The yellow container is for waste which can be recycled (except glass and paper which are also recyclet but collected in separate containers).
Unfortunately the rules what can be disposed into the yellow containers sometimes changes.
Things which are always OK:
At the moment this can also be disposed into the yellow containers:
Metal may be be at the moment also disposed into the yellow containers but it is better to deliver scrap metal to the precision mechanics facility where different kinds of metals are collected.