The robot, Nano, has been built with discarded parts of electronic devices, Xinhua news agency reported.
One of two prototypes, Nano "will open its mouth only when it detects that the item thrown out belongs to the category that it has to eat", creator Pablo Romanos said.
Nano's sensors were salvaged from "an Xbox console that the recyclers found in the street", added Romanos, an electrical engineer who is also a professor at University of the Merchant Marine.
The sensors allow the robot to follow orders "in the same way that kids play games with signs and gestures", explained the engineer.
Nano is also equipped with speakers and will soon have a computer screen.
All of the robot has been composed of recycled items, so it can instruct others how to classify and reuse trash, according to the report.
"Sometimes, people see the colour-coded garbage bins in the street, but don't know where to throw what, so the idea is to have the robot teach them," Romanos said.
He hoped to have similar robots stationed at schools "to teach kids in a fun way how to recycle".
In building the prototypes, which also incorporate components from printers, Romanos used the help of an architect, a specialised mechanic and his students.