صديقي يتطوع في فرز النفايات.

The -ي is the attached pronoun meaning my.

• صديق = friend
• صديقي = my friend

So this is the noun صديق plus the possessive ending ـي.

A learner should also notice that once this suffix is attached, the noun becomes definite automatically, because my friend is already specific.

It is pronounced roughly ṣadīqī.

A few pronunciation points:

• ص is a heavy/emphatic s sound, not the same as plain س
• د = d
• يق contains a long ī before q
• ق is a deep q sound, not an English k
• the final -ي is another long ee sound

So the word has two long ee sounds: ṣa-dī-qī.

يتطوع is an imperfect/present-tense verb meaning he volunteers or he is volunteering.

It comes from the verb تطوّع.

What it tells you:

• يـ at the beginning often marks he in the present tense
• the verb is 3rd person masculine singular
• it can express:
  • a present action: he is volunteering
  • a habitual action: he volunteers

In a sentence like this, the habitual sense is often very natural.

Because it matches the subject صديقي (my friend), which is grammatically singular masculine.

Arabic verbs agree with their subjects in gender and number. So here:

• صديقي = singular masculine
• يتطوع = singular masculine

If the subject were feminine, you would use a different form of the verb.

Arabic allows both orders:

• صديقي يتطوع... = subject first
• يتطوع صديقي... = verb first

Both are grammatical in Modern Standard Arabic.

Using صديقي first gives the sentence a more topic-first feel, something like As for my friend, he volunteers... It can sound slightly more natural when you are introducing or talking about that person specifically.

في literally means in, but in sentences like this it often means something like:

• in
• in the area of
• in
• at

So يتطوع في فرز النفايات means he volunteers in sorting waste, or more naturally, he volunteers to sort waste / in waste sorting.

Arabic often uses في before a verbal noun to describe the activity or field involved.

Because فرز here is a verbal noun (called a maṣdar), meaning sorting.

So:

• فرز = sorting
• في فرز النفايات = in sorting the waste

This is very common in Arabic. After a preposition such as في, Arabic often uses a verbal noun rather than another conjugated verb.

That is why the structure is not something like في يفرز. A conjugated verb generally does not come directly after في in this kind of expression.

النفايات means the waste / the garbage / the trash.

In Arabic, general categories are often made definite where English might use either a definite or an indefinite expression depending on style. So فرز النفايات is a very normal way to say sorting waste or sorting the waste.

Also, فرز النفايات is an iḍāfa-like meaning relationship in English, even though it is not a classic two-noun iḍāfa in the strictest sense here with the maṣdar. The second noun identifies what is being sorted.

The singular is نفاية.

So:

• نفاية = one piece/item of waste, waste material
• نفايات = waste, wastes, garbage/trash

In real usage, the plural نفايات is very common when talking about garbage in general.

Yes. نفايات is a feminine plural form, and its singular نفاية is feminine.

Words ending in ـات are very often feminine plurals. In grammar, non-human plurals in Arabic are also often treated in a special way, especially in agreement patterns. But in this sentence, that does not affect the main verb, because the verb agrees with صديقي, not with النفايات.

After a preposition like في, the following noun is in the genitive case, so فرز is genitive here.

In fully vocalized Arabic, you would see that case ending clearly. In normal unvocalized writing, the short vowel is usually not written, so learners do not see it.

So grammatically, في فرزِ النفاياتِ would be the fully marked form.

It is the subject, so it is nominative in function.

However, because it ends with the possessive -ي, the case ending is not obvious in normal spelling and is often described as estimated or not visibly pronounced in the usual way.

For a learner, the most important point is this:

• صديقي is the subject
• therefore it is nominative in role, even though the ending does not visibly change the way a simple noun like صديقٌ would

Yes. For example:

• صديقي متطوع في فرز النفايات
  = My friend is a volunteer in waste sorting / My friend volunteers in sorting waste

Here متطوع is an active participle meaning volunteer or volunteering person.

The original sentence with يتطوع focuses more on the action. The version with متطوع is a more nominal style.

No. They are related in context, but not the same.

• يتطوع = he volunteers
• يعمل = he works

يتطوع specifically includes the idea of doing something voluntarily, not just working. So it is the right choice if the person is helping without that neutral/basic sense of simply working.

Yes, exactly.

The phrase في فرز النفايات tells you the field/activity of the volunteering. It answers a question like:

• In what does he volunteer?
• What kind of volunteer work does he do?

So the sentence structure is:

• صديقي = subject
• يتطوع = verb
• في فرز النفايات = prepositional phrase describing the activity

A useful breakdown is:

• صديقي = my friend (subject)
• يتطوع = volunteers / is volunteering (present/imperfect verb)
• في فرز النفايات = in sorting waste (prepositional phrase)

So the sentence pattern is basically:

[subject] + [present verb] + [prepositional phrase describing the activity]

That is a very common and useful Arabic sentence pattern.