NEW YORK (AP) -- Platinum and palladium are rising on concerns that supplies of the platinum group metals will shrink.

Zimbabwe's government reportedly gave platinum producers two years to begin refining the metals in Zimbabwe, which likely means the companies will have to build refineries. That spurred speculation on Tuesday that production of platinum will drop.

Platinum for April rose $21.10 to settle at $1,717.20 an ounce. Palladium for March rose $12.80 to $771.40 an ounce.

Platinum-group metals are widely used to make catalytic converters that filter car exhaust The majority of the world's reserves are found in just one country, South Africa. But neighboring Zimbabwe also sits on large reserves.

Grain prices edged lower. Corn fell 6 cents to $6.9625 a bushel and wheat dropped 9.5 cents to $7.32 a bushel.