Little free libraries are fantastic when possible. With that said, assuming the final disposition will be a landfill or pulping via recycling, as a last resort the Internet Archive will accept for scanning and long term cold storage books they have not yet archived. They have an app available to scan UPC codes or OCR ISBNs to dedupe.

https://help.archive.org/help/donate-books-app-for-ios-and-a...

Books that have been scanned can be shipped using the below info.

https://help.archive.org/help/how-do-i-make-a-physical-donat...

(no affiliation)