CONTRACTOR WAS REMOVING PLYWOOD WALLS FROM EACH SIDE OF CEMENT RETAINER WALL AROUND RARE EARTH RECOVERY SYSTEM. WHILE THIS WORK WAS IN PROGRESSANOTHER CONTRACTOR WAS REMOVING TEMP PIPE BRACES FROM INSIDE RETAINER WALLS AND REMOVING THEM TO OUTSIDE, THE METAL BRACE FELL OFF ON ONE END AND STRUCK MAN ON RIGHT SHOULDER AND BACK AREA.