Identify duplicates and remove both from sheet.

Hi to you all
I have been working on a list of 70 odd thousand address records cleaning them. Have been transferring clean data in batches to a second excel sheet and saving it every time I add more and deleting them from the first list. I had not saved the first sheet at all. (idiot) Now received the message that there was not enough memory. Using win7 excel 2007. 4 gb ram. Got a Black screen. Could still open and work fine on other programs. Had this yesterday hence the second sheet. Assumed that Excel would have it in its memory so closed it down as my experience yesterday was that it would not clear itself. Now when I open it I have all the records of 70 odd thousand I started with in the first sheet instead of the 500 odd still to do.
I have a unique numbering system in column A. This is the same in both sheets. If I copy all my clean records into the first sheet. Is there a formula whereby I can delete any record for which there are two entries for a chosen column? IE A. Hope this makes sense.

Mark
PS I intended to put up a post of the memory issue after this was finished.

Hi Richard

Got a bit confused with what you suggested but it did remind me that a colleague of yours at this forum had given me

=COUNTIF($F$2:$F$85000,$G$2:$G$85000) when I was looking for the number of branches particular stores had. Yours is the same - Yes!

so a big thank you