Entropy, disorder, lots of entropy. Actually, the entropy increase in this pile is due to rust. Iron plus oxygen goes to iron oxide.
The original iron and oxygen have more bond energy than does the product iron oxide. The difference in energy was dispersed
to the air and parts themselves when rusting happened. To return these parts to functional form a person would have to clean them,
to remove the rust, to figure out how they fit together, and to assemble them. The person would have to combust a lot of food
by the process of oxydizing hydrocarbons, and the resulting energy dispersal as heat would be added to the world. Even the process
of thinking about this has created entropy in your brain because energy from food is needed for thinking processes to happen. The
heat released by taking more energetic food and oxygen into less energetic waste products destined for exit from the body is dispersed
to the molecules in the body, and ultimately to the surrounding air. This heat dispersal is associated with generation of entropy.
Through many collisions per second (billions), the participating molecules share the burden of this excess energy among themselves,
for nature abhors slackers, especially slacker molecules. The disorder, I suppose, is that the iron doesn't suddenly just unrust.