Which bin for cat litter?
Usual answer in the UK
General waste General waste bin
Used cat litter goes in the general waste bin, bagged.
Common mistakes
Do not put cat or dog waste in garden or food waste bins, even "biodegradable" litter.
Does every council do this?
Most councils follow the answer above, but bins and sorting rules are set locally, and a few councils still do things differently. If your bin has a sticker, or your council sent a leaflet, follow that. Enter your postcode to go straight to your council's guidance.