Afrikaans often leaves out articles when talking about things in a general or material/category sense.
So in this sentence, the words are being used as categories of recyclable material:
This is similar to English when we say We sort paper, cardboard, glass, and metal, not the paper, the cardboard...
If you added die, it would sound more like you meant specific paper, specific glass, and so on.
They are best understood as mass nouns or category words here, not as countable singular items.
So:
Instead, they refer to the material or recycling category as a whole.
This works much like English:
Afrikaans usually does not require a comma before en in a simple list like this.
So this is standard:
papier, karton, glas en metaal
This is similar to English without the Oxford comma. You may sometimes see stylistic variation, but the version without the comma is the normal default in Afrikaans.
A rough English-friendly guide is:
A few helpful notes:
Sorteer is a normal Afrikaans verb and is very commonly used, especially for sorting, classifying, or separating items.
Even if it resembles words in other European languages, learners should just treat it as a standard Afrikaans verb. In everyday contexts like recycling, it is exactly the right word.
Yes, you might hear skei in some contexts, because it means separate. But it is not exactly the same as sorteer.
In recycling, sorteer sounds very natural if the idea is organizing materials by type. Skei can also work if the focus is on keeping them apart.
Yes. In many contexts, simple present Afrikaans can cover both:
So Ons sorteer papier, karton, glas en metaal can mean either, depending on context.
If you really want to emphasize an ongoing action, Afrikaans often uses a construction with besig om te:
Ons is besig om papier, karton, glas en metaal te sorteer.
But the shorter sentence is very natural and common.
Afrikaans usually uses double negation. So:
Ons sorteer nie papier, karton, glas en metaal nie.
Notice the two nie words:
That is a very important Afrikaans pattern.