Flickr has its own tool to export all your account data. This article on Macworld explains the steps you need to take. I've quoted them below:

1.Log into Flickr via the web. (The Yahoo login account requirement is going away soon, too.)
2.Click the account avatar in the upper-right corner, and select Settings.
3.In the bottom panel, “Your Flickr Data,” click Request Flickr Data

Flickr has its own tool to export all your account data. This article on Macworld explains the steps you need to take. I've quoted them below:

1.Log into Flickr via the web. (The Yahoo login account requirement is going away soon, too.)
2.Click the account avatar in the upper-right corner, and select Settings.
3.In the bottom panel, “Your Flickr Data,” click Request Flickr Data

As pointed out in the comments, the above method would leave you with a large number of .zip files to download when you have 52k photos. The java command line utility flickrdownload might be a solution there, as it

allows you to download all of your photos and the associated metadata from Flickr

I don't have a Flickr account, so I can't test, but it appears that with just two commands (one to authenticate, one to download the photos) you can download your whole library.