Metal jest tak ważnym surowcem wtórnym jak szkło.

Tak ... jak is the Polish pattern for as ... as.

So:

• tak ważnym ... jak = as important ... as

It is used for an equal comparison.

Compare:

• Metal jest tak ważny jak szkło. = Metal is as important as glass.
• Metal jest ważniejszy niż szkło. = Metal is more important than glass.

So tak goes with jak, just like English as goes with as.

Because after jest the predicate noun phrase is commonly put in the instrumental case in Polish.

Here, surowiec is the noun in the predicate, so it becomes:

• surowiec → surowcem

And the adjectives modifying it must match its case, gender, and number:

• ważny → ważnym
• wtórny → wtórnym

So:

• ważnym surowcem wtórnym = instrumental singular

This is very common after być when you say what something is:

• On jest nauczycielem. = He is a teacher.
• To jest dobrym rozwiązaniem. = This is a good solution.

If you only use an adjective without a noun, you usually do not use instrumental:

• Metal jest ważny. = Metal is important.

But here the structure is not just an adjective; it is a whole noun phrase: an important secondary raw material.

Because szkło is the second item in the comparison, after jak.

The sentence is essentially shorthand for something like:

• Metal jest tak ważnym surowcem wtórnym, jak szkło (jest ważnym surowcem wtórnym).

The repeated part is omitted, which is very normal.

So szkło stays in its base form here because it functions like the subject of the omitted part.

That is why you get:

• Metal jest ... jak szkło not
• Metal jest ... jak szkłem

Surowiec wtórny is a standard Polish term meaning secondary raw material.

In practice, it refers to material recovered from waste and used again in production, so in many contexts it is close to:

• recyclable material
• recovered raw material
• material for recycling/reuse

Literally:

• surowiec = raw material
• wtórny = secondary / recovered / reused

So the sentence is talking about metal and glass as materials that can be reused in production.

Adjectives often do come before nouns in Polish, but not always.

In this expression, surowiec wtórny is a fairly fixed, technical term. In formal or technical language, Polish often places a classifying adjective after the noun.

So:

• surowiec wtórny sounds natural and standard
• wtórny surowiec is much less natural here

A rough rule:

• adjective before the noun: often descriptive
• adjective after the noun: often classificatory, formal, or part of a set term

That is why surowiec wtórny feels like a label or category.

Yes, but it does not mean exactly the same thing.

• Metal jest tak ważny jak szkło = Metal is as important as glass
• Metal jest tak ważnym surowcem wtórnym jak szkło = Metal is as important a secondary raw material as glass

The shorter version only compares importance in general.

The longer version specifically says that metal is important in its role as a secondary raw material.

So the added noun phrase makes the statement more precise and more formal.

Because Polish has no articles.

English needs words like:

• a
• an
• the

Polish does not. The meaning is understood from context.

So:

• Metal can mean metal in general
• surowcem wtórnym can mean a secondary raw material or, depending on context, the secondary raw material

In this sentence, English naturally needs an article, but Polish does not use one.

It means metal in general, as a material category.

Polish often uses a singular noun this way when speaking about a substance or a whole class:

• Metal
• Szkło
• Papier
• Plastik

So the sentence is not about one specific metal object. It is about metal as a type of recyclable material.

Yes, Polish word order is more flexible than English, but the original order is the most neutral and natural here:

• Metal jest tak ważnym surowcem wtórnym jak szkło.

You could change the order for emphasis, but that would sound less neutral, for example:

• Tak ważnym surowcem wtórnym jak szkło jest metal.

This sounds more marked, as if you are highlighting metal or making a rhetorical point.

For ordinary usage, the original version is best.

Then you would use bardziej / ważniejszy ... niż, not tak ... jak.

For example:

• Metal jest ważniejszym surowcem wtórnym niż szkło.
• Metal jest bardziej ważny niż szkło. — grammatical, but less natural
• Metal jest ważniejszy niż szkło. — natural if you do not need the noun phrase

So the contrast is:

• tak ... jak = as ... as
• ...niejszy / bardziej ... niż = more ... than

In your sentence, tak ... jak shows equality, not superiority.