Currently there are direct flights from Ibiza to Belgium:

Ibiza to Brussels
Ibiza to Liege

Flights from Ibiza to Belgium with one stopover.

Flights via Barcelona (BCN)
From Ibiza (IBZ) with Vueling Airlines
OR
From Ibiza (IBZ) with Iberia Airlines
Transfer at Barcelona (BCN) Then on to Brussels International (BRU) with Vueling Airlines
OR
Then on to Brussels International (BRU) with Iberia Airlines
Flights via London Heathrow (LHR)
From Ibiza (IBZ) with British Airways Transfer at London Heathrow (LHR) Then on to Brussels International (BRU) with British Airways