Chromium and Platinum
Group Metals
©2009 Dr. B. C. Paul
Acknowledgement is given to www.d.umn.edu, webmineral.com, geology.com,
brittanica.com, webmineral.com, geology.about.com, periodictable.com,
mindat.org, johnbetts-fineminerals.com, USGS Bull 1693, earthsci.org, SME
Mineral Processing Handbook, icdachromium.com
Chromium and PGM (Platinum Group Metals)
• Mantle like material intrudes into
continental crust
– Reacts with sulfides and metals settle out at
bottom
– Common way to make Nickel Sulfide Deposits
• Chromium and PGMs tend to settle out in specific
layers
• Get a little from the Sudberry meteor impact too.
Settled Chromium Deposits
The Ocean Floor Mechanism
• Ocean floor comes from mantle like
material forming new crust at a spreading
ocean plate boundary
• Sometimes when continents collide or run
into things just right a chunk of sea floor
gets dragged up into a continent
– Called an Ophiolite sequence
– Bottom part of the ocean floor can contains
pods of Chromium rich ore
Chromium Pods in an Ocean Floor
Sequence
Where Chromium and PGMs are
Found
Green colored areas
At plate edges are
Scooped up ocean
Floor with
Chromium pods
Black areas show
Where chromium
And PGM layers
Settled from mantle
Intrusions into
Continental crust
You can get a few placers from these primary deposits too.
Main Ore Mineral of Chromium is
Chromite
Chromite (black) interlayered with
Sepentine (greenish)
Fe2+Cr2O4 46% Chromium
S.G. 4.5 – 5.1
Hardness 5.5
Color Black to Brownish black
Tends to have granular texture
Fresh Chromite Surface
Weathered
Chromite Surface
Platinum, Osmium, Rhodium,
Ruthenium, Palladium = PGMs
Native Platinum
Native Palladium
PGMs can be native metals or substituted into other minerals
Sperrylite
PtAs2 57% Platinum
S.G. 10.5
Hardness 6-7
Metal to white and brittle
Podform Chromite Deposits are
Smaller
22,000 tons of ore is a median – big ones may be 250,000 tons
Grade of the ore is around 46% Chromic Oxide
PGMs may be in the parts per
billion range
Little Chromite Pods May be Only
143 tons
Ore grades are again around 46% Chromic oxide
Chromium Processing
• Chromite tends to be lumpy big chunks
– Allows some separation in mining
– Rest if needed can usually be done with gravity
separation
• Jigs
• Heavy media separators
• Tables
• Lump Ore is Then Sent to Smelter Furnaces
– Often melted together with iron
– Some very intensive oxygen and ammonia processes
may kill off residual carbon.
The Gravity Concentrators
Use the fact that something is heavy
Heavies have more momentum –
Shaking Tables
Heavies sink faster – Jig
Light stuff floats in a heavy fluid – Heavy Media Separator
PGMs – A Tough Act to Process
• PGMs in a good case are associated with
nickel and copper sulfides
– In nasty cases some of them are trapped in
gangue minerals
• Try to Float out the PGMs
• Then send them to the smelter
What Do We Use Them For
• Chromium is mostly as a stainless steel
alloy with some chemical and plating uses
• PGMs are used mostly for catalysts for air
pollution control systems, with some
laboratory applications, and some jewlery
What is Chromium Worth?
Chromium Price/lb in $2009 to 2007
1.2
1
0.6
$2009/lb
0.4
0.2
2004
1996
1988
1980
1972
1964
1956
1948
1940
1932
1924
1916
1908
0
1900
$2009/lb
0.8
About $0.40 to $0.60/lb (prices based on chrome content of ferro-chrome
What Are PGMs Worth
PGMs Price in $2009 to 2007
25000
$2009/lb
20000
15000
$2009/lb
10000
5000
About $5,000 to $10,000 per lb but varies with metal
Platinum around $12,000, Palladium around $4,500
Rhodium around $12,000 to $48,000
2004
1996
1988
1980
1972
1964
1956
1948
1940
1932
1924
1916
1908
1900
0
Production and Reserves of
Chromium
Chromium Production and Reserves
500000000
metric tonnes
450000000
400000000
Other
South Africa
350000000
300000000
250000000
Kazakhastan
India
U.S
200000000
150000000
100000000
50000000
0
Prod*20
reserves metric
tonnes
PGMs Production and Reserves
Production and Reserves of PGMs
80000
70000
Other
Metric tonnes
60000
Zimbabwe
50000
South Africa
40000
Russia
30000
Columbia
Canada
20000
US
10000
0
Prod*20
Reserves