. Ferrochrome weakly ferro-magnetic high intensity magnetic field
3. Quantity of metal 1% to 3% low recovery : fast process needed.
4. Granulation metal also granulated : small size handling & processing challenges
Magnetic Metallics Mg C Si Al Cr Fe
Magnetic 0.25 7.14 4.72 0.45 59.74 27.01
Feebly Magnetic 0.30 3.87 8.98 6.37 48.88 30.86
Analysis and Magnetic Property of Metal & Slag
Non-Magnetics MgO CaO SiO2 Al2O3 Cr2O3 Fe(T)
Slag 23.97 1.73 24.78 25.48 15.66 5.43

8. 8Slide
B. Overcoming Technical Challenges
Plant designed after multiple, extensive R&D trials along with the vendor :
- Sizing Circuit with Screening for uniformity of particles
- High intensity magnetic separation drums
- Handle sticky material (small size absorb moisture, becomes sticky) – plate type
separator for such material
Smaller size
material – use
jigging
Larger Size :
screen & resize
Slag & Metal seen under 3D
microscope XRD Patterns for different layers of jigged
material : higher intensity : higher metallics
Optimum
Range for
Magnetic
Separation

9. 9Slide
Metallic Particles : wide size range
Size Wise Segregation of Slag Particles (+10mm, 6mm-10mm, 3mm-6mm, -3mm)
Size wise segregation of slag particles(+10, 6-10, 3-6, -3mm)
Metallic-White
Slag - Gray
+10MM
+6M
M
-3MM
+3MM
-10 mm / +6 mm
+ 10 mm
-6 mm / +3 mm -3 mm

10. 10Slide
Slag & Metal Particles in 0 – 3mm makes separation challenging
Slag and Metal Association in Various Fractions
Slag and Metal Particles in 0-3mm size
Slag
Metallic
0-3mm Particles
Slag and Metal association in 0-1mm particle size
Products of the Magnetic Separation Process
Magnetic separation : (Particle Size 3-6mm)
Magnetic
Middling Non-Magnetic
Magnetic separation : (Particle Size 6-10mm)
Magnetic
Middling Non-Magnetic
But slag-metal association in various fraction
is not significant, making it amenable to
magnetic separation!

11. 11Slide
Novel method to recover metallics from the ferrochrome furnace slag by :
a. Grinding of >25mm into <25mm size particles.
b. Screening of slag into 0-1, 1-3, 3-6, 6-10, and 10-25mm size particles.
c. Magnetic separation of segregated particle at optimized process conditions.
Recovered metallics : Cr: 48-60%, C: 3-8%, Si: 4-9%, Fe: 26-31% with the metal recovery >87 %.
Novel Patented Process for FeCr Slag – Metal SeparationNovel Patented Process for FeCr Slag – Metal Separation

12. 12Slide
B. Challenges and Overcoming Them – Implementation Challenges
• Extensive trials at R&D to identify appropriate magnetic strength
• Commercial scale trials with vendor
• Ideal : Heavy Media Separation with High Intensity Magnetic Separation : very costly, low IRR.
• To overcome wide size range : two-stream facility designed.
• Searching for appropriate second vendor with the right skills : commercial scale trials repeated.
• Finally project technical parameters formalized; project implemented successfully.

13. 13Slide
Magnetic Separation Plant Set Up
10 tph x 2 Magnetic Separation Plant set up to process Granulated Slag

14. 14Slide
Some Photographs of the Plant
10 tph x 2 Magnetic Separation Plant Set Up to Process Granulated Slag

15. 15Slide
D. Novelty / Uniqueness
• Due to the weak ferromagnetic nature of high carbon ferro chrome, magnetic separation has never been
successfully implemented ever before in the world on a commercial scale.
• Also, due to the fine size of the granulated slag and the metallic particles, using a heavy media separation
method – the preferred method - would be very costly and perhaps uneconomical. The problem is
compounded by the size distribution of the granulated slag and metal.
• Innovatively, we were able to device a two-stream process to tackle the wide size ranges.
• Multiple rare earth magnets(Neodymium - NdFeB) for high magnetic strength : tackle weak ferromagnetic
nature (1200 G and 2500 G strengths)
This project is unique to the world of High Carbon Ferro Chrome processing globally and to bulk ferroalloys in
India.

16. 16Slide
E. Confirmation of Effects and Way Forward
Effects :
- Recovery of Metallics from slag to extent of ~ 2%
- Slag made free from almost all metallics : no longer attractive for
miscreants to undertake the risky job of climbing on the slag piles to
recover metallics
- EBITDA impact of ~Rs 200 lakhs/annum
Way Forward :
- Treatment of all granulated slag (including stockpile): will eliminate
miscreants from risking their lives (and our jobs)!
- Use of Magnetic Separation technique for mixed metal & slag across all
our ferro alloy plants
Number of miscreants on top
of slag heap panning slag to
recover metallics has reduced,
and gradually will no longer be
a problem

17. 17Slide
Magnetic Separation Plant in Operation
Video Showing the Internal Operation of the Magnetic Drums Video of the Magnetic Separation Plant – External View

18. 18Slide
Thank You
We would like to thank our R&D team comprising of Dr Veerendra Singh,
Dr Y Rama Murthy, Dr Sunil Tripathy & Nilamadhaba Sahu for the
extensive R&D tests & establishing the patented flow sheet, on the basis
of which we set up this commercial plant.