Corian is adhered using color matched epoxy. Any epoxy will work, and to color match it, just sand a piece of Corian of the same color and add the dust to the epoxy. There are dispersed colorants available also.
There's no need to use 80grit, that's really aggressive, and could be noticeable on the end product. Just sand with 220grit, and apply a thin layer of epoxy to both surfaces. I wouldn't suggest the quick cure epoxies since they don't have as good of a final cure strength.
If using epoxy on anything that will directly contact food, be sure to use food safe, FDA CFR 175.300 specification approved epoxy.