Learn Hardcore Portuguese (Portugal): Os resíduos são separados em caixas diferentes antes de serem reciclados. - The waste is separated into different boxes before being recycled.

Because this sentence is in the passive voice: the focus is on what happens to the waste, not on who does it. In Portuguese, you form the passive by combining a form of ser (here são) with the past participle (separados).

What exactly is the tense and structure of são separados?

It’s the present indicative passive. são is the 3rd person plural of ser, and separados is the past participle of separar, agreeing with the plural subject resíduos.

Why is separados masculine plural and not feminine or singular?

In Portuguese passive constructions, the past participle must match the subject’s gender and number. Since resíduos is masculine plural, separados also takes the masculine plural form.

Why doesn’t the sentence say nas caixas diferentes or use a definite article before caixas diferentes?

Here we’re talking about different boxes in general, not specific, identified boxes. In Portuguese, when you refer to something in an indefinite or generic sense, you often drop the article: em caixas diferentes means “in different boxes” (any boxes), whereas nas caixas diferentes would refer to particular boxes you’ve already mentioned.

Could we say em diferentes caixas instead of em caixas diferentes? Does the meaning change?

Both word orders are grammatically correct and convey the same basic idea.
• em caixas diferentes slightly emphasizes that each type of waste goes into a separate box.
• em diferentes caixas shifts a tiny bit of emphasis onto the variety of boxes themselves.
In daily speech, they’re interchangeable.

Why is antes de serem reciclados used, instead of antes de ser reciclado or antes de reciclar?

Because the subject (os resíduos) is explicit and plural, Portuguese requires the personal infinitive to reflect that plurality.
• serem reciclados is the personal infinitive (third person plural).
• ser reciclado would be the impersonal infinitive, ignoring number/gender.
• antes de reciclar shifts the structure to an active infinitive (“before [we] recycle”), which changes the focus.

What’s the difference between resíduos and lixo? Can I swap them here?

resíduos is a more formal term used in environmental and recycling contexts to mean “materials to be processed.” lixo is colloquial, meaning everyday “trash” or “garbage.” You could say O lixo é separado em caixas diferentes..., but using resíduos highlights that we intend to recycle or properly treat those materials.

How do you pronounce resíduos in European Portuguese?

In Portugal, resíduos is pronounced roughly r at the start is a guttural fricative [ʁ].
• e is mid-close [e].
• í is stressed [i].
• u is close back [u].
• Final s is pronounced [ʃ] after a vowel.