Learn Italian: L'alluminio, lo gettiamo nel bidone giallo. - The aluminum, we throw it in the yellow bin.

This is a structure called left dislocation. In Italian, when you want to emphasize the object of a sentence, you can pull it to the very front. However, when you do this, Italian grammar requires you to also include a pronoun—in this case, lo—right before the verb to refer back to that fronted object.

How do I know which pronoun to use before gettiamo?

The pronoun has to match the gender and number of the object you moved to the front. Since alluminio is a masculine singular noun, you must use the masculine singular direct object pronoun lo. If the sentence were about plastic (la plastica), you would use la instead: La plastica, la gettiamo nel bidone giallo.

Could I use buttiamo instead of gettiamo here?

Yes, absolutely! Both gettare and buttare mean to throw or to throw away. Buttare is actually more common in everyday spoken Italian, while gettare can sound slightly more formal, but they are completely interchangeable for talking about trash.

Why is it nel bidone instead of just in il bidone?