How to re-associate keyword tags to files moved to new drive.

If the original catalog is still intact, you have several options:

1. The preferered method would be to back up the catalog and restore the catalog  to your new drive.  The restored catalog will have all of your tag information, including any face recognition that you have performed.  If you don't already have a backup, it would be good to use this method now.  See this HelpX article for more details.
2. Alternatively, create a new main folder on the new drive and, as Monte suggests, use the Organizer folder structure to drag your current folder hierarchy (which I assume is a Pictures folder over to the new folder on the hard drive.   If your hierarchy is something like a Pictures folder, you can drag that directly over to the new drive too.  But I would also recommend that you create a full backup of your catalog before doing this.
3. Another option would be to open the original catalog and write all the metadata to the files.  This requires you to select the files in the grid and press Ctrl+W.  If you have a large catalog, I suggest that you perform this operation a few hundrend at a time.  Once the metadata has been saved, you can copy these original files over to your new drive and import those files into a new catalog.  Import your tag hierarchy to the new catalog, and when you import the files from the new drive, using the from Files and Folders option, you will be given the opportunity to import the tags and in the advanced dialog mode that appears, you are also given the opportunity to map the tags to the hierarchy.   (This should happen automatically but there may be exceptions.)  If you use this method, you will lose all face recognition informatiion but the names that you have identified will be given keyword tags for the name and will be found in the Imported keyword tags category.   So, this is not really the best option.

I think the only way to keep your keywords pristinely intact is to move your files using Organizer.  If it's not too late for you, I would try moving the originals to the new location via Organizer, rather than copying the files.