Excel – supperession

I need some help figuring out how to remove both records of a duplicate set. The details are as follow. I provided a client with a list of 10,000 records or leads on an excel spreadsheet. The client had to request approval from his marketing department to solicit the leads. The marketing department scrubbed the list and sent back 2000 leads. He now has a list of 2000 and a list of 10,000.
I would like to be able to distribute the 8000 that were scrubbed to different clients who are not subject to the same scrutiny by their marketing department. How do I get those 8000 records seperated? Any feedback would be greatly appreciated.

Thank you