After five years since the day of your first arrival, you are eligible to apply for the Permanent Residence Permit (séjour illimité), which will not be dependent on any work permit or authorization. With that in hand, you can immediately apply for Citizenship.
The key requirements for Belgian Citizenship are: Permanent Residence status (card type B), legal presence in the country for at least five consecutive years (i.e., be registered at an address in Belgium—you don’t need to spend all this time in Belgium), working for at least two years, and social integration. While there is no obligation to pass a language exam of a certain level, you should be able to navigate 200-300 daily words of French or Dutch, and a test of advanced beginner (A2 level) is advisable.
You will receive a response on your Belgian Citizenship application normally within four months - this limit is set by law.
If you are refused, you can appeal. The grounds for refusal (determined as a Negative opinion of the Royal Persecution office) are often hidden, but we know that if you have had traffic violations or a police court hearing for any serious case, then the Magistrate is most likely to play against you.
If you apply for Belgian Citizenship, you will not need to renounce your original citizenship.
Your Belgian Passport will normally be issued within four to six weeks after the expiration of the four-month period starting from the day you lodge your application for Belgian nationality.