If the silica gel has been used for standard moisture absorption (dehydration purposes), it can be safely disposed of in your regular household rubbish.
However, if the beads have been used for gas separation applications, they may have adsorbed gases other than moisture due to their small pore size (approximately 20 angstroms). In this case, special disposal is required. The used material must be taken to an authorised waste disposal facility, where a fee may apply for safe destruction.