I have an image that has transparent edges around a main drawing, the edges are a semi-transparent black.
Is there any way to remove all partial transparency from the image instead of removing all of it?
If you want to remove the transparency of the partially transparent pixels, use Layer>Transparency>Threshold alpha. Depending on the threshold this will either make the edge pixels totally transparent or totally opaque.
But these semi-transparent pixels are there to make the edges appear smooth, you normally want to keep them. If you need to remove them the problem may be elsewhere in your workflow.