What?
The most commonly used are disposable razor blades, where you use and dispose if the whole thing or you have the option of changing the heads
Where?
These items are made up of multiple materials and so cannot be recycled, they should be placed in your general waste bin
General Comment / Tip
Why not try a safety or switchblade razor, for these you change only the blade, the used blade can be placed in your recycle bin – it will be picked up by magnets in the sorting facility