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 areasAt plate edges areScooped up oceanFloor withChromium pods

Black areas showWhere chromiumAnd PGM layersSettled from mantleIntrusions intoContinental crust

You can get a few placers from these primary deposits too.

Main Ore Mineral of Chromium is Chromite

Chromite (black) interlayered withSepentine (greenish)

Fresh Chromite Surface

WeatheredChromite Surface

Fe2+Cr2O4 46% ChromiumS.G. 4.5 – 5.1Hardness 5.5Color Black to Brownish blackTends to have granular texture

Platinum, Osmium, Rhodium, Ruthenium, Palladium = PGMs

Native Platinum

Native Palladium

PGMs can be native metals or substituted into other minerals

Sperrylite

PtAs2 57% PlatinumS.G. 10.5Hardness 6-7Metal to white and brittle

Podform Chromite Deposits are Smaller

22,000 tons of ore is a median – big ones may be 250,000 tonsGrade 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

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$200

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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

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$2009/lb

About $5,000 to $10,000 per lb but varies with metalPlatinum around $12,000, Palladium around $4,500Rhodium around $12,000 to $48,000

Production and Reserves of Chromium

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PGMs Production and ReservesProduction and Reserves of PGMs

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