After conducting a search on the ProQuest Platform, you will see a URL similar to this in your browser's address bar.  This is not a permalink that can be used to get back to the search results set:

In order to get a permalink, click Save search/alert -> Get search link

The resulting overlay window will have a permalink that can be used to navigate back to the search results. 

This type of link is good for 1 year.  If you need to save a search for a longer time period, you will want to create a My Research account and save your search there.